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

Abstract

A B S T R A C T 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 ofcastrated 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 ,ug 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-stinriulating 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.

Castration of Male Rats Reduces the Capacity of Granules Isolated from the Median Eminence to Secrete Luteinizing Hormone-Releasing Hormone in Response to Copper

“…Since castration also reduced the MEA content of LHRH and since the yield of granule LHRH from sham and cas trated male rats was similar (table I), it is logical to assume that the reduced capacity of the isolated granules to release LHRH is a consequence of a reduction in the amounts of LHRH available for release in the castrated animals. These findings are complementary to those of Rudenstem et al [18] who noted that the basal release of LHRH from hypo thalami of castrated male rats, incubated under in vitro con ditions, is lower than that of intact rats and that testosterone restored the release of LHRH to the level observed in the intact. The results obtained from these two experimental systems are suggestive that less LHRH is secreted from the hypothalamus of castrated than that from intact male rats.…”

“…In contrast, Rudenstein et al [18] reported that the basal re lease of LHRH from medial basal hypothalami of intact rats was greater than that from castrated rats. Thus, the question arises: Does castration alter the secretory function of LH RH neurons of male rats?…”

Immunocytochemical Evidence for Gonadoliberin in Rat Anterior Pituitary Gland

“…It has been demonstrated that castration is followed by a decrease of hypothalamic GnRH content [I, 30,31]. It is likely related to an increase of GnRH secretion [12] but this increase is controversial [7,26].…”

Pituitary gonadotropin-releasing hormone receptors. Effects of castration, steroid replacement, and the role of gonadotropin-releasing hormone in modulating receptors in the rat.

“…Sarkar et al (16) found elevated pituitary stalk plasma GnRH concentrations at the time of the proestrus LH surge in rats and the same group recently reported increased GnRH concentrations in pituitary stalk plasma 4 and 28 d following ovariectomy and adrenalectomy (17). Other studies have shown that orchidectomy reduced and subsequent testosterone or estradiol replacement restored hypothalamic GnRH content to normal in male rats (18)(19)(20). These data suggest that gonadal steroids influence either hypothalamic synthesis or release ofGnRH.…”