SEX STEROIDS INFLUENCE LH-RH-RECEPTOR INTERACTION

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  • 1 January 1975
    • journal article
    • research article
    • Vol. 9  (3) , 167-176
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 .mu.g estradiol benzoate (EB) and a mixture of TP plus EB, respectively. The release of LH (luteinizing hormone) and FSH (follicle stimulating hormone) from anterior pituitaries of steroid hormone pretreated animals induced by the administration of LH-RH (releasing hormone) was studied in vitro. LH-RH stimulated FSH release from pituitaries of I and OR was inhibited by high doses of EB or a mixture of EB plus TP. 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 occurred. LH-RH induced LH release was only observed at this dose level in I pretreated with TP and OR pretreated with EB. Pretreatment of ovariectomized rats (OV) with sex steroids (5 .mu.g 17 .beta.-estradiol, 3 mg progesterone, and a mixture of 5 .mu.g 17 .beta.-estradiol and 3 mg progesterone, each injected through 6 days) resulted in restoration of LH-RH induced FSH release lost 30 days after ovariectomy. LH-RH induced release of LH and FSH from male rat pituitaries at different times after orchidectomy exhibited a pattern different from that recorded for ovariectomized animals. [125I] LH-RH binding assays with anterior pituitary plasma membrane fractions isolated from I revealed 2 binding sites with apparent affinity constants of 4.3 .times. 10-9 M and 2.2 .times. 10-8 M, respectively. The low affinity binding site is lost upon orchidectomy. LH-RH induced gonadotropin release is affected by sex steroids at the pituitary plasma membrane level. One hypothalamic hormone may specifically control LH and FSH release. Mechanisms controlling LH-RH induced gonadotropin release are different in the male and female.