Investigation of the effects of progesterone on neuropeptide Y-stimulated luteinizing hormone-releasing hormone secretion from the median eminence of ovariectomized and estrogen-treated rats.
We have investigated the hypothesis that administration of progesterone to estrogen-treated ovariectomized (OVX) rats enhances the stimulatory effects of neuropeptide Y (NPY) on the secretion of luteinizing hormone-releasing hormone (LHRH) from median eminence (ME) fragments in vitro. Adult rats were bilaterally OVX and after 2-4 weeks various doses of estrogen were administered subcutaneously in Silastic capsules. Three days later animals were injected subcutaneously with progesterone (1, 2 or 19 mg) or oil vehicle. Three hours later animals were killed, trunk blood collected, and the ME dissected and rinsed in culture medium. Incubation medium was collected after 30 min (control) and synthetic porcine NPY (0.1-10 microM) was applied during the test period. LHRH released into the medium and plasma luteinizing hormone were measured with RIA. NPY significantly stimulated LHRH secretion from MEs obtained from estrogen-treated OVX rats injected with oil vehicle. This stimulation was directly dependent on the degree of estrogen replacement. Administration of physiological doses of progesterone had no effect on NPY-stimulated LHRH release at low physiological levels of estrogen replacement. However, injection of 1 or 2 mg of progesterone into animals receiving the high physiological dose of estrogen slightly, although not significantly, reduced NPY (10 microM)-stimulated LHRH secretion. Treatment with the pharmacological dose of progesterone (19 mg) significantly decreased the ability of NPY to stimulate LHRH release when compared to vehicle-injected controls or to animals receiving 1 mg of progesterone. These results do not support the hypothesis that progesterone enhances NPY-stimulated LHRH secretion.(ABSTRACT TRUNCATED AT 250 WORDS)
Sabatino
F D
FD
Department of Anatomy and Cell Biology, Emory University School of Medicine, Atlanta, Ga.
Collins
P
P
McDonald
J K
JK
D000818:Animals; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000008:administration & dosage / Q000494:pharmacology*; D004971:Estrus / Q000097:blood; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000097:blood; D008473:Median Eminence / Q000187:drug effects / Q000378:metabolism*; D009478:Neuropeptide Y / Q000494:pharmacology*; D010052:Ovariectomy; D011359:Proestrus / Q000097:blood; D011374:Progesterone / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
D009478:Neuropeptide Y; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone