Mechanisms of the antifertility effects of LHRH agonists in the male rat.

Treatment with LHRH agonist on castrated and noncastrated male rats causes a marked decrease in testicular luteinizing hormone (LH) receptors; in weights of testis ventral prostate and seminal vesicles; and in concentration of plasma testosterone. Daily administration of 1 mcg of [D-A1a6]-LHRH-EA causes changes in levels of testicular LH prolactin and follicle stimulating hormone (FSH) receptors all correlated with changes in steroidogenesis. A progressive and dramatic fall in testicular androstenedione and testosterone levels has also been observed; in contrast no change in testicular estrogen level was noted. LHRH agonists are also responsible for the loss of pituitary gonadotropin responsiveness. Treatment with [D-A1a6]-LHRH-EA did not cause histologic alterations in the testes after 1 week of treatment; changes were noted after 2-8 weeks of treatment. It is possible that the main factor involved in the antifertility effects observed is gonadal desensitization induced by LHRH agonist-induced endogenous LH release.