Effect of GnRH superactive analogs (alone and combined with androgen) on testicular function in man and experimental...

GnRH long acting agonists, when given chronically, are potent inhibitors of testicular function in both man and experimental animals. Administration of these agents to male rats and to men results in suppression of testosterone secretion and diminished sperm counts. Despite the similarity of these observations the mechanisms by which these agents effect the testes appear to be different in the two species. In man GnRH analogs have an early stimulatory effect on LH and FSH secretion with down regulation evident by the 10th day of daily treatment. Longer treatment results in suppressed LH, FSH and testosterone levels. In the rat the stimulatory phase of GnRH analogs on LH and FSH secretion persisted for a much longer period of time (20-60 days). In the rat, direct testicular effects of analogue were the most likely cause of early suppression of testosterone and impaired sperm production. In both species combined testosterone and GnRH analog had additive effects on gonadotropin hormone suppression; combined therapy is being tested as a male contraceptive regimen.