Sex steroids influence LH-RH-receptor interaction

Abstract

Intact male rats (I) and rats 30 days after orchidectomy (OR) were treated in vivo with a single dose of 1.5 or 0.5 mg testosterone propionate (TP), 22.5 or 7.5 mug estradiol benzoate (EB) and a mixture of TP plus EB, respectively. The release of LH and FSH from anterior pituitaries of steroid hormone pretreated animals induced by the administration of LH-RH was studied in vitro. LH-RH stimulated FSH release from pituitaries of I and OR was inhibited by higher doses of EB or a mixture of EB plus TP. On the other hand, EB and combination of EB plus TP stimulated LH release in I, whereas EB and TP inhibited LH-RH induced release of LH in OR. At the lower dose levels no inhibition of LH-RH stimulated FSH release from pituitaries of steroid pretreated I or OR animals occured. LH-RH induced LH release was only observed at thise dose level in I pretreated with TP and OR pretreated with EB. On the other hand, pretreatment of ovariectomized rats (OV) with sex steroids (5 mug 17 beta-estradiol, 3 mg progesterone, and mixture of 5 mug 17 beta-estradiol and 3 mg progesterone, resp., each injected through 6 days) resulted in restoration of LH-RH induced FSH release lost 30 days after ovariectomy. Furthermore, LH-RH induced release of LH and FSH from male rat pituitaries at different times after orc dectomy exhibited a pattern from that recorded for ovariectomized animals. [125I] LH-RH binding assays with anterior pituitary plasma membrane fractions isolated from I revealed two binding sites with apparent affinity constants of 4.3 x 10(-9) M and 2.2 x 10(-8) M, respectively. The low affinity binding site is lost upon orchidectomy. Scatchard plot analyses of binding data obtained for LH-RH reaction with plasma membrane fractions isolated from anterior pituitaries of OR pretreated with sex steroids showed that the second binding site could be regenerated by treatment with the low dose of TP. From the present experiments it is concluded that: 1. LH-RH induced gonadotropin release is affected by sex steroids at the pituitary plasma membrane level. 2. One hypothalamic hormone may well specifically control LH and FSH release. 3. Mechanisms controlling LH-RH induced gonadotropin release are different in the male and female.