Effects of Castration, Steroid Replacement, and Hypophysectomy on Hypothalamic LHRH and Serum LH

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Abstract
The effect of castration (CAS), hypophysectomy (HYPOX) and gonadal steroids on hypothalamic luteinizing hormone-releasing hormone (LHRH) content was studied in male and female rats. Hypothalamic LHRH content was significantly reduced by 1 wk after castration in male rats and was further reduced by 2 wk. HYPOX decreased LHRH content in male rats to the same extent as in CAS rats alone, suggesting that loss of gonadal function was mainly responsible for the fall in hypothalamic LHRH in these rats. In castrated male rats testosterone propionate (TP) at a dose of 0.5 mg/300 g body wt raised hypothalamic LHRH content above that of intact rats and reduced serum LH below the intact level. However, in castrated-hypophysectomized rats, TP treatment only returned hypothalamic LHRH content to the intact level. Ovariectomy for 3 wk decreased hypothalamic LHRH content significantly, whereas estradiol benzoate (EB, 1 .mu.g) replacement for 1 wk returned LHRH content to intact levels and reduced serum LH significantly. Progesterone (PRG) (2.5 mg) alone had no effect on hypothalamic LHRH content, but decreased serum LH levels slightly in ovariectomized rats. Treatment with a combination of EB and PRG raised hypothalamic LHRH content to levels even higher than those in intact rats, but this difference was insignificant. Gonadal steroids can regulate LH secretion by acting on the hypothalamus to modulate LHRH secretion. The effect of hypophysectomy in reducing LHRH content is probably due mainly to loss of testosterone secretion.