Endocrine regulation of testicular function in men: implications for contraceptive development.

The testicle has two important and complimentary functions in the adult male: the production of sperm and the synthesis of testosterone. Testicular function is directed by the central nervous system through its effects on the pituitary gland. Precise regulation of testicular function is accomplished by an elegant endocrine feedback loop in which the secretion of pituitary gonadotropins is stimulated by the pulsatile release of GnRH from the hypothalamus and modulated by testicular hormones. Inhibin, testosterone and its metabolites inhibit the secretion of the gonadotropins both directly at the pituitary and centrally at the level of the hypothalamus. In the testis, LH mainly stimulates testosterone production and FSH promotes spermatogenesis, but the exact details of these actions are only now being elucidated. The discovery of novel mutations in gonadotropin structure and signaling provide unique insight into the roles of these crucial hormones in the development and function of the male reproductive axis. A key goal of research into hormonal regulation of testicular function is the development of reversible, safe and effective male hormonal contraceptives. Recent promising trials of hormonal contraceptive combinations may soon bring the promise of male contraception to fruition.