Male Reproductive Physiology

The Hypothalamic-Pituitary-Gonadal Axis

The hypothalamus is the integrative center of the reproductive axis and receives messages from both the central nervous system and the testes to regulate the production and secretion of gonadotropin releasing hormone (GnRH). Neurotransmitters and neuropeptides have both inhibitory and stipulatory influence on the hypothalamus. The hypothalamus releases GnRH in a pulsatile nature which appears to be essential for stimulating the production and release of both luteinizing hormone (LH) and follicle stimulating hormone (FSH). Interestingly and paradoxically, after the initial stimulation of these gonadotropins, the exposure to constant GnRH results in inhibition of their release. LH and FSH are produced in the anterior pituitary and are secreted episodically in response to the pulsatile release of GnRH. LH and FSH both bind to specific receptors on the Leydig cells and Sertoli cells within the testis. Testosterone, the major secretory product of the testes, is a primary inhibitor of LH secretion in males. Testosterone may be metabolized in peripheral tissue to the potent androgen dihydrotestosterone or the potent estrogen estradiol. These androgens and estrogens act independently to modulate LH secretion. The mechanism of feedback control of FSH is regulated by a Sertoli cell product called inhibin. Decreases in spermatogenesis are accompanied by decreased production of inhibin and this reduction in negative feedback is associated with reciprocal elevation of FSH levels. Isolated increased levels of FSH constitute an important, sensitive marker of the state of the germinal epithelium.

Prolactin also has a complex inter-relationship with the gonadotropins, LH and FSH. In males with hyperprolactinemia, the prolactin tends to inhibit the production of GnRH. Besides inhibiting LH secretion and testosterone production, elevated prolactin levels may have a direct effect on the central nervous system. In individuals with elevated prolactin levels who are given testosterone, libido and sexual function do not return to normal as long as the prolactin levels are elevated.

The Testes

Leydig Cells

Testosterone is secreted episodically from the Leydig cells in response to LH pulses and has a diurnal pattern, with the peak level in the early morning and the trough level in the late afternoon or early evening. In the intact testis, LH receptors decrease or down-regulate after exogenous LH administration. Large doses of GnRH or its analogs can reduce the numbers of LH receptors and therefore inhibit LH secretion. This has been applied clinically to cause medical castration in men with prostate cancer. Estrogen inhibits some enzymes in the testosterone synthetic pathway and therefore directly effects testosterone production. There also appears to be an intratesticular ultra short loop feedback such that exogenous testosterone will override the effect of LH and inhibit testosterone production. In normal males, only 2% of testosterone is free or unbound. 44% is bound to testosterone-estradiol-binding globulin or TeBG, also called sex hormone-binding globulin. 54% of testosterone is bound to albumin and other proteins. These steroid-binding proteins modulate androgen action. TeBG has a higher affinity for testosterone than for estradiol, and changes in TeBG alter or amplify the hormonal milieu. TeBG levels are increased by estrogens, thyroid administration and cirrhosis of the liver and may be decreased by androgens, growth hormone and obesity. The biological actions of androgens are exerted on target organs that contain specific androgen receptor proteins. Testosterone leaves the circulation and enters the target cells where it is converted to the more potent androgen dihydrotestosterone by an enzyme 5-alpha-reductase. The major functions of androgens in target tissues include 1) regulation of gonadotropin secretion by the hypothalamic-pituitary axis; 2) initiation and maintenance of spermatogenesis; 3) differentiation of the internal and external male genital system during fetal development; and 4) promotion of sexual maturation at puberty.

Seminiferous Tubules

The seminiferous tubules contain all the germ cells at various stages of maturation and their supporting Sertoli cells. These account for 85-90% of the testicular volume. Sertoli cells are a fixed-population of non-dividing support cells. They rest on the basement membrane of the seminiferous tubules. They are linked by tight junctions. These tight junctions coupled with the close approximation of the myoid cells of the peritubular contractile cell layers serve to form the blood-testis barrier. This barrier provides a unique microenvironment that facilitates spermatogenesis and maintains these germ cells in an immunologically privileged location. This isolation is important because spermatozoa are produced during puberty, long after the period of self-recognition by the immune system. If these developing spermatozoa were not immunologically protected, they would be recognized as foreign and attacked by the body's immune system. Sertoli cells appear to be involved with the nourishment of developing germ cells as well as the phagocytosis of damaged cells. Spermatogonia and young spermatocytes are lower down in the basal compartment of the seminiferous tubule, whereas mature spermatocytes and spermatids are sequestered higher up in the adluminal compartment.

The germinal cells or the spermatogenic cells are arranged in an orderly manner from the basement membrane up to the lumen. Spermatogonia lie directly on the basement membrane, and next in order, progressing up to the lumen, are found the primary spermatocytes, secondary spermatocytes and spermatids. There are felt to be 13 different germ cells representing different stages in the developmental process.

Spermatogenesis is a complex process whereby primitive stem cells or spermatogonia, either divide to reproduce themselves for stem cell renewal or they divide to produce daughter cells that will later become spermatocytes. The spermatocytes eventually divide and give rise to mature cell lines that eventually give rise to spermatids. The spermatids then undergo a transformation into a spermatozoa. This transformation includes nuclear condensation, acrosome formation, loss of most of the cytoplasm, development of a tail and arrangement of the mitochondria into the middle piece of the sperm which basically becomes the engine room to power the tail. Groups of germ cells tend to develop and pass through spermatogenesis together. This sequence of developing germ cells is called a generation. These generations of germ cells are basically in the same stage of development. There are six stages of seminiferous epithelium development. The progression from stage one through stage six constitutes one cycle. In humans the duration of each cycle is approximately 16 days and 4.6 cycles are required for a mature sperm to develop from early spermatogonia. Therefore, the duration of the entire spermatogenic cycle in humans is 4.6 cycles times 16 days equals 74 days.

Hormonal Control of Spermatogenesis

An intimate structural and functional relationship exists between the two separate compartments of the testis, i.e. the seminiferous tubule and the interstitium between the tubules. LH effects spermatogenesis indirectly in that it stimulates androgenous testosterone production. FSH targets Sertoli cells. Therefore, testosterone and PSH are the hormones that are directed at the seminiferous tubule epithelium. Androgen-binding protein which is a Sertoli cell product carries testosterone intracellularly and may serve as a testosterone reservoir within the seminiferous tubules in addition to transporting testosterone from the testis into the epididymal tubule. The physical proximity of the Leydig cells to the seminiferous tubules and the elaboration by the Sertoli cells of androgen-binding protein, cause a high level of testosterone to be maintained in the microenvironment of the developing spermatozoa. The hormonal requirements for initiation of spermatogenesis appear to be independent of the maintenance of spermatogenesis. For spermatogenesis to be maintained like for instance after a pituitary obliteration, only testosterone is required. However, if spermatogenesis is to be re-initiated after the germinal epithelium has been allowed to regress completely, then both FSH and testosterone are required.

Transport-Maturation-Storage of Sperm

Although the testis is responsible for sperm production, the epididymis is intimately involved with the maturation, storage and transport of spermatozoa. Testicular spermatozoa are non-motile and were felt to be incapable of fertilizing ova. Spermatozoa gain progressive motility and fertilizing ability after passing through the epididymis. The coiled seminiferous tubules terminate within the rete testis, which in turn coalesces to form the ductuli efferentes. These ductuli efferentes conduct testicular fluid and spermatozoa into the head of the epididymis. The epididymis consists of a fragile single convoluted tubule that is 5-6 meters in length. The epididymis is divided into the head, body, and tail. Although epididymal transport time varies with age and sexual activity, the estimated transit time of spermatozoa through the epididymis in healthy males is approximately four days. It is during the period of maturation in the head and body of the epididymis that the sperm develop the increased capacity for progressive motility and also acquire the ability to penetrate oocytes during fertilization. The epididymis also serves as a reservoir or storage area for sperm. It is estimated that the extragonadal sperm reservoir is 440 million spermatozoa and that more than 50% of these are located in the tail of the epididymis. The sperm that are stored in the tail of the epididymis enter the vas deferens which is a muscular duct 30-35 cm in length. The contents of the vas are propelled by peristaltic motion into the ejaculatory duct. Sperm are then transported to the outside of the male reproductive tract by emission and ejaculation.

During emission, secretions from the seminal vesicles and prostate are deposited into the posterior urethra. Prior to ejaculation peristalsis of the vas deferens and bladder neck occur under sympathetic nervous control. During ejaculation, the bladder neck tightens and the external sphincter relaxes with the semen being propelled through the urethra via rhythmic contractions of the perineal and bulbourethral muscles. It is true that the first portion of the ejaculate contains a small volume of fluid from the vas deferens which is rich in sperm. The major volume of the seminal fluid comes from the seminal vesicles and secondarily the prostate. The seminal vesicles provide the nourishing substrate fructose as well as prostaglandins and coagulating substrates. A recognized function of the seminal plasma is its buffering effect on the acidic vaginal environment. The coagulum formed by the ejaculated semen liquefies within 20 to 30 minutes as a result of prostatic proteolytic enzymes. The prostate also adds zinc, phospholipids, spermine, and phosphatase to the seminal fluid. The first portion of the ejaculate characteristically contains most of the spermatozoa and most of the prostatic secretions, while the second portion is composed primarily of seminal vesicle secretions and fewer spermatozoa.

Fertilization

Fertilization normally takes place within the uterine tubes after ovulation has occurred. During the menstrual mid cycle, the cervical mucus changes to become more abundant, thinner and more watery. These changes serve to facilitate entry of the sperm into the uterus and to protect the sperm from the highly acidic vaginal secretions. Physiologic changes in the spermatozoa known as capacitation occur within the female reproductive tract in order for fertilization to occur. As the sperm cell interacts with the egg, there is initiation of new flagellar movement called hyperactive motility and morphologic changes in the sperm that result in the release of lytic enzymes and exposure of parts of the sperm's structure known as the acrosome reaction. As a result of these changes, the fertilizing sperm cell is able to reach the oocyte, traverse it's various layers, and become incorporated into the ooplasm of the egg.

Clinical Findings

History

The cornerstone of the evaluation of infertile man is a careful history and physical examination. Specific childhood illnesses should be sought including cryptographies, post pubertal mumps orchitis and testicular trauma or torsion. Precocious puberty may indicate the presence of an adrenal-genital syndrome, whereas delayed puberty may indicate Klinefelter's syndrome or idiopathic hypogonadism. Prenatal exposure to diethylstilbesterol should be ascertained because this may cause an increased incidence of epididymal cysts or a slightly increased frequency of cryptorchidism. A detailed history of exposure to occupational and environmental toxins, excessive heat, or radiation should be elicited. Cancer chemotherapy has a dose-dependent and potentially devastating effect on the testicular germinal epithelium. The drug history should be reviewed for anabolic steroids, cimetidine, and spironolactone which can effect the reproductive cycle. Medications like sulfasalazine and nitrofurantoin may effect sperm motility. Illicit drugs and excessive alcohol consumption are associated with a decrease in sperm count and hormonal abnormalities. Previous medical and surgical diseases and their treatment may occasional compromise reproductive function. Men with unilateral undescended testes will have overall semen quality of considerably less than normal. Previous surgical procedures such as bladder neck operations or retroperitoneal lymph node dissection for testicular cancer may cause retrograde ejaculation or absent emission. Diabetic neuropathy may result in either retrograde ejaculation or impotence.

Both the vas deferens and the testicular blood supply can easily be injured during hernia repair. In patients with cystic fibrosis, the vas deferens or epididymis and seminal vesicles are usually absent. Any generalized fever or illness can impair spermatogenesis. The ejaculate may be affected for three months after the event, as spermatogenesis takes about 74 days from initiation to the appearance of mature sperm. There is also a variable transport time in the ducts. Sometimes events that have occurred in the previous 3-6 months are extremely important. Sexual habits including frequency of intercourse, frequency of ejaculation, use of coital lubricants and the patient's understanding of the ovulatory cycle should be discussed. Previous infertility evaluation and treatment and the reproductive history from previous marriages should be ascertained. A history of recurrent respiratory infections and infertility may be associated with the immotile cilia syndrome, in which the sperm count is normal but the spermatozoa are completely non-motile due to ultrastructural defects. Kartagener's syndrome, which is a variant of immotile cilia syndrome, consists of chronic bronchiectasis, sinusitis, situs inversus and immotile spermatozoa. In Young's syndrome, also associated with pulmonary disease, the cilia ultrastructure is normal but the epididymis is obstructed due to inspissated material, and these patients present with azoospermia. Loss of libido associated with headaches, visual abnormalities and galactorrhea may suggest a pituitary tumor. Other medical problems that have been associated with infertility include thyroid disease, seizure disorders, and Liver disease. Interestingly it is not the seizure disorder itself that causes infertility but it is the typical treatment of it with Dilantin (phenytoin). Dilantin decreases FSH. Chronic systemic diseases such as renal disease and sickle cell disease are associated with abnormal reproductive hormonal parameters.

Physical Examination

During the physical examination, particular attention should be paid to discerning features of hypogonadism. Typically this would be viewed as poorly developed secondary sexual characteristics, eunuchoidal skeletal proportions i.e. arm span two inches greater than height, ratio of upper body segment (crown to pubis) to lower body segment (pubis to floor) less than 1, and the lack of normal male hair distribution ie. sparse axillary, pubic, facial, and body hair in conjunction with lack of temporal hair recession. One should be on the lookout also for infantile genitalia ie. small penis, testes, and prostate with under-developed scrotum. One may see a diminished muscular development and mass.

A careful examination of the testes is an essential part of the examination. Normal adult testes are on the average about 4.5 cm long and 2.5 cm wide with a mean volume of about 20 cc. A caliper or orchidometer may be used to measure testicular size. If the seminiferous tubules were damaged before puberty, the testes are small and firm. With postpubertal damage, they are usually small and soft. 

Gynecomastia is a consistent feature of a feminizing state. Men with congenital hypogonadism may have associated midline defects such as anosmia, color blindness, cerebellar ataxia, hair lip, and cleft palate. Hepatomegaly may be associated with problems of hormonal metabolism. Proper neck examination may help rule out thyromegaly, a bruit or nodularity associated with disease. Neurologic exam should test the visual fields and reflexes.

Irregularities in the epididymis suggest a previous infection and possible obstruction. Examination may reveal a small prostate with androgen deficiency or slight tenderness (bogginess) in men with prostatic infection. Any penile abnormalities like hypospadias, abnormal curvature, phimosis, should be looked for. The scrotal contents should be carefully palpated with the patient in both the supine and standing positions. Many varicoceles are not visible and may only be discernible when the patient stands or performs the Valsalva maneuver. Varicoceles can often result in a smaller left testis, and a discrepancy in size between the two testes should arouse suspicion. Both vas deferens should be palpated, as 2% of infertile men have congenital absence of the vasa and seminal vesicles.

Pre-Testicular Causes OF Infertility

  • Hypothalamic disease

  • Isolated gonadotropin deficiency (Kallmann's syndrome)

  • Isolated LH deficiency ("Fertile eunuch")

  • Isolated FSH deficiency

  • Congenital hypogonadrotropic syndromes

  • Pituitary disease

  • Pituitary insufficiency (tumors, infiltrative processes, operation, radiation)

  • Hyperprolactinemia

  • Hemochromatosis

  • Exogenous hormones (estrogen-androgen excess, glucocorticoid excess, hyper and hypothyroidism).

Hypothalamic Disease

Kallmann's syndrome which is an isolated gonadotropin (LH and FSH) deficiency occurs in both a sporadic and familial form and although uncommon i.e. 1 in 10,000 men, it is second to Klinefelter's syndrome as a cause of hypogonadism. The syndrome is often associated with anosmia, congenital deafness, hair lip, cleft palate, craniofacial asymmetry, renal abnormalities, color blindness. The hypothalamic hormone GnRH appears to be absent. If exogenous GnRH is administered, both LH and FSH are released from the pituitary. Except for the gonadotropin deficiency, anterior pituitary function is intact. The syndrome appears to be inherited either as an autosomal recessive trait or an autosomal dominant trait with incomplete penetrance. The differential diagnosis should include delayed puberty. Kallmann's syndrome distinguishing features though are testes less than 2 cm in diameter and positive family history with the presence of anosmia. "Fertile eunuch" are individuals with isolated LH deficiency. They have eunuchoid proportions with variable degrees of virilization and gynecomastia. They characteristically have large testes and semen containing a few sperm. Plasma FSH levels are normal but both the serum LH and testosterone concentrations are low normal. The cause appears to be a partial gonadotropin deficiency in which there is adequate LH to stimulate testosterone production with resultant spermatogenesis but insufficient testosterone to promote virilization. In isolated FSH deficiency which is rare, patient's are normally virilized and have normal testicular size and baseline levels of LH and testosterone. Sperm counts range from O to a few sperm. Serum FSH levels are low and do not respond to GnRH stimulation. Congenital hypogonadotropic syndromes are associated with secondary hypogonadism and a multitude of other somatic findings. Prader-Willi syndrome is characterized by hypogonadism, hypomentia, hypotonia at birth and obesity. Laurence-Moon-Bardet-Biedel syndrome is an autosomal recessive trait characterized by mental retardation, retinitis pigmentosa, polydactyly and hypogonadism. These syndromes are felt to be due to a defect in hypothalamic deficiency of GnRH.

Pituitary Disease

Pituitary insufficiency may result from tumors, infarctions, iatrogenic causes like surgery and radiation or one of several infiltrative processes. If pituitary insufficiency occurs prior to puberty, growth retardation associated with adrenal and thyroid deficiency is the major clinical presentation. Hypogonadism that occurs in a sexually mature male usually has its origin in a pituitary tumor. Decreasing libido, impotence and infertility may occur years before symptoms of an expanding tumor i.e. such as headaches, visual abnormalities, or thyroid/adrenal hormone deficiency. Once an individual has passed through normal puberty, it takes a long time for secondary sexual characteristics to disappear unless adrenal insufficiency is present. The testes will eventually become small and soft. The diagnosis is made by low serum testosterone levels with low or low normal plasma gonadotropins concentrations. Depending on the degree of panhypopituitarism, plasma corticosteroids will be reduced with plasma TSH and growth hormone levels.

Hyperprolactinemia can cause both reproductive and sexual dysfunction. Prolactin-secreting tumors of the pituitary gland whether from a microadenoma (less than 10 mm) or a macroadenoma, can result in loss of libido, impotence, galactorrhea, gynecomastia and alter spermatogenesis. Patients with a macroadenoma usually first present with visual field abnormalities and headaches. They should undergo CT or MRI scanning of the pituitary and laboratory testing of anterior pituitary, thyroid and renal function. These patients have low serum testosterone levels but basal serum levels of LH and FSH are either low or low normal and reflect an inadequate pituitary response to depressed testosterone.

Approximately 80% of men with hemochromatosis have testicular dysfunction. Their hypogonadism may be secondary to iron deposition in the liver or may be primarily testicular as a result of iron deposition in the testes. Iron deposits have also been found in the pituitary, implicating this gland as the major site of abnormality.

With regard to the role of exogenous hormones, adrenocortical tumors, Sertoli cell tumors, interstitial cell tumors of the testes may all at times be estrogen-producing. Hepatic cirrhosis is associated with increased endogenous estrogens. Estrogens act primarily by suppressing pituitary gonadotropin secretion, resulting in secondary testicular failure. Androgens can also suppress pituitary gonadotropin secretion thereby leading to secondary testicular failure. The current use of anabolic steroids by certain athletes may result in temporary sterility. Endogenous androgen excess may be due to an androgen-producing adrenocortical tumor or testicular tumor but more likely to congenital adrenal hyperplasia. As a consequence of this disease, the production of androgenic steroids by the adrenal cortex is increased, resulting in premature development of secondary sexual characteristics and abnormal phallic enlargement. The testes failed to mature because of gonadotropin inhibition and are characteristically small. In the absence of precocious puberty, the diagnosis is extremely difficult since excessive virilization is difficult to detect in an otherwise normally sexually mature man. Careful laboratory evaluation is essential. Infertility caused by documented congenital adrenal hyperplasia is treatable with corticosteroids. Physicians have used corticosteroids in individuals with idiopathic infertility, but unless these abnormalities can be documented, steroid therapy has no place.

Sometimes glucocorticoid excess (prednisone usage) is exogenous in the therapy of ulcerative colitis, asthma, or rheumatoid arthritis. The result is decreased spermatogenesis. The elevated plasma cortisone levels depress LH secretion and can cause secondary testicular dysfunction. Correction of the glucocorticoid excess results in improvement in spermatogenesis. Hyper and hypothyroidism can alter spermatogenesis. Hyperthyroidism effects both pituitary and testicular function with alterations in the secretion of releasing hormones and increased conversion of androgens to estrogens.

Several somatic chromosomal abnormalities are associated with male infertility. In a study of 1,263 barren couples, it was found that the overall incidence of male chromosome abnormalities was 6.2%. In a subgroup in which the male partner's sperm count was less than 10 million, the incidence rose to 11%. In azoospermic subjects, 21% had significant chromosomal abnormalities. Only in isolated cases however, has infertility been documented in association with a specific chromosomal abnormality i.e. D-D translocations, ring abnormalities, reciprocal translocation, and various other aberrations. Chromosomal studies though should be considered in men with severe oligospermia or azoospermia to look for autosomal and sex chromosomal abnormalities.

Klinefelter's Syndrome is a genetic disorder due to the presence of an extra X chromosome in the male, the common karyotype being either 47,XXY which is the classic form or 46,XY/47,XXY the mosaic form. The incidence is about 1:500 males. Characteristically, these individuals have small, firm testes, delayed sexual maturation, azoospermia and gynecomastia. Because the features of hypogonadism are not evident until puberty, the diagnosis is delayed. The decrease in testicular mass is usually due to sclerosis and hyalinization of the seminiferous tubules. The testes characteristically have a length of less than 2 cm and 12 cc volume. LH and FSH levels are characteristically elevated. Testosterone levels can range from normal to low and decrease with age. Serum estradiol levels are often increased. The higher estrogen levels relative to testosterone cause the feminized appearance in gynecomastia. About 10% of these patients have chromosomal mosaicism. The mosaics have less severe features of Klinefelter's Syndrome and may be fertile, as there may be a normal clone of the cells within the testes. Mild mental deficiency and restrictive pulmonary disease occur more frequently in these patients than in the general population. The infertility is reversible and later in life most of these men will require androgen replacement therapy for optimal virilization and normal sexual function.

XX Disorder or Sex Reversal Syndrome is a variant of Klinefelter's Syndrome. The signs are similar except for the average height is less than normal, hypospadias is common and a decreased incidence of mental deficiency. These patients have a 46,XX chromosome complement. This paradox is explained by the fact that their cells express H-Y antigen and are presumed to have a Y chromosome somewhere in their genomes. The incidence of the XYY syndrome is the same as that of Klinefelter's Syndrome but its phenotypic expression is more variable. Semen from these subjects may vary from azoospermic to normal. These patients are excessively tall and have had pustule acne. A percentage have anti-social behavior. Most have a normal LH and testosterone level with the FSH level dependent on the extent of germ cell damage. There is no treatment for their infertility.

Noonan's Syndrome is the male counterpart of Turner's Syndrome (X0), and these individuals typically have similar features i.e. short stature, web neck, low-head ears, cubitus valgus, ocular abnormalities and cardiovascular abnormalities. Most males with Noonan's Syndrome have cryptorchidism and diminished spermatogenesis and are infertile. Those with diminished testicular function will have elevated serum FSH and LH levels. They demonstrate on chromosomal analysis a sex chromosome abnormality such as X0/XY mosaicism. There is no treatment for their infertility.

Patients with myotonic dystrophy suffer from delayed muscle relaxation after initial contraction. The major clinical features also include lenticular opacities, frontal baldness and testicular atrophy. Inheritance is autosomal dominant and the expression is variable though 80% will develop testicular atrophy. Pubertal development is usually normal and testicular damage occurs later in adult life. Leydig cell function remains normal and there is no gynecomastia.

Bilateral anorchia or vanishing testes syndrome is an extremely rare disorder effecting about 1 in 20,000 males. Patients will present at birth with non-palpable testes and sexual immaturity later in life because of the absence of testicular androgens. The karyotype is normal, but LH and FSH levels are elevated and testosterone is extremely low. In utero the testes may have been lost due to torsion, trauma, vascular injury or infection. However, functioning testicular tissue must have been present at least for the first trimester of fetal life in order for the male reproductive ducts and for the external genitalia to differentiate along male lines. Testosterone does not increase in response to HCG stimulation. These patients have eunuchoid proportions but no gynecomastia. Therapy can only be directed at the testosterone deficiency.

Sertoli-cell-only syndrome or germinal cell aphasia may have several causes including congenital absence of the germ cells, genetic defects, or androgen resistance. Upon testicular biopsy there will be complete absence of germinal elements. Clinical findings include azoospermia in association with normal virilization, testes of normal consistency but slightly smaller in size, and no gynecomastia. Testosterone and LH levels are normal but FSH levels are usually elevated. Sometimes in patients who have had other testicular disorders like mumps, cryptorchidism or radiation/toxin damage, the seminiferous tubules may also contain only Sertoli cells, but in these men the testes are small and the histologic pattern is not as uniform. These patients are more likely to have severe sclerosis and hyalinization as prominent features as well. There is no treatment for their infertility.

Gonadotoxins like drugs and radiation can effect the germinal epithelium because it is a rapidly dividing tissue and susceptible to interference of cell division. Cancer chemotherapy has a dose-dependent effect on testicular germinal epithelium. The germinal epithelium appears to be more resistant to toxic drugs before puberty than in adulthood. The alkylating agents like chiromancies, cyclophosphamide and nitrogen mustard are particular toxic to the testes. In some patients, cryopreservation of semen can be performed before cancer chemotherapy is begun. Cyproterone, ketoconazole, spirolactone and alcohol all interfere with testosterone synthesis. Cimetidine is a testosterone antagonist, blocking peripheral testosterone action. These men will often present with gynecomastia and have decreased sperm counts.

Recreational drugs like marijuana, heroin, and methadone are associated with lower serum testosterone levels without a concomitant elevation in LH levels. This suggests a central abnormality as well as a testicular defect. Certain pesticides like dibromochloropropane have been found to impair testicular function in men. Germ cells are particularly sensitive to radiation while the Leydig cells are relatively resistant. At exposures below 600 rads, germ cell damage is reversible. Above this level of exposure though permanent damage is likely. Recovered spermatogenesis may take up to 2-3 years even in men who receive low doses of radiation. Elevated FSH levels reflect the impaired spermatogenesis, with return to normal once the testes recover.

About 15-25% of adult men who contract mumps can develop orchitis which is more commonly unilateral though bilateral involvement occurs in about 10% of affected men. Testicular atrophy can develop within 1 to 6 months or may take years. Fewer than one-third of men with bilateral orchitis recover normal semen parameters.

The exposed position of the testicles make them susceptible to trauma and subsequent atrophy. Iatrogenic injury may occur during inguinal surgery and interfere with testicular blood supply or damage the vas deferens.

Systemic diseases like renal failure resulting in uremia in males is associated with decreased libido, impotence and altered spermatogenesis and gynecomastia. LH and FSH levels are elevated and testosterone levels are decreased. The cause of hypogonadism in uremia is probably multifactorial. It has been found that serum prolactin levels are elevated in one-fourth of the patients. An excess in estrogen may be contributory. Anti-hypertensive drugs and uremic neuropathy may also play a role in uremic impotence and hypogonadism. After successful renal transplantation, uremic hypogonadism improves. A large percentage of males with cirrhosis of the liver have testicular atrophy, impotence and gynecomastia. Testosterone levels are decreased. Estradiol is increased as a result of decreased hepatic extraction of androgens with increased conversion to estrogen peripherally. LH and FSH levels are only moderately elevated relative to the low serum testosterone levels. Ethanol also acutely reduces testosterone levels by inhibiting testicular testosterone synthesis. Many men with sickle cell disease have evidence of hypogonadism. Even though LH and FSH levels may be variable, testosterone levels are low. Hypogonadism of sickle cell disease is likely secondary to a mixture of testicular and pituitary-hypothalamic causes.

Rare heredity disorders due to enzymatic defects can result in defective testosterone synthesis and are associated with an adequate virilization that is evident at birth as ambiguous genitalia. Several forms of androgen resistance result in under masculinization and infertility in males with otherwise normally developed external genitalia. Diagnosis is made by the finding of abnormal androgen receptors in a culture of genital skin fiberblasts. Characteristically, there is an elevation testosterone and LH levels. Proof of this is costly and there is no treatment for their infertility.

Cryptorchidism is a common developmental defect incidence of 0.8% in adult males. The undescended testes become morphologically abnormal after age 2. Though in spite of prophylactic orchidopexy, unilateral cryptorchid patients have reduced fertility potential. It appears that in the cryptorchid individual, there is dysgenesis of both the normally and abnormally descended testis. Semen quality is particularly poor in patients with bilateral undescended testicles. Even though baseline serum FSH, LH and testosterone levels may be normal, there is a super normal response of both LH and FSH to generate stimulation which reflects compromised testicular function.

A scrotal varicocele is the most common causative finding in infertile men. It results from backflow of blood secondary to incompetent or absent valves in the spermatic veins. This valvular deficiency combined with the long vertical course of the internal spermatic vein on the left side, leads to the formation of most varicoceles on the left side (90%). Varicoceles are not as commonly seen on the right side because of the oblique course of the right internal spermatic vein from the vena cava. A unilateral right-sided varicocele suggests venous thrombosis/tumor or situs inversus. Newer diagnostic tests have shown the incidence of bilateral varicoceles to be greater than 40%. The incidence of varicoceles in the adult male population is approximately 20% and in the infertile population approximately 40%. 50% of men with varicoceles will have impaired semen quality, but many men varicoceles are fertile. To explain the abnormalities in spermatogenesis with varicocele, the following theories have been proposed:

  • Elevation of testicular temperature due to venous stasis

  • Retrograde flow of toxic metabolites from the adrenal or kidney

  • Blood stagnation with germinal epithelial hypoxia; and

  • Alterations in the hypothalamic-pituitary-gonadal axis.

Recent experimental evidence has demonstrated bilateral increase in both testicular blood flow and temperature with altered spermatogenesis. Unfortunately, at least 25-40% of infertile men have idiopathic infertility for which no cause can be identified. More known causes will be discovered hopefully as knowledge of male reproductive physiology expands.

Post- Testicular Causes Of Infertility

  • Disorders of sperm transport

  • Congenital disorders

  • Acquired disorders

  • Functional disorders

  • Disorders of sperm motility or function

  • Congenital defects of the sperm tail

  • Maturation defects

  • Immunologic disorders

  • Infection

  • Sexual dysfunction

Disorders Of Sperm Transport

Congenital disorders of sperm transport are rarely due to absence or atresia of portions of the male ductal system. Males with cystic fibrosis have a high incidence of congenital hypoplasia or absence of the major portion of the epididymis, vas deferens, and seminal vesicles. Absence of the seminal vesicles is always associated with azoospermia, semen that does not coagulate at ejaculation, and absence of fructose. In Young's Syndrome which is associated with pulmonary disease, the ultrastructure of the cilia is normal but the epididymis is obstructed due to inspissated material leaving these patients azoospermic.

Acquired disorders of sperm transport are usually due to bacterial infections which may acutely or chronically involve the epididymis with subsequent scarring and obstruction. Apart from vasectomy, the vas may accidentally be ligated during hernia repair, orchiopexy, and even during varicocelectomy

Functional obstruction of sperm transport results from neuropathic insults like injuries to the sympathetic nerves during retroperitoneal lymph node dissection or pelvic surgery. This may cause lack of peristalsis of the vas deferens with resultant lack of emission and/or failure of the bladder neck to close at the time of ejaculation leading to retrograde ejaculation. Diabetic males with autonomic neuropathy frequently present with both erectile dysfunction and/or retrograde ejaculation. Spinal cord injury can result in paraplegia or quadriplegic with resultant erectile dysfunction and lack of emission and ejaculation. There are many medications such as tranquilizers, antidepressants, and antihypertensives that may interfere with the sympathetic nervous system as well.

Disorders of Sperm Motility or Function

Disorders of sperm motility and function exist secondary to problems that include congenital defects of the sperm tail, maturation defects and immunologic defects. Immotile cilia syndrome is a group of disorders characterized by immotility or poor motility of spermatozoa tie. Kartagenerss Syndrome). In these disorders, testicular biopsy is normal and the sperm count adequate but sperm motility is either markedly reduced or absent. The defective structural abnormality leading to impairment of both the cilia and spermatozoa is seen only with the electron microscope. The defects known to cause immotile cilia syndrome include absent dynein arms, short or absent spokes with no central sheath and missing central microtubules. Motility problems may also be associated with a deficiency of the protein carboxylmethylase in the tail of the sperm. Normal sperm counts with poor motility following vasectomy reversal may be a result of epididymal dysfunction. Chronic intratubular pressure following vasectomy may have a deleterious effect on the epididymis such that spermatozoa may not gain their usual maturation and capacity for motility. Breakdown of the blood-testes barrier by infection, trauma or operation allows sensitization of the spermatozoa antigens. Sperm antibodies may be a relative cause of infertility in about 3-7% of infertile males. Immunity does not appear to be an all-or-none phenomenon but may contribute to reduced fertility potential.

Infections. High concentrations of gram-negative bacteria like E-coli in the semen can impair sperm motility. Sexually transmitted organisms such as chlamydia trichomatous, mycoplasma hominis and ureaplasma urealyticulum have rarely been implicated in reproductive failure. In both animals and humans, there is no convincing evidence to support the use of routine cultures or empiric therapy in asymptomatic infertile males.

Sexual dysfunction has been reported in up to 20% of infertile males. Decreased sexual drive, erectile dysfunction, premature ejaculation and failure of intromission are all potentially correctable causes of reproductive failure. Decreasing libido and erectile dysfunction may reflect low serum testosterone levels with an organic cause. Performance anxiety is also often reported and often abated with reassurance.

Diagnostic Testing

Semen Analysis

Although semen analysis is not a test of fertility, a carefully performed semen analysis is a highly predictive indicator of the functional status of the male reproductive hormonal cycle, spermatogenesis and the patency of the reproductive tract. The initiation of a pregnancy is the only true measure of fertility and is a couple-related phenomenon. One must keep in mind that normal values have been difficult to determine for fertile men in their reproductive years. Clinical studies of infertile patients have established "limits of adequacy" below which the chance of initiating a pregnancy becomes more difficult. These parameters are not absolute because some fertile men may have values below these "limits of adequacy". Conversely, infertile men may have normal semen parameters by standard analysis techniques because standard evaluation does not assess the functional integrity of the sperm. The World Health Organization Laboratory Manual for Examination of Human Semen and Semen-Cervical Mucous Interactions is highly recommended for technical details.

Most specialists collect at least three specimens in which the seminal parameters are within 20% of each other before establishing a baseline for semen quality. The semen specimen is best obtained by masturbation after a two to three day period of abstinence. The specimen should be assessed within 1-2 hours of collection. Samples obtained by coitus interruptus or from silastic condoms devoid of spermatocidal agents are less desirable but satisfactory. Therefore, collection at the site of analysis is ideal. Besides laboratory error, there are variations in sperm density, motility and morphology among multiple samples from a given man. Abstinence intervals give s large source of variability. With each day of abstinence (up to one week) semen volume increases by 0.4 cc, sperm concentration by 10-15 million per cc, and total sperm count by 50-90 million. Sperm motility and morphology appear to be unaffected by 5-7 days of abstinence, but longer periods lead to impaired motility. Interpretation of semen analysis must take into consideration the variations between samples that exist in individuals. The minimum number of specimens to define good or poor quality of semen is three samples over a 6-8 week interval with a consistent period of abstinence of 2-3 days. In a longitudinal analysis of semen from both fertile and infertile men, it was found that 97% of men with initial good sperm concentration would continue to show good density after as many as 3-6 specimens. Those rated poor at first also remained poor in future visits. For those rated equivocal, first visit was of little value and at least three visits were needed to obtain stability.

Semen volume must be taken into consideration assessing total sperm production by the testes. Semen volume per se, however, effects fertility only when it falls below 1.5 cc due to the inadequate buffering of vaginal acidity or when the volume is greater than 5 cc. Low volumes may be associated with incomplete collection, retrograde ejaculation, ejaculatory duct obstruction, or androgen deficiency. For most clinicians, a sperm concentration of less than 20 million per cc is the lower limit of normal. Sperm motility is the single most important measure of semen quality and can be a compensatory factor in men with low sperm counts.

Sperm motility is usually rated in two ways: the number of motile sperm as a percentage of the total, and the quality of forward progressive sperm movement i.e., how fast and how straight the sperm swims. The degree of forward progression is a classification based on the pattern displayed by the majority of motile sperm. It ranges from zero (no movement) to 4 (excellent forward progression). Typically, you want to see at least 50% of the sperm with good forward progression. Microscopic evaluation of the liquefied semen may reveal agglutination (clumping) of sperm. Agglutination may be head-to-head, head-to-tail, or tail-to-tail and may suggest an inflammatory or immunologic process. Sperm morphology is subject to great variation and it is unusual to see specimens that contain more than 80% normal sperm heads.

Morphology is assessed on stained seminal smears and is scored; after viewing at least 100 cells. Typically, you like to see at least 30% of the sperm having normal oval heads, mid piece and tail. No longer is it felt that increased numbers of tapered, amorphous and immature cells (stress pattern) are pathonomic of varicoceles, but rather represent altered testicular function. Semen from normal men coagulates and then over 20-30 plus minutes liquefies. Delayed liquefaction of semen greater than 60 minutes may indicate disorders of accessory gland function. Diagnosis of the liquefaction problem should be made if there is absence of sperm in the post coital test. If sperm are capable of reaching the cervical mucus, problems of semen liquefaction are not clinically relevant. Increased semen viscosity, which is unrelated to the coagulation-liquefaction phenomenon, signifies a disorder of accessory gland function and may effect the accuracy of assessment of both sperm density and motility. It is only clinically relevant when there are very few sperm in the post coital test.

The presence of white blood cells in semen should be noted. It is difficult to differentiate between white blood cells and immature spermatozoa on routine analysis, because both may appear as round cells in the semen. Peroxidase stain and, more recently monoclonal antibodies have been utilized to aid in this differentiation. Excessive white cells ( > 1 million/cc) may indicate an infection that may contribute to subfertility. If no spermatozoa are observed, a qualitative test for fructose should be performed. A low ejaculate volume and lack of fructose, along with failure of the semen to coagulate, suggest congenital absence of the vas deferens and seminal vesicles or obstruction of the ejaculatory ducts. Fructose is androgen-dependent and is produced in the seminal vesicles.

Computer-assisted semen analysis (CASA) systems couple video technology and sophisticated microcomputers for automatic image digitalization and processing. This technology was developed for more objective measurements of seminal parameters over the subjective measures of standard semen analysis. CASA permits the measurement of additional motility parameters such as curvalinear velocity, straight-line velocity, linearity, and flagellar beat frequency. Under certain circumstances, CASA has been found to be less accurate than the standard semen analysis and the biological and clinical relevance of some of these new parameters has yet to be validated. 

Hormone Evaluation

Most cases of male infertility are non-endocrine in origin. Routine evaluation of hormonal parameters is not warranted unless sperm density is extremely low or there is clinical suspicion of an endocrinopathy. The incidence of primary endocrine defects in infertile men is less than 3%. Such defects are rare in men with a sperm concentration of greater than 5 million per cc. When an endocrinopathy is discovered, however, specific hormonal therapy is often successful. Because of the episodic nature of LH secretion and its short half life, a single LH determination has an accuracy of plus or minus 50%. Similarly, testosterone is secreted episodically in response to LH pulses and has a diurnal pattern with an early morning peak. Serum FSH has a longer half life, and these fluctuations are less obvious. Therefore, I usually just check an FSH and testosterone level. A low testosterone level is one of the best indicators of hypogonadism of hypothalamic or pituitary origin. Low LH and FSH values concurrent with low testosterone levels indicate hypogonadotropic hypogonadism. Elevated FSH and LH values help to distinguish primary testicular failure (hypergonadotropic hypogonadism) from secondary testicular failure (hypogonadotropic hypogonadism). Most patients with primary hypogonadism have severe, irreversible testicular defects. On the other hand, secondary hypogonadism has a hypothalamic or pituitary origin and infertility may be correctable. Elevated FSH levels are usually a reliable indicator of germinal epithelial damage and are usually associated with azoospermia or severe oligospermia, depicting significant and usually irreversible germ cell damage. In azoospermic and severely oligospermic patients with normal FSH levels, primary spermatogenic defects cannot be distinguished from obstructive lesions by hormonal investigation alone. Therefore, scrotal exploration and testicular biopsy should be considered. An elevated FSH level associated with small, atrophic testes implies irreversible infertility and a biopsy is not warranted.

The diagnostic value of prolactin measurement is extremely low in men with semen abnormalities unless these are associated with decreased libido, erectile dysfunction, and evidence of hypogonadism. Prolactin measurement is warranted in patients with low serum testosterone levels without an associated increase in serum LH levels.

Individuals with gynecomastia, obesity, history of alcohol abuse, or suspected androgen resistance should have a serum estradiol level. In men with a history of precocious puberty, one should consider congenital adrenal hyperplasia. In the common variant (21-hydroxylase deficiency), serum levels of 17-hydroxyprogesterone are elevated. In 11-hydroxylase deficiency, serum 11-Deoxycortisol levels are elevated.

In patients with hypogonadotropic hypogonadism, the pituitary hormones other than LH and FSH should also be assessed like adrenal corticotropic hormone (ACTH), thyroid stimulating hormone (TSH), and growth hormone (GH). Thyroid dysfunction is such a rare cause of infertility that routine screening for thyroid abnormality should be discouraged.

Chromosomal Studies

Only in isolated cases has infertility been documented in association with a specific chromosomal abnormality. Subtle genetic studies can be considered in men with severe oligospermia and azoospermia to look for both autosomal and sex chromosomal abnormalities. The diagnostic yield is greatest in men with small testes, azoospermia, and elevated FSH levels. 

Immunologic Studies

Antisperm antibodies, although not an absolute cause of infertility, appear to be capable of reducing the likelihood of pregnancy. The concentration of antisperm antibodies in the semen influence the degree of impairment. Antisperm antibodies do not lyse or immobilize sperm. They have not generally been found to be associated with decreased density or motility, but they do appear to interfere with sperm function by simply attaching to the plasma membrane of the spermatozoa. Sperm agglutination may be caused by antisperm antibody attachment. Infections may lead to agglutination of sperm as well though. Whenever agglutination is observed, the possibility of infection should be evaluated with appropriate semen cultures. Antisperm antibodies should be suspected in couples with repeated abnormal post coital tests. Antisperm antibodies appear to interfere with normal penetration and transit of sperm through normal cervical mucus.

Antisperm antibodies also should be suspected in subfertile men with a history compatible with disruption of the integrity of the genital tract, and when sperm agglutination or reduced motility is observed on semen analysis. Immunological factors may also play a role in the pathogenesis of 10-20% cases of "unexplained infertility". Antisperm antibodies can be found either in the circulation or in the seminal plasma or directly on the sperm surface. Studies have shown a discordance between the results of sperm antibody tests in matching serum and sperm samples. The presence of humoral antibodies directed against sperm is not relevant to fertility unless these circulating antibodies are also present within the reproductive tract. Therefore, the convenience of assaying blood for antisperm antibodies is outweighed by the lack of clinical relevance of these measurements in comparison with assays that identify the immunoglobulins directly on the sperm surface. It appears therefore that tests capable of detecting antisperm antibodies on living sperm are the most direct way to determine whether a significant autoimmunity to sperm exists. The immunobead binding test (IBT) is one of the most informative and specific of all assays currently available to detect antisperm antibodies bound to the surface of sperm.

Special And Sperm Function Tests

 
Sperm-Cervical Mucus Interaction

For fertilization to take place in-vivo, the sperm must be able to get past the cervical mucus. The post coital test assesses the ability of sperm to penetrate and progress through cervical mucus. Cervical mucus is examined 2-8 hours after intercourse at the time of expected ovulation. The presence of greater than 10-20 motile sperm per high power field is generally accepted as a normal post coital test. Post coital testing is a bio-assay that provides information concerning sexual function, motility of the sperm, and the sperm-mucus interaction. A positive result implies normal semen and mucus. A poor result in an individual with normal semen parameters implies either cervical abnormality or the presence of sperm antibodies. Sperm-mucus interaction may also be assessed in-vitro. This allows for some degree of standardization. Human or bovine ovulatory mucus is placed in a capillary tube. Sperm penetration into the mucus is measured over a fixed period of time. These in-vitro techniques enable one to compare patient specimens with fertile sperm and control some of the variables associated with standard post coital testing.

Sperm Penetration Assays

Penetration of an oocyte requires sperm capacitation, acrosome reaction, fusion and incorporation into the oocyte. Cross-species fertilization is normally prevented by the zona pellucida. Hamster eggs stripped of the zona pellucida can be penetrated by human sperm. This in-vitro functional test measures the penetration ability of the sperm. The end point of this assay is penetration of the ovum and decondensation of sperm heads. The percentage of oocytes penetrated and the number of sperm penetrating each oocyte are measured. Sperm that are capable of multiple penetrations per oocyte appear to have greater fertilizing potential than sperm that do not penetrate. The results of the sperm penetration assay (SPA) have primarily been used to predict the results of assisted reproductive techniques, in particular, in-vitro fertilization. Men with sperm of low SPA score are less likely to achieve a spontaneous pregnancy than those with a high SPA score. It must be emphasized that the abnormal penetration does not indicate that fertilization cannot occur, nor does good penetration assure fertilization. Although variations still exist between laboratories, there appears to be general agreement that less than 10% penetration is evidence of sperm dysfunction and male infertility. Indications for SPA include unexplained infertility, and its use is also recommended prior to expensive assisted reproductive techniques. Although the SPA is a reliable indicator of the fertilizing capacity of human spermatozoa, it does not predict the ability of sperm to bind to and penetrate zona pellucida or the sperm's motility and progression in the female reproductive tract.

For as SPA with zona free hamster eggs can demonstrate completion of the human sperm acrosome reaction and sperm oocyte plasma membrane fusion, only tests with human zona pellucida can assess the capability of human sperm to bind to the human oocyte. The hemizona assay uses zona pellucida from non-living human oocytes that have been microsurgically bisected. Sperm are allowed to interact and bind with the hemizona. The patient's sperm and fertile sperm are compared utilizing the identical halves of hemizona. The results are expressed as the hemizona index, i.e. bound sperm by the subfertile man divided by bound sperm from the fertile donor multiplied by 100. This assay requires significant expertise in micromanipulation. The hemizona assay is not indicated in the routine evaluation of the subfertile man.

Acrosome Evaluation

The acrosome reaction is necessary for fertilization to take place. Evaluating the ability of sperm to undergo the acrosome reaction may provide an additional assessment of sperm function. It is possible to determine the acrosomal status of sperm by utilizing electron microscopy, staining, immunofluorescent techniques and monoclonal antibodies. It is also possible to induce an acrosome reaction with ionophores and human zona pellucida. These techniques are labor-intensive and the ability of the acrosomal status to predict fertility must be confirmed.

Hypo-Osmotic Swelling

It has been found that when sperm from normal fertile men are exposed to a known solution of fructose and sodium citrate, 33-80% of the spermatozoa will exhibit tail swelling. Sperm that are not viable or sperm with non-functioning membranes do not swell. This appears to be explained by the ability of the normal cell membrane to maintain an osmotic gradient. Attempts have been made to correlate this finding with the fertilization potential for semen samples. Samples with greater than 62% swelling are able to fertilize ova, whereas less than 60% swelling is observed in samples of infertile semen. This test has not been widely embraced and is currently a research tool.

Bacteriologic Investigation

If urinalysis is abnormal or bacterial prostatitis is implicated by either the history or physical examination, appropriate cultures are indicated. The common sexually transmitted organisms such as chlamydia trachomatis, mycoplasma hominus and ureaplasma urealyticulum have been implicated in reproductive failure in animals and humans. On the basis of this supposition, physicians have instituted antibiotic therapy without obtaining evidence of infection in the hope of improving fertility. We currently could find no evidence for the role of current asymptomatic infection due to the above organisms in male infertility. Without evidence of inflammation, there is no indication for routine culture or antibiotic treatment of infertile men.