ONE CLASSY AFFAIR DINNER DANCE SATURDAY

HANDBOOK OF
ANDROLOGV
The American Society of Andrology
@)
Copyright © April 1995, by the American Society of Andrology
74 New Montgomery, Suite 230, San Francisco, CA 94105
Phone: (415) 764-4823; Fax: (415) 764-4915
Second printing (July 1998) made possible with financial support
from Pharmacia & Upjohn and Alza Pharmaceuticals.
Printed by Allen Press, Inc.; 1041 New Hampshire Street, Lawrence, KS 66044
This paper meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper).
'
/'·
PREFACE
tion for anyone interested in Andrology. The
material covered is geared toward first year
medical, veterinary and graduate students and
will hopefully serve as a useful teaching aid.
It is clearly only a brief introduction to this
complex and exciting field of research.
In addition to the essential contributions of
the co-authors, many individuals have made
the preparation of this Handbook possible. Jon
Pryor and Jacquetta Trasler have done an
outstanding job of bringing together a superb
collection of authors, and of editing their texts
in order to facilitate the reading of the volume
as a whole. Sue Grant subedited the text in a
highly professional manner. The dedicated
secretarial support of Gail Wolfenden provided
a needed degree of cohesion to this project.
The American Society of Andrology is grateful
to The Upjohn Company for having kindly provided essential financial support, with no restrictions, for the preparation and publication
of this Handbook.
With its twentieth anniversary, the American
Society of Andrology celebrates a milestone in
the evolution of the field of science specifically
dedicated to the the male reproductive system. Tremendous strides have been made in
our understanding of each component of the
male reproductive system, how these components communicate with each other, and
how pathological conditions arise. We have
also seen significant breakthroughs in developing effective therapies for dysfunctions of
the male reproductive system.
In bringing together world renown experts
on most facets of andrology for the creation of
this introductory Handbook, the American Society of Andrology has sought to provide introductory, up-to-date knowledge of both fundamental and clinical aspects of male
reproductive function. Indeed one of the hallmarks of the American Society of Andrology
is the effective communication that takes
place between scientists dedicated to understanding male reproduction and treating
pathological conditions of male reproduction.
This Handbook is designed as an introduc-
Bernard Robaire
Past president
American Society of Andrology 1993-1994
iii
List of Contributors
Co-editors
Bernard Robaire, Ph.D.
Department of Pharmacology &
Therapeutics
McGill University
3655 Drummond Street
Montreal, Quebec
H3G 1Y6 Canada
Jon L. Pryor, M.D.
Department of Urologic Surgery
University of Minnesota
420 Delaware Street, SE
P.O. Box 394 UMHC
Minneapolis, MN 55455
Jacquetta M. Trasler, M.D., Ph.D.
McGill University
Montreal Children's Hospital
2300 Tupper Street
Montreal, Quebec H3H 1P3
Authors
Nancy J. Alexander, Ph.D.*
Contraceptive Development Branch
Center for Population Research, NICHD
6100 Executive Blvd., Room 8B13
Bethesda, MD 20892
Rupert P. Amann, Ph.D.*
Animal Reproduction and
Biotechnology Laboratory
Colorado State University
Fort Collins, CO 80523
Andrzej Bartke, Ph.D.*
Department of Physiology
Southern Illinois School of Medicine
Carbondale, IL 62901
Marc R. Blackman, M.D.
Johns Hopkins University School
of Medicine
Johns Hopkins Bayview Medical
Center
4940 Eastern Avenue
Baltimore, MD 21224
Gabriel Bialy, Ph.D.
Contraceptive Development Branch
Center for Population Research, NICHD
6100 Executive Blvd., Room 8B13
Bethesda, MD 20892
Runa Brinkmann, M.D.
Department of Surgery
Division of Urology
Clinical Science Center
University of Wisconsin, Madison
600 Highland Avenue G5/344
Madison, WI 53705
Terry R. Brown, Ph.D.
Department of Population Dynamics
Division of Reproductive Biology
Johns Hopkins University School of
Hygiene and Public Health
615 N. Wolfe Street
Baltimore, MD 21205
Reginald C. Bruskewitz, M.D.
Department of Surgery
Division of Urology
Clinical Science Center
University of Wisconsin, Madison
600 Highland Avenue G5/344
Madison, WI 53705
Yves Clermont, Ph.D.
Department of Anatomy and Cell Biology
McGill Univesity
3640 University Street
Montreal, Quebec
H3A 2B2 Canada
v
vi
Handbook of Andrology-List of Contributors
Donald S. Coffey, Ph.D.
Johns Hopkins School of Medicine
600 N. Wolfe St.
Baltimore, MD 21205
Richard A. Fayrer-Hosken, BVS, Ph.D.
Department of Large Animal Medicine
University of Georgia
College of Veterinary Medicine
Athens, GA 30602
Michael D. Griswold, Ph.D.
Program in Biochemistry
Washington State University
Synthesis Bldg. Room 675
Pullman, WA 99164
Barbara F. Hales, Ph.D.
Department of Pharmacology &
Therapeutics
McGill University
3655 Drummond Street
Montreal, Quebec
H3G 1Y6 Canada
S. Mitchell Harman, M.D., Ph.D.
Gerontology Research Center
National Institute on Aging, NIH
4940 Eastern Avenue
Baltimore, MD 21224
Louis Hermo, Ph.D.
Department of Anatomy and Cell Biology
McGill University
3640 University Street
Montreal, Quebec
H3A 2B2 Canada
Barry T. Hinton, Ph.D.
Department of Cell Biology
University of Virginia Health Sciences Center
Charlottesville, Virginia 22908
Morten Jonler, M.D.
Department of Surgery
Division of Urology
Clinical Science Center
University of Wisconsin, Madison
600 Highland Avenue G5/344
Madison, WI 53705
David F. Katz, Ph.D.
Dept. of Obstetrics/Gynecology
Duke University
School of Medicine
Durham, NC 95616
Ronald W. Lewis, M.D.
Department of Surgery
Division of Urology
Medical College of Georgia
Augusta, GA 30912-4050
Claude J. Migeon, M.D.
Department of Pediatrics
Johns Hopkins University School of
Medicine
Pediatric Endocrine Clinic
CMSC 3-110
Baltimore, MD 21205
Diana G. Myles, Ph.D.
Department of Physiology
University of Connecticut Health Center
263 Farmington Avenue
Farmington, CT 06030
Claude M. Nagamine, Ph.D.
Department of Cell Biology
Vanderbilt University School of Medicine
Nashville, TN 37232
Joseph E. Oesterling, M.D.
Department of Urology and
The Michigan Prostate Center
University of Michigan
1500 East Medical Center Drive
Ann Arbor, Ml 48109
vii
Handbook of Andro/ogy-List of Contributors
Jon L. Pryor, M.D.
Department of Urologic Surgery
University of Minnesota
420 Delaware Street, SE
P.O. Box 394 UMHC
Minneapolis, MN 55455
Bernard Robaire, Ph.D.*
Department of Pharmacology &
Therapeutics
McGill University
3655 Drummond Street
Montreal, Quebec
H3G 1Y6 Canada
Kenneth P. Roberts, Ph.D.
Department of Urologic Surgery
University of Minnesota Medical School
420 Delaware Street SE
Minneapolis, MN 55455
Susan A. Rathmann, Ph.D.
Fertility Solutions Inc.
13000 Shaker Blvd.
Cleveland, OH 44120
Peter N. Schlegel, M.D.
James Buchanan Brady Foundation
The New York Hospital Cornell
Medical Center
525 East 68th Street
New York, NY 10021 and
The Population Council
Center for Biomedical Research
New York, NY 10021
Richard J. Sherins, M.D.*
Division of Andrology
Genetics & IVF Institute
3020 Javier Road
Fairfax, Virginia 22031
Donald J. Tindall, Ph.D.
Urology Research
Mayo Clinic
Guggenheim 17
200 First Street
Rochester, MN 55905
Philip Troen, M.D.*+
Department of Medicine
University of Pittsburgh School of Medicine
3459 Fifth Avenue
Pittsburgh, PA 15213
Christina Wang, ERACP
Harbor-UCLA Medical Center
Clinical Study Center
1000 West Carson Street
Box 16
Torrance, CA 90509
Barry R. Zirkin, Ph.D.
Division of Reproductive Biology
Johns Hopkins University
615 N. Wolfe Street
School of Hygiene and Public Health
Baltimore, MD 21205
*Past President, American Society of Andrology
+Past President, International Society of Andrology
"What a piece of work is a man"
Shakespeare, Hamlet, Act ii, scene 2, line 316
citing breadth of andrology and the opportunity
it holds for graduate students in the biological
sciences, veterinary students, and medical
students.
Why become an andrologist? In choosing a
career one, first of all, tries to identify an area
of interest. Then one looks at the opportunity
to succeed and the likelihood of making a contribution. As an andrologist for 40 years, I can
testify to the continued excitement and interest
the discipline has held for me. As noted
above, there has been a rapid escalation of
growth so that our discipline now ranges from
genetic studies to pubertal changes in the
male and from infertility and assisted reproduction techniques to disorders of the prostate, sexual function and contraception. Advances in these and other areas have been
made possible by a remarkable series of clinical studies and scientific discoveries using
the classical disciplines of physiology, biochemistry, neuroscience, and molecular biology. As we have entered each new stage of
understanding and science, there has been no
waning of the stimulus that I and my colleagues experience. At the same time, because of the multidisciplinary nature of andrology,
unsolved
problems
present
themselves and the opportunities for advancement and success continue to expand. As Alexander Albert has noted, "Nature has experimented lavishly with the reproductive
system." This fact provides both challenge
and opportunity. Andrology covers a wide
spectrum from before conception to aging. As
you peruse this handbook, we hope you will
appreciate the scope of the field and share our
excitement in the study of andrology.
Why a handbook of andrology? Some handbooks are published to bring together multiple
aspects of a diversified subject. Some handbooks are designed to present an overview of
a rapidly expanding subject for those working
in the field while other handbooks are intended to codify the progress already made. Although there are elements of each of these
approaches in this handbook of andrology, our
main purpose is to present to scientists/clinicians early in their careers the scope, importance, and excitement of our discipline.
What is andrology? Simplistically, one might
say that andrology is to the male what gynecology is to the female. That is, andrology
deals with matters affecting the male reproductive system. The earliest use of the term
andrology, as reported by Mikko Niemi, appears to have been in 1891 in the Journal of
the American Medical Association, reporting
on the formation of the American Andrological
Association. Little more was heard from that
association and it was not until the latter half
of this century that there emerged an andrology journal in 1969 and an active andrology
organization, Comite lnternacional de Andrologia, in 1970. In the quarter century since,
there has been a veritable explosion of journals and publications, of societies and congresses, and of workshops and symposia devoted to andrology. Thus, we appear to be on
a rapidly rising growth curve of knowledge and
application in andrology. The scope of modern
day andrology is strikingly indicated by the
range of topics discussed in this handbook.
Written by distinguished leaders in their fields,
these topics were chosen to indicate the ex-
ix
Handbook of Andrology
Contents
PREFACE
B. Robaire
LIST OF CONTRIBUTORS
FOREWORD
P. Troen
1. What are the components of the male reproductive system?
Topics: CNS, pituitary, testis, epididymis, prostate, seminal vesicles, scrotum,
penis-K.P. Roberts
1
2. What is the relationship between the various endocrine components of the
male reproductive system?
Topics: Hypothalamo-pituitary-testicular axis, feedback loops -B.R. Zirkin
5
3. What compounds mediate communication within the male reproductive systern? Where and how are male-associated hormones produced?
Topics: Gonadotropins, steroids and their sites of synthesis -M.D. Griswold
8
4. How is communication mediated within the male reproductive system?
Topics: Hormone receptors, signal transduction -D.J. Tindall
10
5. How are germ cells produced and what factors control their production?
Topics: Germ cell development in the testis (including mitosis, meiosis, spermiogenesis), Sertoli cells, other cell types -L. Hermo, Y. Clermont
13
6. What are the unique chromosomal events leading to the formation of a haploid
male germ cell?
Topics: Stages of meiosis, chromosomal events, genetic recombination -J.L.
Pryor
16
7. What does the epididymis do and how does it do it?
Topics: Physiology, sperm maturation -B.T. Hinton
18
8. What is the prostate and what is its function?
Topics: Physiology, function (anatomy, embryology) -D. Coffey
21
9. What is semen? How does semen analysis assist in understanding the reproductive status of the male?
Topics: Semen composition and analysis (animal, human), related tests -R.P.
Amann, D.F. Katz, C. Wang
25
10. What is sperm banking? When and how is it (or should it be) used in humans?
Animals?
Topics: Sperm banking, consequences of its use in animal and clinical practice
-S.A. Rathmann
31
xi
xii
Handbook of Andrology-Contents
11. How does the spermatozoon make its way to the egg and how does fertilization take place?
Topics: Capacitation, acrosome reaction, zona binding -D.G. Myles
35
12. What factors determine the sex of an individual?
Topics: X, Y, SRY (loci, genes), sequence of events in development of normal
male-C.M. Nagamine
38
13. Are there specific genetic defects affecting the male reproductive tract? What
are the underlying molecular mechanisms?
Topics: Androgen insensitivity, Turner's and Klinefelter's syndrome, chromosomes, gene loci -T.R. Brown
40
14. Is there a trigger for puberty in the male? Should early or delayed puberty
be treated? If so, how?
Topics: Early, normal, delayed puberty, treatment -C.J. Migeon
46
15. How is male infertility defined? How is it diagnosed?
Topics: Epidemiology, causes, work-up (history, physical, lab tests) -R.J. Sherins
48
16. What are the existing and future therapeutic approaches for male infertility?
When should IVF be used for male infertility? What is the role for psychological counselling for infertility?
Topics: Treatment -medical, empirical, surgical, alternative, adoption, donor,
psychological -P. Schlegel
52
17. How is fertility assessed in domestic animals?
Topics: Infertility diagnosis in the different species, evaluation of the male for
clinical management -R. Fayrer-Hosken, R. Amann.
56
18. What are the existing male contraceptives and what is the outlook for new
ones?
Topics: Androgens, GnRH antagonists, antibodies to sperm surface antigens,
compounds that act on sperm maturation in the epididymis -N.J. Alexander,
G. Bialy
60
19. How prevalent is erectile dysfunction? What can be done to treat it?
Topics: Erectile physiology, etiology, work-up and treatment of erectile dysfunction, psychological counselling -R.W. Lewis
63
20. Can spermatozoa be targets for drugs? If so, what are the consequences of
such drug exposure? Is there a need for pre-conception counselling for
men?
Topics: Drugs that affect sperm structure or function, male-mediated developmental toxicity, prevention, tests to detect damage to spermatozoa -B. Robaire, B. Hales
68
21. Do environmental factors affect male reproductive functions? If so, which
ones and how?
Topics: Season, length of day and chemical exposure effects on the male -A.
Bartke
70
Handbook of Andrology-Contents
xiii
22. Is there an andropause, the analog to menopause, and if so what tissues are
affected and how?
Topics: Fertility, androgen production and sensitivity, and sexual function in aging men -S.M. Harman, M.R. Blackman
72
23. What is BPH? Why is it so prevalent? What treatments are available?
Topics: Pathophysiology, treatment -J. Oesterling
76
24. Are some men more susceptible to prostate cancer than others and why?
What are the treatments and their effectiveness? What are the possibilities
for improvements in therapy?
Topics: Pathophysiology, present and future treatments -R. Brinkmann, M. Jonler, R.C. Bruskewitz
80
Copyright © American Society of Andrology
What are the components of the male reproductive system?
CNS, pituitary, testis, epididymis, prostate, seminal vesicles, scrotum, penis
The male reproductive system consists of a
number of individual organs acting together to
produce functional spermatozoa, and to deliver these spermatozoa to the female reproductive tract. The haploid germ cells originate in
the testis and continue their maturation as
they transit the epididymis. The vas deferens
carries the spermatozoa from the epididymis
to the ampulla, provides a site for the mixing
of seminal vesicle secretions, and continues
as the ejaculatory duct through the prostate,
emptying into the prostatic urethra (Fig. 1).
The germ cells, mixed with ejaculatory secretions from the accessory sex glands (seminal
vesicles, prostate, bulbourethral gland), then
exit the body through the penile urethra. The
entire system is dependent upon neuro-endocrine regulation from the pituitary and hypothalamus. Knowledge of the anatomy and
embryological origins of each of the components of the male reproductive tract is important in developing a basic and thorough understanding of the system as a whole. Although the discussion of male reproductive
anatomy and embryology in this chapter is
confined to the human system, subsequent
chapters will show that much of our understanding of reproductive biology has been
gained from research using various experimental animal models.
Testis
The testis is central to the male reproductive
system. It is the organ which generates the
haploid germ cell by the process of spermatogenesis and it is the site of androgen production. The testis arises from the primitive gonad
on the medial surface of the embryonic mesonephros. Primitive germ cells, which migrate
to this region from the yolk sac, cause the coelomic epithelial cells to proliferate and form the
sex cords. Formation of the sex cords gives
this region a raised contour that is called the
genital ridge. By the seventh week of fetal de-
velopment, proliferation of the mesenchyme
has separated the sex cords from the underlying coelomic epithelium. During the fourth
month, the sex cords become U-shaped and
their ends anastomose to form the rete testis
(Fig. 2A). At this point, the primordial sex cells
are referred to as pre-spermatogonia and the
epithelial cells of the sex cords as Sertoli cells.
The mesenchymal tissue in the interstitial
space between the tubules gives rise to the
Leydig cells that are the site of androgen production. The rete testis extends into the mesonephric tissue and will anastomose with
some of the mesonephric tubules forming the
efferent ducts which communicate with the epididymis (discussed below). The sex cords will
become the seminiferous tubules, although
the tubules do not develop a lumen until after
birth.
The testis develops abdominally and successful descent into the scrotum is essential
for fertility. The scrotum is formed as coelomic
epithelium penetrates the abdominal wall and
protrudes into the genital swelling as the processus vaginalis. An outgrowth of each layer
of the abdominal wall is carried with this epithelium, giving rise to the fascial layers of the
scrotum. The testis then descends behind the
processus vaginalis and the layers of fascia
covering the testis on each side, with the overlying skin of the genital swelling, fuse to form
the scrotum.
Epididymis
The epididymis, vas deferens and seminal
vesicles have their origin in the mesonephric
duct (or Wolffian duct). Initially formed as the
early embryonic excretory system, the mesonephric system is comprised of the longitudinal duct and a series of tubules that branch
from the duct toward the developing gonad.
Although most will degenerate, several of
these tubules persist and anastomose with the
confluence of the seminiferous tubules (rete
2
Handbook of Andrology-What are the components of the male reproductive system?
testrs
B
FIG. 2. A. The immature testis and mesonephric
duct system in the fourth month of development. B.
The immature mesonephric duct system after testicular descent. (From: Langman J. Medical Embryology. Baltimore. MD: Williams & Wilkins; 1969).
Vas Deferens
FIG. 1. The organs of the male reproductive system. (From: Kiss & Szentagothai. Atlas of Human
Anatomy, Oxford, England: Pergamon Press;
1964.)
testis), forming the efferent ducts (or ductuli
efferentes) through which spermatozoa exit
the testis (Fig. 28). The portion of the mesonephric duct closest to the ductuli efferentes
elongates, becomes extensively convoluted,
and forms the epididymis (Fig. 28). Because
it arises from a single duct, the epididymis, unlike the testis, consists of a single tubule
through which all spermatozoa must pass.
The epididymis remains in close contact with
the testis and descends with the testis into the
scrotum.
Testicular spermatozoa are non-motile and
incapable of fertilization . The function of the
epididymis is to bring testicular spermatozoa
to maturity. How this maturation process is accomplished by the epididymis is currently unknown but is an area of active research in reproductive biology. It is known that the epididymis secretes proteins that become part of the
surface architecture of the mature spermatozoa and presumably are important in postejaculatory function of the spermatozoa.
That portion of the mesonephric duct extending from the caudal end of the epididymis
to the seminal vesicles (discussed below) becomes thickened and muscular and forms the
vas deferens (or ductus deferens). That portion of the duct which continues distal to the
seminal vesicle is known as the ejaculatory
duct and is contained entirely within the prostate gland. In its course the vas deferens ascends from the scrotum, with the vessels that
vascularize the testis and epididymis, through
the inguinal canal, over the pubic ramus, over
the superior lateral aspect of the bladder medial to the ureter, and enters the posterior superior aspect of the prostate, just distal to the
seminal vesicle (Fig. 1). The primary function
of the vas deferens and ejaculatory duct is
transport of mature spermatozoa and seminal
vesicle secretions to the prostatic urethra.
Seminal Vesicles
The seminal vesicle develops as an outpocketing of the mesonephric duct, distal to
the epididymis (Fig. 28). Consequently, this
gland shares a common embryological origin
with the epididymis and vas deferens. The fully developed seminal vesicle resides immediately above the prostate gland (Fig. 1). It is
comprised of a series of tubular alveoli, lined
with a very active secretory epithelium. In fact,
•
Handbook of Andrology-What are the components of the male reproductive system?
the seminal vesicle contributes the majority of
the fluid volume of the ejaculate. Seminal vesicle secretions are rich in fructose and prostaglandins. While fructose may be an important energy source for spermatozoa, the role
of prostaglandins is unknown. The seminal
vesicle also produces several androgen-dependent secretory proteins that are involved in
the rapid clotting of the ejaculate.
Prostate
The prostate gland is located in the space
below the bladder and above the urogenital
diaphragm (Fig. 1). It is separated posteriorly
from the rectum by the rectovesical (Denonvillier's) fascia. Its location immediately anterior to the rectum allows the prostate to be palpated and biopsied from the rectum. The prostate arises from several distinct sets of tubules
that evaginate from the primitive posterior urethra. Each set of tubules develops into a separate lobe: the right and left lateral lobes,
which are the largest, the middle lobe, and the
very small anterior and posterior lobes. The
lobes are composed of alveoli, lined with a secretory epithelium, that drain through a series
of converging tubules into the prostatic urethra. Although the lobes arise independently,
they are continuous in the adult with no apparent gross or morphologic distinctions. Consequently, a more useful subdivision of the
prostate has been recently developed which
distinguishes prostatic zones based on morphologic and functional properties (i.e., central, peripheral and transitional zones).
Prostatic secretions contribute to the fluid
volume of the ejaculate. These secretions are
high in zinc, citric acid and choline. The function of these substances is unknown, although
an anti-microbial activity for zinc has been
postulated. The prostate also secretes several
proteins including acid phosphatase, seminin,
plasminogen activator and prostate specific
antigen (PSA). The exact roles of most prostatic secretions are unknown, although they
are presumed important for the function of
spermatozoa during and after ejaculation. For
instance, plasminogen activator and seminin
are proteases involved in the liquification of
3
coagulated ejaculate. Although the function of
PSA is not known, an elevated level of this
protein in the blood is often diagnostic of abnormal prostatic growth such as occurs with
cancer of the prostate.
Penis
The penis arises from the genital tubercle,
a region just cranial to the cloacal folds in the
embryo. Under the influence of androgens
produced by the fetal testis, the cells of the
genital tubercle proliferate causing elongation
of the tubercle into the primitive phallus. The
penile urethra is formed from the urethral folds
as the phallus elongates. In the adult penis the
urethra is divided into the membranous portion, which extends through the urogenital diaphragm, and the pendulous portion, which
courses through the penis. Lateral to the urethra are the two corporal bodies, the corpus
cavernosi, which become engorged with blood
to produce the penile erection. The physiology
of erection is complex and is subject to a number of clinical disorders. The importance of
proper erectile function to sex and reproduction, and the common occurrence of erectile
dysfunction (affecting 10-20 million men in the
United States), has made erectile dysfunction
a primary clinical concern in andrology.
Endocrine and nervous control of the male
reproductive tract
The entire male reproductive tract is dependent on hormones for proper function. The pituitary produces the gonadotropins, folliclestimulating hormone (FSH) and luteinizing
hormone (LH), under the control of the hypothalamus. FSH is required for spermatogenesis and LH stimulates androgen production by
the testicular Leydig cells. The testis requires
testosterone to maintain the process of spermatogenesis and the accessory organs are
dependent on androgen for proper secretory
function. The production of LH is regulated by
feedback inhibition of circulating testosterone
on the pituitary and hypothalamus. FSH secretion is regulated by inhibin, a peptide hormone produced by Sertoli cells, and also by
4
Handbook of Andrology-What are the components of the male reproductive system?
circulating testosterone. This endocrine loop is
known as the hypothalamic-pituitary-testicular
axis. In addition to hormonal control, the reproductive organs are also subject to sympathetic and parasympathetic nervous control.
This is particularly true for the erectile function
of the penis, which is under parasympathetic
control, and for ejaculation, which is under
sympathetic control.
Conclusion
This brief introduction to the male reproductive tract demonstrates the integrated nature
of the system. The seminiferous tubules are
continuous with the penile urethra via the vas
deferens, with the accessory organs contributing their secretions along this course. The
entire system is maintained by androgens, secreted by the testis under the control of the
pituitary and hypothalamus. It is important to
remember that many of these structures are
embryologically distinct and, consequently,
that developmental abnormalities will affect
these structures in different ways. Knowing
the embryology and anatomy of the tract will
help the student of male reproductive medicine to understand the common, and the notso-common, disorders encountered in the
clinic.
Suggested Reading
McNeal JE. The Prostate Gland: Morphology & Pathology. In: Stamey TA, ed. Monographs in
Urology, Vol 9. Princeton: Medical Directions Publishing; 1988:36-54.
Langman J. Medical Embryology. Baltimore: Williams & Wilkins; 1975:160-200.
Tanagho EA. Anatomy of the Lower Urinary Tract. In: Walsh PC, Retik AB, Stamey TA,
Vaughan ED, Jr, eds. Campbell's Urology. Philadelphia: WB Saunders; 1992:54-69.
Copyright © American Society of Andro/ogy
What is the relationship between the various endocrine
components of the male reproductive system?
Hypothalamo-pituitary-testicular axis, feedback loops
Integration of the hypothalamus, pituitary
and testis is of critical importance to reproductive function. The hypothalamus comprises
the lateral walls of the lower part of the third
ventricle of the brain. The pituitary, an endocrine gland connected to the hypothalamus at
the base of the brain (Fig. 1), is divided into
two major parts: the neurohypophysis (or posterior lobe), and the adenohypophysis (or anterior lobe) (Fig. 1). The neurohypophysis,
which is composed of the median eminence,
infundibular stem and infundibular process, receives neural input from the brain. In contrast,
the adenohypophysis, composed of the pars
tuberalis, pars intermedia and pars distalis, is
glandular tissue and, thus, must be regulated
by factors delivered via the circulation.
Some of the neurosecretory neurons from
the hypothalamus send their axons down the
neural stalk to terminate in the neurohypophysis (Fig. 1). When stimulated to depolarize,
these neurons release the hormones vasopressin (also called antidiuretic hormone) and
oxytocin from secretory granules into the
bloodstream. Oxytocin causes contraction of
smooth muscle, including that in the male reproductive tract, and vasopressin acts in the
kidneys to cause water retention. In contrast
to the neurohypophysis, the adenohypophysis
is regulated by peptides and monoamines that
are synthesized and secreted by specific hypothalamic neurons whose axons end, not in
the adenohypophysis, but in the median eminence near the infundibular stem (Fig. 1).
These hormones (hypophysiotropic hormones) are transported by the portal blood
system of the pituitary from the median eminence to the adenohypophysis where they
stimulate the synthesis and secretion of the
adenohypophysial hormones.
There are three general classes of adenohypophysical hormones synthesized and secreted by the pars distalis of the adenohy-
pophysis: glycoprotein hormones, corticotropin-related peptides and somatomammotropin
hormones. The glycoprotein hormones, luteinizing hormone (LH) and follicle-stimulating
hormone (FSH), have well established effects
on the testis; LH stimulates the secretion of
testosterone by the Leydig cells, and FSH acts
on the seminiferous tubules to promote spermatogenesis. The synthesis and secretion of
LH and FSH are regulated, in part, by a decapeptide from the hypothalamus, gonadotropin-releasing hormone (GnRH). When administered to humans or to laboratory mammals,
GnRH causes LH, and to a lesser extent FSH,
to be secreted into the blood. Based on the
known structure of GnRH, a number of analogs have been synthesized, some of which
are far more potent than natural GnRH and
are able to increase LH and FSH secretion
when administered. GnRH antagonists or antisera block the effects of endogenous GnRH
thereby reducing gonadotropin levels.
LH is secreted in distinct, short-term pulses
in response to pulsatile release of GnRH (Fig.
2). The importance of pulsatile secretion of
GnRH is clearly illustrated by the effect of intermittent versus continuous GnRH administration on the secretion of LH and FSH in
GnRH-deficient hypogonadal men; LH and
FSH can be restored to normal levels in the
serum when GnRH is administered intermittently, but not when it is administered continuously. Indeed, sustained hormonal signals
can shut down, rather than stimulate, target
cells.
The episodic LH signals that are delivered
to the testis via the testicular vascular system
stimulate the synthesis and secretion of testosterone by Leydig cells. As is the case for
LH, testosterone is secreted in pulses (Fig. 2).
Simple, one-to-one, relationships between LH
pulses from the adenohypophysis and testosterone pulses from the Leydig cell are often
5
6
Handbook of Andrology-What is the relationship between the various endocrine components
of the male reproductive system?
e
3
10.0
:§,
:z:
7.5
...J
5 .0
2 .5
'5 1 500 , . . - - - - - - - - - . . , . . - - - - - - - .
.....
0
.s
(I)
..g
1000
(I)
Ill
-:
.....
..
0
500
E
;;,
0
-·()Of
FIG. 1. The hypothalamus and pituitary gland.
(From: © 1995 by Ciba. Reprinted with permission
from Ciba Publications, illustrations by F.H. Netter,
M.D. All rights reserved.)
seen, although there are reports that LH pulses are not necessarily followed or preceded by
a testosterone pulse. Interestingly, maximal
steroidogenesis occurs at concentrations of
LH that are sufficient to occupy only a small
fraction of the total number of LH receptors
available on the surface of Leydig cells. The
significance of this relative overabundance of
receptors is unclear. Fig. 3 shows testosterone production during the lifetime of the human male. Peaks of testosterone occur in the
peripheral blood of the 12-18 week-old fetus,
and of the 2 month-old neonate. In the prepubertal period, testosterone declines to low
levels. It then increases markedly during puberty (ages 12 to 17 years) , and reaches its
maximum during the second and third decades of adult life. Slow decline then occurs
through the fifth decade, with more dramatic
decline thereafter. Superimposed on these episodes are annual, daily and hourly fluctuations in testosterone production.
~
0~-T~~T-~~~~T-~~~
0
500
1000 1500 2000 2500
Time (min)
FIG. 2. Profiles of serum LH and testosterone in
blood samples from a healthy man drawn at 1aminute intervals. (From: Veldhuis et al, J Clin Endocrinol Metab 1987; 65:929-941.)
......
B
- ~
~' :
&
600
400
I:P
oe
't •
I
I
I
I
I
I
I
o
I
l
I
I
ADULT
'
•
a
1:)
'-.........!
I
SENESCE~
FIG. 3.
Testosterone concentrations in the peripheral blood of the human male at different times
of the life cycle. (From: Greep RO, ed. International
Review of Physiology, Volume 22. Baltimore: University Park Press; 1980:41.)
Handbook of Andrology-What is the relationship between the various endocrine components
of the male reproductive system?
In addition to regulation by hypothalamic
Gn RH pulses, LH and, to a lesser extent, FSH
are regulated by the negative feedback effects
of the steroid hormones produced by the testis. Testosterone, for example, negatively
feeds back at the level of the hypothalamus,
slowing the GnRH pulse generator and thereby inhibiting pituitary LH pulses. Additionally,
the testis is capable of metabolizing testosterone to estradiol via aromatase activity in the
seminiferous tubules and interstitium. Estradiol, when present in physiological concentrations, is also able to dampen the frequency
and amplitude of episodic LH release. The effect of this negative feedback is apparent in
7
men following castration; the loss of testicular
steroids results in markedly increased secretion of both LH and FSH. When these men are
given exogenous testosterone, LH levels in
the blood diminish, and LH pulsatility returns
to normal.
The importance of the integration of the hypothalamic-pituitary-testicular axis is obvious
in light of the critical roles of LH , FSH and testosterone in spermatogenesis. Testosterone,
regulated by LH , is an absolute requirement
for normal spermatogenesis. FSH plays a significant role in the initiation of spermatogenesis at puberty but its role in the adult is less
certain.
Suggested Reading
Everett JW. Pituitary and hypothalamus: Perspective and overview. In: Knobil E and Neill JD,
eds. The Physiology of Reproduction, Second Edition, New York: Raven Press, ltd.; 1994:
1509-1526.
Bremner WJ, Bagatell CJ , Christensen RB and Matsumoto AM. Neuroendocrine aspects of the
control of gonadotropin secretion in men. In: Whitcomb RW and Zirkin BR, eds. Understanding Male Infertility: Basic and Clinical Aspect. New York: Raven Press; 1993:29-41 .
Hall PF. Testicular steroid synthesis: Organization and regulation. In: Knobil E and Nelli JD,
eds. The Physiology of Reproduction, Second Edition New York: Raven Press, ltd.; 1994:
1335-1362.
Sharpe AM. Regulation of spermatogenesis. In: Knobil E and Neill JD, eds. The Physiology of
Reproduction, Second Edition, New York: Raven Press, Inc.; 1994:1363-1434.
Copyright © American Society of Andro/ogy
What compounds mediate communication within the male
reproductive system? Where and how are male-associated
hormones produced?
Gonadotropins, steroids and their sites of synthesis
receptor stimulates an intracellular signal
transduction and amplification system that results in a biochemical change within the target
cell. Receptors for FSH , LH and thyroid stimulating hormone constitute a closely related
subfamily of G-protein coupled receptors that
is distinguished by a relatively large external
domain. Structurally, G-protein coupled receptors are characterized by a region of hydrophobic helices which span the membrane seven times and anchor the external portion of the
protein to the plasma membrane where it can
interact with its ligand. In the testis, Sertoli
Production of gonadotropins
Gonadal regulation begins in the hypothalamus which synthesizes and releases, in a
pulsatile manner, the decapeptlde gonadotropin-releasing hormone (GnRH)(Fig. 1). GnRH
acts directly on the gonadotrophs which are
the specific cells in the anterior pituitary that
synthesize and secrete the gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH and LH are glycoproteins which share structural similarity with thyroid-stimulating hormone and chorionic gonadotropin and which are the primary
hormonal mediators of testicular function.
These glycoproteins are comprised of two
non-covalently linked polypeptides. One pro-
GnRH
tein, the a-subunit, is common to both of these
hormones while the [3-subunit is unique to
each. Formation of the a-[3 heterodimer within
the endoplasmic reticulum of the gonadotrophs is essential for the hormonal activity of
the gonadotropins. Synthesis and release of
the gonadotropins within the pituitary involves
a complex regulatory process. Individual gonadotrophs are capable of secreting either FSH
or LH , or both FSH and LH. LH is known to
be released in a pulsatile fashion as a result
of the pulsatile stimulus of GnRH arriving from
the hypothalamus. FSH is released with less
frequent and more irregular pulses that have
smaller amplitudes. In some species, especially those with seasonal variations in spermatogenesis, another pituitary hormone, prolactin, may play a role in stimulating the reinitiation of spermatogenesis.
--
Paracrlneo
Factors
Germ cells
FIG 1. Components of the normal pituitary-testis
axis. GnRH acts on the pituitary to stimulate the
release of the gonadotropins. In this figure the testis is represented by the large oval. LH acts on the
Leydig cells to stimulate testosterone (T) synthesis
and secretion while FSH acts on Sertoli cells. T
stimulates spermatogenesis through actions on
peritubular and Sertoli cells and inhibits LH release
through a classical feed-back pathway. lnhibin can
negatively regulate FSH release from the pituitary
while the development of germ cells to sperm is a
result of the biological activities of the Sertoli cells.
Sertoli cells and germ cells communicate through a
number of paracrine factors.
Transduction of the LH/FSH signal
Glycoprotein hormones such as FSH and
LH elicit responses in target cells by interacting with specific receptor proteins on the plasma membrane. Binding of the hormone to its
8
Handbook of Andro/ogy-What compounds mediate communication within the male reproductive
system?
cells have the membrane receptors that make
them the target cells for the action of FSH. LH
binds to membrane receptors on Leydig cells
and stimulates the production of testosterone.
The G-proteins are a large family of membrane-associated intracellular proteins that
transduce the initial signal (hormone binding
to receptor) into a biochemical event such as
the production of cAMP and the subsequent
stimulation of protein phosphorylation through
kinases. Most of the changes in cellular activities that occur because of the actions of the
gonadotropins are the result of phosphorylation of specific proteins.
Sites of action of gonadotropins
LH-stimulated Leydig cells convert cholesterol to testosterone which subsequently accumulates in the interstitium and the seminiferous tubules at relatively high concentrations.
Extracellular androgens are bound to related
carrier proteins such as androgen binding pro-
9
tein (ASP) produced by the Sertoli cells or testosterone binding globulin (TeBG) produced
by the liver. The adrenal also produces androgens; however, the contribution of adrenal
steroids to testicular function in normal males
is negligible. The target cells for testosterone
within the testis are the peritubular myoid cells
and the Sertoli cells. There is good evidence
that the germinal cells do not respond directly
to androgens. In some species, a portion of
the testosterone may be converted to estrogens by Sertoli or germ cells. The estrogens
then feed back to reduce LH stimulation of testosterone biosynthesis by Leydig cells.
FSH stimulates a variety of functions in Sertoli cells including the synthesis of secreted
proteins, like transferrin, that are involved in
the transfer of nutrients to germ cells. In response to FSH action Sertoli cells also produce inhibin which, along with testosterone, is
involved in feedback regulation of pituitary
function. lnhibin greatly reduces the release of
FSH while testosterone inhibits the secretion
of LH.
Suggested Reading
Sinha Hikim AP, Amador A, Klemcke H, Bartke A, Russell LD. Correlative morphology and
endocrinology of Sertoli cells in hamster testes in active and inactive states of spermatogenesis. Endocrinology 1989;125:1829-1843.
Griswold MD. Action of FSH on mammalian Sertoli cells. In: Griswold MD, Russell LD, ed. The
Sertoli Cell. Clearwater, FL: Cache River Press; 1993:493-508.
Salesse R., Remy JJ, M. LJ, Jallal 8, Garnier J. Towards understanding the glycoprotein hormone receptors. Biochemie 1992;73(1):109-120.
Fritz I. Sites of actions of androgens and follicle stimulating hormone on cells of the seminiferous tubule. In: Litwack G, ed. Biochemical Actions of Hormones. New York: Academic
Press; 1978:249-278.
Cooke BA, Choi MC, Dirami G, Lopez-Ruiz MP, West AP. Control of steroidogenesis in Leydig
cells. J Steroid Biochem Mol Biol1992;43(5):445-449.
Copyright © American Society of Andrology
How is communication mediated within the male reproductive
system?
Hormone receptors, signal transduction
Androgenic steroids are essential for the development and maintenance of the male phenotype. Testosterone, the predominant androgenic steroid hormone, is produced in testicular Leydig cells under the control of the glycoprotein hormone, luteinizing hormone (LH).
Testosterone may be metabolized to the more
active androgen, 5a-dihydrotestosterone (5aDHT) or to 17[3-estradiol. Both of these metabolites play important roles in reproductive
physiology: testosterone and 5a-DHT are essential for differentiation of the accessory sex
organs and external genitalia; whereas 17[3estradiol is critical for differentiation of sexual
dimorphic nuclei in the brain. In this review we
will focus on the mechanism of action of 5aDHT in the male reproductive tract.
have been demonstrated to be regulated at
the transcriptional level by androgens in vitro.
These include the human prostate-specific
genes PSA and hKLK2, the rat prostate-specific genes probasin and the C subunit of prostatein, and the rat liver-specific gene sip. Each
of these has been shown to contain a functional ARE in either the promoter or intronic
regions. Evidence for post-transcriptional regulation is also available for four secretory proteins (SVP 1-4) that are the major constituents
of the seminal fluid.
The AR gene itself is regulated by androgens, although the exact mechanism has not
been defined. In the majority of cases, steadystate levels of AR mRNA in androgen target
tissues are increased following castration and
decreased with androgen treatment. Moreover, changes in AR protein levels often parallel the response of mRNA to androgen availability . Recent evidence also suggests that
transcription of the AR gene is modulated by
agents acting through second messenger
pathways such as cAMP.
Androgen Receptor
The biological functions of androgens are
mediated through the androgen receptor (AR)
protein (Fig. 1). This protein binds both testosterone and 5a-DHT, although it has a much
higher affinity for the latter. Once the steroid
enters the cell and binds to the AR there is a
conformational change in this protein, that
causes the dissociation of several accessory
proteins from the AR, including heat shock
proteins. This conformational change exposes
the DNA binding domain on the AR, which can
then interact with specific sequences of DNA
termed androgen responsive elements
(AREs). AREs have been identified in the promoter and intronic regions of androgen responsive genes. Binding of the AR to an ARE
has the functional property of regulating transcriptional activity of the gene.
Pathological actions of androgens
If androgens are absent or their normal
route of action is blocked, then severe deficits
are observed in the male physiological state.
Androgen insensitivity syndrome (AIS) is
caused by functional defects in the AR protein
stemming from mutations affecting predominantly the steroid-binding domain or the DNAbinding domain of the AR gene. Complete AIS
is distinguished by an XIY genotypic individual
with abdominal testes, absence of Wolffian
derivatives and male levels of serum testosterone, who has female phenotypic characteristics including normal breast development, a
blind-ending vagina and a paucity of pubic
hair. This mutation emphasizes the critical necessity of a normally functioning AR in male
reproductive development.
Androgen Regulated Genes
Although the expression of many mRNAs
and proteins have been described as being
under androgenic control, only a few genes
10
Handbook of Andro/ogy-How is communication mediated within the male reproductive system?
11
Mechanism of Androgen Action
•······················································································
I
:
~C&I'l...-:s.a::lphao~HuTc:e-
1
Cytoplasm
-
-
-
-
-
-
1~
I
-
-
-
-
-
-
-
Nucleus
""DHT
de novo
AR
synthesis
ARE
-
mRNA I
------------
-ProteiJ
~-----------~----•••••••••••••••••••••••••••••••••••••••••••••••••e••••••••••••••••••••
FIG. 1. Mechanism of androgen action. Testosterone (T) enters the cell and is converted by 5 alpha
reductase to 5a-dihydrotestosterone (DHT). DHT binds to the androgen receptor (AR) leading to a conformational change in the protein and the dissociation of several accessory proteins, including heatshock
proteins (HSP). Binding of the AR to the androgen response element (ARE), along with other transcription
factors (TF) regulates the transcription of mRNAs. (From: Lindzey J, Kumar MV, Grossmann M, Young
C, Tindall DJ. Molecular Mechanisms of Androgen Action. In: Litwack G, ed. Vitamins and Hormones.
Orlando, Florida: Academic Press, Inc.; 1995;49:383-432.)
Sa-Reductase deficiency is caused by a
mutation in the enzyme Sa-reductase, which
is responsible for converting testosterone to
Sa-DHT. The absence of Sa-DHT in an X/Y
genotypic individual results in a female phenotype until puberty at which time there is
growth of the phallus into a penis-like organ.
This phenotypic change is thought to be the
result of increased availability of testosterone to bind to the AR, albeit at reduced affinity.
Although prostate cancer and benign prostate hyperplasia (BPH) are both associated
with androgenic influences on the prostate,
there is no evidence that androgens are directly responsible for these conditions. It is
likely that androgens play a supportive role in
maintaining prostatic cells in such a state that
environmental, dietary or genetic insults could
induce mutations of key genes such as protooncogenes or tumor suppressor genes.
Thus, androgens appear to be necessary but
not sufficient for these pathologic conditions.
Summary
The development and maintenance of the
male phenotype is highly dependent upon the
presence of the male sex steroid testosterone
and its conversion to the more active androgen Sa-DHT. Sa-DHT interacts with the androgen receptor and regulates transcriptional ac-
12
Handbook of Andrology-How is communication mediated within the male reproductive system?
tivity of androgen responsive genes through
an ARE sequence. This sequence of events
regulates the synthesis of proteins which are
critical for development of the male accessory
sex tissues and for growth of the external genitalia.
Suggested Reading
Chan L, Johnson MP, Tindall, OJ. Steroid Hormone Action. In: Collu R, Ducharme JR, Guyda
H, eds. Pediatric Endocrinology. New York: Raven Press; 1989:81-124.
Griffin JE, Wilson JD. Disorders of the Testes and the Male Reproductive Tract. In: Wilson JD,
Foster OW, eds. Williams Textbook of Endocrinology. Philadelphia: W.B. Saunders Co.;
1992:799-852.
Lindzey JK, Grossmann, ME, Kumar MV, Tindall OJ. Regulation of the 5'-flanking region of the
mouse androgen receptor gene by cAMP and androgen. Molecular Endocrinology 1993;
7:1530-1540.
Lindzey J, Kumar MV, Grossmann M, Young C, Tindall OJ. Molecular Mechanisms of Androgen
Action. In: Litwack G, ed. Vitamins and Hormones. Orlando, Florida: Academic Press, Inc.;
1995;49:383-432.
Murtha P, Tindall OJ, Young CY-F. Androgen induction of human prostate-specific kallikrein:
Characterization of an androgen response element in the 5'-promoter region of the gene.
Biochemistry 1993; 32:6459-6464.
Copyright © American Society of Andro/ogy
How are germ cells produced and what factors control their
production?
Germ cell development in the testis (including mitosis, meiosis,
spermiogenesis), Sertoli cells, other cell types
Spermatogenesis is an elaborate process of
cell differentiation starting with a non-differentiated spermatogonial germinal stem cell
and terminating with a fully differentiated highly specialized motile cell called a spermatozoon (Fig. 1). The formation of spermatozoa
takes place within narrow coiled seminiferous
tubules which form the bulk of the testis. Each
seminiferous tubule, approximately half a millimeter in diameter, may be close to one meter
in length. These tubules have a central fluidfilled lumen and a wall called the seminiferous
epithelium composed of germinal cells and of
somatic cells, the Sertoli cells, which support
and nourish the germinal·cells.
Spermatogenesis may be subdivided into
three main phases, each involving a class of
germinal cells.
First phase: The spermatogonia are immature germinal cells located at the base of the
seminiferous epithelium. In man, there are
three types of spermatogonia: the pale type A
spermatogonia or Ap, the dark type A spermatogonia or Ad, and the type B spermatogonia. The Ap spermatogonia divide by mitosis and give rise either to new type Ap cells or
to the more differentiated type B spermatogonia. Thus, the Ap cells may be thought of
as self-renewing stem cells since they can
produce both new Ap stem cells and a new
class of type B spermatogonia. The Ad spermatogonia, which rarely divide in normal
adults, are tentatively considered as dormant
reserve stem cells. The type B spermatogonia
produced by the Ap cells all divide by mitosis
to yield differentiated spermatocytes. Thus,
the spermatogonial population not only maintains itself, but continuously yields crops of
spermatocytes.
Second Phase: Spermatocytes are cells
which are unique in undergoing two successive special cell divisions, the so-called reduc-
tional or meiotic divisions, that produce, the
spermatids. These cells have exactly half the
number of chromosomes contained by the nuclei of cells that compose the rest of the body.
Spermatids are said to be haploid while somatic cells are diploid. In man, somatic cells
contain 46 chromosomes and spermatids and
spermatozoa contain 23 chromosomes. The
fusion of an haploid spermatozoon with an
equally haploid ovum restores the diploid
number of chromosomes in the cells of the
embryo.
Because there are two meiotic divisions,
there are two generations of spermatocytes:
primary and secondary. At an early or preleptotene stage, the nuclei of primary spermatocytes replicate their DNA content. Fine filamentous chromosomes subsequently appear
in the nucleus and the cells are at the leptotene stage. Soon after, homologous chromosomal filaments approximate each other and
form close pairs, a phenomenon called synapsis, and the cell is at the zygotene stage.
Then each chromosomal pair shortens and
thickens and the chromosomes assume the
pachytene configuration. The spermatocytes
go through an early, mid and late pachytene
stage during which the cell and its nucleus
progressively increase in volume. The pachytene nucleus also has a prominent nucleolus
indicating that these nuclei are actively synthesizing ribosomal RNA which enters the cytoplasm and contributes to the active protein
synthesis observed in these cells. Following
the long pachytene stage, the primary spermatocytes rapidly complete their first meiotic
division going through metaphase, anaphase
and telophase during which the homologous
chromosomes separate and migrate to the
poles of the cell which then splits to form two
daughter cells called secondary spermatocytes. These cells undergo a second matura13
14
Handlx>Ok of Andrology-How are germ cells produced and whallacJOtS ccnlrollheir prrxJIJCtlon?
lion division after a short interphase which,
this time, Is not accompanied by DNA repli·
cation. During this division, the chromosomes
(of which there is an haploid number) split in
half and each half reaches the nucleus of the
daughter cells, which are now referred to as
the spermallds. Thus spermatocytes, through
complex regulatory mechanisms and elabo·
rate cell division processes. are converted to
haploid spermatids. This process of meiosis is
covered in more detail in the following chapter.
Third phase: The newly formed spermatid,
a small spheroidal cell, undergoes a dramatic
metamorphosis referred to as spermiogenesis. The nucleus progressively elongates as
its chromatin condenses, and gradually takes
on the flaHened and pointed paddle shape that
characterizes the head of human spermatozoa. The Golgi apparatus elaborates a secretory·fike granule which gradually grows to produce a cap·like structure, the acrosome. over
the nuclear membrane. This structure con·
tains the hydrolytic enzymes necessary for the
fertilization of the ovum and partly covers the
nucleus of the spermatozoon. The centrioles
reach the membrane of the nucleus at the pole
opposite to that occupied by the acrosome.
bind to It and initiate the formation of the con·
tractlle components of the tall, I.e. the microtubules that form the axoneme. Tha mitochon·
dria migrate toward a segment of the growing
tall and form the mitochondrial sheath, whloh
constitutes the respiratory organ of the sper·
matoloon. The spermatid bulk of cytoplasm is
eventually discarded as the residual body,
which Is phagocytosed and eliminated from
the seminiferous epithelium by the Sertoll cell.
Thus. the spermatozoon Is a streamlined
cell 60 ~~om long with a head and a tail com·
pletely encased in a cell membrane. The head
is composed of a small compact nucleus cov·
ered by the acrosome. The tail Is made up of
the contractile axoneme associated with other
complex cytoskeletal elements and is parHy
covered by mitochondria. This cell will contin·
ue to develop and mature during Us transit
through the epididymis.
FIG. 1. The various steps of spermatogenesis in
man. Labels !rom the top to the bottom: Ad, dark
type A spermatogonium; />9, pale type A spermat·
ogonium: 8. type 8 spermatogonium; M. m1toses of
Ap 01 8 spermatogonia; PI , preleptotene primal)'
spermatocyte&: L, Z. EP. MP and LM correspond
to the various stages ol the prophase ol primal)'
spermatocytes (I.e .. leptotene. zygotene, earty, mid
and tate pachytene); II, secondal)' spermatocytes.
Oiv t and Dlv 2. correspond to maturation divisions
of the first and seconds!)' spermatocytes; In spor·
matocytes end spermalids the following elements
are labelled: G, Golgl apparatus. n. nucklOius: N,
nucleus. A, acrosome; c. centrioles: t, tail; m. ml·
tocllondria; R8. residual body. The spermatozoon
is seen in side view (left) 01 face view (right).
The complexity of the whole process of
spermatogenesis explains its marked sensltlv·
ity to toxic substances or hormonal Imbalance.
In addition, many abnormal and degenerating
germinal cells are observed during spermatogenesis I n normal men. Spermatogenesis
takes approximately 60 days. a duration that
does not appear to vary from one individual to
the next
Spermatogenesis is possibly one of the
most complex processes of cell differentiation
taking place In the tissues of adult Individuals.
Many of Its lacets remain to be studied and
clarified at the molecular level.
Handbook of Andrology-How are germ cells produced and what factors control their production?
15
Suggested Reading
Dym M. The male reproductive system. In: Weiss L, ed. Histology. Cell and Tissue Biology,
fifth edition. New York, Amsterdam, Oxford: Elsevier Biomedical; 1983:1000-1053.
Desjardins C, Ewing LL, eds. Cell and Molecular Biology of the Testis. New York, Oxford:
Oxford University Press, Inc., 1993.
Copyright © American Society of Andrology
What are the unique chromosomal events leading to the
formation of a haploid male germ cell?
Stages of meiosis, chromosomal events, genetic recombination
Meiosis is a unique form of cell division restricted to gametes (spermatocytes and oocytes). There are two primary purposes of
meiosis:
MEIOSIS I
1)
To have a reduction division.
2) To provide genetic variation by exchanging segments of homologous chromosomes.
Prophase I
Primary
Spermatocyte
Spermatogonia divide by mitosis and differentiate until they become primary spermatocytes. They will then stay in the primary spermatocyte stage until puberty. At puberty, primary spermatocytes begin to divide by meiosis, which consists of two divisions. In the first
meiotic divisions, the prophase is long and involves so many specific nuclear events, that it
is subdivided into five parts: leptotene, zygotene, pachytene, diplotene and diakinesis.
In the leptotene stage, the chromosomes
are evident as thin, delicate filaments which
attach themselves to the nuclear envelope
(Fig. 1). Each chromosome is composed of
two sister chromatids. In the subsequent zygotene stage, there is intimate pairing of homologous chromosomes; in the human, 23
homologous chromosomes pair and form a trilaminar structure called the synaptonemal
complex. In the pachytene stage, there is exchange of genetic material between homologous chromosomes that is mediated by the
synaptonemal complex and a large recombinant nodule. This stage lasts 16 days in the
human. In the diplotene stage, desynapsis occurs and the areas where there was exchange
of genetic material are clearly seen at connecting sites called chiasmata. In the final
stage , diakinesis, the chromosomes condense.
The cells then proceed with metaphase
where the paired chromosomes align at the
FIG. 1. An illustration of the division of spermatocytes by meiosis, as described in the text. Each
chromosome is composed of two sister chromatids
in the leptotene stage, but the two sister chromatids
are closely opposed at this stage and are therefore
difficult to differentiate from each other until the
pachytene stage of the first prophase.
16
Handbook of Andrology-What are the unique chromosomal events leading to the formation of
a haploid male germ cell?
equatorial plate. Chiasmata separate and the
homologous chromosomes move to opposite
poles of the cell during anaphase. This division is in distinction to mitosis, during which
each pair of sister chromatids separates and
moves to opposite poles. In telophase, cytokinesis occurs and two separate daughter
cells result. At the end of this first meiotic division, the cells have differentiated to become
secondary spermatocytes.
There is a very short interphase between
the first and second meiotic divisions, and no
DNA synthesis occurs during this interphase.
Almost immediately, the second division begins with the secondary spermatocyte progressing from prophase through metaphase,
anaphase and telophase. The second division
closely resembles mitosis where there is separation of the sister chromatids along the centromere. At the end of the second division, the
secondary spermatocyte has become a spermatid.
In summary (Fig. 1), at the end of the first
meiotic division, one primary spermatocyte
has divided into two secondary spermatocytes. At the end of the second meiotic division, each secondary spermatocyte has divided into two spermatids so that there are a total
of four spermatids that were derived from the
primary spermatocyte (Table 1). Interestingly,
cytokinesis in both the first and second divisions is incomplete so that very small intercellular bridges form between the cells. This
bridge is termed a "syncytium" and allows for
simultaneous communication amongst the
cells.
17
Table 1. Diploid Versus Haploid: The 4N, 2N,
1N Quandary "N" can refer to either the number of chromosomes or the amount of DNA in
a cell.
A. If N refers to the number of chromosomes,
2N is diploid and 1N is haploid. Since all
somatic cells have 46 chromosomes or 23
homologous pairs (one paternal and one
maternal), somatic cells are diploid (2N).
Likewise, spermatogonia are also diploid
(2N). At the end of the first meiotic division,
the secondary spermatocytes have 23
double-stranded (containing a pair of
daughter chromatids) unpaired chromosomes and are, therefore, haploid (1 N). At
the end of the second meiotic division,
there are 23 single-stranded chromosomes
and these are also considered haploid
(1 N).
B. N can also refer to the amount of DNA in
a cell. In this particular case, N refers to
the minimal amount of chromosomal material which contains all of the genes.
Therefore, spermatogonia prior to the Sphase are diploid and have 2N amount of
DNA. After the S-phase (at the beginning
of meiosis) the primary spermatocytes
have doubled their amount of DNA and,
therefore, are 4N. At the end of the first
meiotic division, the secondary spermatocytes are haploid, but contain 2N amount
of DNA since they are double-stranded
chromosomes (sister chromatids). At the
end of the second meiotic division, the
spermatids are haploid and contain 1N
amount of DNA.
Copyright © American Society of Andro/ogy
What does the epididymis do and how does it do it?
Physiology, sperm maturation
matozoa are eventually stored within the cauda region. The gross structure of the human
epididymis is unique among the species studied in that it does not have a prominent cauda
region. Hence the human epididymis has little
capacity to store large numbers of spermatozoa as compared with many other species, for
example the ram or bull.
Histologically the epididymis is composed of
several cell types including principal, basal,
apical, halo, clear, and narrow cells, each of
which vary in number and size along the epididymal duct. The principal cells in the more
proximal regions of the epididymis tend to be
very tall resulting in a duct with a small luminal
diameter whereas, in the distal regions, the
principal cells are low columnar cells and the
luminal diameter much larger (Fig. 1). Such
dramatic differences in the cellular architecture are primarily due to the functional roles of
each cell within each epididymal region. In the
proximal region there is considerable absorption of water, hence the cells take on the classical appearance of a water absorbing epithelium -large apical surface area with long stereocilia, and many mitochondria in the basal
aspects. The distal epididymis is primarily a
sperm storage region, hence the cells are
much smaller and some cells, for example the
clear cells, are specialized for removing cellular debris. Ultrastructurally, epididymal cells
in general can be seen to have an extensive
endoplasmic reticulum and an elaborate Golgi
apparatus, reflecting the involvement of this
tissue in protein synthesis. Tight junctional
complexes between the epididymal cells form
what is referred to as the blood-epididymis
barrier, an important physiological and anatomical barrier that allows the epididymis to
create a specialized fluid environment for the
maturing spermatozoa. It has also been suggested that another function of the blood-epididymis barrier is immunological protection of
the spermatozoa. Spermatozoa are immunogenic and must be protected from the immune
"If anyone asks what the epididymis is,
we shall answer that it is a vessel constituting by various twists a body affixed to
the back of the testicle" (deGraaf, 1668;
see Jocelyn and Setchell, 1972).
Spermatozoa leave the testis neither fully
motile nor able to recognize or fertilize an egg,
but must traverse a long duct, the epididymis,
to acquire these abilities. These transformations of spermatozoa are called sperm maturation. For a number of years, the epididymis
was considered a holding-tube for the spermatozoa; the epididymis did not influence the
process of sperm maturation, but was a place
where spermatozoa aged. It was felt that
sperm maturation was inherent to the spermatozoa and had little to do with the epididymis. Because it takes anywhere from 1 to 14
days for spermatozoa to traverse the epididymis, the aging hypothesis seemed reasonable. However, it is now very clear that the
epididymis is actively involved in the sperm
maturation process, not only providing an appropriate environment but also providing many
of the molecules needed by the spermatozoa
to allow them to fertilize an egg.
Structure of the epididymis
Looking at the gross structure of the epididymis of several species, the organ can be divided into a number of segments or regions:
initial segment, caput (head), corpus (body),
cauda (tail) and the vas deferens (Fig. 1).
There has been much discussion of the precise delineation of each epididymal region as
it related to the gross structure of the organ,
to the physiological process within the organ
and to the localization of discrete stages of
sperm maturation. For example, sperm motility is generally observed as the spermatozoa
pass through the caput region whereas sperm
fertilizing ability is usually achieved as the
spermatozoa pass through the corpus. Sper18
Handbook of Andrology-What does the epididymis do and how does it do it?
initial
segment
caput
corpus
cauda
FIG. 1. Schematic representation of an epididymis showing the different regions: initial segment,
caput, corpus and cauda. To the right are shown
cross-sectional representations of the epididymal
duct at each region. Note how the luminal diameter
increases and the cell height decreases from the
initial segment to the cauda.
system during their transit along the epididymal duct.
Maturation of spermatozoa
It is the fluid microenvironment within the
epididymis that has been suggested to promote maturation of the spermatozoa. The fluid
is hyperosmotic and distinctly different in composition from blood plasma. In the epididymis
of many species the major constituents are organic solutes: L-carnitine, myo-inositol, glutamate, taurine, glycerophosphorylcholine, sialic
acids, lactate, and certain steroids such as
dihydrotestosterone. Concentrations of these
organic solutes can reach anywhere from 20
to 90 mM depending upon the species and the
epididymal region . The luminal fluid also contains several ions: sodium, potassium, chloride and bicarbonate. The fluid in the proximal
19
epididymis is quite acidic with pH values in the
6.5 range increasing 1o approximately 6.8 in
the distal epididymis. The role of each organic
solute and ion is not precisely known but several studies suggest they are involved in the
acquisition of motility, in osmoregulation for
spermatozoa and epididymal epithelial cells,
and in sperm and epididymal cell metabolism.
There are also several proteins found within
the lumen including transferrin, albumin, clusterin (SGP-2}, immobilin, retinoid-binding proteins, metalloproteins, proenkephalin, and enzymes such as glycosyltransferases, glycosidases, glutathione peroxidase, and gammaglutamyl transpeptidase. Several of these
proteins have been shown to be associated
with spermatozoa suggesting a role in sperm
maturation and/or sperm-egg interactions.
However, the role of most of these proteins is
not yet clear.
Other functions of the epididymis
In addition to promoting sperm maturation
and providing a place for sperm storage, the
epididymis plays a role in the transport of
spermatozoa along the duct and protects
spermatozoa from harmful substances. Spermatozoa within the epididymis of several species are held in a quiescent state by luminal
fluid factors and, therefore, do not propel
themselves along the duct. Transport of spermatozoa is achieved by two processes, contractions of the smooth muscle that surrounds
the epididymal epithelium, and the continuous
production and movement of fluid originating
from the testis. Protection of spermatozoa
from harmful substances such as xenobiotics
and oxygen radicals is an important aspect of
epididymal function. The manner by which this
is achieved is unclear, but it appears that the
epididymis has evolved elaborate protective
mechanisms. For example, the blood-epididymis barrier regulates the entry of solutes and
ions into the lumen, and the luminal fluid contains antioxidants, e.g., glutathione, and enzymes such as gamma-glutamyl transpeptidase, superoxide dismutase and glutathioneS-transferase involved in antioxidant defense
and protection against xenobiotics .
20
Handbook of Andrology-What does the epididymis do and how does it do it?
In summary, the epididymis promotes
sperm maturation, facilitates the transport of
spermatozoa along the duct, stores sperm and
protects spermatozoa from harmful sub-
stances. All these functions are coordinated
with remarkable precision to ensure production of fully viable spermatozoa.
Suggested Reading
Jocelyn HD, Setchell BP. Regnier de Graaf on the human reproductive organs. J Reprod Fert
1972; Suppl. 17:1-222.
Setchell BP, Brooks DE. Anatomy, vasculature, innervation, and fluids of the male reproductive
tract. In: Knobil E, Neill JD, eds. The Physiology of Reproduction. New York: Raven Press
Ltd.; 1988:753-836.
Robaire B, Hermo L. Efferent ducts, epididymis, and vas deferens: structure, functions, and
their regulation. In: Knobil E , Neill JD, eds. The Physiology of Reproduction. New York:
Raven Press Ltd.; 1988:999-1080.
Copyright © American Society of Andrology
What is the prostate and what is its function?
Physiology, function (anatomy, embryology)
unknown function. The proteins from the seminal vesicle cause the ejaculate to clot and
form a coagulum within a few minutes after
ejaculation. Subsequently, a serine protease
called prostatic specific antigen, secreted from
the prostate, lyses the clot. In rodents, a hard
elastic plug is formed and it is thought that the
slow release of sperm from the coagulum and
copulatory plug reduces reflux of sperm from
the female tract. Other proteins from the sex
accessory tissues coat the sperm and are believed to protect sperm from environmental
shock and agglutination, and to mask sperm
antigens from the female's immune system.
Other proteolytic enzymes in the secretions
help sperm traverse cervical mucus, while the
prostaglandins stimulate the female reproductive system to transport the sperm toward the
ovum. A cascade of activation of proteases
and cell signalling pathways is now being
studied to resolve how the sex accessory secretions work in temporal concert to assist the
sperm to fertilize the ovum.
The sexual accessory glands
The sexual accessory glands consist of the
seminal vesicles, the prostate, and Cowper's
glands (Fig. 1). They are involved in maintaining the viability and motility of the sperm and
in assuring the successful transfer of the
sperm to the female system, ultimately to fertilize the ovum. Over 95% of the ejaculate volume originates from the sex accessory tissues
and not from the testes, as is often mistakenly
believed. A human male's ejaculate volume is
about 3 ml and ranges from 2 to 6 mi. Of the
3 ml of an ejaculate, a very small proportion,
0.2 ml, originates from the bulbourethral gland
(Cowper's gland) and 0.5 ml from the prostate
gland. The largest portion, approximately 2 ml,
is secreted from the seminal vesicles and appears in the latter portion of the ejaculate volume. These exocrine glands that form the
ejaculate are located at the base of the bladder and empty their secretions directly into the
urethra at the time of ejaculation. The growth
of these glands and their secretory activity require androgen production from the testes as
well as a functioning androgen receptor within
the cells of the sex accessory tissues. Removal of testicular function by castration, drug
action or failure of the hypothalamic-pituitarytesticular axis will result in diminished circulation of androgens in the serum. As a consequence, the sex accessory tissues will involute and markedly shrink in size and function thus drying up the ejaculate.
In the normal male, the ejaculate is a rich
source of proteins and enzymes (20-40 mg/
ml), as well as highly bioreactive components
such as prostaglandins (200 1-Lg/ml), citrate ion
(4 mg/ml), spermine (3 mg/ml) and fructose (2
mg/ml). The term prostaglandins is a misnomer since these compounds are primarily derived from the seminal vesicles, which also
produce fructose. The prostate gland contributes high concentrations of citric acid, as well
as spermine, a very basic organic molecule of
Structure of the prostate gland
So what is the prostate? It is a small gland
the size of an English walnut and normally
weighs 25g. The gland is located at the base
of the bladder and surrounds the urethra (Fig.
1). The vas deferens, a muscular tube carrying the sperm from the testes, joins the duct
from the seminal vesicles, now becoming the
ejaculatory duct, and then immediately courses through the structure of the prostate to deposit the sperm and seminal vesicle fluid into
the urethra, at the center of the prostate gland.
The ejaculatory ducts enter the urethra at the
verumontanum. In the urethra, just beyond the
verumontanum, the ducts of the prostate appear allowing direct entry of the prostate secretions. There are 15-30 excretory ducts from
the prostate entering the urethra as it passes
through the prostate. This part of the urethra
is called the prostatic urethra. Each of these
21
22
Handbook of Andrology- What is the prostate and what is its function?
Lum en
O
Secretory
g ranules
~
0
Export~O
; !
Golgo a pp ara tus
Q
~
~
u
E
~
0£
:l
,
~
;.
..
c.t>
Lysosomes Q
memb,
_ ,•;,....-
o..,
,
~
;
<'
i ! ~ {;RNAt~S
"'!) Plj-;>
c:
"'
-5,
~
., _
Oct
V 0
d:~ 1z
f
E
~n
\
exporlo-ble
Ac!tvotoonf
Androgen
receptor
lfillllllllliJ
11
II
-<
..
?
~
)
OHT
.......,_...
t
Hormone~ ep~complex
Ool\ydrotesto steroneiOHTI
~----·-·- -}-··-Testosterone
FIG. 1 . Anatomy of the prostate and seminal ves·
icles. (From: @ 1995 by Ciba. Reprinted with permission from Ciba Publications, illustrations by F.H.
Netter, M.D. All rights reserved.)
excretory ducts receives prostatic secretions
from 4-6 prostatic lobules that contain prostatic acini surrounded by tall columnar epithelium. It is the acinar glands that respond to
androgen stimulation by producing secretory
proteins which are stored as viscous secretions in the ascinar spaces. During ejaculation,
nerves to the prostate from the hypogastric
plexus, under sympathetic stimulation, cause
muscular contraction of the prostate and excretion of the ascinar contents into the ducts
and out through the urethra and penis to form
the ejaculate.
Role of androgens in the prostate
Androgens control the growth of the prostate
and formation of the prostatic secretions. T estosterone, synthesized in the Leydig cells of the
testes under luteinizing hormone (LH) stimula-
FIG . 2. Androgen action in the prostate. Free testosterone diffuses into the prostatic cell and is converted to DHT by 5-alpha reductase. DHT binds
with androgen reGertor which in turn is translocated
into the nucleus, where it binds to the androgen
responsive element (ARE). Binding to the ARE induces transcription of mANA which leads to translation of proteins in the cytoplasm. (From: Aumuller
G. Morphologic and endocrine aspects of prostate
function. The Prostate 1983;4:195-214. Reprinted
by permission of John Wiley ana Sons Inc.)
tion , enters the serum, is complexed to a steroid binding globulin and is transported to the
prostate. The free testosterone, in equilibrium
with its bound and free form in the serum, then
diffuses across the epithelial and stromal cell
membranes and enters the prostatic cells (Fig.
2) . The testosterone is then metabolized to a
more androgenic substance called dihydrotestosterone (DHT) through reduction of a double
bond at the 5-position of testosterone. The enzyme, termed 5-a reductase, forms the more
potent DHT which then binds in a highly specific manner to the androgen receptor within
the cell. The DHT-bound androgen receptor attaches to a promoter area on DNA at a sequence called the androgen responsive element (ARE). This binding participates in andro-
23
Handbook of Androfogy-What is the prostate and what is its function?
THE PROSTATIC FUNCTIONAL UNIT
(CANI NE PROSTATE )
EPITHELIUM
SECRE TORY CELLS
BIONATRIX
Lumtn
CYTOSKEl.ElON
Apocal plasma
M tctO'\'IIIous COf't
membrane
s ~crttory
fermtnc.l web
gro.nult5
M tcrotubules
Coattd vts.clfS
Condtnsong vacuoles
Oesmosomes
Golgo apparatus
Rough tndoplasmoc
tttlculu m
Nud eus,
Nud~tus
M tcrofJioments
Port comptu
Prot~n network
Lomtnat
Motnx bound
repl1somes
MtiOChOf'ldrtC
l ysosomes
BASAl CELLS
Otsmosomes
Loloral and basal
STROMA
ptosmo mf'mbrones
Basal lomtno
BASAL LAMINA
ConnE-cllvt
elemtnts
t f tbtrs~ l omtntn, f•bronechn,
Ntrvf' terrn•nals
praltogl(tans )
Muse It colts ( acton, myoson PIC I
Ca~llan e 5
Fobrocytos
Connecltvt hssue
ftbt rs
Smooth musct•
Ground substance
~Is
FIG. 3. Prostatic cell showing epithelial and stromal components. (From: Aumuller G. Morphologic and
endocrine aspects of prostate function. The Prostate 1983;4:195-214. Reprinted by permission of John
Wiley and Sons Inc.)
gen-induced expression of genes such as prostatic specific antigen. In addition , growth
factors and their receptors can be induced by
DHT and there is much crosstalk between the
epithelial cells that form the secretions and
their surrounding stromal (connective tissue)
cells (Fig. 3). Short range cell-cell interactions
mediated through growth factors are termed
paracrine effects and this is an important pathway for the exchange of stromal-epithelial interactions. The stromal and epithelial cells also
excrete highly insoluble components forming
the extracellular matrix and basement membrane that creates a physical interface and solId state support between the prostate epithelial
and stromal components. The cooperation and
integration of these systems during development, growth, function and pathology of the
prostate is a most active area of research. We
also await the definition of precise mechanisms
by which the prostate influences fertility.
Prostate gland disease
The bad news is that the prostate is probably the leading gland in the American male
for causing medical problems. One of four
males will be operated on some time in their
lifetime to surgically relieve benign prostatic
hyperplasia (BPH) that compresses the urethra and produces urinary outflow obstruction.
BPH-related operations, most commonly a
transurethral resection of the prostate (TURP) ,
are the second leading cause of surgery in
males (400,000/yr)in the United States, second only to cataract operations. Far more serious is the high incidence of malignant
growths in the prostate gland. Prostate cancer
is the leading cause of cancers diagnosed in
the American male, now exceeding even lung
cancer. The diagnosis of prostate cancer is
being aided by detecting the presence of the
prostatic specific antigen (PSA) protein in serum. This protein from the prostate is in high
concentrations in the ejaculate (1-2 mg/ml)
and, when the prostate is damaged by abnormal growth of BPH or cancer, the PSA protein
inadvertently enters the serum where detection of greater than 4 mg/ml, indicates a prostate problem such as BPH or cancer.
24
Handbook of Andrology-What is the prostate and what is its function?
Suggested Reading
Luke MC, Coffey DS. Male Sex Accessory Tissues Structure, Androgen Action, and Physiology.
In: Knobil E, Neill JD, eds. The Physiology of Reproduction, 2nd edition. New York: Raven
Press; 1994.
Copyright © American Society of Andrology
What is semen? How does semen analysis assist in
understanding the reproductive status of the male?
Semen composition and analysis (animal, human), related tests
cauda epididymal fluid, or even blood plasma,
and others are unique products of that gland.
Thus, seminal plasma includes a broad spectrum of chemical constituents contributed by
the epididymis and the accessory sex glands.
The relative contributions of the epididymis
or different accessory sex glands to the seminal plasma of a given ejaculum are dependent on many factors including the interval of
sexual abstinence, duration of foreplay, pathophysiological processes in the male, and the
species. Because semen is a mixture of spermatozoa and fluids moved by emission from
the cauda epididymidis and vas deferens with
fluids from the accessory sex glands, the
sperm to fluid ratio is quite variable. The more
important attribute is the total number of normal sperm in an ejaculum rather than the concentration of sperm per unit volume. For similar reasons, in analyses of constituents of
seminal plasma, the total amount of a component should be considered in parallel with
its concentration. A human might ejaculate 40300 million spermatozoa, not greatly different
from the number ejaculated by a rabbit (1 00300 million), but substantially less than a dog
(0.2-2 billion) or horse (5-25 billion).
What is semen?
Semen is composed of spermatozoa
(sperm), produced in the seminiferous epithelium of the testis, and seminal plasma, the
components of which are secreted by the excurrent duct system and accessory sex
glands. When a spermatozoon is released
from the seminiferous epithelium the major
structural elements are in place, but additional
changes are induced by exposure to sequential milieus provided by the epididymis and
mixture with fluids from the accessory sex
glands at ejaculation. Typical spermatozoa of
the rat, human and stallion are shown in Fig.
1 and the important elements of a spermatozoon are depicted in Fig. 2. A partial list of
spermatozoal attributes essential for fertility is
presented in Table 1. Collectively, these attributes depend on the normal development and
function of the genomic package, the mitochondria, dense fibers and microtubular elements of the axoneme, the acrosome and enzymes therein, and the multi-compartmentalized plasma membrane.
Seminal plasma is the fluid portion of an ejaculum, but only one of several distinctly different fluids to which sperm are exposed. Spermatozoa are transmitted from the seminiferous epithelium in a fluid milieu, and the solutes
therein are removed and replaced within the
efferent ducts and epididymis. Ultimately,
sperm in cauda epididymal fluid are conveyed
through the vas deferens at the time of ejaculation and mixed with fluids from the accessory sex glands, namely the prostate gland,
vesicular glands (i.e., seminal vesicles), and
bulbourethral glands. Some species have a
complete array of accessory sex glands, including the above three types. Other species
lack the bulbourethral glands or vesicular
glands. Certain proteins and other molecules
in the secretion of one or more accessory sex
glands are identical to some components of
What is the goal of seminal analysis?
For a clinician, evaluation of seminal quality
is linked with a desire to predict potential fertility, identify causes of infertility, or detect
changes in potential fertility. The clinician is
concerned with minimal requirements to
achieve fertilization or contraception. For an
epidemiologist or toxicologist, seminal evaluations are the basis of assessing hazards in
the workplace, environmental factors, or risk
assessments relating to drugs and chemicals.
Detection of a significant probability of reduced fertility in a population is more important than accurate prediction of fertility for an
individual. For the animal breeder, the primary
25
26
Handbook of Andrology- What is semen?
Human
Horse
FIG. 1.
10pm
Typical spermatozoa of the rat, human, and stallion as viewed by scanning electron microscopy.
B.
A.
Plasma Mem brane
~~•+~--
...... r.....--
Mitochondri on
Plasma Membrane
Mitochondrion
Principal
Piece
~--
Fibrous Sheath
~--Axon eme
End
PieceC
FIG. 2. A. Major elements common to mammalian spermatozoa. B. Middle piece (top), principal (center)
and end piece (bottom) of a spermatozoon viewed in cross section.
27
Handbook of Andrology-What is semen?
Table 1. A Partial List of Attributes of Sperm Essential for Fertility*
"Acceptable" morphology
Metabolism for production of energy
Progressive motility
Capacity for hyperactivated motility
Membrane lipids
Stabilize plasma and acrosomal membranes
Flippase enzyme activity
Facilitate timely fusion, but not premature fusion
of membranes
Membrane proteins
Immunosuppressive factors
Attachment ligands available but masked to prevent premature binding
Acrosome reaction-inhibiting factor
Integral enzymes associated with fertilization
Enzymes modifying membrane glycoproteins
Acrosomal enzymes
*In addition, the genome of the fertilizing spermatozoon may affect
embryo development and apparent fertility. The genome
package must contain genes needed for development, and
lack lethal mutations or extra genetic material altering or inhibiting development
Reprinted with permission from the Journal of Andrology 14:397406, 1993.
goal is to determine which male(s) will be the
most fertile of genetically superior sires. Evaluations of sperm quality and estimation of potential fertility are the basis for management
decisions which might lead to production of
several hundred thousand offspring from an
individual sire. For each application, the implied goal is to predict accurately the potential
fertility of a seminal sample from an individual
male.
Unfortunately, this goal is not easily
achieved. Success in predicting fertility is limited by features of spermatozoa, the process
of fertilization, and approaches used for evaluation in vitro of seminal quality. Also, spermatozoal attributes necessary for fertilization
will depend on the methodology used to join
the gametes, i.e., copulation or in vitro fertilization; on prior history of the sperm, i.e.,
freshly ejaculated sperm or frozen-thawed
sperm; and on female factors, i.e., age or uterine and tubal environments.
Sometimes the conclusion from a seminal
analysis is obvious. When the semen analysis
reveals azoospermia, no progressively motile
spermatozoa, or a high proportion of morpho-
logically abnormal spermatozoa, the fertilizing
potential of the individual is poor. In most
cases the challenge is more complex. The
goal of a clinician or animal breeder is to predict correctly that a given male probably will
be infertile or will be reasonably fertile, relative
to the average value for males of that race or
species, or that a given seminal sample will
provide fertility similar to that previously obtained with other samples from the same
male. As contrasted to lack of fertilizing capability, considered above, accurate prediction
of high fertilizing capability is extremely difficult, or impossible, because a spermatozoon
must retain function of each of a number of
essential attributes (see Table 1) to be capable of fertilizing an oocyte. It follows that a
number of spermatozoa in a sample could be
incapable of fertilizing an oocyte, each for a
different reason. Limitations of current approaches for evaluation of seminal quality provide great opportunity for individuals intrigued
by investigating male reproductive function.
How is semen evaluated?
Traditionally, evaluations of seminal quality,
regardless of species, include measurement
of seminal volume, determination of spermatozoal concentration and, by multiplication
(volume x concentration), calculation of the total number of spermatozoa in an ejaculum.
This provides quantitative information which,
with knowledge of the interval since the previous ejaculations by that male, and with information on testicular volume, is an indication
of the capability of that individual's testes to
produce sperm. Absence of spermatozoa in
an ejaculate could be evidence of retrograde
ejaculation, blockage of excurrent ducts, or
testicular failure. There is no cut-off for the total number of sperm in an ejaculum below
which fertilizing potential is reduced or eliminated. Males of most species, but less so for
humans, typically ejaculate a number of sperm
far in excess of that necessary for maximum
fertilizing potential when deposited in the vagina or uterus by copulation. For many species, < 1% of the number of sperm in a typical
ejaculation will result in maximum fertility
28
Handbook of Andrology-What is semen?
when sperm are deposited by artificial insemination, provided the sperm are of good quality.
Quality traditionally is considered in terms of
the percentages of progressively motile sperm
or morphologically normal sperm. Until recently, both were subjective evaluations and
influenced by substantial observer bias. Despite these problems, the visual assessment
of sperm motility and morphology is the standard method used by most clinical andrology
laboratories. Computerized image analysis
systems are now available for determining
both percentage of motile sperm and the distribution profiles for velocity or other kinematic
attributes of individual cells. Relatively simple
imaging systems for objective evaluation of
sperm morphology are being introduced, but
have not yet gained wide acceptance.
Functional tests are used to further define
quality of a seminal sample in an infertility
practice or research laboratory. These include
capability of the spermatozoa to undergo an
acrosome reaction (spontaneously or stimulated), penetrate into a heterologous oocyte or
bind and penetrate into homologous zona pellucida, swim through cervical mucus, undergo
motility hyperactivation, or simply swim rapidly
away from a population of immotile or slow
sperm. Often one or more of these tests is
supplemented by immunological tests to determine if the spermatozoa or seminal plasma
contains auto-antibodies associated with reduced fertility. In a research setting, one might
perform more detailed analyses for the
amounts of certain enzymes normally present
in sperm, or analyze the presence and surface
distribution of glycoproteins thought to be involved in the fertilization process. Better predictions may be possible after image or flow
cytometric analysis of permeability of the
sperm plasma membrane, mitochondrial function, surface properties of the plasma membrane, and/or denaturation of nuclear proteins.
Finally, it is increasingly obvious that peroxidation of lipids of the plasma and acrosomal
membranes of spermatozoa is associated with
decreased quality. The extent of lipid peroxidation can be quantified. Many of these analyses provide only a mean value for the pop-
ulation of sperm, rather than a distribution of
values for the individual cells. Unfortunately,
information is needed on how many cells
"pass" for the full set of essential attributes.
Applications of semen analysis
Infertility occurs in approximately 15% of all
human couples. In general, 30% of these couples have a predominant male factor, 30%
have a predominant female factor, and the remainder have factors in both or no demonstrable cause. Semen analysis is the first step
taken to establish a diagnosis of male factor
infertility, and is performed in the initial screening tests of an infertile couple. Because of
large day to day variation in the quality of the
semen from an individual, at least two, and
preferably three, semen analyses at least a
week apart are usually performed to evaluate
the male partner of an infertile couple. In general, an analysis of human semen is regarded
as normal if:
1)
2)
3)
4)
ejaculate volume is :::::2 ml,
sperm concentration :::::20 million/ml,
::::50% of the sperm are progressively
motile, and
:::::30% of the sperm are morphologically
normal (WHO, 1992).
These assessments are performed in an andrology laboratory, usually by visual examination using a light microscope. The diagnosis
is based on the semen analysis together with
information from a physical examination and
medical history. If a patient has azoospermia
(no sperm) or very severe oligozoospermia
(less than 5 million/ml), endocrine status is
evaluated by measurements of serum concentrations of follicle-stimulating hormone, luteinizing hormone and testosterone. This helps in
diagnosis of the underlying etiology and assessment of prognosis.
For > 70% of the patients with >2-3 abnormal semen analyses, no specific cause of abnormal testicular function can be identified.
With these patients, specialized tests of sperm
function (Table 2) focusing upon sperm surface proteins, autoantibodies against sperm,
acrosome reaction, zona-free hamster oocyte
29
Handbook of Andrology-What is semen?
Table 2. Clinical Laboratory Evaluation of Human Semen
Routine
Specialized
Seminal fluid volume,
Sperm count, motility, and morphology
Leukocytes in semen
Sperm antibodies
Sperm-cervical mucus interaction
Computer-aided sperm analysis (motility,
morphology, sperm hyperactivation)
Acrosome reaction
Semen biochemistry
Sperm biochemistry
Sperm membrane lipids, proteins
Zona-free hamster oocyte penetration test
Zona pellucida binding test
penetration, human zona pellucida penetration
and binding, and other functions may be required. Through a combination of these tests,
more specific sites of dysfunction causing abnormality of the spermatozoa may be identified, and appropriate therapy planned. For instance, if investigations revealed that most
spermatozoa in an ejaculum are unable to
bind to the zona pellucida, the appropriate advice to the couple would be in vitro fertilization
by subzonal injection of spermatozoa or direct
intracytoplasmic injection of a spermatozoon
into each oocyte. With these new andrologic
techniques, fertilization and subsequent pregnancies have occurred in couples where the
male partner has very severe sperm dysfunction.
In veterinary medicine and animal breeding,
there are two general types of semen evaluation. The first is by a clinician evaluating a
male for breeding soundness and potential
fertility. Typically, testicular size is measured
and a single seminal sample evaluated. Animals whose testes are substantially smaller
than average values for males of the same
breed and age are rejected, as are males
whose semen contains <80% morphologically
normal sperm or <50% progressively motile
sperm. Failure to meet these criteria does not
mean that the male is sterile, but rather that
there is a reasonable probability the male will
not- be highly fertile.
The second type of evaluation is used in a
facility housing males, such as bulls or boars,
for wide-spread commercial distribution of
their spermatozoa, or a facility where dogs,
stallions or males of other species are brought
to enable collection and cryopreservation of a
limited number of doses for artificial insemination. To enable cryopreservation, the semen is mixed with an "extender", a salt solution containing egg-yolk or milk proteins and
sugars, and 4-12% glycerol, which is an essential cryoprotectant. Determination of the total number of sperm in the ejaculum is crucial
to enable extension of the semen to a concentration which provides the requisite number of sperm in each insemination dose, and
is linked with evaluations of sperm quality before processing. The extended semen is then
sealed in a series of plastic containers which,
for most species, are shaped like a drinking
straw and contain 0.25, 0.5 or 4.0 ml; each
straw is one insemination dose. Representative straws of cryopreserved semen are
thawed and the cells evaluated immediately,
and after several hours of incubation at 3rC,
to establish the percentage of progressively
motile sperm, their velocity, and often the percentage of sperm with a normal-appearing acrosome. Similar approaches also are utilized
by individuals involved in preservation of
sperm from humans or sperm from exotic animals, ranging from antelopes to zebras.
What of the future?
It is likely that approaches for seminal analysis in a clinical setting will remain similar to
those in use today, with primary reliance on
the manual counting of the number of spermatozoa and visual estimation of the percentage of motile sperm and the percentage of abnormal sperm. As a secondary screening,
30
Handbook of Andro/ogy-What is semen?
these classic tests may be augmented by
binding or enzyme-linked assays measuring
one or more attributes of the plasma membrane or a sperm enzyme. More importantly,
it is likely that some secondary and most tertiary laboratories will have access to instruments which characterize multiple attributes
on several thousand individual sperm representing the population. Flow cytometers now
serve this purpose. New imaging instruments
and techniques likely will be developed to
evaluate motion and morphology of individual
sperm in a wet preparation concurrently with
multiple probe assessment of biochemical attributes. Such analyses would add data for 3
to 5 functional attributes to those for 2 or 4
selected attributes of sperm motion and morphology. These newer tests may be able to
replace some of the biological tests currently
being used such as the zona-free hamster oocyte penetration and human zona pellucida
tests which are imprecise, time consuming,
technically demanding and expensive. With
appropriate selection of independent attributes
essential for sperm to have fertilizing capability, improved prediction of fertility should be
possible.
Suggested Reading
Amann RP. Can the fertility potential of a seminal sample be predicted accurately? J Androl
1989; 10:89-98.
Amann RP, Hammerstedt RH. In vitro evaluation of sperm quality: An opinion. J Androl1993;
14:397-406.
Davis RO, Katz OF. Operational standards for CASA instruments. J Androl1993;14:385-394.
Wang C, Swerdloff RS. Evaluation of testicular function. Bail/iere's Clin Endocrinol Metab 1992;
405-434.
WHO Laboratory Manual for the Examination of Human Semen and Sperm-Cervical Mucus
Interaction. Cambridge, England: Cambridge University Press; 1992.
Copyright © American Society of Andrology
What is sperm banking? When and how is it (or should it be)
used in humans? Animals?
Sperm banking, consequences of its use in animal and clinical practice
ease and other lymphomas, leukemia, nephrotic syndrome, diabetes, and multiple sclerosis.
2) Prior to elective sterilization or exposure
to hazardous environments. Occupational exposure to radiation, pesticides, and chemicals
can affect sperm function or genetic integrity.
Men engaging in military operations where
risks of death or exposure to sperm toxicants
exist also are candidates for sperm storage.
3) Before participating in fertility treatments
which require semen collection at a specific
time. For men who develop anxiety-related impotency or emission failure, sperm banking
ensures that treatment cycles can proceed as
planned. Patients whose occupations require
unscheduled travel also find that sperm banking reduces the risk of cancelled treatment cycles.
One of the concerns often expressed by
physicians about referring patients with systemic diseases for sperm banking is whether
the patient's sperm are of sufficient quality and
number to achieve a pregnancy. Although
sperm count, motility, and physiology may be
impaired before treatment is initiated, the technological advances in assisted reproduction,
such as direct sperm injection into the ooplasm, often can, at the present time, or will, in
the near future, be able to overcome many abnormalities present. Having many sperm
stored is definitely an advantage, since it may
reduce the need for in vitro fertilization and increase the chance for a successful pregnancy
outcome, but the desire to bank multiple ejaculates must be balanced against the necessity
of treatment initiation and financial constraints.
The use of cryopreserved sperm obtained
from anonymous donors as a treatment for infertility caused by absent or defective sperm
is the other major medical application of
sperm banking. In a 1987 survey, the United
States Office of Technology Assessment es-
Sperm banking, more formally referred to as
sperm cryopreservation, is a process intended
to preserve sperm function by freezing and
storage at ultra-low temperature. Upon thawing, sperm are introduced into a suitable recipient female by insemination into either the
endocervical canal or the intrauterine cavity,
or are used to inseminate oocytes during in
vitro fertilization. Sperm freezing originated in
the late eighteenth century, but the widespread uses of sperm cryopreservation began
after 1950. The discovery that glycerol had
cryoprotectant properties, and the availability
of liquid gases, especially liquid nitrogen, to
achieve ultra low temperatures for freezing
and storage, stimulated the development of
many sperm banking applications. The advantages of frozen sperm over fresh sperm include the following: they can be stored almost
indefinitely (at least for decades), allowing
preservation of genetic characteristics that
would be lost due to onset of disease, infertility, or death; they can be readily shipped anywhere in the world using small liquid nitrogen
containers which can withstand the rigors of
transport; and they can be placed in frozen
"quarantine", while the human or animal donor can be tested for semen-borne infections
or genetic problems.
Human Clinical Applications of Sperm
Banking
An important medical use of sperm banking
is patient autologous sperm cryopreservation,
called client depositor sperm banking. Client
depositor sperm banking is used in the following medical situations:
1) Medical disorders which inherently, or
through the treatment used to cure or stabilize
the disease, can impair fertility by causing decreased sperm count and function, early fetal
loss, genetic mutation, or impotence. Examples include testicular cancer, Hodgkin's Dis31
32
Handbook of Andrology-What is sperm banking?
timated that 30,000 births resulted from artificial insemination of donor sperm, with approximately 11 ,000 physicians providing the treatment to about 86,000 women. The practice
has probably increased and the demand for
fertile and safe sperm remains high. It is virtually impossible to adequately screen donors
for infectious diseases with long incubation
periods such as human immunodeficiency virus and hepatitis viruses or which are detected
with tests that require more than a few minutes to perform, i.e., most infectious diseases.
If the sperm are quarantined in the freezer,
however, the donor can be examined repeatedly for disease exposure over months or
years before the sperm are used. The Centers
for Disease Control has cautioned that fresh
anonymous donor sperm should not be used
for artificial insemination, and frozen anonymous donor sperm should be used only if the
donor tests negative for human immunodeficiency viruses after a minimum of 180 days
quarantine.
The ability to store sperm from men with
many different phenotypes and genotypes increases the selection that patients have in
choosing a donor, and reduces excessive use
of a donor within a limited geographic area.
Population statistics can allow determination
of the number of pregnancies that can be
achieved without increasing the risk of consanguinity in future generations. Generally,
sperm from a single individual are used to
achieve no more than 10-15 pregnancies in a
medium-sized city (500,000 to 1,000,000 inhabitants) in the United States. In other countries where ethnic diversity and ethnic intermarriage are not as common, the number
could be smaller, but depends in any case on
the live birthrate and number of inhabitants.
Usually, sperm banks attempt to package
donor sperm in plastic vials or straws containing at least 10 million motile sperm post-thaw,
which has been suggested as the minimum
adequate insemination dose. Since frozenthawed sperm have shorter longevity than
fresh sperm, the route and timing of insemination is critically important to achieving a successful pregnancy. Using qualitative urinary
luteinizing hormone (LH) measurement to de-
termine ovulation, and one or two intrauterine
inseminations within 20 to 40 hours of the LH
surge, approximately 70% of patients who
elect donor sperm insemination conceive, the
majority within six insemination cycles.
The American Association of Tissue Banks
(AATB) has standards for both donor and client depositor sperm banking, and accredits
banks by peer inspection. The AATB also
maintains a list of non-accredited sperm
banks. Several states have certification programs and the Food and Drug Administration
has recently begun to regulate tissue banking,
including gametes.
Sperm Banking in Animals
Sperm cryopreservation has important uses
in the livestock industry, especially in the
breeding of cattle, pigs, sheep and poultry,
and in animal husbandry for domesticated animals such as horses, cats and dogs. Sperm
from genetically desirable or "prized" animals
can be used to inseminate many females to
increase the number of offspring with the desired characteristics. The ability to easily
transport sperm has permitted the improvement of existing herds or the establishment of
new herds in regions of the world needing development of native food sources. Sperm
banking has also become an important way to
perpetuate endangered or exotic species in
the wild and in zoological parks.
The ability to use sperm banking to preserve important research animal strains has
been appreciated recently. Sperm cryopreservation could reduce the extraordinary cost of
maintaining genetic lines that now must be
preserved by continual breeding of the animals, increase the accessibility of various
strains to researchers since frozen sperm are
easier to transport than live animals, and reduce the risk of losing a valuable genetic line
through catastrophic accident, impaired reproductive efficiency, genetic drift, or disease. Because the millions of sperm normally present
in a single ejaculate represent millions of meiotic recombination events, cryopreserved
sperm can be stored for future studies of gene
recombination frequency and mapping of ge-
Handbook of Andrology-What is sperm banking?
33
netic loci when new DNA probes become
available.
es, the solutes present in the liquid phase surrounding the sperm rapidly become concentrated. Glycerol lowers the intracellular water
freezing point, thus the cells remain unfrozen
and become supercooled well below their actual freezing point. In response to high extracellular solute concentration and the osmotic
tendency of supercooled intracellular water to
leave the cells, sperm undergo a second volume adjustment as water moves outward, and
the cells become dehydrated. When extracellular water freezes and therefore solidifies, an
exothermic reaction known as the "heat of fusion" occurs, which can cause serious disruption of the cells unless externally reduced by
controlled cooling of the environment. Upon
reaching the temperature of liquid nitrogen,
-196°C, the sperm are placed in storage indefinitely, where they are presumed to reside
in a quiescent state of minimal molecular motion.
During thawing, the sperm are subjected to
similar rapid and dramatic changes in cell volume and membrane permeability. As the extracellular ice melts and becomes liquid, solute concentrations are rapidly diluted and water rushes into the sperm. As the temperature
rises, and as glycerol leaves the cells, the
sperm cell volume continues to expand. In order for function to be restored, the surface
area and volume must return to normal, the
membrane proteins and lipids must redistribute to restore molecular structure and mobility,
and bioenergetic demands must be met. For
maximum functional recovery to take place,
both the freezing and the thawing protocols
must be optimized, a very difficult task given
the paucity of data available about the processes.
Research efforts to improve sperm banking
techniques and post-thaw survival have intensified in the last decade and offer many career
opportunities for basic and applied research.
As protocols improve, the success of cryopreserved sperm applications will undoubtedly increase.
The Process of Sperm Cryopreservation
In spite of the important uses for cryopreserved sperm, little is known about the physical
and biochemical events which occur during
sperm freezing, storage, and thawing, or
about methods for detecting cryogenic damage. Sperm from most species survive current
cryopreservation protocols very poorly, and
best efforts usually result in recovery of only
about half of the original sperm motility. Sperm
function is also impaired, as manifested after
thawing by shorter longevity and reduced
membrane stability.
The goal of any sperm freezing protocol is
to prevent lethal intracellular ice crystal formation, control wide fluctuations in cell volume, and reduce membrane damage that accompanies temperature-induced phase
changes. The process is complicated by the
biochemically and physically diverse compartments of the sperm cell (acrosome, nucleus,
mitochondrial-flagellar network), all of which
may respond quite differently to freezing and
thawing. The sperm also are subject to damaging oxygen radical exposure during their
transit through wide temperature changes. Attempts to maximize post-thaw survival have
led to the development of sperm cell diluents
(extenders), cryoprotectants, and various
rates of temperature change to control alterations in extracellular and intracellular solvents and solutes.
In most cryopreservation protocols, the
ejaculated sperm are mixed with a buffered
diluent that contains an energy source such as
fructose or glucose, lipid, and a penetrating
cryoprotectant such as glycerol. After dilution,
the sperm initially undergo rapid shrinkage as
intracellular water leaves the cell, then slowly
return to their original volume as the glycerol
enters. Rapid cooling is initiated at a rate of
about -20°C per minute. Extracellular formation of ice crystals begins and, as water freez-
34
Handbook of Andrology-What is sperm banking?
Suggested Reading
Alvarez JG, Storey BT. Evidence for increased lipid peroxidative damage and loss of superoxide dismutase activity as a mode of sublethal cryodamage to human sperm during cryopreservation. J Andro/1992;24:232-241.
Hammerstedt RH, Graham JK, Nolan JP. Cryopreservation of mammalian sperm: what we ask
them to survive. J Andro/1990; 11 :73-88.
Li H, Cui X, Arnheim N. Direct electrophoretic detection of the allelic state of single DNA molecules in human sperm by using the polymerase chain reaction. Proc Nat/ Acad Sci 1990;
87:4580-4585.
Paige C. Freezing spermatozoa. In: Ashwood-Smith MJ, Parrant J, eds. Low Temperatures
Preservation in Medicine and Biology. Pitman; 1980:45-64.
Watson, P.F. Artificial insemination and the preservation of semen. In: Lamming GE, ed. Marshall's Physiology of Reproduction 4th Ed., Vol. 11. Churchill Livingstone; 1990:747-896.
Watson PF, Critser JK, Mazur P. Sperm preservation: fundamental cryobiology and practical
implications. In: Templeton AA, Drife JO, eds. Infertility. Springer-Verlag; 1992:101-114
Copyright © American Society of Andrology
How does the spermatozoon make its way to the egg and
how does fertilization take place?
Capacitation, acrosome reaction, zona binding
After a sperm leaves the male reproductive
tract and enters the female reproductive tract
it still has a long way to travel and many obstacles to overcome before it can fertilize the
egg. When sperm first enter the female reproductive tract they are not capable of fertilization, but require a maturation step called capacitation. Capacitation has not been completely defined but it is thought to involve cell
surface and metabolic changes. As a result of
capacitation the sperm have an altered pattern
of motility (called hyperactivation) and are capable of undergoing an acrosome reaction.
Acrosome reaction
The acrosome reaction is a Ca 2 ' -stimulated
exocytosis involving reorganization of the
membranes in the head of the spermatozoan.
Multiple fusions occur between the outer region of the acrosomal membrane and the
plasma membrane that overlies the acrosome.
The hybrid vesicles which result are released
into the surrounding environment along with
the fluid contents of the acrosome. Loss of
these anterior portions of membrane reveals
the inner acrosomal membrane which, together with the original posterior head plasma
membrane, form the new head cell membrane
of the acrosome-reacted sperm (Fig. 1). There
are specific movements of proteins from one
membrane region to another during the reorganization, although mixing of the membrane
components is incomplete. The acrosomal
contents are a rich source of enzymes, including hyaluronidase and the protease, acrosin,
that may function in penetration of the sperm
through the egg investments. The hybrid vesicles released during the acrosome reaction
could also carry such enzymes on their surfaces. The newly exposed inner acrosomal
membrane represents a further source of molecules that could be involved in digestion of a
pathway for the sperm though the egg invest-
ments or in binding sperm to the zona pellucida.
Where the sperm are when they acrosome
react and what signal(s) causes them to acrosome react are not completely clear. Binding
of sperm to the zona pellucida (an extracellular coat surrounding the oocyte) can induce
the acrosome reaction, but molecules that the
sperm contacts earlier in its progress through
the female reproductive tract may also facilitate or induce the acrosome reaction. These
include molecules in oviductal and follicular
fluids (e.g. progesterone) and also components of the matrix surrounding cells of the cumulus oophorus (see below). It is possible that
subpopulations of sperm acrosome react at
different sites on their passage to the egg (Fig.
2).
Cumulus penetration
When sperm reach the egg (more correctly
referred to as an oocyte because it has not
yet completed meiosis) they first encounter a
mass of cells, the cumulus oophorus, that surrounds the egg (Fig. 2). The cumulus cells are
follicular cells that encase the oocyte and are
ovulated along with the egg. Sperm swim between these cells to reach the egg, apparently
dissolving the extracellular matrix that holds
the cells together. The sperm carry with them
in the acrosomal contents and in the plasma
membrane the enzyme hyaluronidase that is
required for the penetration of sperm through
this cell layer rich in hyaluronic acid. Depending on whether sperm acrosome react in the
cumulus mass or remain intact, either pool of
hyaluronidase could be used for cumulus penetration.
Zona pellucida
When sperm reach the zona pellucida they
recognize it and bind to it. Although there is
35
36
Handbook of Andrology-How does the spermatozoon make its way to the egg and how does
fertilization take place?
Outer Acrosoma! Membrane
Anterior Head
Inner
Acrosomal
Membrane
Plasma
Membrane
Inner
Acrosomal
/Membrane
ACROSOME
REACTION
]- Equatorial
Region
Posterior Head
Plasma Membrane
Posterior Head
Plasma
Membrane
FIG. 1. A guinea pig sperm head before and after the acrosome reaction. During the acrosome reaction,
the anterior head plasma membrane (except for the posterior-most equatorial region) is lost after fusion
with the outer acrosomal membrane. Acrosome intact sperm bind to the zona pellucida by the anterior
head plasma membrane. Acrosome reacted sperm bind via the inner acrosomal membrane. The equatorial and/or posterior head region initiates fusion with the egg plasma membrane. The inner acrosomal
membrane does not participate in the membrane fusion but is incorporated into the egg cytoplasm. (Reproduced from the Journal of Cell Biology, 1984;99:163-164, by copyright permission of the Rockefeller
University Press.)
not a strict species specificity in terms of which
sperm will bind to a particular zona pellucida,
there is often a strong preference for binding
between sperm and zona of the same species.
In mouse, the zona pellucida is composed
of three glycoproteins called ZP1, ZP2 and
ZP3. Numerous studies have indicated that
acrosome-intact mouse sperm initially bind to
FIG. 2. A diagrammatic representation of sperm
penetration of the oocyte cumulus and zona pellucida during fertilization.
the carbohydrate region of ZP3. The identity
of the partner molecule on the sperm surface
is not yet firmly established; however, there is
excellent evidence that a galactosyl transferase on the sperm surface binds to one of its
substrates (N-acetylglucosamine) on the zona
and, because the second substrate (UDP galactose) is missing, the sperm remain bound.
Other candidates exist that could operate instead of, or in addition to, galactosyl transferase. If sperm are acrosome-intact when they
bind to the zona, they are induced to undergo
the acrosome reaction as a result of binding.
The acrosome reaction has been induced experimentally by the clustering of sperm surface molecules using the multivalent zona protein ZP3, or using antibodies that recognize
specific sperm membrane molecules.
Acrosome-reacted sperm are also able to
bind to the zona pellucida. It has been shown
in guinea pig that acrosome-reacted sperm
can initiate binding to the zona pellucida as
effectively as acrosome-intact sperm, and this
may also be true of rabbit and human sperm.
In all species it is presumed that, after the ac-
Handbook of Andrology-How does the spermatozoon make its way to the egg and how does
fertilization take place?
rosome reaction, the sperm must bind or rebind at least until zona penetration has begun
so that they will not be lost from the zona surface. In mouse there is some evidence that
the binding of acrosome-reacted sperm occurs to ZP2. The identity of the binding partner(s) on acrosome reacted sperm is still being researched.
In order for sperm to reach the egg plasma
membrane they must penetrate through the
zona pellucida (Fig. 2). This may involve digestion of a path through the zona and could
require enzymes either released by acrosome reacting sperm, or associated with the
sperm surface, including the newly inserted
inner acrosomal membrane. Only acrosomereacted sperm have been observed to penetrate through the zona. Motility is maintained
during penetration and the narrow penetration slit in the zona that the sperm move
through may also be created, in part, by mechanical forces.
When sperm penetrate the zona they come
to lie in the narrow space between the inner
boundary of the zona and the egg plasma
37
membrane, the perivitelline space (Fig. 2). At
this stage the sperm will first bind to the egg
plasma membrane and then fuse with it. There
may be more than one mechanism that allows
sperm to bind, because sperm from heterologous species or acrosome-intact sperm can
bind without being able to fuse. The binding
that is required for fusion may involve a sperm
membrane protein called fertilin (or PH-30)
which probably has an egg membrane integrin
as an adhesion partner. If this binding step is
blocked, then fusion is also blocked. One region of the fertilin/PH-30 protein that may participate in the fusion of the two lipid bilayers
contains a sequence that resembles the fusion peptide of viral fusion proteins.
Fusion results in confluency between the
sperm and egg membranes as well as the
sperm and egg cytoplasms. At the time of fertilization, the egg receives an unknown signal
that results in a rise in intracellular free Ca 2 +
and thereby activates the egg to initiate development of the new embryo. One of the consequences of activation is completion of meiosis, including production of the second polar
body, and the initiation of mitotic divisions.
Suggested Reading
Florman HM, Babcock OF. Progress toward understanding the molecular basis of capacitation.
In: Wassarman PM, ed. Elements of Mammalian Fertilization. Boca Raton: CRC Press;
1991:105-203.
Kopf GS, Gerton GL. The mammalian sperm acrosome and the acrosome reaction. In: Wassarman PM, ed. Elements of Mammalian Fertilization. Boca Raton: CRC Press; 1991:153203.
Myles DG. Molecular mechanisms of sperm-egg membrane binding and fusion in mammals.
Dev Biol1993; 158:35-45.
Ward C, Kopf G. Molecular events mediating sperm activation. Dev Bioi 1993;158: 9-34.
Yanagimachi R. Mammalian Fertilization. In: Knobil E, Neill J, eds. The Physiology of Reproduction. New York: Raven Press, Ltd.; 1988:135-185.
Copyright © American Society of Andrology
What factors determine the sex of an individual?
X, Y, SRY (loci, genes), sequence of events in development of normal male
degenerate and the Mullerian ducts develop
into the oviducts, uterus, cervix, and upper vagina.
One can view mammalian sex determination as occurring in three steps. First is the
establishment of chromosomal sex. This occurs at fertilization when either an X- or Ybearing sperm fertilizes an X-bearing oocyte
giving rise to an XX or XY zygote. Second is
the establishment of the primary sexual characteristics: the testes or ovaries. In XY fetuses, the fetal gonads differentiate into testes; in
XX fetuses, ovaries form. Third is the establishment of the secondary sexual characteristics which is dependent upon hormones secreted by the gonads.
What induces development of the gonads
into testes or ovaries?
It was initially assumed that humans had a
sex determining mechanism similar to the well
studied fruitfly, Drosophila, since in both species males are XY and females are XX. In the
fruitfly, sex is determined by the ratio of the
number of X chromosomes to autosomal sets
such that an XXY individual is female and an
XO is male. However, in 1959, the identification of an XXY male patient with Klinefelter
syndrome, an XO female patient with Turner
syndrome, and an XO female mouse suggested that, in mammals, the Y induces testes
development. Cytogeneticists have since
identified individuals with varying numbers of
X or Y chromosomes. All individuals who had
at least one Y chromosome had testes and a
male phenotype, irrespective of the number of
X chromosomes. The locus on the human Y
that induces testes development was designated the testes-determining factor ( TDF).
How does sexual differentiation occur?
A fetus is initially sexually indifferent and
has the primordia for both the male and female accessory sex organs, the Wolffian and
Mullerian ducts, respectively. In the 1940s
Jost demonstrated that the male phenotype is
imposed on a fetus that would inherently develop into a female. Jost surgically removed
the testes from fetal male rabbits at a stage
when Wolffian and Mullerian ducts were present and then allowed fetal development to proceed in utero. When Jost examined the fetuses at a later date, the castrated males were
phenotypic females (Fig. 1). Jost concluded
that the fetus is programmed to develop into
a female. However, if testes are present they
secrete two factors that override the female
program and masculinize the fetus. The first
factor, secreted by Leydig cells, is testosterone which induces the Wolffian ducts to differentiate into the epididymides, vas deferens,
and seminal vesicles. Male external genitalia
form when the cells of the urogenital tubercle
metabolize testosterone into dihydrotestosterone which induces the development of the penis and scrotum. The second factor, secreted
by Sertoli cells, is Mullerian inhibiting substance (anti-Mullerian hormone), which induces the Mullerian ducts to regress. In the absence of these two factors the Wolffian ducts
How does the Y chromosome control masculinization?
By correlating deletions on the Y with the
presence or absence of testes and by studying XX males which carry a tiny portion of the
Y on one of their X chromosomes, investigators mapped TDF to a 35-kb region of the Y
short arm. Cloning of this region resulted in
the identification of a gene designated sex-determining region Y (SRY). Convincing evidence that SRY is the testis-determining gene
was obtained when a 14.6-kb genomic sequence of the mouse SRY locus was shown
to be capable of inducing XX fetuses to develop into males in transgenic experiments.
The hypothesis is that SRY is a master reg38
39
Handbook of Andrology-What factors determine the sex of an individual?
~tullerian
duct
¥
~'"'~""""
Indifferent Fetal Gonad
undirTerentiated
/
\
Ovary
Testis
/'\...
uterus
degenerating
Wolman duct
MIS
0
FIG. 1.
Male rabbits castrated at a fetal stage at
which the secondary sexual characteristics are undifferentiated, develop as phenotypic females
(adapted from Jost 1947).
ulatory gene that initiates a cascade of gene
interactions that transforms the fetal gonad
into a testis (Fig. 2). SRY encodes a member
of the High Mobility Group-1/-2 (HMG) protein
family whose members are characterized by
an 80-amino acid DNA-binding motif called the
HMG domain. Several HMG proteins, including SRY, are transcription factors that recognize and bind a specific DNA target sequence
and cause the bound DNA to bend into an angle. The SRYtarget sequence has been identified in the promoter region of genes controlling sexual differentiation such as Mullerian inhibiting substance and P450 aromatase, an
enzyme that converts testosterone to estradi-
T
PHENOTYPE
FIG. 2. Model of mammalian sex determination.
Male development is imposed on a fetus that would
inherently develop ovaries and a female phenotype. TheY chromosome with its testis-determining
gene, SRY, induces the indifferent fetal gonads to
differentiate into testes. The testes secrete Mulierian inhibiting substance (MIS) and testosterone (T)
which give rise to the male phenotype.
ol. Furthermore it is present in the promoter
region of SRY itself suggesting a positive
feedback loop.
It took over three decades from the recognization of the Y as testis-determining to the
identification of SRY as TDF. The cloning of
SRY is undoubtedly a milestone in our understanding of mammalian sex determination.
The difficult job of deciphering how SRY regulates transcription and identifying the genes
upstream and downstream of SRY in the sex
determination cascade must now be addressed.
Suggested Reading
Affara NA. Sex and the single Y. BioEssays 1991;13(9):475-478.
Koopman P, Gubbay J, Vivian N, Goodfellow P, Lovell-Badge R. Male development of chromosomally female mice transgenic for SRY. Nature 1991;351:117-121.
Mclaren A. Sex determination in mammals. Trends in Genetics 1988;4(6): 153-157.
Mclaren A. What makes a man a man? Nature 1990;346:216-217.
Copyright © American Society of Andrology
Are there specific genetic defects affecting the male
reproductive tract? What are the underlying molecular
mechanisms?
Androgen insensitivity, Turner's and Klinefelter's syndrome, chromosomes,
gene loci
of Mullerian inhibiting substance (MIS) bytesticular tissue causes variable degrees of bilateral Mullerian duct regression, whereas local
secretion of high concentrations of testosterone are required for ipsilateral development of
the Wolffian ducts. If a uterus is present on
one side, an associated fallopian tube is often
also present. Approximately half of subjects
develop a uterus, but the cervix may be absent. The external genitalia are usually ambiguous, although relatively normal male or female appearance is possible. Hypospadias,
cryptorchidism or an inguinal hernia containing a gonad or Mullerian remnant may also
occur. The majority of true hermaphrodites are
raised as males due to the external appearance of the genitalia, even though over 50%
of subjects have a 46XX karyotype. Other karyotypes, such as 46XY, 46XX/XY chimerism
or various forms of mosaicism, may be present. Many 46XX true hermaphrodites do not
possess the SRY gene suggesting that the etiology of 46XX true hermaphroditism differs
from that of 46XX males who have a translocation of the Y chromosomal SRY gene locus.
Klinefelter Syndrome: Seminiferous tubular
dysgenesis occurring in 47XXY subjects with
Klinefelter syndrome represents the most
common cause of testicular failure, with an incidence of 1:1000 males. Prior to puberty, arm
span is increased and upper-to-lower body
segment ratio is decreased for age in affected
subjects. They are often diagnosed as a result
of personality disorders and mental retardation. Prepubertal subjects have small testes
but the histology is generally normal for that
age, except for a progressive tendency toward
decreased numbers of spermatogonia. With
the onset of puberty, gonadotropin (luteinizing
hormone and follicle-stimulating hormone)
concentrations in the serum increase but tes-
Sex differentiation occurs as a sequential
process during the first trimester of fetal life.
Genetic sex (Fig. 1) is established at the time
of fertilization, leading to development of gonadal sex and culminating in formation of sex
phenotypes (Fig. 2). Under normal circumstances, chromosomal sex agrees with phenotypic sex; however, occasionally chromosomal sex differs or ambiguity occurs in the
sex phenotype. Abnormalities of sex development are usually not life-threatening and occur at many levels. The clinical consequences
of abnormalities occurring early in sex development may result in conditions of intersex
whereas defects in more terminal phases of
male development may be represented by isolated cryptorchidism (failure of testes to descend into the scrotum) or microphallus (normally formed, but abnormally small penis).
Disorders of sex differentiation are often inherited as single gene mutations, and the
analysis of these disorders has been especially informative in defining the molecular and
genetic determinants of normal sex development.
Gonadal Disorders
True Hermaphroditism: The diagnosis of
true hermaphroditism is predicated upon the
presence of both testicular and ovarian tissue
in the same individual. Oocytes should be
present within the ovarian tissue. The majority
of subjects have a testis or ovary on one side
and a contralateral ovotestis containing both
ovarian and testicular tissue (50%), or have a
testis on one side and an ovary on the other
(30%), or bilateral ovotestes, or even bilateral
ovary and testis combinations (20%). The
amount of functional testicular tissue determines the internal duct structures. Secretion
40
Handbook of Andro/ogy-Are there specific genetic defects affecting the male reproductive tract?
ECG~SPERM
GeneUc Sex
•
•
Gonadal Sex
Phenryprc~sex
Internal
rogenltal System
r
External Features
External Genitalia
~
Secondary Sex
Characterlsilics
CNS
r~
Pituitary Gonadotropin
Secretion
Sexual
Behavior
FIG. 1. Sequential events in the determination of
genetic, gonadal, and phenotypic sex.
tosterone levels remain relatively suppressed
in accordance with the degree of testicular failure. Whereas the onset of puberty often occurs at a normal age, secondary sexual
changes may not progress to the normal adult
stage. Gynecomastia occurs, probably due to
the increased estradiol:testosterone ratio. In
all cases, seminiferous tubular function is impaired and spermatogenesis is absent.
Turner Syndrome: Turner syndrome, does
not strictly qualify as a disorder of sex differentiation. In the classic case, the phenotype is
female, but with an absence of secondary sexual characteristics typical of puberty. Subjects
lack a normal X chromosome (45X karyotype)
and their ovaries degenerate into streak structures. The common anomalies of Turner syndrome include short stature, epicanthal folds,
high arched palate, low nuchal hair line,
webbed neck, shield-like chest, coarctation of
the aorta, ventricular septal defect, renal
anomalies, pigmented nevi, lymphedema, hypoplastic nails and inverted nipples.
XX Males: Subjects with an apparent 46XX
karyotype but male phenotype result from the
translocation of a fragment of the Y chromosome containing the testicular determining,
SRY, gene to another chromosome, usually
the X chromosome. Subjects may have undescended testes (15%) and hypospadias
(1 0%) and usually have small testes that may
be soft early in life but become firm with increasing age. Testicular histology reveals no
spermatogonia, a decrease in the diameter of
41
the seminiferous tubules, and Leydig cell hyperplasia, similar to that in Klinefelter syndrome. 46XX male subjects are shorter than
those (47XXY) with Klinefelter syndrome. Testosterone production is low whereas gonadotropin levels are elevated.
XY Gonadal Dysgenesis: Gonadal dysgenesis may be of the "pure" or "mixed" form
with the former referring to the presence of an
aplastic or "streak" gonad on both sides and
the latter referring most often to a unilateral
streak gonad on one side and testicular tissue,
usually within a dysgenetic testis, on the other
side. The pure form may occur in subjects with
a 46XY karyotype, whereas the mixed form
commonly involves chromosomal mosaicism
(45X, 46XY), but also occurs in 46XY subjects
with variable degrees of functional testicular
tissue in each of the gonads. The etiology may
be deletion of the Y chromosome or deletion
or mutation affecting the SRY gene.
Female Pseudohermaphroditism
Female pseudohermaphroditism occurs
when the external genitalia are virilized in a
female subject with a 46XX karyotype. These
subjects have ovaries; virilization is caused
by excessive androgen of extragonadal origin. The most common etiology is increased
adrenal androgen secretion as a consequence of congenital virilizing adrenal hyperplasia (CVAH). The predominant form of
CVAH is 21-hydroxylase (cytochrome
P450c21) deficiency which accounts for 8090% of female pseudohermaphroditism (Fig.
3). In addition to increased adrenal androgen
(dehyd roepiand rosterone and androstenedione) and reduced cortisol secretion, severe
deficiencies in P450c21 also result in salt-losing nephropathy due to coincident reductions
in mineralocorticoid (aldosterone and its precursors) synthesis. Less frequently, neonatal
genital ambiguity may result from 11 [3-hydroxylase (P450c11 and P450c18) or 3[3-hydroxysteroid dehydrogenase/ 6 5 -6 4 isomerase (3[3-HSD) deficiency. The former condition is often accompanied by hypertension
(low aldosterone, normal/high deoxycorticosterone) and the latter may involve coincident
42
Handbook of Andrology-Are there specific genetic defects affecting the male reproductive tract?
UndlfferanUated
Karyotype
XX~
Gonad~
XV
~
I
I
..,
TOF
No
Testosterone
I
Internal
1
ducts _ _ ~ __
1
I Wolffian
r1
--..
No Masculinization
J..-
Wolffian
Development
Mullerian
Development
~e_[~l~n.J
-
-
Testosterone
I
_1
/
"'
DHT ~Andr~en Receptor
.}
Gene Expre&Sion
Mascullnzlatlon of
Urogenital sinus &
External genitalia
Determinants of normal male and female sex differentiation in the human. In the presence of
FIG. 2.
the testis determining factor (TDF) gene the undifferentiated gonad in the male undergoes testis determination. Sertoli cells develop and secrete Mullerian inhibiting substance (MIS) that promotes regression
of Mullerian structures. Leydig cells in the testis produce testosterone (T) which acts locally to promote
Wolffian duct development. By four months in the female, the male ducts have disappeared and the
Mullerian ducts have fused to form the fallopian tubes, uterus and upper two-thirds of the vagina. In the
male, the Mullerian ducts have regressed and testosterone from the ipsilateral testis has stimulated the
Wolffian ducts to proliferate, forming the epididymides, vasa deferens, and seminal vesicles. Testosterone
carried by the fetal circulation is converted locally to dihydrotestosterone which interacts with androgen
receptors to promote masculinization of the external genitalia. The genital tubercle grows to form the
penis. The urethral folds fuse and are incorporated to form the urethra while the labioscrotal folds fuse
to form the scrotum. Later in gestation, the testes descend into the scrotum.
salt-losing nephropathy (low deoxycorticosterone ~aldosterone). In rare cases, excessive transplacental passage of androgen, either from an exogenous source or from
pathologic maternal production, has been reported to cause masculinization of the genitalia of a female in utero. The external genitalia of females may also appear to be virilized in association with other congenital
anomalies unrelated to steroid hormone effects and most often include imperforate
anus, renal agenesis and malformations of
the lower intestine and urinary tract.
Male Pseudohermaphroditism
Sexual ambiguity in the presence of symmetric gonads in a 46XY individual with testes
is classified as male pseudohermaphroditism.
This condition may be associated with varying
degrees of incomplete external and internal virilization.
Handbook of Andrology-Are there specific genetic defects affecting the male reproductive tract?
43
Cholesterol
I P,.;Oscc I
P450c17
Andrc>sf--5-ene--38, 17~iol
5
30-HSD /!1 - A•- Isomerase
Proglsterone1
~17~H
-: 7;'-~~ne.=
Prog;steroneU /
1
.-~~------P-45_0_c_2_1--~~~)
1
~
Deoxycorticosterone
~
Corticosterone
~--~----&rR---ed--u+~~se------~--.
l
P450aro
11-deoxycortisol \
Androstanedione - -
I
P450c18 and P450c11
~
Cortisol
-'Te-fecone \
l
IP450aro I
)
Dihydrotestosterone
f
Estrone
-
Estradiol
18-DH Corticostemne
I
I P450c18
t
Aldosterone
FIG. 3. Schematic representation of the major steroidogenic pathways. Those enzymes essential in testosterone biosynthesis by testicular Leydig cells are discussed in the text. Cytochrome P450c21 catalyzes
21-hydroxylation in the adrenal gland and is encoded by the CYP21 8 gene. Cytochrome P450c18 mediates 11 [3-hydroxylation and the further reactions involved in the biosynthesis of aldosterone. This enzyme is encoded by the CYP11 82 gene which is expressed only in the adrenal glomerulosa. Cytochrome
P450c11 is encoded by the CYP11 81 gene and exhibits exclusively 11 [3-hydroxylase activity. Cytochrome
P450aro catalyzes the aromatization of li 4 -3-keto C19-steroids into estrogens and is encoded by the
CYP19 gene. Sa-reductase activity is expressed predominantly in extragonadal tissues and is also discussed in the text.
Disorders of Androgen Biosynthesis: These
disorders affect the virilization of the internal
and external genitalia of the male embryo but
do not interfere with regression of the MOilerian system. These defects may be of variable
severity, partial or complete, and may present
at puberty as well as in the newborn period.
Variable degrees of ambiguity, from complete
feminization to mild hypospadias, may be
present at birth. All but one of the enzymes
(Fig. 3) involved in these defects are present
in both the gonad and the adrenal and the primary symptoms of hypertension and/or severe
renal salt loss in an affected subject may be
those of congenital adrenal hyperplasia. In
both cholesterol desmolase (cholesterol side
chain cleavage; P450scc) and 17a-hydroxylase/17,20-lyase (P450c17) deficiencies, male
infants are undervirilized due to decreased
testosterone synthesis. By contrast, the occurrence of these same enzyme deficiencies
in a female infant would not affect the otherwise female external genitalia. In 3[3-HSD deficiency, male infants are undervirilized whereas female infants are virilized. Severe deficiencies of P450scc and 3[3-HSD lead to extreme
salt-loss
due to
deficits
in
mineralocorticoid synthesis, and diminished
P450c17 activity results in hypertension. Defects of 17[3-hydroxysteroid dehydrogenase
(17[3-HSD), an enzyme present in the gonad
but not adrenal, result in deficient male genital
44
Handbook of Androfogy-Are there specific genetic defects affecting the male reproductive tract?
development and these subjects with ambiguous genitalia may virilize at puberty.
Defects in Androgen Action: Abnormalities
of androgen effect can be characterized as
those due to defects of the androgen receptor,
both partial and complete androgen insensitivity, and to deficiency of Sa-reductase enzyme
activity.
a. Sa-Reductase Deficiency: Male pseudohermaphroditism may result from inadequate
conversion of testosterone to dihydrotestosterone due to deficiency of steroid Sa-reductase 2 isoenzyme activity. Inadequate concentrations of dihydrotestosterone within the genital tubercle and labioscrotal folds lead to only
partial masculinization of the external genitalia. Sa-Reductase activity in the fetal genital
area peaks between weeks 7-12 of fetal life
when masculinization of the male genitalia
takes place. Later androgen exposure fails to
correct any defect during this period. This condition is also referred to as pseudovaginal perineoscrotal hypospadias because of the specific anatomical ambiguity most often observed. Testicular testosterone and Mullerian
inhibiting substance (MIS) production is normal so that Mullerian regression occurs and
internal Wolffian structures develop to varying
degrees. However, the sperm carrying ducts
end blindly before the prostate gland, so even
if spermatogenesis occurs, the ejaculate is
azoospermic. Inheritance is autosomal recessive and is common among some ethnic
groups due to consanguinity. In the undiagnosed subject or those in whom orchiectomy is
not accomplished by the age of puberty, the
ambiguous genitalia become further virilized
with phallic growth and development of a muscular male habitus and male body hair patterns. Hormonal profiles include normal or elevated testosterone levels with low DHT levels
in relation to testosterone and a high ratio of
Sf3- to Sa-reduced urinary steroid metabolites.
Stimulation with human chorionic gonadotropin further accentuates this altered ratio.
b. Complete androgen insensitivity (CAIS) is
characterized by the development of female
external genitalia and failure to masculinize
the Wolffian system in a subject with a 46XY
karyotype. Inguinal or labial testes may be pal-
pable, although they may only be discovered
during exploration of an apparent inguinal hernia. The vagina is short due to secretion of
MIS by testicular Sertoli cells. Increased testicular stimulation by elevated gonadotropins
at puberty results in normal or elevated testosterone levels to which the subject is nonresponsive. However, the peripheral aromatization (P4SOaro; Fig. 3) of testosterone and
androstenedione in skin and adipose tissue
leads to normal or elevated levels of estrogens (estradiol and estrone) which promote
female breast development when unopposed
by androgen action. Sexual and body hair is
scant. If the diagnosis is not made before puberty, primary amenhorrea or infertility may be
the presenting complaint. Additional studies
may include in vitro androgen receptor binding
measurements, hCG stimulation of testicular
androgen secretion, or assessment in vivo of
testosterone effect. The abnormality lies with
a molecular defect in the X-chromosomal androgen receptor gene causing an abnormality
in receptor function.
There is an increased risk of testicular tumors in CAIS and, therefore, orchidectomy
should be performed by the end of the second
decade of life, following completion of puberty.
However, if there is a possibility that the subject has a partial form of androgen insensitivity
(PAIS), with the risk of masculinization during
puberty, the testes should be removed prior to
that time. Carcinoma in situ as evidenced by
abnormal morphology of germ cells has been
observed in testes of a few subjects with AIS
during adolescence. Later in life, adenomataus transformation of both Sertoli and Leydig
cells has been reported to occur.
c. Partial androgen insensitivity presents
with highly variable degrees of virilization. The
phenotype ranges from slightly virilized female
genitalia, to penile hypospadias, undescended
testes and adolescent gynecomastia, to micropenis, and to isolated infertility. Subjects
who present with ambiguous genitalia or micropenis in the neonatal period may have hormonal profiles of elevated testosterone, luteinizing hormone and follicle stimulating hormone, which are characteristic of androgen insensitivity. Further diagnostic testing involves
Handbook of Andrology-Are there specific genetic defects affecting the male reproductive tract?
androgen stimulation in vivo. The lack of detectable or adequate penile growth in response to androgen is consistent with the diagnosis of androgen insensitivity. Marked ambiguity and biochemical evidence of severe
androgen insensitivity dictates a female sex of
rearing. In addition, a partial defect may allow
further masculinization at puberty in response
to increased testosterone secretion and therefore, gonadectomy should be performed prior
to puberty to prevent this occurrence. Mutations in the androgen receptor gene are responsible for the various presentations of
PAIS.
d. Hypospadias or micropenis may occur as
isolated phenotypic events or in association
with the observance of sexual ambiguity. Hypospadias is defined as failure of complete development and incorporation of the penile ure-
45
thra within the shaft of the penis. The urethral
opening may therefore be at any position on
the ventral surface of the penis from the perineum to the glans. The position of the urethral
opening forms the basis of classification as a
glandular, coronal, distal or midshaft, penoscrotal or perineoscotal hypospadias. Because
hypospadias reflects the failure of androgenstimulated midline fusion, it represents a form
of ambiguous genitalia. Its estimated occurrence is 8 per 1000 males. Micropenis refers
to the presence of a fully formed but small penis in the absence of other abnormalities of
sex differentiation. The definition is statistical
and refers to a penis which is 2.5 SO below
the normal standards for age and stage of pubertal development. Normal stretched penile
length for newborns is 2.8 to 4.2 em. The lower limit for 2.5 SO is 1.9 em.
Suggested Reading
Brown TR, Scherer PA, Chang Y-T, Migeon CJ, Ghirri P, Murano K, Zhou Z. Molecular genetics
of human androgen insensitivity. Eur J Pediatr 1993;152:S62.
Hum OW, Miller WL. Transcriptional regulation of human genes for steroidogenic enzymes.
C/in Chem 1993;39:333.
Lee MM, Donahoe PK. Mullerian inhibiting substance: a gonadal hormone with multiple functions. Endocr Rev 1993; 14:152.
Migeon CJ, Berkowitz GB, Brown TR. Male sex differentiation and development. In: Kappy M,
Blizzard R, Migeon CJ, eds. The Diagnosis and Treatment of Endocrine Disorders in Childhood and Adolescence. Springfield, IL: Thomas. 1994: Chap. 12.
Thigpen AE, Davis DL, Milatovich A, Mendonca BB, lmperato-McKinley J, Griffin JE, Francke
U, Wilson JD, Russell OW. Molecular genetics of steroid Sa-reductase deficiency. J Clin
Invest 1992;90:799.
Copyright © American Society of Andrology
Is there a trigger for puberty in the male? Should early or
delayed puberty be treated? If so, how?
Early, normal, delayed puberty, treatment
Physiology of puberty
Precocious Puberty
Reproductive function in man starts with sex
differentiation in fetal life and is followed by
maturation at puberty and then heterosexual
intercourse in adulthood. The same basic phenomenon governs all these aspects of reproductive function. Its starting point is the "gonadotropin releasing hormone (GnRH) pulse
regulator", described by Knobil, located in the
arcuate nucleus of the medial basal hypothalamus. The pulsatile secretion of GnRH activates the pulsatile secretion of luteinizing hormone (LH) and follicle-stimulating hormone
(FSH) which in turn activate the secretion of
testosterone by the Leydig cells in the testes.
A restraining system modulates the function of
the GnRH pulse regulator. During fetal life and
in the neonatal period there is very little restraint. By 4 to 6 months of age, greater (but
not complete) control is imposed over the
pulse regulator, and this degree of repression
is maintained until the early stages of puberty
at which time there is a progressive lessening
of restraint. An important question remaining
to be answered about the physiology of puberty is where the restraining system originates, and how it modulates the pulse regulator.
Although testicular maturation or "gonadarche" is the main hormonal event in puberty, it
is preceded by 6 to 12 months of adrenal androgen secretion or "adrenarche". The trigger
of adrenarche is probably a pituitary peptide
related to, but different from, adrenocorticotropic hormone (ACTH). This putative hormone has been termed adrenal androgen
stimulation hormone (AASH). The modulator
of AASH secretion is as elusive as that of the
GnRH pulse regulator.
Puberty begins in boys at 9 to 14 years and
is completed within 3 to 4.5 years. Table 1 lists
the developmental stages of external genitalia
and pubic hair as described by Tanner.
When the first signs of puberty occur prior
to 9 years of age in boys, puberty is considered precocious. The precocity is called central if its etiology is related to an early activation of the hypothalamus and pituitary with episodic production of gonadotropins. Treatment
with a long acting GnRH analogue will be effective in arresting the sexual maturation because constant levels of GnRH eventually turn
off the endogenous secretion of LH. A magnetic resonance imaging scan (MRI) may
show abnormalities of the central nervous system (CNS). Often precocious puberty is related to a benign hamartoma. Rarely, a malignant tumor is discovered in which case surgery is indicated. When the MRI reveals no
CNS abnormality the precocity is referred to
as idiopathic.
Precocious puberty is called peripheral
when it occurs in the absence of secretion of
pituitary LH/FSH. In rare cases, a tumor (such
as a hepatoma) can secrete human chorionic
gonadotropin (hCG) which in turn activates the
secretion of testosterone by the Leydig cells.
Also rare are the tumors of Leydig cells which
produce testosterone. Adrenal tumors can be
virilizing. One can also encounter a mild form
of congenital adrenal hyperplasia which produces signs of virilism. Finally, patients with
McCune-Albright Syndrome show the triad of
precocious puberty, bone fibrous dysplasia,
and cafe au lait spots of the skin. The etiology
of this syndrome is thought to be a mutation
of the G-proteins which are coupled to various
membrane receptors.
Delayed Puberty
Puberty is considered delayed in boys when
there is no noticeable enlargement of the testes by 14 years of age. As with precocious
puberty, delayed puberty can be due to central
46
Handbook of Andro/ogy-ls there a trigger for puberty in the male?
47
Table 1. Developmental stages of puberty
Stage*
Mean Age
(years ± SD)
G2
P2
11.6 + 1.1
13.4 + 1.1
Testes 2.5-3.2 em; thinning of scrotum
Sparse, long
G3
P3
12.8 + 1.1
13.9 + 1.5
Testes 3.3-4.0 em; pigmentation of scrotum; penis enlarged
Darker, curlier, coarser
G4
P4
13.7 + 1.1
14.3 + 1.1
Testes 4.1 em; further penile enlargement
Extend to pubis
G5
P5
14.9 + 1.6
15.1 + 1.1
Testes 4.5 em; adult penis
Adult
G gonadal stage, P pubic hair stage, G1: prepubertal testes, P1: no pubic hair
causes (hypogonadotropic hypogonadism) or
peripheral causes (hypergonadotropic hypogonadism).
The lack of gonadotrophic secretion may be
secondary to various CNS tumors or destructive disorders (histiocytosis, sarcoidosis, Lupus). It can also be related to congenital malformations of the brain such as pituitary aplasia, Kallmann syndrome, septo-optic dysplasia, or to head trauma with hemorrhage. In
some of these patients, it might be possible to
re-establish episodic LH secretion by episodic
administration of GnRH. Such therapy is rather cumbersome and usually patients choose
testosterone replacement treatment using an
intramuscular injection of testosterone enanthate every 3-4 weeks.
Primary gonadal failure is associated with
hypersecretion of LH/FSH, hence the term hypergonadotropic hypogonadism. This situation
can result from several abnormalities of sex
chromosomes such as Klinefelter syndrome
(47,XXY) and its variants including the socalled "46-XX males" in whom the Y-chromosome gene responsible for testicular determination (SRY) has been translocated to the
pseudoautosomal region of an X-chromosome. Testicular failure can be due to bilateral
trauma or tumor, radiation or an auto-immune
disorder. Poorly explained cases of partial gonadal dysgenesis, Noonan Syndrome
(46,XY,male Turner) and anarchia ("Vanishing
Testes") will also result in hypergonadotropic
hypogonadism. In most of these situations, the
only possible therapy is testosterone replacement.
Suggested Readings
Germak JA, Knobil E. Control of puberty in the rhesus monkey. In: Grumback MM, Sizonenko
PC, Aubert ML, eds. Control of the Onset of Puberty. Baltimore, MD: Williams and Wilkins
Pub.; 1990:69.
Grumbach MM, Sizonenko PC, Aubert ML, eds. Control of the Onset of Puberty. Baltimore,
MD: Williams and Wilkins Pub.; 1990.
Migeon CJ, Berkovitz GD, Fechner PY. Diagnosis of Pediatric Disorders in Biochemical Basis
of Pediatric Disease. Soldin SJ, Rifai N, Hicks JMB, eds. Washington, D.C.: AACC Press
Pub.; 1992:165.
Kappy, M, Blizzard RM, Migeon CJ. Wilkins -The Diagnosis and Treatment of Endocrine Disorders in Childhood and Adolescence. 4th ed., Springfield, IL.: Charles C. Thomas Pub.,
1994.
Copyright © American Society of Andrology
How is male infertility defined? How is it diagnosed?
Epidemiology, causes, work-up (history, physical, lab tests)
Defining infertility
their infertility is unknown and could be congenital or acquired. Recognition of a male reproductive component in an infertile partnership is often delayed because, traditionally,
women have been the primary focus of the
infertility evaluation and have ready access to
gynecological care; men are much more reluctant to seek advice. Men are also more apt
to confuse fertility with sexual potency (the
ability to have an erection), ejaculation and
ability to perform sexually, and they assume
that if they produce seminal fluid at orgasm
then they also produce sperm.
The known causes of male infertility are
quite numerous but can be grouped into a
moderate number of major categories (Table
1). In addition, a man may be mistakenly labelled as infertile because of failure to recognize subtle abnormalities in his sexual performance or in his partner's gynecologic function
(Table 2).
Infertility is defined as the inability of a sexually active, non-contracepting couple to
achieve pregnancy in one year, the time in
which about 90% of couples succeed. When
a female is in her 20s, the average time to
pregnancy is six months. This time frame reflects not only the limited few days in the middle of a woman's menstrual cycle when she
ovulates and conception is possible, but also
the fact that most conceptions do not survive
beyond early embryonic development and are
lost before a woman's next menstrual period.
In addition, about 15% of couples with a clinical pregnancy go on to a spontaneous miscarriage. The female partner's reproductive
age is also an important determinant of the
man's ability to initiate pregnancy since the
length of time required to establish pregnancy
increases progressively with advancing maternal age. Fertilization of the egg is more difficult and early pregnancy loss is more frequent as a woman becomes older. As
demonstrated from abortuses, chromosomal
abnormalities from aging eggs are frequent
among women with advancing maternal age,
but there may also be uterine factors that contribute to early pregnancy loss.
Among couples of reproductive age, about
10% are involuntarily infertile. Of such couples, about 30-50% are infertile because of
male reproductive dysfunction and, not uncommonly, both partners have reproductive
problems. An additional 40% of reproductiveage couples are infertile because of medically
or surgically acquired problems, including voluntary sterilization. Thus, only about half of reproductive-age couples can easily achieve
pregnancy.
Clinical evaluation
Considering all of the above issues, infertility requires a detailed evaluation of both partners. Meticulous attention to potential risk factors in the history plus a careful physical
examination of the man can provide important
clues to the origin of the problem(s) and guide
the selection of laboratory tests and methods
for subsequent treatment. In addition to assessing the state of virilization, presence of
gynecomastia and phallic competence, the
physician should also specifically document
testicular size, presence of epididymis and vas
deferens, prostate status, and whether a varicocele can be palpated and/or becomes evident following valsalva. With regard to testicular size, a calibrated orchidometer is
recommended, rather than just length and
width, as the volume of a sphere is a cubic
function of the radius and a more accurate and
convenient estimate of testicular mass. De-
Causes of male infertility
Male infertility is a multifactorial syndrome
encompassing a wide variety of disorders. In
more than half of infertile men, the cause of
48
49
Handbook of Andrology-How is male infertility defined?
Table 1. Known causes of male infertility
gonadotropin deficiency
chromosome aberrations
genetic disorders
excurrent duct obstruction
environmental toxicants
alcohol/recreational drugs
medications, chemotherapy, radiation
systemic illnesses
infectious disease (systemic and genital)
neurologic disorders
varicocele
autoimmune disease
impotence
creased testicular volume and turgor (atrophy)
provide important clinical clues to reduced testicular germ cell content.
Laboratory evaluation
Laboratory testing provides additional insight into both the extent and mechanism of
testicular dysfunction (Fig. 1). The hormonal
profile is essential in differentiating gonadotropin deficiency from primary testicular dysfunction. Regardless of cause, as the testicle fails,
the serum follicle-stimulating hormone (FSH)
level rises in proportion to the amount of spermatogenic tissue lost, while the serum luteinizing hormone (LH) level increases only when
testicular dysfunction is severe. The testosterone level is maintained within the normal
range, even in many men with clinical hypogonadism, because sex hormone binding
globulin levels become markedly elevated in
response to decreased androgen production
and increased estrogen concentrations. However, the free or unbound testosterone level
decreases. In contrast, disorders due to gonadotropin deficiency are characterized by a
profound fall in testosterone level and a failure
of reciprocal increases in FSH and LH. While
prolactin concentration is elevated in the presence of a prolactin producing pituitary adenoma, and in some men with acromegaly, the
production of this hormone remains unchanged in other testicular disorders.
Obstruction of the excurrent ducts (epididymis, vas deferens and ejaculatory ducts) is
characterized by the triad of azoospermia,
Table 2. Subtle abnormalities which can lead to
an erroneous diagnosis of male infertility
poor coital timing
retrograde ejaculation or anejaculation
anovulation, despite cyclic menses
corpus luteum deficiency
pelvic adhesions/tubal disease
recurrent early embryo loss
normal testicular size and a normal serum
FSH level. In this setting, a testicular biopsy is
essential in order to demonstrate complete
spermatogenic progression. The anatomical
site of the obstruction can then be determined
using a combination of procedures such as
vasogram, scrotal and rectal ultrasound, and
scrotal exploration with sampling of ductal fluids. In the special case of congenital absence
of the vas deferens, seminal vesicles and
Normal
Aplasia
Klinefelter
Cirrhotic
Castrate
FIG. 1. Schematic representation of hormonal relationships with progressive degrees of testicular
dysfunction.
50
Handbook of Andrology-How is male infertility defined?
Table 3. Traditional semen characteristics in
normal men
sperm concentration
volume
motility
forward progression
morphology
viability
>20 x 106/ml
:o>2.0 ml
>50%
>3 (scale 1-4)
:o>30% normal forms
:o>75%
ejaculatory ducts, semen is uniquely characterized by a small volume of non-coagulating
seminal fluid which lacks fructose.
In the majority of infertile men, detailed semen analyses are required to fully characterize their reproductive dysfunction. Several important caveats are worthy of note. Semen
should be collected with a consistent controlled abstinence interval (36 to 48 hours are
recommended). Sperm count, motility and other characteristics change with prolonged abstinence, making comparison between samples and between different men misleading.
Statistically, three semen samples are required to establish a stable estimate of values
because of inherent variability of this excretory
function. In addition, some noxious influences
on testicular function (hot baths, viral illnesses, and toxicants) may produce transient effects on semen quality which can last for 1 to
2 sperm cycles (3 to 6 months) necessitating
a moderately long term basal evaluation, especially when contemplating a therapeutic
intervention.
Conventionally, semen analysis includes
measurement of sperm concentration, semen
volume, percent of motile sperm, quality of forward progression of these motile sperm, viability and morphology (Table 3). Recently,
computer-assisted sperm analysis (CASA)
has become available, providing more sophisticated measures of sperm motion, such as
velocity, linearity and lateral head displacement. This automated method requires considerable technical attention to semen dilution
and randomized cell sampling to avoid selection bias. With regard to the various semen
parameters, there is clearly a progressive increase in the frequency of male infertility as
values for sperm concentration, motility and
Table 4. Specialized tests of sperm function
sperm autoantibodies
hypo-osmotic sperm tail swelling
reactive oxygen species
hyperactivation of sperm motility
acrosin content
acrosome reaction
hamster egg sperm penetration assay
hemizona binding
computer-assisted sperm analysis (CASA)
cervical mucus penetration
morphology by strict criteria
morphology deteriorate. However, there are
many exceptions. Some men with oligospermia (low count) can easily impregnate their
partner, and other men with normal semen parameters are infertile.
The above paradox has stimulated the development of a number of specialized sperm
function tests which provide considerable information beyond the traditional semen parameters (Table 4). Sperm count and motility
are primarily bulk parameters, while newer
measures address cell membrane integrity,
sperm capacitation and ability to acrosome react as well as sperm-egg interaction. With the
advent of in vitro fertilization, we can now directly assess sperm fertilizing ability. We have
come to recognize that male fertility involves
a complex series of events, wherein abnormalities in one or more steps block the ability
of that man to initiate a viable pregnancy (Table 5).
Table 5. Biological events normally required to
obtain pregnancy
vaginal deposition of sperm at ovulation
vigorous sperm motility
cervical mucus penetration
sperm capacitation
zona pellucida binding
acrosome reaction
zona penetration
oolemma binding
ovum penetration
sperm nucleus decondensation
syngamy
embryo development
uterine implantation
embryo and fetal survival
Handbook of Andrology-How is male infertility defined?
51
Suggested Reading
Liu, DY and Baker HWG. Tests of human sperm function and fertilization in vitro. Ferti/ Steri/
1992;58:465-483.
Clark RV, Sherins RJ. Male infertility. In: K.L. Becker, ed. Principles and Practice of Endocrinology and Metabolism. Philadelphia: J.B. Lippincott Co.; 1990:985-991.
Burris AS, Clark RV, Vantman OJ, Sherins RJ. A low sperm concentration does not preclude
fertility in men with isolated hypogonadotropic hypogonadism after gonadotropin therapy.
Fertil Steri/ 1988;50:343-347.
Calvo L, Dennison-Lagos L, Banks SM, Dorfmann A, Thorsell LP, Bustillo M, Schulman JD
and Sherins RJ. Acrosome reaction inducibility predicts fertilization success at IVF. Hum
Rep rod 1994;9: 1880-1886.
Sherins RJ. Clinical use and misuse of automated semen analysis. New York Academy of
Science 1991 ;637:424-435.
Copyright © American Society of Andro/ogy
What are the existing and future therapeutic approaches for
male infertility? When should IVF be used for male infertility?
What is the role for psychological counselling for infertility?
Treatment -medical, empirical, surgical, alternative, adoption, donor,
psychological
tuitary tumor can also result in a lack of production of LH and FSH by the pituitary with a
subsequent drop in testosterone production in
the testicle and loss of sperm production.
Bromocriptine suppression of a prolactin-producing tumor is highly successful in restoring
both normal hormone levels and sperm production. An initial dose of 5 mg per day is gradually increased until side effects occur or there
is normalization of gonadotropins and testosterone. Exogenous gonadotropin may still need
to be used in these cases because the tumor,
or treatment of the tumor with surgery or radiation therapy, can cause destruction of the pituitary itself. Finally, other effective specific
medical treatments include eradication of infection with antibiotics and decreasing antisperm
antibodies with corticosteroids. Although treating antisperm antibodies with corticosteroids is
treatment for a specific problem, it needs to be
emphasized that this treatment is controversial
because the effectiveness is sporadic, and the
steroids themselves can have serious side effects (e.g., aseptic hip necrosis).
Empiric medical therapy involves administration of an agent that somehow supports the
normal processes of sperm production in a
man who is infertile, but who has normal hormone levels. Approaches used include estrogen receptor blockers (e.g., tamoxifen, clomiphene citrate) to stimulate the pituitary to increase LH and FSH release, with a resultant
increase in intratesticular testosterone production. Chemicals known to artificially improve
sperm motility or appearance in vitro, such as
the protease kallikrein or the phosphodiesterase inhibitor pentoxifylline, have been given
systemically in an attempt to improve sperm
function. However, it must be stressed that empiric therapies are, in general, not successful in
improving male fertility when evaluated in con-
Infertility affects approximately 10-15% of all
reproductive-age couples and a male factor is
present in 40-50% of those couples. Specific
interventions to treat an abnormality in the male
partner is not possible for some affected couples. Fortunately, assisted reproductive techniques (ART) can help bypass the abnormality
in many patients without problems amenable to
specific treatment.
Current treatment of male factor infertility
The key to treatment of male factor infertility
is identification of a specific cause of abnormal
fertility.
Medical treatment
Specific treatment of males with hormonal
abnormalities is frequently effective. For men
without production of gonadotropin releasing
hormone (GnRH), and the subsequent lack of
pituitary release of the gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH), puberty is not achieved until exogenous LH, FSH or testosterone is given. Initial treatment with testosterone injections (in oil)
will activate the onset of puberty and the development of secondary sexual characteristics.
When the man is interested in fertility, sperm
production may be stimulated by intramuscular
replacement of the pituitary hormones LH (in
the form of human chorionic gonadotropin,
hCG) and FSH (as human menopausal gonadotropin, hMG; or recombinant human FSH).
Replacement of deficient hypothalamic hormones may also be provided with pulsatile subcutaneous GnRH given by a small portable
pump, but this treatment is awkward since the
patient must carry around the pump at all
times. Abnormal production of prolactin by a pi52
Handbook of Andrology-What are the existing and future therapeutic approaches for male
infertility?
Left internal
spermatic vein
53
trolled trials. A semen analysis may be abnormal for many reasons and, in addition, sperm
quality is highly variable in serial semen analyses from a single man over time. An apparent
improvement in sperm production temporally
related to an empiric intervention is more often
due to natural variability than to an actual effect
of the treatment on the man's fertility.
Left testicular
artery
FIG. 1. Illustration of the relationships between
the left renal vein and left internal spermatic vein
important in causation of a varicocele. Varicoceles
are much less common on the right side because
of the direct drainage of the right internal spermatic
vein into the vena cava.
Surgical intervention
Surgical intervention will allow correction of
obstructions of the reproductive tract or of
structural abnormalities that can affect sperm
production, such as a varicocele. A varicocele
results from enlarged testicular veins that are
thought to occur because of reflux of blood
from the left renal vein down into the left internal spermatic vein (Fig. 1). The reflux manifests
clinically as enlargement of the scrotal testicular veins (Fig. 2}, which may be easily seen
from across the room for a man with a large
varicocele in a standing position. The enlarged
veins are corrected by a direct surgical dissec-
FIG. 2. Schematic illustration of the external appearance of a large left varicocele and the underlying
enlargement of scrotal testicular veins.
I
54
Handbook of Andrology-What are the existing and future therapeutic approaches for male
infertility?
tion of the vessels of the spermatic cord with
division of the internal spermatic veins which
prevents reflux of blood in the testicular veins;
outflow of blood from the testis can then occur
via the external spermatic veins and vasal
veins. Alternatively, the veins can be obstructed angiographically via the inferior vena cava
by retrograde sclerosis. Overall, there is an improvement in the semen analysis in two-thirds
of patients after treatment of a varicocele.
Obstructions in the epididymis or vas deferens can be microsurgically corrected. An operating microscope is helpful to accurately
identify and reconstruct these structures that
are only a fraction of a millimeter in luminal diameter. Obstructions of the epididymis or vas
may be congenital, due to infection, or due to
iatrogenic intervention, such as a prior inguinal
hernia repair. Reversal of a vasectomy is typically very successful if a second blockage or
"blowout" has not occurred in the epididymis.
Vasal reanastomosis (i.e., vasovasostomy) under an operating microscope will yield patency
rates above 90% (and subsequent pregnancy
rates of 50-70%) in experienced hands, when
sperm are present in the testicular side of the
vas deferens. Pregnancy is not achieved by all
couples that have undergone a successful vasectomy reversal because of antisperm antibodies, female factor infertility, restricture of the
vas deferens and other poorly understood factors.
Obstruction of the ejaculatory duct may also
occur from congenital, infectious or iatrogenic
reasons. Resection of a small area of the prostate and ejaculatory duct can relieve these obstructions. Highly successful results are possible when a specific obstruction or obstructions
of the male reproductive tract can be identified
and corrected.
Bypassing abnormal sperm quality: assisted
reproduction
After all factors affecting male fertility have
been corrected and pregnancy has not occurred, it is appropriate to use assisted reproductive techniques (ART), which include intrauterine insemination (lUI), in vitro fertilization
(IVF), IVF with micromanipulation of sperm
etc., in an attempt to improve interaction between sperm and egg and, thus, increase the
chance of pregnancy. In selected cases, where
the female partner has an abnormality that will
require ART, it may be appropriate to proceed
directly to these techniques. For example, if the
female partner of a man with abnormal sperm
quality has obstructed fallopian tubes and IVF
will be necessary, it may be indicated to proceed directly to IVF without correcting the primary cause of abnormal male fertility. On the
other hand, treating a correctable male problem can result in improved semen quality and
better results at the time of IVF. In general,
these interventions in male and female partners must be closely coordinated to optimize
chances of achieving pregnancy with a minimum of treatments.
Intrauterine insemination involves processing
sperm into a small volume and placement of
the washed, concentrated sperm specimen directly into the female partner's uterus, timed to
the woman's ovulation. After 3-4 cycles (attempts) at lUI, pregnancy is rarely achieved.
The overall results with lUI are little better than
natural intercourse alone for male factor infertility. Specific success rates with lUI are also
dependent on sperm quality. If very poor sperm
motility is present, pregnancy rates are usually
less than 10% over a total of three or four cycles. With only minor impairment of semen parameters, pregnancy rates approach 50%.
These numbers differ by less than 5-1 0% from
expected pregnancy rates for natural intercourse over 10-12 natural cycles. IVF involves
stimulation of egg production in the female
partner, followed by transvaginal ultrasoundguided egg retrieval from the ovaries. Eggs and
sperm are then brought together outside of the
body. Up to four fertilized eggs (embryos) are
returned to the uterus after 2-3 days of incubation in vitro. Overall pregnancy rates of 1015% are achieved nationwide per attempt with
IVF. Optimal pregnancy rates (up to 50% per
attempt) can be achieved at a select number
of centers in which injection of a single sperm
into the egg is performed as part of IVF, an
involved and expensive process referred to as
intracytoplasmic sperm injection (ICSI).
Handbook of Andrology-What are the existing and future therapeutic approaches for male
infertility?
Substitutive treatments
In some cases, a couple will elect to use
sperm provided by an anonymous donor or to
proceed with adoption instead of having children that are genetically their own. This is a
difficult decision to make, as one's sense of
gender and identity sometimes are closely related to the ability to have children. In other
cases, the extremely high cost of assisted reproductive techniques and male infertility treatment are not covered by insurance, and the
only option for having children is to use donor
sperm or proceed with adoption. The use of
donor sperm is applied in those cases where
male factor infertility cannot be treated to allow
for pregnancy to occur, and/or assisted reproduction is unsuccessful or not an alternative for
the couple. Sperm is provided anonymously
from donors who are carefully screened by history for the presence of genetic and infectious
diseases. Donated sperm are frozen for a quarantine period of at least 6 months to allow serial
testing of the donor for the presence of HIV
antibodies. The donor is also tested for hepatitis and other sexually transmissible diseases.
The donor is usually identifiable by religious,
ethnic and physical characteristics, as desired
by the recipient couple. In some centers sperm
from a designated donor can be used. However, donation by a known donor is often discouraged because of the potential legal paternity liability that could later occur.
Psychological Counselling
Male infertility is often a psychologically disruptive situation, as fertility is assumed to be
natural and essentially automatic. In addition,
any disturbance in male sexual or fertility functions is likely to deeply affect a man's sense of
55
gender identity. Although men are unlikely to
immediately verbally express their psychological difficulty with the identification of a male fertility problem, jokes, denial and other seemingly
inappropriate behavior are common. In other
cases, depression may occur without an apparent cause. Any suspicion that the man may
be psychologically affected by the identification
of male infertility is an indication for referral for
psychological evaluation. In addition, any couple considering lUI with donor sperm should
consider psychological counselling. The issues
of masculine identity for an infertile man, and
lack of genetic parenthood may arise after the
"donor child" is born and cause psychological
difficulty for the father if not addressed prior to
donor insemination. An additional problem for
the couple who chooses substitutive treatments for infertility is what to tell friends, family
and the child him/herself. All of these issues
should be explored and discussed openly prior
to the initiation of pregnancy.
Summary
Male infertility is a common problem and can
be addressed successfully with a number of interventions. Direct treatment of the male problem, assisted reproduction, donor insemination,
and adoption are all alternatives for management of this situation. Modern technological advances, including ICSI and microsurgical correction of obstructive problems, allow many
couples who were not previously treatable to
successfully have children. Future developments in diagnosing and treating subtle endocrinopathies, better methods of treating antisperm antibodies, and identification of environmental causes of infertility are expected and
await the next generation of andrologists.
Suggested Reading
Pryor JL, Howards SS. Varicocele. Ural Clin North Am 1987;14:499-513.
Van Steirteghem AC, Nagy Z, Joris H, et al. Higher success rate by intracytoplasmic sperm
injection than by subzonal insemination. Report of a second series of 300 consecutive treatment cycles. Hum Rep rod 1993;8: 1061.
Lipshultz Ll, Howards SS, Buch JP. Male infertility. In: Gillenwater JY, Grayhack JT, Howards
SS, Duckett JW, eds. Adult & Pediatric Urology, 2nd edition. St. Louis, MO: Mosby-Year
Book; 1991.
Copyright © American Society of Andrology
How is fertility assessed in domestic animals?
Infertility diagnosis in the different species, evaluation of the male for clinical
management
to 5 days of this transit time are required for
maturation of sperm within the caput and corpus epididymidis, and the remaining 4 to 14
days are used for maintenance and storage
within the cauda epididymidis until ejaculation
or voiding concomitant with urination. For the
species being considered, each spermatozoon has a similar but distinctive paddle-shaped
head with a compact acrosome over the rostral portion of the nucleus, under the plasma
membrane. Other characteristics are as depicted in Fig. 1 of the chapter on semen. Numerous detailed analyses of sperm morphology have been completed and, at least for
boars and bulls, a number of specific spermatozoal defects have been linked with the
inability of that spermatozoon to fertilize an
oocyte or to produce a normal embryo.
Daily sperm production typically is 10-19 x
10 6/g testis in bulls, dogs and stallions and 2125 x 106/g testis in sheep and swine. Because
weight of a single testis can range up to
> 700g for the pig, daily sperm production per
male ranges from approximately 0.4 x 109 for
dogs, 5-8 x 109 for bulls, rams and stallions,
to 16 x 109 for boars. For dogs, the paired epididymides contain 2-5 x 109 sperm, whereas
those of the bull or stallion contain 30-80 x 109
and those of boars and rams 100-130 x 109
sperm. Frequent ejaculation reduces the number of sperm stored in the cauda epididymidis
and repetitive ejaculations in a single day
could remove up to 50% of the number previously present.
Endocrine regulation of reproductive function involves gonadotropin-releasing hormone
(GnRH), luteinizing hormone (LH), folliclestimulating hormone (FSH), testosterone and
estradiol (in a negative feedback control
mechanism) as in other mammals. In most domestic or pet species there is diurnal and/or
seasonal variation in the frequency or amplitude of pulsatile secretion of LH, and concomitant changes in the concentration of testos-
Andrological or breeding soundness examinations are common for bulls, boars, dogs,
rams and stallions. This chapter describes the
comparative evaluation of anatomy and physiology for a breeding soundness examination
(BSE). Further, the chapter summarizes the
diagnosis of common reproductive problems.
Species-specific reproductive function
There are subtle anatomical differences in
the basic structure and architecture of the testis and epididymis among species, and all, except the dog, have a full component of accessory sex glands (seminal vesicles, prostate
and bulbourethral glands). The dog has only
a prostate gland which, like that in man, is bulbous, surrounds the urethra, and with age often undergoes benign prostatic hypertrophy
(BPH). Anatomically, there are three types of
penis. In all cases, the penis remains in a
sheath when non-erect. The boar, bull and
ram have a fibroelastic penis which is semirigid even when non-erect and withdrawn into
an S-shaped curve; erection is a result of engorgement of the corpus cavernosum. The
stallion has an erectile penis, like the human,
and undergoes substantial enlargement of
length and diameter upon engorgement of the
corpus cavernosum. In the dog, an os penis
allows intromission prior to complete erection
with vascular engorgement of the corpus cavernosum. This is accompanied by engorgement of the bulbus glandis, a specialized area
of the corpus spongiosum. Muscular contractions of vaginal-vestibular muscles around the
engorged bulbus glandis create a mechanical
lock between the bitch and stud dog. In all
species except the boar, the testes hang between the back legs. In the boar the testes are
located on the caudal aspect of the back legs.
Depending on the species, spermatogenesis requires 39 to 61 days and transit through
the epididymis an additional 7 to 17 days. Two
56
Handbook of Andrology-How is fertility assessed in domestic animals?
terone as measured in peripheral blood. This
seasonal variation is especially significant in
horses and sheep, where the female typically
is sexually receptive only during a portion of
the year. There is a distinct seasonal cycle to
gonadal stimulation provided by the hypothalamic-pituitary axis, and sperm production
fluctuates by 30-50% annually, although
sperm are produced throughout the year. This
endogenous seasonality of the reproductive
cycles is synchronized by the effect of photoperiod length on animals.
Why a breeding soundness examination?
Semen collection from domestic and pet animals is relatively easy, which is a distinct advantage to the clinician. This is especially true
of cattle for which there has been tremendous
utilization of genetically superior sires for artificial insemination. A clinician evaluating a
male before sale/purchase or before the start
of a breeding season will perform a thorough
clinical examination augmented by detailed
examination of the reproductive organs and
collection of one or more samples of semen.
The question addressed is "Is this male likely
to be of low fertility or, for other reasons, not
useful as a breeding male at this time?'' If the
answer is yes, because the male fails to pass
one or more elements of the examination (Table 1), the owner would be advised not to use
him for breeding at that time. The male, however, might pass a similar examination in 1-6
months. If the male passes the BSE, it is likely
that the male will be of reasonable fertility
when mated to normal females, but factors not
detected (or subsequent changes) may intervene. In another situation, a male is presented
because the owner is suspicious or knows that
fertility is reduced relative to what it had been
earlier or relative to normal males of that species, or that seminal quality is "poor." This is
an all too frequent occurrence with valuable
stud dogs, stallions or bulls. The clinician attempts to address two questions: "Why is semen quality or fertility, or sexual behaviour of
this male low?" and "What is the prognosis for
improvement?" In some cases, the prognosis
and treatment may be obvious, but more typ-
57
ically a limited knowledge of reproductive
pathophysiology or economic conditions preclude an effective treatment other than allowing the passage of time.
Semen collection and analysis
There are three standard methods for collection of semen. An artificial vagina (A V) can
be used with a male of each species, and semen collected by deflecting the penis into the
artificial vagina as the male mounts a teaser
animal or phantom. The AVis a latex-lined cylinder which contains warm water to provide
heat and/or pressure. This approach produces
a very physiological condition, apparently satisfying to the male, and usually provides an
ejaculum most representative of that particular
male. Stallions and bulls are the prime candidates for the AV and the primary limitation to
its use is that the male must be accustomed
to the procedure. With boars and dogs, the
male is allowed to mount an estrous female or
phantom and the collector simply grasps the
free end of the protruded penis to mimic the
spiral interior of the cervix of the female pig or
the encircling vaginal vestibular muscles of the
female dog, and masturbates the male. The
alternative method of seminal collection, useful with bulls and rams, is electroejaculation
(EE). This is achieved by placing a probe
transrectally over the innervation dorsal to the
intrapelvic accessory sex glands, and applying
a mild electrical stimulation in a rhythmic manner. Appropriate restraint of the male is required. The resulting ejaculum typically is
more dilute than that obtained by an artificial
vagina, but the motility and morphology of
sperm is not altered by the procedure. It is important to recognize that collection of semen,
especially with an A V, can be potentially dangerous to the collector or the stud male. More
importantly, although the number and quality
of spermatozoa collected may be diagnostic,
especially if multiple samples are collected
over the course of 2 to 4 hours or at a uniform
interval over several days, absence of spermatozoa in a particular ejaculum does not
mean the male is permanently abnormal or infertile. Occasionally a normal male will provide
58
Handbook of Andrology-How is fertility assessed in domestic animals?
Table 1. Minimal normal values for breeding soundness examination parameters for domestic species.
Parameter+
Stallion
Bull
Ram
Stud Dog
Clinical examination
Normal
Normal
Normal
Normal
Motility
>50%
>30%
>30%
>70%
Morphology (normal cells)
Specific parameters
>80%
Not relevant
>70%
Scrotal
circumference
>70%
>80%
Scrotal
circumference
Not relevant
Insemination dose
(sperm number)
500xl06
Not checked
Not checked
100
X
106
+Society for Theriogenology Handbook. 1994. Society for Theriogenology, American College of Theriogenologists, Hastings, NE.
seminal fluid devoid of sperm, although frequent occurrence of this will be symptomatic
of a disease state.
In bulls and rams, ejaculation is essentially
instantaneous, occurring over a few seconds
with the semen discharged in a single jet. For
boars, dogs and stallions, the ejaculatory process includes a series of emissions and ejaculations, and it is possible to collect the semen
as a pre-sperm fraction, a sperm-rich fraction,
and a post-sperm fraction.
Evaluating infertility in stud animals
In order to diagnose pathology in the male,
a thorough history, clinical examination and
semen examination are essential. The history
of a subfertile male typically reflects multiple
breedings and no offspring. If clinical examination reveals gross congenital or acquired lesions then the diagnosis of infertility is simple.
However, a complete BSE must usually be
performed to pinpoint a problem. The normal
values of BSE parameters for several species
are listed in Table 1.
Clinical problems in our domestic animals
can be grouped into a number of primary
causes.
Environmental effects might be the most
common cause of reproductive problems in
domestic animals. Heat is probably the greatest offender, especially in stallions, bulls, and
boars. Rams are less affected because they
are fall breeders. Stud dogs are usually kennelled in cooler areas; however, veterinarians
see more cases of heat- and stress-induced
oligospermia and increased numbers of mor-
phologically abnormal cells. Excessively cold
temperature can also limit a male's fertility,
and freezing of testicular tissue results in sterility. Temperature-induced changes are diagnosed on history and BSE results. Therapy
involves reversing the initial insult.
Infectious agents are common problems,
especially venereal diseases. Brucellosis is a
venereal disease that causes epididymitis, orchitis and azoospermia. Brucellosis is primarily a problem in cattle, sheep and dogs and
usually requires euthanizing affected animals.
Other bacterial infections are common in stallions and stud dogs. Diseases are diagnosed
by the presence of white blood cells, culture/
sensitivities and BSE. Therapy is as indicated
by the culture and sensitivity.
Neoplasms are rare in domestic animals except in the dog where Sertoli cell tumors and
seminomas are seen. In older stud dogs, prostatic tumors are fairly common. Non-neoplastic prostatic disease (hyperplasia or prostatitis)
is also common in the stud dog. Therapy of
prostatitis, prostatic hyperplasia and prostatitic
neoplasia are antibiotics, castration, and ablation, respectively. Trauma is a common
problem, especially in the herd situation. This
is easy to diagnose clinically and therapy involves surgical intervention or medical therapy. Parasitism, metabolic problems and congenital problems are less common. These are
usually diagnosed on history and clinical presentation which then guide medical treatment.
Congenital problems are usually heritable and
these animals should be removed from the
breeding program. Finally, lack of libido can
Handbook of Andrology-How is fertility assessed in domestic animals?
be a significant factor that is difficult to diagnose and treat.
Summary
Diagnosis of fertility problems in domestic
animals is fairly simple if approached correctly. Clinical problems of domestic and pet animals can be grouped by primary cause, such
as environmental effects, infections, neoplasms and trauma. Idiopathic azoospermia or
infertility are also common and abnormalities
secondary to congenital, metabolic or parasite
problems also occur. Decreased semen quality due to high environmental temperature or
humidity during the summer is a frequent
problem in bulls, boars, dogs and stallions.
Venereal diseases, including brucellosis, are
common in dogs, cattle and sheep; epididym-
59
itis, orchitis and azoospermia typically result.
Dogs and stallions commonly present other
bacterial infections. The diagnosis of autoimmune and endocrinological problems is rare;
however, we must be ever vigilant for their
presence. The acquisition of a thorough history and completion of a comprehensive BSE
will usually pinpoint the problem.
Failure to produce offspring is the most
common manifestation of a fertility problem
and can lead to substantial financial loss for
the owner. Potential problems can be minimized by use of a breeding soundness examination prior to purchase of a breeding
male; diagnosis of a fertility problem can often
be relatively simple. Factors such as humananimal bonding and economics, as well as the
underlying etiology of the infertility problem,
dictate the appropriate course of action.
Suggested Reading
Barth AD, Oko RJ. Abnormal Morphology of Bovine Spermatozoa. Ames, lA: Iowa State University Press; 1989.
Cupps PT. Reproduction in Domestic Animals (4th Ed.). New York, NY: Academic Press Inc.;
1991.
McKinnon A, Voss J, eds. Equine Reproduction. Philadelphia: Lea and Febiger; 1993.
Morrow DA. Current Therapy in Theriogenology. Philadelphia, PA: W.B. Saunders Company;
1986.
Roberts SJ. Veterinary Obstetrics and Genital Diseases (Theriogenology). MA: Roberts Woodstock; 1986.
Copyright © American Society of Andrology
What are the existing male contraceptives and what is the
outlook for new ones?
Androgens GnRH antagonists, antibodies to sperm surface antigens,
compounds that act on sperm maturation in the epididymis
Hormonal-based contraceptive approach-
es
Production of spermatozoa in the seminiferous tubules and of the male sex hormone,
testosterone, by Leydig cells, depends on pituitary gonadotropins. The two pituitary gonadotropins responsible for testicular function
are luteinizing hormone (LH) and follicle-stimulating hormone(FSH). These gonadotropins
are regulated by the pulsatile release of the
hypothalamic decapeptide gonadotropin-releasing hormone (GnRH). There is a finely
tuned relationship between the testes and the
pituitary-hypothalamic axis called negative
feedback. It is based on the fact that testosterone or ovarian hormones administered to
the male in large quantities will suppress pituitary-hypothalamic production and the release of gonadotropins which in turn will stop
spermatogenesis. Historically, many combinations of androgens, progestins and estrogens have been utilized to stop normal pituitary function, an action that has been termed
"pharmacological hypophysectomy".
Recently, it has been shown that men injected with large doses of testosterone have a
complete absence of spermatozoa in their
ejaculates. This absence is termed azoospermia and is a highly effective contraceptive
method. Testosterone-induced azoospermia
occurs only in 60-70% of treated Caucasian
men, but in a greater proportion of Chinese
and Indonesian men (>90%). Most of the men
who do not develop azoospermia become oligozoospermic and have very low sperm
counts. Studies are now underway to ascertain whether severe, but incomplete, suppression of sperm production renders most of
these men infertile.
Studies on GnRH have included development of synthetic derivatives that mimic (agonists) or oppose (antagonists) the action of
60
GnRH. Agonistic compounds, when given in
large doses, initially stimulate the pituitary
gland to release LH and FSH but then suppress pituitary release of these gonadotropins,
a phenomenon known as down-regulation.
Despite this paradoxical decline in gonadotropin levels, agonistic analogs of GnRH have
not been very effective at inducing azoospermia, at least at the doses used. However, exploratory clinical studies using GnRH antagonists in combination with androgens suggest
that azoospermia can be reached more readily, and in a greater proportion of volunteers,
than with any of the previous hormonal approaches. This data base must be substantially expanded before the true potential of this
approach is realized. Two important factors
must be kept in mind concerning the GnRH
antagonist approach. First of all, androgen
substitution therapy is needed because the
use of antagonists leads to the loss of libido.
Secondly, the current generation of antagonists is too expensive to be of practical contraceptive use.
In addition to hormonal drug approaches,
attempts are being made to utilize vaccines
based on GnRH and FSH as potential male
contraceptives. These approaches are in the
early stages of clinical investigation and their
full utility will not be known for several years.
Direct inhibition of spermatogenesis
Accidental observations have shown that
the rapidly dividing cells within the seminiferous epithelium are exceedingly sensitive to a
variety of chemicals. Unfortunately, the effect
of many of these chemicals are not testesspecific and other end organs are affected,
which can result in systemic toxicity.
The best known agent that directly affects
the testes is gossypol, a yellow pigment found
in cotton seed oil. It has been extensively
Handbook of Andro/ogy-What are the existing male contraceptives and what is the outlook for
new ones?
61
Secretory neurones
HYPOTHALAMUS
I
LHRH
' • • • • • - LHRHanalogues
PITUITARY
[ _ _ _G_o_n_a_d_o_tr-op_h_s____]
1...1 • I••• • FSH
LH
't '
Androgen-dependent
target tissues
T
...,.
1
Leydig
cells
TESTIS
Sex steroids
Sertoli cells
I Spermatogonia
I Sperm!tocytes
I
~
• • • Gossypol
1
• • • lndazole-3-carboxylic acid
I
spe
atids
7
Spermatozoa
I
EPIDIDYMIS
C---------------------J
Spermatozoa
.
_
a-Chlorohydrin
• • • 6-Chloro-6-deoxy sugars
Sulphasalazine
I
Spermatozoa
1
"t • • • •
FIG. 1.
Condom
• - Vasectomy
Antibody
Approaches to male contraception.
studied in China and some other countries.
This drug appears to have a very narrow safety margin and the effective dose must be
closely controlled. Potassium metabolism and
kidney function can be disturbed in individuals
receiving this drug. Moreover, a relatively
large proportion of men fail to regain their fertility after prolonged exposure.
lndinopyridines represent a category of
drugs that rapidly disrupt spermatogenesis
without affecting male sex hormone production. Experiments are underway in animal
models to determine the specificity and reversibility of the action of these compounds.
The mechanisms by which these compounds
act is not known at this time.
62
Handbook of Andrology-What are the existing male contraceptives and what is the outlook for
new ones?
Sperm antigen-based vaccines
Interference with sperm maturation
Spermatozoa contain a number of unique
chemical components that are not observed in
somatic cells and which can be utilized as antigens in vaccine development. Many of these
antigens arise during the early stages of spermatogenesis before the fully formed spermatozoon is released into the lumen of the seminiferous tubule. When a male is immunized
with these sperm components, antibodies
against them penetrate into the seminiferous
epithelium and react with the antigens of the
early sperm cells resulting in an immunologically-mediated inflammatory process. If severe, this process destroys the seminiferous
epithelium leading to permanent infertility.
Women are potential recipients of antisperm
vaccines. Immunized women will produce antibodies that attack spermatozoa that enter the
female reproductive tract after coitus, thus
preventing fertilization of the ovum.
Spermatozoa acquire certain membrane
components during their epididymal maturation process, after they are released from the
seminiferous epithelium. These components
have not been well characterized as yet, but,
in theory, immunization against them should
result in infertility although normal sperm production would continue.
Conclusions
Development of a practical male contraceptive agent is being studied by a number of investigators. Drug and vaccine approaches
have had limited success to date and it appears unlikely that a male contraceptive will be
available before the year 2000. A somewhat
greater success may arise from methods that
promote vasectomy as a contraceptive by
making it more readily reversible.
Suggested Reading
Bernstein ME. Agents affecting the male reproductive system: effects of structure on activity.
Drug Me tab Rev 1984; 15:941-996.
Nieschlag E, Behre HM, Weinbauer GF. Hormonal male contraception: a real chance? In:
Nieschlag E, Halbernich UF, eds. Spermatogenesis -Fertilization -Contraception: Molecular, Cellular and Endocrine Events in Male Reproduction. Heidelberg: Springer; 1992:447501.
RayS, Verma P, Kumar A. Development of male fertility regulating agents. Med Res Rev 1991;
11 :437-472.
Swerdloff RS, Wang C, Bhasins. Male contraception: 1988 and beyond. In: Burger HG, de
Kretser DM, eds. The Testis, 2nd edn. New York: Raven Press; 1989:547-568.
Waites GMH. Male fertility regulation: the challenges for the year 2000. Brit Med Bu//1993;49:
210-221.
Wu FCU. Male contraception: current status and future prospects. C/in Endocrinol1988;29:
443-475.
Copyright © American Society of Andrology
How prevalent is erectile dysfunction? What can be done to
treat it?
Erectile physiology, etiology, work-up and treatment of erectile dysfunction,
psychological counselling
of the cavernous tissue just beneath the tunica
albuginea or lining of the corpus cavernosum.
These venules form a number of veins traversing the tunica albuginea called emissary
veins, which usually drain into the circumflex
veins on the outer surface of the tunica albuginea, that in turn drain into the deep dorsal
vein of the penis located in the dorsal midline
of the penile shaft (Fig. 2, 3A). Functionally, in
the flaccid condition, there is a high-resistance, low-flow arterial state in the cavernous
tissue, primarily regulated by the contracted
smooth muscles surrounding the cavernous
spaces. lntracavernous pressure in this flaccid
state is usually equal to resting venous pressure. With the initiation of erection, relaxation
of the sinus and arterial smooth muscle occurs
and a low-resistance system is produced with
blood flow increasing to 6 -10 times that of the
flaccid state. As the sinus spaces expand, the
subtunical venules are collapsed beneath the
tunica albuginea. The emissary veins are also
further collapsed by the expanding tunica albuginea so that venous efflux is markedly decreased and intracavernous pressure rises to
80 to 100 mm Hg, which is the pressure necessary for rigidity (Fig. 3B).
One of the essential recommendations to
come from a National Institute of Health Consensus Development Conference on Impotence held in December 1992 was to educate
health care providers and the public on aspects of human sexuality, sexual dysfunction,
and availability of successful treatment. Impotence, or to use the more appropriate term,
erectile dysfunction, affects approximately 30
million American men. It is only over the last
decade that the rigors of a more scientific approach to this dysfunction of the corporeal
cavernosal tissue have begun to unlock some
of the causes of and treatment for this disorder. This effort was the result of interaction between multidisciplined clinical specialists, and
basic scientists.
Anatomy and physiology
An erection is a psychosomatic-dependent
event -an integration of several mutually occurring actions in several different systems
(vascular, endocrine, and neurologic). Three
sets of peripheral nerves have a role in erectile function: thoracolumbar sympathetic, sacral parasympathetic and sacral somatic. The
most important neurotransmitter in initiation of
penile erection may be nitric oxide, also
known as endothelium-derived relaxing factor.
The spongy erectile tissue is located in paired
cylinders, called corpora cavernosa, which are
located on the dorsum of the penis. The internal pudendal artery, which generally arises
from the anterior division of the hypogastric or
internal iliac artery, is usually the source for
the penile arteries (Fig. 1). The corpora cavernosal sinus tissue is supplied by a slightly
eccentric central vessel (the cavernosal artery), which is derived from the pudendal artery, and branches to form the helicine arteries
(Fig. 2). The sinus spaces drain into a system
of venules that coalesce on the outer surface
Diagnosis
The causes of male erectile dysfunction
have traditionally been separated into two
broad areas, organic and psychogenic. For
the most part, this is a rather difficult distinction because the impact of this disorder on the
psychological state of the patient is devastating and can make treatment directed at a specific physical defect difficult. Similarly, psychological disease such as depression may result
in changes in the internal chemical milieu that
produce a true organic effect on the cavernosal tissue. Organic causes of impotence
can be classified as hormonal, neurogenic,
63
64
Handbook of Andrology- How prevalent is erectile dysfunction?
Internal
pudendal a~-- -
Obturator a.--
Superficial --- ---perineal a.-
I
I
I
I
I
Ureth~al a.
I
I
I
I
~sal
penile a.
FIG. 1. Diagrammatic representation of the penile arterial blood supply.
vascular (arteriogenic or venogenic) , or mus- of the patient is a crucial early step in the dicular, the latter involving disease of the agnostic process.
smooth muscle of the cavernous sinus or tisLaboratory studies generally obtained in all
sue.
patients are serum testosterone and prolactin
It is impossible to discuss diagnostic steps levels and urinalysis. Other laboratory tests
without stressing how this process is tailored are tailored to the patient and include: comfor each individual and his partner. Not every plete blood count and serum chemical profile
step is necessary for each patient. The vari- in the patient who has not had these recently;
ous diagnostic steps will be presented as in- fasting blood sugar or glycosylated hemogloformation about what is available for the mod- bin in patients with a family history of diabetes
ern evaluation of this disorder. As with other or who have this disease and are unsure of
disease evaluations, taking a history of the their current disease control; lipid profiles in
disorder for each individual is paramount be- patients with family history of lipid disorders or
fore making any further diagnostic plans (Ta- with other vascular disease history, and cerble 1). Physical evaluation should concentrate tain other endocrine evaluations when history
on the genital and rectal examination (Table or physical examination suggests the possi2). An evaluation of the psychological status bility of an endocrine disease. Many consider
Handbook of Andro/ogy-How prevalent is erectile dysfunction?
65
FIG. 2. Cross-section of the anatomical components of the penis.
the evaluation of nocturnal erection mandatory
by either a home monitoring machine or in a
formal sleep laboratory. All agree that these
studies are useful in patients when a psychological cause is thought to be the primary etiology of the erectile dysfunction, or a major
sleep disorder is suspected from the history.
Measuring the erectile response of the patient to an intracavernous injection of a
smooth muscle relaxant has become an important tool in the evaluation of erectile dysfunction. A full erectile response that lasts for
thirty minutes is usually indicative of no major
vascular nor sinus smooth muscle disease. A
lack of response does not definitely establish
organicity of the erectile dysfunction. Some
patients with psychologic-based impotence or
patients who are apprehensive in the testing
situation will not respond with a full erection.
Other more sophisticated diagnostic studies,
some of which are, more invasive are listed in
table 3. These other tests are more important
for those patients who are considered candidates for more invasive therapeutic choices
(e.g., arteriography if you are considering arevascularization procedure) . As mentioned
above, the diagnostic workup is directly controlled by the therapeutic goal decisions made
by the patient and his partner.
FIG. 3. A. Diagrammatic representation of a
wedge resection of the intracavernosal tissue
showing the condition of the arteries, veins and
constricted sinus spaces of the penis in the flaccid
state. B. Diagrammatic representation of a wedgeshaped intracavernosal space during the erect
state with relaxation of the sinus smooth muscles
allowing for engorgement of the sinus spaces and
collapse of the subtunical veins with flattening and
collapsing of the emissary veins leading to poor or
little flow to the circumflex veins.
Treatment
Today the focus of the physician who treats
erectile dysfunction is to identify the probable
primary etiologies of the condition in the individual patient and to design a therapeutic regimen that will deal with the physical and psychological aspects of the disease. Successful
treatment for male erectile dysfunction depends on the motivations and goals of the patient and his partner.
Rarely an endocrine or hormonal primary
etiology is found and this problem is best managed by the endocrinologist. Treatment may
66
Handbook of Andrology-How prevalent is erectile dysfunction?
Table 1. Evaluation of impotency
History
Genitourinary disease or surgery
Symptoms of vascular or endocrine disease
Systemic debilitating disease
Neurologic disease
Vascular, neurologic, spinal, or inguinal surgery
Genital, pelvic, or spinal trauma
Table 2. Evaluation of impotency
Physical Exam
Secondary sex characteristics
Gynecomastia
Genitalia
Palpation of penile corporeal tissue for plaques
Neurological
Perineal and penis sensation to touch and pin prick
Bulbocavernosus reflex
Sleep disorders
Psychologic history
Marital and sexual history
Nocturnal, early morning, nonintercourse erections
Medications
Pulses
Femoral
Distal extremities
Rectal
Prostate examination
Tobacco or alcohol use
Other drug use or abuse
consist of parenteral testosterone therapy or
therapy directed at specific endocrine disease.
If the patient is a diabetic with poor control of
his disease, sometimes return of this control
will improve erectile function. Treatment of
other conditions such as prostatitis, sleep disorders or hyperlipidemia sometimes leads to
improvement in sexual function. Modification
of medications, such as certain antihypertensives, or avoidance of substances such as tobacco and other drugs may be the most appropriate therapeutic intervention. Success
with such oral medications, such as vitamin E
or yohimbine has been anecdotal or not statistically verified in placebo-controlled trials.
lntraurethral delivery of vasoactive agents is
currently being studied. If psychological disease or disorder is the underlying etiology, the
psychiatrist or sexual therapist becomes the
primary caregiver for the patient and his partner.
Vacuum/constriction devices are a therapeutic choice for almost any type of erectile
dysfunction. They have become very popular
as the first choice of therapy with very little risk
for the patient, since these are purely external
devices. Proper expectations from the devices
and ongoing availability of the physician to an-
swer questions about the device are important
for success of this treatment.
Intermittent home self-injection therapy with
smooth muscle relaxants is the only accepted
pharmaceutical therapy directed at the cavernosal tissue. The agents most commonly used
for injection therapy are papaverine with or
without phentolamine, prostaglandin E-1, or a
combination of the three. These agents relax
arterial and sinus smooth muscle tissue converting the corpora cavernosa to a low resistance, high flow system, and mimicking natural erection. Priapism (prolonged erection) and
intracavernous fibrosis are the potential complications from this type of therapy, but with
proper controlled use, these complications are
neither common nor serious. This therapy has
Table 3. Other diagnostic tests for evaluation of
erectile dysfunction
Neurologic (Sensory)
Biothesiometry (measurement of vibratory
sensation)
Bulbocavernous reflex latency time
Arterial
Color duplex Doppler of cavernosal artery
Penile plethysmography
Pelvic and penile arteriography
Venous
Cavernosometry
Cavernosography
Handbook of Andrology-How prevalent is erectile dysfunction?
become quite popular worldwide and has
proven effective for patients with neurogenic
impotence (who are quite sensitive to very low
doses of the medication), medication-associated impotence, diabetes mellitus, minor or
even moderate arteriogenic erectile dysfunction, and, under some controlled situations for
patients with primarily psychogenic erectile
dysfunction.
Penile prostheses have been available as a
treatment option for almost two decades now
and have been placed in approximately
250,000 men in the United States. They are
basically inflatable or noninflatable rigid or
semi-rigid devices. The material that makes
up most of these devices is solid silicone, not
gel; polyurethanes are contained in one product. They are reliable (particularly with improved engineering) and resistant to wear.
Nevertheless, they are prosthetics and are not
guaranteed for life. Reoperation because of
mechanical or surgical complications such as
infection realistically occurs in 10-15% of patients over a 5-10 year period. Since this therapy is essentially non-reversible, the patient
and partner should be carefully told what the
67
prosthesis can and cannot do, and the risks of
reoperation and infection. Studies of patient
and partner satisfaction, although infrequently
reported in the literature, indicate high satisfaction for these prosthetic devices.
Vascular surgery, either arterial revascularization or venous ablation surgery, have been
presented as an option for treatment in a highly selected group of patients. Long-term success with this type of surgical intervention is
still lacking and, for the most part, this surgery
should be performed in centers with experience in this type of procedure.
The Future
What we know today about erectile dysfunction has only begun to scratch the surface. Some of the basic physiology and anatomy of the corpora cavernosa tissue remains
to be discovered; pathophysiological details of
erectile dysfunction are needed, particularly in
regards to the function and integrity of the sinusoidal smooth muscle. The epidemiology of
and risk factors for erectile dysfunction are
also poorly understood.
Suggested Readings
de Groat WC, Steers WD. Neuroanatomy and neurophysiology of penile erection. In: Tanagho
EA, Lue TF, McClure RD, eds. Contemporary Management of Impotence and Infertility.
Baltimore: Williams and Wilkins; 1988:3-27.
Krane RJ, Goldstein I, de Tejada IS. Impotence. N Eng/ J Med 1989;321 :1648-1659.
Lewis RW. Erectile dysfunction. In: Stein B, ed. Practice of Urology 1993 UPDATE. Pennsylvania: W. W. Norton & Company; 1993:21-38.
Lue TF. Impotence: a patient's goal-directed approach to treatment. World J Urol1990;8:67-74.
Lue TF. Tanagho EM. Physiology of erection and pharmacological management of impotence.
J Urol1987; 137:829-836.
Copyright © American Society of Andrology
Can spermatozoa be targets for drugs? If so, what are the
consequences of such drug exposure? Is there a need for
pre-conception counselling for men?
Drugs that affect sperm structure or function, male-mediated developmental
toxicity, prevention, tests to detect damage to spermatozoa
offspring, paternal smoking has been associated with low birth weight and increased perinatal mortality. In addition, an increased incidence of childhood cancer has been associated with paternal occupational exposures.
The exposure of men to motor vehicle exhaust
fumes or the products of combustion engines
has been associated with an increase in childhood leukemia. An increased occurrence of
Wilm's tumour has been reported in the children of vehicle mechanics, auto body repairmen and welders.
Thus, certain paternal chemical or drug exposures, including exposure to fuel combustion products, organic solvents and metals
such as lead and mercury, are consistently associated with an elevated incidence of abnormal progeny outcomes. In various studies, the
increased risk of an abnormal progeny outcome associated with a particular paternal occupation has ranged from 1.5 times to as high
as 5 times the risk for the control group. However, there are a number of professions which
have not been associated with an increased
likelihood of abnormal progeny outcome.
Therapeutic drug exposures are also of
concern with respect to progeny outcome. After men are treated with anticancer drugs,
there is a high incidence of transient or permanent infertility. However, when these men
have fathered children, the proportion of malformed children has not been higher than in
control groups.
The inherent limitation to most epidemiological and clinical studies is an inability to identify the specific chemicals or to control the exposures. These difficulties can be circumvented using well controlled animal studies. There
is convincing evidence from animal studies
that paternal exposures to specific environmental or therapeutic agents result in a higher
It is well established that there are dangers
to the progeny associated with maternal exposure to a variety of chemicals and drugs.
Interest in this area may be traced back to the
discovery in the 1960s that women exposed
to thalidomide during the first trimester of
pregnancy had offspring with severe limb malformations. Can exposure of men to xenobiotics (foreign chemicals) also result in an increased incidence of adverse effects on progeny? Such adverse progeny outcomes might
include early or late pregnancy loss, preterm
delivery or delivery of a small-for-gestational
age infant, malformations, behavioral abnormalities, or cancer. Two major approaches
have been taken to identify instances in which
paternal exposure to xenobiotics adversely affects progeny outcome, namely epidemiological studies and animal experiments.
Epidemiological studies have focused principally on determining the effects of paternal
occupational exposures on fetal development
and childhood cancers. Paternal occupation
as a motor vehicle mechanic is associated
with an increased incidence of spontaneous
abortions in the spouse. Fathers employed in
occupations associated with solvent exposures are more likely to have offspring with
anencephaly, with painters having the highest
risk. Other paternal occupations which are associated with an increased risk of having a liveborn child with a birth defect include employment as a fireman, janitor, forestry and logging
worker, printer, or plywood mill worker. Further, an increased risk of stillbirth, preterm delivery, or of delivery of a small-for-gestational
age infant is associated with paternal employment in the art or textile industries. Although
there is no definitive evidence that life style
exposures, such as paternal smoking or alcohol consumption, cause birth defects in the
68
Handbook of Andrology-Can spermatozoa be targets for drugs?
incidence of adverse progeny outcomes. A
wide range of environmental chemicals (e.g.,
lead, dibromochloropropane) and drugs (e.g.,
the anticancer alkylating agent, cyclophosphamide) produce abnormal progeny outcomes after paternal exposure. Drugs or environmental chemicals to which the male is exposed may be present in his seminal fluid, and
thus may have direct effects on the ovulated
egg, on the process of fertilization, or on embryo development. Alternatively, drugs or other chemicals may have adverse effects on the
fetus by "functionally" altering male germ
cells. The adverse effects on progeny outcome which have been observed include preand post-implantation loss (spontaneous abortions), physical malformations evident at birth,
69
behavioral alterations, and a higher incidence
of cancer later in life. Furthermore, it is of concern that the germ cell line of the progeny may
be affected, thus increasing the risk for subsequent generations. An example of an experimental approach used to demonstrate the
risks to progeny due to paternal exposure is
treatment with the anticancer drug cyclophosphamide during spermatogenesis.
It is apparent from both epidemiological and
animal studies that there are paternal exposures to chemicals that can result in abnormal
progeny outcome. Men exposed to certain
chemicals as a consequence of their occupation should be made aware that there is
concern with respect to an increased risk of
adverse progeny outcome.
Suggested Reading
Robaire B, Hales BF. Paternal exposure to chemicals before conception. Some children may
be at risk. Brit Med J 1993;307:341-342, .
Olshan AF, Mattison DR, eds. Male Mediated Developmental Toxicity, New York: Plenum
Press; 1994.
Copyright © American Society of Andro/ogy
Do environmental factors affect male reproductive functions?
If so, which ones and how?
Season, length of day and chemical exposure effects on the male
In the human, reproductive functions in both
sexes continue throughout the year without any
major or obvious changes in different seasons.
However, it is important to remember that in the
overwhelming majority of species inhabiting the
earth, reproductive functions are restricted to a
well defined and often quite short breeding
season. The annual cycles of transitions between reproductive activity and quiescence are
driven by environmental signals and assure arrival of the young at the time when conditions
are optimal for their survival. Of the environmental signals that influence male reproductive
activity in mammals inhabiting the temperate
zone, the role of photoperiod is best understood and probably most important. Annual
changes in the day length provide an organism
with reliable information about progression of
the seasons and thus, in effect, allow "prediction" of upcoming changes in temperature and
availability of food.
The golden (Syrian) hamster is a popular
model for the study of the effects of photoperiod on reproduction. Exposure of adult male
hamsters to short photoperiod inhibits the release of prolactin (PRL) and the gonadotropins
luteinizing hormone (LH) and follicle-stimulating
hormone (FSH)(Fig. 1). There is an associated
loss of testicular LH, FSH and PRL receptors,
suppression of spermatogenesis, inhibition of
testicular testosterone production and sexual
behavior, a drastic reduction of testicular mass
and sterility which persists for several months
or until the animals are again exposed to long
photoperiod. These effects are mediated by the
action of photoperiod on the pineal gland, altering the diurnal pattern of melatonin release.
The effects of short photoperiod can be completely prevented by prior removal of the pineal
gland, and mimicked by appropriately timed injections or infusions of melatonin. Melatonin
acts primarily within the hypothalamus by altering the release of neurotransmitters which
control pituitary hormone release.
70
In other species of small animals, photoperiod controls not only adult testicular function
but also sexual maturation. Typically, increasing day lengths of the spring promote early onset of puberty while shortening photoperiod of
the late summer leads to postponement of puberty until the next spring. Interestingly, regulation of puberty in these species involves
transfer of information about photoperiod from
the pregnant female to the developing fetuses.
In effect, the juvenile animal obtains precise information about the season of the year by
"comparing" the photoperiod it is exposed to
after birth with the photoperiod to which its
mother was exposed during pregnancy.
In large species in which pregnancy lasts for
several months rather than several weeks, arrival of the young in the spring is assured by
breeding taking place in the fall. Thus, in male
deer annual recrudescence of the testes, increase in plasma testosterone levels, conspicuous growth of neck muscles, and appearance
of aggressive and sexual behavior take place
in the late summer and fall in response to a
short, rather than a long, photoperiod. Similar
annual changes, but of lesser magnitude, occur
in males of most breeds of domestic sheep.
Seasonal fluctuations in male reproductive
functions do not depend solely on annual
changes in photoperiod. Both temperature and
food availability can exert important effects and
either dampen or amplify the effects of photoperiod. Reproductive functions can also be influenced by specific, often strictly seasonally
available, diet components and by chemical
messages received from other members of the
same species. For example, male puberty in
some rodents is hastened by the presence or
proximity of adult females. Chemical (pheromonal) communication between the members
of the same species is among many social and
density dependent factors that can affect reproduction. These include territorial behavior and
71
Handbook of Andrology-Do environmental factors affect male reproductive functions?
35
D---D Pa1red Testis WI. ( Q)
30
t:r -c. nq FSH /ml Serum
o--~
CJl
2.5
- 20
90
.£:
0"
Q)
~
E 70
.......
-
-~
CJl
c
(/)
~----+.
1.5
~
_j
1.0
.
'\
I
I
,/I
\ 'l
\
'~,
I
I 1'I\
\
\
05
'zh,,....
',
(:f'
I
~/{+--1!
J---<7'
I
,J ~r:::
l'f /1
I
I
I
I
I
I''
',
'
E
.......
CJl
c
300
I
(f)
~200
100
I
'
400
u...
''?---/I
I
500
I
I If
\
I
\
I
I
'
30
'I'
I
I
~
50
10
~
I
I
110
I
nq LH/ml Serum
_J
0
0
0
3
7
II
15
19
23
Weeks in LD 6:18
FIG. 1. Effect of short photoperiod (6:18) on testicular weight and on serum LH and FSH levels in adult
male hamsters transferred from a long photoperiod on day 0. Means ± SE. During both regression and
spontaneous recrudescence of the testes, changes in serum gonadotropins (particularly FSH) precede
changes in testicular weight. (From: Biology of Reproduction 1975;13:475-481.)
aggressive interactions between males that
can impose major stress and interfere with access to food sources. Both stress and malnutrition can suppress reproductive development
and function.
In the human, seasonal fluctuations have
been detected in sperm count, motility and
morphology, blood levels of LH and testosterone, as well as sexual activity and are believed
to be related primarily to the effects of photoperiod. However, these fluctuations are rela-
tively subtle and fertility continues throughout
the year. Of much greater clinical significance
are effects of environmental influences unique
to our own species such as occupational or accidental exposure to chemicals, use of alcohol,
psychotropic drugs, prescription and over-thecounter medication, and illicit use of androgenic and anabolic steroids. Each of these factors
is capable of exerting profound suppressive effects on the production of spermatozoa and androgens by the testis, on libido and on potency.
Suggested Reading
Reiter RJ. The pineal and its hormones in the control of reproduction. Endocr Rev 1980;1 :109131.
Gilmore DP, Cook B, eds. Environmental factors in mammal reproduction. Baltimore: University
Park Press; 1981.
Bronson FH. Mammalian reproduction: an ecological perspective. Bioi Reprod 1985;32:1-26.
Steger RW, Bartke A. Environmental modulation of neuroendocrine function. In: Gass GH, Kaplan
HM, eds. Handbook of Endocrinology, Vol. II. Boca Raton: CRC Press; 1987:111-141.
Bartke A, Steger RW. Seasonal changes in the function of the hypothalamic-pituitary-testicular
axis in the Syrian hamster. Minireview, Proc Soc Expr Bioi Med 1992;91:139-148.
Copyright © American Society of Andrology
Is there an andropause, the analog to menopause, and if so
what tissues are affected and how?
Fertility, androgen production and sensitivity, and sexual function in aging
men
with age, most prominently in men with the
most marked changes in seminiferous tubular
morphology. There is a corresponding decrease in basal serum inhibin levels. Thus, evidence favors the hypothesis that an intrinsic
age-related reduction in seminiferous tubular
function leads to reduced inhibin secretion
with secondary effects on pituitary function.
Menopause in women is a discrete event in
the life cycle, and is marked by the cessation
of menses, in association with a sharp fall in
circulating estradiol levels and a rise in folliclestimulating hormone (FSH). Although no single event delineates reproductive senescence
in men, results of many investigations suggest
that aging men experience reductions in androgen levels, virility, and fertility, along with
related metabolic changes. Nonetheless, the
question of a "male menopause" remains controversial, in part because of the difficulty in
discriminating the effects of age-related confounding variables such as stress, nonendocrine illnesses, malnutrition, obesity and drug
or medication use, from aging per se.
Aging effects on sex hormone secretion
and bioavailability
As for sex hormone secretion, early studies
demonstrated a reduction in bioassayable urinary androgen, and subsequent investigations
of small numbers of older men showed decreased testicular vein testosterone levels,
and reductions in both metabolic clearance
and production rates of testosterone. Initially
basal levels of total plasma testosterone were
shown to decrease progressively after age 50.
Because subjects in these studies were not
always carefully screened for health factors,
the confounding effects of illness, medications, etc. may have accounted for some of
the results observed. Illness does affect reproductive function as is demonstrated by a report of decreased plasma free testosterone in
men with benign lung disease and a reduced
total and free hormone level in men with lung
malignancy. In some studies of exceptionally
healthy men, no age effect on circulating testosterone concentration was found. Subsequent investigations examining multiple samples over a 24 hour period demonstrated that
morning peak (but not afternoon nadir) and 24
hour mean integrated testosterone levels were
decreased in older men, but in a similar study
no age effect on circadian levels was observed. Thus, the question whether aging per
se significantly reduces morning peak testosterone secretion or total levels remains controversial.
Aging of seminiferous tubules and fertility
With regard to fertility, despite occasional
reports of paternity in men in their 90s, there
is clearly a decrease in the rate of conception
in old male/young female marriages. Semen
analyses in elderly men reveal normal sperm
numbers, but decreased sperm motility and increases in abnormal forms. Changes in seminiferous tubules with age include thickening
of the basement membrane, peritubular fibrosis, sclerotic narrowing or collapse of the lumen, patchy impairment of germ cell maturation, and immaturity or degeneration of spermatocytes, as well as increases in multinucleated Sertoli cells. Studies have also revealed
a small but measurable, decrease in average
testis size with advancing age, whether studied at necropsy or in vivo. Functioning seminiferous tubules exercise negative feedback
control on the pituitary gonadotrope by producing inhibin, a peptide that acts to reduce
FSH production. Thus, with damage or destruction of the tubules, FSH increases, even
if Leydig cell testosterone secretion remains
normal. In fact, basal levels of FSH increase
72
Handbook of Andrology-/s there an andropause, the analog to menopause, and if so what
tissues are affected and how?
The fraction of circulating testosterone
bound to sex hormone binding globulin
(SHBG) is considered to be biologically unavailable. Because an increase occurs with
age in circulating SHBG, older men may exhibit reductions in bioavailable testosterone,
and hence its effects, disproportionate to what
would be expected from measurements of total testosterone. However, in healthy men the
increase in plasma testosterone binding to
SHBG appears insufficient to significantly alter
the apparent free concentration.
Although there are no large longitudinal investigations of the effects of age on sex steroids in men, two cross-sectional studies, each
examining more than 1000 individuals, have
recently been reported. In one study there was
a significant downward trend with age in both
total and non-SHBG bound testosterone concentrations, while in another no significant
trend in plasma testosterone was found. Neither study demonstrated an increase with age
in the number of men with truly hypogonadal
androgen levels. A recent meta-analysis of
studies of androgens in aging men revealed a
significant inverse correlation of total plasma
testosterone with age which disappeared
when reports which included men with ill
health were omitted. This analysis also found
that investigations which included ill or institutionalized subjects consistently showed lower levels of testosterone overall.
5a-Dihydrotestosterone (DHT) is produced
from testosterone and is the "activated" form
which binds to cytoplasmic androgen receptor
in most tissues. This testosterone metabolite
can be formed in the liver and also "leaks
back" from androgen target tissues, so that it
circulates in plasma at about 20% of total testosterone levels. Both reduced and unaltered
plasma levels of total or free DHT have been
reported in older men. In one study of elderly
men, many of whom had benign prostatic hyperplasia, there were high plasma levels of
DHT, but subnormal levels of testosterone,
suggesting an increase with age in peripheral
5a reduction of testosterone, possibly in prostate tissue.
Necropsy studies have generally revealed
an age-related decrease in number, and an
73
increase in morphological abnormalities, of
the Leydig cells, but in some of these investigations patients had died of a malignant disease or other protracted illness. Mean basal
plasma levels of luteinizing hormone (LH), as
well as urinary excretion of bioassayable gonadotropins, increase progressively in men
beyond the age of 50, and human chorionic
gonadotropin (hCG) stimulation tests have
uniformly revealed diminutions in the testosterone secretory response in older men, consistent with an age-related decrease in Leydig
cell number and/or reserve secretory capacity.
Thus, the evidence favors some degree of primary testicular failure in aging men.
There is also evidence for an effect of aging
on hypothalamic-pituitary function. For example, there is a pattern of low or normal LH in
a significant fraction of older men with diminished testosterone levels. Stimulation of the
pituitary with exogenous gonadotropin-releasing hormone (GnRH) has revealed decreases
in the magnitude of LH and/or FSH responses
in older men. Clomiphene citrate treatment
also results in less gonadotropin response in
older men. The finding that there is an attenuation of the amplitude of spontaneous LH secretory bursts in normal older men also provides evidence of altered hypothalamic-pituitary function. The relative contribution of hypothalamic versus pituitary dysfunction
remains uncertain, but in two recent studies,
repeated pulsing of GnRH appeared to restore
LH secretory responsiveness in older men,
suggesting that the decrease in pituitary gonadotropin secretion is mainly due to reduced
hypothalamic GnRH production.
Aging effects on androgen target tissues
Aging might also reduce androgen effect by
causing a loss of sensitivity of target tissues
to testosterone or DHT. Both decreased and
increased sensitivity of pituitary gonadotropin
secretion to feedback regulation by androgens
have been reported in older men. Binding of
DHT to sex hormone responsive skin is also
decreased with age, suggesting that an agerelated reduction in responsivity to androgens
may result from alterations in receptor number
74
Handbook of Andrology-ls there an andropause, the analog to menopause, and if so what
tissues are affected and how?
or affinity. To date, there are no published reports regarding effects of aging on specific
post-receptor actions of sex steroids.
Reproductive aging and sexual function,
body composition and metabolism
It is not known whether the changes in androgen levels or action in aging men have any
deleterious clinical effects. Many studies have
recorded progressive declines in male sexual
interest, activity and performance with age,
and there is a striking increase in the prevalence of impotence to as much as 50-75% in
men over 75. However, after adjustment for
age and body mass index (BMI = weight/
height squared), there is no difference in bioavailable testosterone levels in potent versus
impotent old men, suggesting that hypogonadism and impotence are independently distributed conditions. Because impotence in older
men is likely to be due mainly to neurologic or
vascular changes, the value of replacing testosterone to improve erectile function in the elderly is questionable.
In young hypogonadal men reduced sex
drive rather than impotence is the primary
symptom of diminished androgen action. The
most important predictors of sexual interest
and activity in old men are their characteristic
level of sexual activity in youth, their health,
and the health of the spouse or partner. Nonetheless, old men with relatively high sexual activity levels have been reported to have greater
total or bioavailable plasma testosterone than
age-matched men with less sexual activity.
Other studies have shown weak, but statistically significant, inverse correlations of free or
bioavailable testosterone levels with sexual
thoughts, sexual activity, and morning erections in aging men, although statistical significance may be lost when data are adjusted for
the effects of age. Thus, while decreases in serum testosterone may contribute to the dimin-
ished sexual activity in older men, this effect is
probably minor compared with the contributions
of age-related alterations in psychological, social, neurological, vascular and health factors.
If it is to be used at all, testosterone replacement should probably be reserved for older
men who are frankly hypogonadal.
In old age, there are decreases in muscle
and bone mass and increases in body fat, with
fat redistribution from peripheral to central depots. The latter changes are associated with
altered glucose and lipid metabolism and increased risk of diabetes mellitus and cardiovascular disease. Because men have lower
levels of high density lipoprotein (HDL)-cholesterol and a greater risk of coronary vascular
disease than do women, it might be expected
that a decrease in serum testosterone would
beneficially affect atherosclerotic risk. However, in one recent study HDL-cholesterollevels were positively correlated with serum free
testosterone in men aged 30-79 years, and in
another study middle-aged men treated with
testosterone had decreases in intra-abdominal
fat, as measured by computed tomography,
and in insulin resistance, as measured by the
glucose clamp technique. Testosterone treatment also produced decreases in fasting glucose, diastolic blood pressure and serum cholesterol. Although testosterone treatment has
been shown to improve bone density and skeletal muscle mass and strength in older hypogonadal men, the contribution of diminished
testosterone to the loss of muscle or bone
mass during normal aging is unknown.
Summary
Although there is no inevitable event leading
to age-related hypogonadism in men, there is
evidence that a significant number of older
men have modest reductions in androgen levels. The metabolic and clinical sequelae of this
change remain to be defined as does the risk/
benefit ratio of androgen supplementation.
Suggested Reading
Gary A, Berlin JA, McKinlay JB, Longcope C. An examination of research design effects on
the association of testosterone and male aging: results of a meta-analysis. J Clin Epidemiol
1991 ;44:671-684.
Handbook of Andrology-ls there an andropause, the analog to menopause, and if so what
tissues are affected and how?
75
Vermeulon A. Clinical review 24: androgens in aging male. J C/in Endocrinol Metab 1991 ;73:
221"224.
Blackman MR, Elahi D, Harman SM. Endocrinology and aging. In: DeGroot LJ et al, eds.
Endocrinology (3rd ed.) New York: Grune and Stratton, 1995:Chap. 147, 2702-2730.
Veldhuis JD, Urban RJ, Lizarralde G, Johnson ML, lranmanesh A. Attenuation of luteinizing
hormone secretory burst amplitude as a proximate basis for the hypoandrogenism of
healthy aging in men. J Clin Endocrinol Metab 1992;75(52-58).
Korenman SG, Morley JE, Mooradian AD. et al. Secondary hypogonadism in older men: Its
relation to impotence. J Clin Endocrinol Metab 1990;71 :963-969.
Marin P, Holmang S, Jonsson L, et al. The effects of testosterone treatment on body composition and metabolism in middle-aged obese men. tnt JObes 1992;16:991-997
Copyright © American Society of Andrology
What is BPH? Why is it so prevalent? What treatments are
available?
Pathophysiology, treatment
The condition
Benign prostatic hyperplasia (BPH) is a
nonmalignant enlargement of the prostate
gland that is due to both epithelial and stromal hyperplasia. Although the exact origin of
this condition is not well defined, it is thought
to arise as microscopic nodules in the periurethral tissue (transition zone) of the prostate gland in men as young as their late 20s.
With advancing age and the presence of androgens, this histologically identifiable hyperplastic tissue progresses to a macroscopic
state, which is a palpably enlarged prostate.
This enlarged prostate can cause clinically
significant obstruction of the bladder outlet in
many men due to constriction of the urethra
as it courses from the bladder neck to the
external urinary sphincter. The constellation
of symptoms associated with this intravesical
obstruction is known as prostatism.
It is estimated that more than 16 million
men in the United States suffer from prostatism or clinically significant BPH. Fifty percent
of men over the age of 50 years have some
degree of hyperplastic enlargement of the
prostate, while 95% of men will experience
symptoms related to this enlargement of the
prostate by the time they reach the age of 85
years. Twenty-five percent of all patients
seen by urologists suffer from BPH. Over
400,000 patients were treated surgically during 1990 in the United States, and worldwide
during the same year, 1,200,000 men underwent a prostatectomy for symptomatic BPH.
Although this represents only 4% of the number of patients with this condition, intervention can be expected to increase with the advent of efficacious, less invasive therapies.
One source estimates that 2,250,000 interventions (medical, minimally invasive, and
surgical) for BPH will be performed in the
United States by the year 2000. Thus, it is
safe to say that BPH is the single most prev-
alent condition treated in urologic practice today.
Making the diagnosis
When evaluating a patient with symptoms
of prostatism, it is important to: 1) make sure
that the symptoms are truly due to an enlarged prostate gland, and 2) assess the severity of the condition to determine whether
therapeutic intervention is necessary. With
regard to the first concern, a list of potential
conditions causing symptoms of prostatism is
contained in Table 1. All patients with prostatism should be evaluated with both a digital
rectal examination and serum prostate-specific antigen (PSA) determination to exclude
a clinically significant prostate cancer. A urinalysis also should be performed to eliminate
the possibility of an infectious process. In addition, it is wise to obtain a serum creatinine
level to determine the baseline renal function;
marked, longstanding bladder outlet obstruction due to BPH can result in kidney damage.
Intravenous pyelography (IVP) should only
be performed for select patients, such as
men with a history of nephrolithiasis or an upper tract transitional cell carcinoma.
To assess the degree of bladder outlet obstruction, the single most useful test is the
American Urological Association symptom index. This is a self-administered questionnaire
consisting of seven questions relating to the
ability to urinate (Fig. 1). A score between 0
and 7 is consistent with mild prostatism, 8 to
18 is indicative of moderate prostatism, 19 to
35 is compatible with severe prostatism. Only
patients with moderate or severe bladder outlet obstruction should be considered candidates for therapy of any type.
Another diagnostic test that can provide
objective information about a patient's ability
to urinate is the urinary flow rate. It is an electronic recording of the velocity of the urine
76
Handbook of Andro/ogy-What is BPH?
77
Table 1. The differential diagnosis for
symptoms of prostatism
Benign prostatic hyperplasia
Urethral stricture
Prostatitis
Prostate cancer
Bladder neck contracture
Hypotonic bladder
being expelled from the bladder during micturition and represents the single best noninvasive urodynamic test to assess bladder
outlet obstruction. From several investigations, it has been learned that the peak value
more specifically identifies men with BPH
than does the mean rate. Also of importance
is the fact that flow rate is dependent upon
the patient's age and the volume of urine
voided; with advancing age and decreasing
urine volume, the flow rate diminishes. Nevertheless, for a man in the seventh and eighth
decade of life who voids 150 ml or more, a
peak urinary flow rate of 15 ml/second or
greater should be interpreted as appropriate.
On the other hand, a peak flow rate less than
10 ml/second in the same clinical setting is
consistent with significant bladder outlet obstruction. Only in select patients is it necessary to obtain a "pressure-flow" study, in
which the intravesical pressure is monitored
while the peak urinary flow rate is recorded.
Cystoscopy should not be a part of the diagnostic evaluation unless a specific indication exists, such as hematuria.
Treatment options
In 1994, there are numerous medical, minimally invasive, and surgical treatments available for the management of symptomatic BPH
(Table 2). It is beyond the scope of this chapter to discuss the scientific rationale, clinical
The AUA Symptom Index
1. Over the past month or so, how often
have you had a sensation of not emptying
your bladder completely after you
finished urinating?
Not at
all
Less
than 1
time in
5
Less
than
half
the
time
About
half
the
time
More
than
half
the
time
Almost
always
[!]
OJ
[!]
~
[!]
[!]
3. Over the past month or so, how often
have you found you stopped and started
again several times when you urinated?
7. Over the last month, how many times did you most typically get up to urinate
from the time you went to bed at night until the time you got up in the morning?
[!]
None
OJ 1 time
[!] 2 times
~ 3 times
[!]
4 times
[!]
5 or more times
~9A.~P~9i~•e!lmiiii~llllflll
I
FIG. 1. The American Urology Association symptom index. This is a self-administered questionnaire to
quantitate symptoms of prostatism (From: Barry MJ, Fowler FJ and O'Leary MP, J Uro/1992;148:15491557, with permission).
78
Handbook of Andrology-What is BPH?
Table 2. Treatment options for benign prostatic
hyperplasia
I.
Medical
A. Androgen deprivation therapy
1. LHRH Agonists
2. Antiandrogens
3. Sa-Reductase inhibitors
B. a-Adrenergic antagonists
II.
Minimally invasive
A. Transurethral incision of the prostate (TUIP)
B. Balloon dilatation of the prostate
C. Laser prostatectomy
D. Microwave Therapy
E. Prostatic stents
F. Transurethral needle ablation of the prostate
(TUNA)
G. Transrectal high-intensity focused ultrasound therapy (HIFU)
Ill.
Surgical
A. Transurethral resection of the prostate
(TURP)
B. Retropubic prostatectomy
C. Suprapubic prostatectomy
results, advantages, and disadvantages of
each. In the discussion that follows, a general
overview is provided.
For the past 50 years, transurethral resection of the prostate (TURP) has been the
mainstay of treatment for this condition. In recent times, it has been the second most common operation performed in men over 65
years of age in the United States; only cataract extraction was performed more frequently. Although TURP is an effective treatment for
most patients with symptomatic BPH, it appears that approximately 20 to 25% of patients
undergoing a TU RP do not obtain a satisfactory, long-term outcome. Complications do occur and include retrograde ejaculation in most
men (70-75%), impotence in 5 to 10%, some
degree of urinary incontinence in 2 to 4%, and
postoperative urinary tract infection in 5 to
10% of patients. Based on recent investigations published in the urologic literature, the
risk of blood transfusion for patients undergoing a TURPis approximately 5 to 10%, and,
thus, is a significant concern to many men in
this era when various types of hepatitis and
AIDS are increasing in prevalence. Another
concern with TURPis that the reoperation rate
is approximately 15 to 20% when patients are
followed for 10 years or longer (2.2% per
year). Also, several large-scale investigations
have shown that the life expectancy of patients undergoing a TURP is less than that for
men who receive an open prostatectomy as
treatment for symptomatic BPH.
Because of these issues as well as the desire by men in our society to avoid surgery
whenever possible, there has been tremendous interest in developing alternative treatments to TU RP for the management of symptomatic BPH (Table 2). These options include
medical therapies, such as drugs that produce
a state of androgen deprivation (luteinizing
hormone-releasing hormone analogues, antiandrogens, and Sa-reductase inhibitors), aadrenergic antagonists which eliminate the dynamic component of BPH, and aromatase inhibitors which eliminate the biosynthesis of
estrogens in the male. In 1993, finasteride
(Proscar), a potent 5 a-reductase inhibitor, became the first medication approved by the
Food and Drug Administration (FDA) for the
treatment of BPH. Terazosin (Hytrin), also with
FDA approval for the indication of BPH, and
doxazisin (Cardura) are selective a-1 adrenergic antagonists that are being used for the
management of BPH. Adrenergic receptors in
the prostatic adenoma and capsule mediate
the tension in the smooth muscle of the prostate and blocking these receptors can decrease the resistance along the prostatic urethra.
Transurethral incision of the prostate
(TUIP), a minimally invasive procedure, is being used with increasing frequency. When
compared to TURP, TUIP is technically easier,
can be performed more quickly, and has fewer
side effects; patients can be discharged home
the same or the following day, and the convalescence period is shorter than that for
TURP. While enthusiasm for balloon dilatation
of the prostate is diminishing as results of re-
Handbook of Andro/ogy-What is BPH?
cent studies indicate that it is not an effective,
long-term treatment, there is increasing interest in laser prostatectomy, and microwave
therapy. Although both of the latter procedures
are still investigational and not FDA-approved
for widespread clinical use, preliminary data
suggest that they can improve voiding symptoms. Prostatic stents, in FDA-approved clinical trials, have been demonstrated to improve
the peak urinary flow rate and decrease the
obstructive symptom score to a level similar to
that of TUIP and TURP. Most recently, two
other therapeutic modalities, transurethral
needle ablation of the prostate (TUNA) and
transrectal high-intensity focused ultrasound
therapy (HIFU) have been developed and are
currently being investigated in clinical trials in
both the United States and Europe.
Summary
At the present time, the management of
BPH is in a state of transition. TURP is no
longer the only therapeutic option available.
While it is still the most efficacious with regard
to relieving bladder outlet obstruction and remains the gold standard of care, there are other treatment modalities that are attractive. The
single most important advantage of medical
therapies is that the patient can avoid a pro-
79
cedure; however, all medical treatments must
be regarded as a life-time commitment, and
their efficacy is not as good as the minimally
invasive treatments. The surgical procedures,
on the other hand, are a one-time event, but
they are associated with greater risk and a recovery period.
In the future, it will be necessary to develop
methods for deciding, on a scientific basis, the
most appropriate treatment for each individual
patient. However, once the physician has informed the patient of the benefits and risks of
each therapy, the patient's preference must be
considered because what is a risk to one may
not be to another. With the physician and patient working together, the treatment can be
tailored to the patient's specific needs and expectations.
Up to this point in time, the primary focus of
investigation has been to develop the "perfect" treatment for BPH. In the years ahead, it
will be important to gain a better understanding of both the pathogenesis of this disease
process as well as the functional interaction
that exists between the prostate gland and the
bladder. In this manner, it may be possible to
develop methods to prevent the disease or to
identify it at an early stage so that clinically
manifest BPH (prostatism) does not occur. Society would benefit tremendously.
Suggested Reading
Oesterling JE. Benign prostatic hyperplasia: its natural history, epidemiologic characteristics,
and surgical treatment. Arch Fam Med 1992; 1 :257-266.
Barry MJ, Fowler FJ, Jr, O'Leary MP, Bruskewitz RC, Holtgrewe HL, Mebust WK, Cockett ATK
and The Measurement Committee of the American Urological Association. The American
Urological Association symptom index for benign prostatic hyperplasia. J Urol1992;148:
1549-1557.
Lepor H. Medical therapy for benign prostatic hyperplasia. Urology 1993;42:483-501.
McConnell JD, Barry MJ, Bruskewitz RC, et al. Benign Prostatic Hyperplasia: Diagnosis and
Treatment. Quick reference guide for clinicians. No. 8. Rockville, M.D.: Department of
Health and Human Services, 1994. (AHCPR publication no. 94-0583).
Oesterling JE. Benign prostatic hyperplasia: medical and minimally invasive treatment options.
New England Journal of Medicine 1995;332:99-1 09.
Copyright © American Society of Andrology
Are some men more susceptible to prostate cancer than
others and why? What are the treatments and their
effectiveness? What are the possibilities for improvements in
therapy?
Pathophysiology, present and future treatments
Are some men more susceptible to prostate cancer than others and why?
Prostate cancer (PC) is the most common
cancer in American men and is the second
leading cause of male cancer deaths with
35,000 deaths annually. Autopsy studies have
demonstrated histological evidence of PC in
15% of men in the 6th decade; that rate increases to 50% in the 9th decade. Recent
studies demonstrate higher rates with up to
30% of men age 30-39 showing microscopic
foci of PC. This prevalence is constant worldwide so that the rate of histological PC is independent of place of birth and of race. In
contrast, death rates of PC vary from country
to country suggesting that environmental influences might be crucial in developing clinical
PC. Studies of migrating populations have further supported this viewpoint. Men moving
from Asia, where PC death is uncommon, to
the United States gradually achieve the same
death rates from PC as the general population
in the United States.
The pathogenesis of PC, is poorly understood. Men castrated before puberty almost
never have clinical PC. Therefore androgens
are thought to have a permissive role. Other
factors influencing the rate of clinical PC are:
Genetics - Prostate cancer in a first degree
relative doubles the risk for PC and this risk
increases as more relatives are affected.
Race - African-American men in the United
States are among the most susceptible in the
world. Their risk for developing PC is 120
times higher than for Chinese men and 1 1/3
higher than for Caucasian men of a similar educational and socioeconomic class.
Dietary fat- High intake of saturated fat from
animal sources, especially red meat, elevates
the relative risk for development of clinically
evident PC. Some studies have demonstrated
80
a correlation with intake of dairy products,
obesity and PC.
Vasectomy - The overall relative risk for
men of developing PC following a vasectomy
is found to be elevated in some studies; however, this association is very controversial and
remains under investigation. Most likely further study will show that vasectomy will have
no influence on PC.
What are the treatments and their effectiveness?
Prostate cancer can be divided into clinical
stages on the basis of tumor volume and anatomical extension (Fig. 1). Each clinical stage
has different treatment options and prognosis
(Table 1).
The prognosis depends on the stage as well
as on the histological grade of the tumor. A
poorly differentiated tumor tends to metastasize more often than a well- or moderately differentiated tumor. The prognosis of PC without initial treatment is not clear, but a few studies have found that the 10 year disease-specific survival for men with a clinical diagnosis
of organ-confined PC is approximately 86%,
and for regional PC (not organ-confined) the
5 year survival rate is approximately 50%.
Organ-confined disease
Treatment is intended to be curative, which
in the United States includes either radical
prostatectomy or radiation therapy. A watchful-waiting policy is preferred in elderly (age
> 70 or > 75 years) men with an asymptomatic
organ-confined PC. In the elderly, the diseasespecific survival may approach 100% because
elderly patients generally die of causes other
than PC.
Handbook of Andrology-Are some men more susceptible to prostate cancer than others and
why?
81
c.
A.
Aorta--------~
Ductus
Lymph node------------+-+~
deferens~
Seminal
vesicle
Lymph node
with cancer --------...
Internal
lilac a. --l.,.......l,.------Arf4,.4Jt:------:::\lt'-..
Cancer--~:....
Urethra _ _----::~.,__-+ ,
External
lilac a.
---"~--+
B.
FIG. 1. Clinical stages of Prostate Cancer. A. Organ confined disease. B. Not organ confined disease
with capsular penetration and/or extension into seminal vesicle. C. Metastatic disease, shown here with
metastases to lymph nodes and vertebrae, pelvis, femur.
Table 1. Therapy and Prognosis for Prostate Cancer
Clinical Stage
Organ Confined
A
B
A
B
A
B
Treatment
Life Expectancy
Radical prostatectomy
Radical prostatectomy
5(15)-year:
77%(40%)
Radiation therapy
Radiation therapy
5(15)-year:
5(15)-year:
95%(45%)
75%(28%)
Watchful waiting
Watchful waiting
5-year:
5-year:
75%
64%
Radiation therapy
Watchful waiting
5(15)-year:
5-year:
64%(20%)
50%
Mono therapy
Comb. androgen blockade
Median:
Median:
41 months
61 months
Mono therapy
Comb. androgen blockade
Median:
Median:
28 months
36 months
Not Organ Confined C
Metastatic PC
Minimal' 01
Extensic· 02
A
B
PC found incidentally at prostatectomy for benign disease.
PC palpable on digital rectal examination.
# Metastases confined to pelvic lymph nodes.
+ Metastases to bone.
Mono therapy bilateral orchiectomy or LH-AH analog therapy.
Combined androgen therapy mono therapy (i.e. bilateral orchiectomy or an LHAH agonist) plus androgen receptor blockade.
82
Handbook of Andrology-Are some men more susceptible to prostate cancer than others and
why?
Radical prostatectomy has been preferred
throughout the last decade after new techniques like nerve sparing surgery and autologous transfusions decreased morbidity and
mortality. The mortality after radical prostatectomy is 0-2%. Morbidity primarily consists of
impotence (20-80%), incontinence (5%) and
urethral stricture (1 0%). Radical prostatectomy is generally reserved for men with more
than 10 years life expectancy.
Radiation
therapy is performed most often as external
beam radiation. The therapy is associated with
side effects consisting primarily of impotence
(1 0-20%), incontinence (1 %), rectal injury
(2%), lymphedema (1 0%) and urethral stricture (6%). A major concern with radiation therapy is the fact that up to 50% of patients will
have a positive prostate biopsy 18-24 months
after treatment, indicating recurrent or persistent PC.
The ten year survival for both therapies is
approximately 60%, being perhaps slightly
better in the surgically treated group. However, a prospective study randomizing patients
to either radiation therapy or radical prostatectomy is not available making any comparison
between the two treatment options and between treatment and watchful waiting difficult.
Regional but not organ-confined disease
Untreated regional PC causes local complications due to growth into adjacent structures,
e.g., urethra, bladder, ureters, nerves and rectum, leading to bleeding, obstructive symptoms of bowel and bladder, and pain. A common approach to regional disease is radiation
therapy, but therapy varies from watchful waiting to radical prostatectomy, radiation therapy
or hormonal treatment. The 10 year survival is
approximately 40% and does not differ essentially from one therapy to another.
Metastatic disease
Initial metastasis is often to pelvic lymph
nodes. Another prime metastatic site is to
bone, especially vertebrae, pelvis, ribs and femur, causing isolated or diffuse pain due to
bone fractures. Neurologic symptoms also oc-
cur due to compression of the spinal cord and
brain metastasis. Anemia may be seen because of reduced hematopoiesis.
Many patients present with metastatic disease or eventually progress to advanced
stage disease. Therapy may target a specific
complication, e.g., transurethral resection of
the prostate to relieve urinary obstruction or
hematuria, or radiation therapy to painful bony
metastases. Hormonal therapy attempts to
control metastatic growth by androgen depletion since growth of PC is androgen dependent in most cases. When to start androgen
suppression is controversial, but recent investigations have reported a slightly better survival rate when therapy is started immediately after metastatic disease is identified, compared
with when symptoms from metastases begin.
Bilateral orchiectomy reduces androgen
concentrations by approximately 95% with the
remaining amount produced by the adrenal
glands. Orchiectomy is still widely used as a
safe, cost-effective method. The major concern is the permanent loss of potency and libido, and the occurrence of hot flushes in approximately 40% of patients. An alternative is
therapy with a luteinizing hormone-releasing
hormone (LH-RH) analog that inhibits testosterone production in the testes by decreasing
(LH) release from the pituitary gland. In the
past, diethylstilbestrol was widely prescribed
but its association with congestive heart failure
and thromboembolism has led to a decline in
its use.
To obtain maximum androgen blockade, it
is necessary to add an antiandrogen (e.g., flutamide) to either orchiectomy or LH-RH therapy. An antiandrogen exerts its effect by competing with the remaining androgens for the
intracellular androgen receptor in the target organs. This approach improves longevity by a
matter of months in selected groups of men.
What are the possibilities for improvements in therapy?
Prostatic cancer is the most prevalent cancer in men and the second leading cause of
cancer death. Despite intensified efforts to improve the diagnosis and treatment of PC, the
Handbook of Andrology-Are some men more susceptible to prostate cancer than others and
why?
death rate has remained unchanged for decades. While it is hoped that new screening
approaches, including PSA testing, and increased use of radical prostatectomy will drop
the death rate, the impact of these approaches on survival will not be known for another
10-15 years. A large scale prospective clinical
trial is necessary to decide the relative benefits of potentially curative treatment such as
radical prostatectomy and radiation therapy
versus observation. Plans for such trials are
now underway.
It has been 50 years since a Nobel Prize
was awarded for the demonstration that PC
responds to androgen deprivation, knowledge
that led to treatment (orchiectomy) which has
palliated and perhaps modestly improved the
survival of untold thousands. Unfortunately
there has been little progress in the area of
treatment of metastatic disease since then, although the concept of total androgen blockade
using an androgen receptor blocker has im-
83
parted some modest gains. Trials of chemotherapeutic agents applied early in the course
of PC, when metastasis is first noticed, have
not resulted in any improvement. Prostate
cancer is a slow growing tumor and the hope
for newer chemotherapeutic agents improving
survival is slight.
In the near future, management of PC
should focus on patient selection. Patients
with localized cancer which is likely to progress need to be identified and targeted for
treatment. The notion that there is considerable benefit to aggressive diagnosis and treatment in men beyond the age of 70 or 75 years
is not supported by the literature and this approach needs to be reassessed. Finally, a
long-term study to examine the drug finasteride for prevention of prostate cancer by the
reduction of prostate glandular activity has
been initiated by the National Cancer Institute;
however, these results are at least 5 years in
the future.
Suggested Reading
Pienta KJ, Esper PS. Risk factors for prostate cancer. Annals of Internal Medicine. 1993;118:
793-802.
Garnick MB. Prostate cancer: screening, diagnosis, and management. Annals of Internal Medicine. 1993; 118:804-818.
Lynch JH. Treatment of advanced prostate cancer. The Journal of Family Practice. 1993;37(5):
448-493.
Stanley T, McNeal J. Adenocarcinoma of the Prostate. In: Walsh PC, Retik AB, Stamey TA,
Vaughan ED, eds. Campbell's Urology, 6th edition, Vol. 2. Philadelphia: W. d. Saunders
Company; 1992:1159-1222.
`