title: Direct pituitary effects of estrogen and progesterone on gonadotropin secretion in the ovariectomized ewe.
abstract: The direct pituitary effects of estrogen and progesterone on the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were studied in ovariectomized (OVX) ewes in which the pituitary had been disconnected surgically from the hypothalamus (hypothalamo-pituitary disconnection, HPD). Gonadotropin secretion was restored with hourly pulses of 500 ng gonadotropin-releasing hormone (GnRH) via intra-atrial cannulae. Intramuscular injections of 50 micrograms estradiol benzoate (EB) to 5 sheep initially caused reductions (approximately 50%) in plasma LH baseline, peak values and LH pulse amplitude. Thereafter all parameters of plasma LH concentration increased 2- to 3-fold above starting values. After these 5 sheep had received 2 subcutaneous progesterone implants (mean +/- SEM plasma levels 5.3 +/- 1.5 nmol/l), the biphasic LH response to EB was still apparent and increases in LH peak values (267 +/- 19%) and LH pulse amplitudes (262 +/- 23%) were greater (p less than 0.05) than those seen with EB alone (195 +/- 11 and 172 +/- 14%, respectively). The presence of 2 progesterone implants alone did not change plasma LH baseline, peak values or pulse amplitude, or plasma FSH values. In the second experiment, where 4 OVX-HPD ewes were given 4 progesterone implants (plasma progesterone 27.7 +/- 3.4 nmol/l), there were no effects on basal plasma LH or plasma FSH values. The LH responses to EB were more marked in 4 OVX-HPD ewes given 4 progesterone implants than in the animals given EB alone. Also, the estrogen-induced LH surge occurred earlier in the ewes given 4 progesterone implants than in those given estrogen alone.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D002369:Castration; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood / Q000378:metabolism*; D007031:Hypothalamus / Q000502:physiology; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D011374:Progesterone / Q000494:pharmacology*; D012756:Sheep
chemical_list: D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone