title: Estrogen inhibition of LH and FSH secretion: effects of a GnRH antagonist.
abstract: Follicle-stimulating hormone (FSH) levels are not suppressed as rapidly or to the same degree as luteinizing hormone (LH) levels in ovariectomized rats treated with either gonadotropin-releasing hormone (GnRH) antagonist or estrogen. The acute inhibitory effects of various doses of estrogen on FSH and LH secretion were examined in cannulated, 2-wk ovariectomized rats. No dose of 17 beta-estradiol, up to 2,500 ng injected intravenously, suppressed FSH, although LH secretion was inhibited 50% within 1 h by 100 ng. In another experiment, estradiol benzoate (EB; 10 or 250 micrograms; sc injection in oil) was only marginally effective in suppressing FSH, compared with LH, levels in serum. Treatment with EB 24 h before or after a 500 micrograms dose of a GnRH antagonist did not reduce LH or FSH to levels lower than those achieved with antagonist alone. These results indicate that the GnRH-dependent component of FSH release and the GnRH-independent component that is unmasked in the presence of GnRH antagonist are sensitive to negative feedback by estrogen, indicating that this steroid is not the primary inhibitory ovarian factor regulating FSH in the rat.
authors.forename: M C
authors.initials: MC
authors.lastname: Charlesworth
authors.forename: N B
authors.initials: NB
authors.lastname: Schwartz
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D004958:Estradiol / Q000494:pharmacology; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000378:metabolism*; D010052:Ovariectomy; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
chemical_list: D004967:Estrogens; D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; C036959:LHRH, Ac-dehydro-Pro(1)-4-F-Phe(2)-Trp(3,6)-; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone