The following points highlight the top six roles of androgens in males. The roles are: 1. Regulation of Spermatogenesis 2. Sexual Differentiation 3. Development of Male Secondary Sex Characters 4. Anabolic Effects 5. Effects on Brain and Nervous System 6. Aging.
Role # 1. Regulation of Spermatogenesis:
During sexual maturation, FSH and testosterone are required for the initiation of spermatogenesis. It is suggested that FSH following binding to the receptor on Sertoli cell membrane stimulates cAMP production which is turn activates a protein kinase. This kinase leads to genomic production of a mRNA coding for androgen binding protein (ABP).
The ABP is then secreted in seminiferous lumen where it serves as a binding protein for testosterone and maintains the high androgen levels all the way to epididymis. Testosterone, being secreted by Leydig cells may interacts with androgen receptors in Sertoli cells to activate specific genes necessary for germ cell differentiation process, particularly the formation of spermatogonia and the meiosis of spermatocytes.
Role # 2. Sexual Differentiation:
During the early stages of pregnancy, human chorionic gonadotropin (hCG) is secreted from placenta which stimulates interstitial tissue growth, steroidogenesis and secretion of testosterone from embryonic testes.
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Almost at the same time, anti Mullerian hormone is secreted from the testicular Sertoli cells which regresses the Mullerian duct system in the male embryo to suppress its differentiation into Uterus, Fallopian tubes and vagina.
Testosterone, secreted from Leydig cells on the other hand, stimulates the Wulffian duct to differentiate into male secondary sex organs like epididymis, seminal vesicles, vas deferens and ejaculatory duct.
Testosterone is also converted to dihydrotestosterone (DHT) that causes the differentiation of the urogenital sinus and tubercle of the embryonic primordial genital tract into the prostate, male urethra, penis and scrotum. During the later stages of pregnancy FSH and testosterone of the foetus help in the descent of testes from abdomen to scrotum.
Role # 3. Development of Male Secondary Sex Characters:
At puberty, increased secretion of testosterone results in several changes like enlargement of testis, pubic hair growth, enlargement of prostate, seminal vesicle and epididymis; development of moustache, and beard, regression of scalp line; appearance of body and extremity hair, enlargement of larynx and thickening of vocal cords resulting in lower pitch of voice etc.
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There is an enhanced rate of linear growth resulting in height spurt somewhat later in puberty to a rate of about 3 inches (7.5 cm) per year. At this time the androgen sensitive muscles of the pectoral region and the shoulder also increase in their characteristic male pattern.
The haematocrit increases and libido and sexual potency develop. These various maturation processes take place over about 4 years and also depend on genetic and nutritional factors of the concerned individual.
Role # 4. Anabolic Effects:
Testosterone and DHT have protein anabolic effects that are shown by the growth of musculature and cartilage of the larynx of the human.
The myotropic actions of androgen result from their ability to:
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(i) Increase retentions of Na+, Ca2+; phosphates, Na+ and K+ in the body and
(ii) Stimulate DNA replication, transcription and translation of proteins.
Testosterone also stimulates the closure of bony epiphyses to stop elongation of long bones after puberty; though, during puberty, the steroid increases cellular proliferation and mitosis in many tissues like epiphysial cartilage, long bones, kidneys, liver and skin.
Role # 5. Effects on Brain and Nervous System:
In the foetus, development of brain is stimulated by both testosterone and DHT. Testicular androgens exert a tonic inhibitory feedback action on pituitary gonadotropin secretion (control of testosterone secretion). Nuclear androgen-binding sites are present in the brain of higher vertebrates, where the steroid exerts its role on the activation of sexually related behaviour.
Role # 6. Aging:
In humans, there is an age related decrease in serum-testosterone levels. Young men with low testosterone (hypogonadism) after suffer a loss of bone, muscle, energy and libido. Testosterone therapy can reverse these changes.
Thus, testosterone is expected to reduce the effects of aging. It was observed that elderly men taking testosterone have increased muscle mass, though testosterone therapy might enhance the growth of prostate cancer and raise the risk of stroke.