Administration of Gonadal Steroids to the Castrated Male Rat Prevents a Decrease in the Release of Gonadotropin-Releasing Hormone from the Incubated Hypothalamus

The influence of testosterone on gonadotropin-releasing hormone (GnRH) secretion was assessed indirectly by altering the serum testosterone concentration of male rats and measuring GnRH release from their incubated hypothalami 1 wk later.GnRH release from hypothalami of castrated rats was 13.4+/-1.2 (SE) pg/h, compared to 35.3+/-3.8 pg/h from hypothalami of intact rats (P < 0.001). GnRH release from the hypothalami of castrated rats treated with testosterone propionate, 100 or 500 mug daily, was 25.0+/-3.4 pg/h and 27.9+/-3.6 pg/h, which is significantly greater (P < 0.05 and P < 0.01, respectively) than that from hypothalami of castrated rats treated only with sesame oil.A similar decrease in GnRH release from hypothalami of hypophysectomized rats and prevention of this decrease by treating the hypophysectomized rats with testosterone propionate is evidence that the observed effects of testosterone are not mediated via luteinizing hormone and(or) follicle-stimulating hormone secretion. Treatment of castrated rats with either dihydrotestosterone propionate or estradiol benzoate also prevented the decrease in GnRH release from the hypothalami of castrated rats.We conclude that testosterone, dihydrotestosterone, and estradiol all prevent the decrease in GnRH release from hypothalami of castrated rats treated with these steroids. The possibility exists that these steroids may also maintain GnRH secretion in vivo.