title: Selective release of follicle-stimulating hormone by 5 alpha-dihydroprogesterone in immature ovariectomized estrogen-primed rats.
abstract: The effect of 5 alpha-dihydroprogesterone (5 alpha-DHP) on gonadotropin release was examined in the immature acutely ovariectomized (OVX) rat primed with a low dose of estradiol (E2). Treatment with various doses of 5 alpha-DHP given in combination with E2 increased levels of follicle-stimulating hormone (FSH) but had no effect on serum luteinizing hormone (LH). A single injection of a maximally stimulating dose of 5 alpha-DHP (0.4 mg/kg) stimulated increases in serum FSH at 1200 h and, 6 h later, at 1800 h. Pituitary LH and FSH content was dramatically enhanced by 1600 h and levels remained elevated at 1800 h. The administration of pentobarbital at 1200 h, versus 1400 h or 1600 h, prevented the increase in basal serum FSH levels at 1800 h, implying that the release of hypothalamic LH releasing hormone (LHRH) is modulated by 5 alpha-DHP. In addition, changes in pituitary sensitivity to LHRH as a result of 5 alpha-DHP were measured and a significant increase in the magnitude of FSH release was observed at 1200 h and 1800 h. Although the LH response to LHRH in 5 alpha-DHP-treated rats was not different from controls, the duration of LH release was lengthened. These results suggest that 5 alpha-DHP may stimulate FSH release by a direct action at the pituitary level. Together, these observations support the theory that 5 alpha-DHP mediates the facilitative effect of progesterone on FSH secretion and further suggests an action of 5 alpha-DHP in this phenomenon at both pituitary and hypothalamic sites.
mesh_terms: D004092:20-alpha-Dihydroprogesterone / Q000494:pharmacology*; D000818:Animals; D002369:Castration; D002940:Circadian Rhythm / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects*; D007986:Luteinizing Hormone / Q000097:blood; D011374:Progesterone / Q000031:analogs & derivatives*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D004092:20-alpha-Dihydroprogesterone; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone