{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,11,5]],"date-time":"2026-11-05T08:00:31Z","timestamp":1793865631888,"version":"4.6.1"},"reference-count":0,"publisher":"S. Karger AG","license":[{"start":{"date-parts":[[2008,3,28]],"date-time":"2008-03-28T00:00:00Z","timestamp":1206662400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/karger.com\/pages\/terms-and-conditions"},{"start":{"date-parts":[[2008,3,28]],"date-time":"2008-03-28T00:00:00Z","timestamp":1206662400000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/karger.com\/pages\/terms-and-conditions"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Neuroendocrinology"],"abstract":"<jats:p>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 \u00b5g estradiol benzoate (EB) to 5 sheep initially caused reductions (\u223c5O%) in plasma LH baseline, peak values and LH pulse amplitude. Therafter 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 \u00b1 SEM plasma levels 5.3 \u00b1 1.5 nmol\/1), the biphasic LH response to EB was still apparent and increases in LH peak values (267 \u00b1 19%) and LH pulse amplitudes (262 \u00b1 23%) were greater (p &lt; 0.05) than those seen with EB alone (195 \u00b1 11 and 172 \u00b1 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 \u00b1 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. The addition of 2 or 4 subcutaneous progesterone implants did not affect estrogen-induced suppression of FSH secretion in GnRH-pulsed OVX-HPD ewes. These data indicate that estrogen has a direct pituitary effect to influence the action of GnRH and that progesterone alone does not influence the secretion of LH or FSH by a direct pituitary effect. Progesterone may enhance the feedback effects of estrogen on LH secretion by a direct action at the pituitary level.<\/jats:p>","DOI":"10.1159\/000123990","type":"journal-article","created":{"date-parts":[[2008,3,28]],"date-time":"2008-03-28T16:47:51Z","timestamp":1206722871000},"page":"267-274","source":"Crossref","is-referenced-by-count":99,"title":["Direct Pituitary Effects of Estrogen and Progesterone on Gonadotropin Secretion in the Ovariectomized Ewe"],"prefix":"10.1159","author":[{"given":"Iain J.","family":"Clarke","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"James T.","family":"Cummins","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"127","published-online":{"date-parts":[[2008,3,28]]},"container-title":["Neuroendocrinology"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.karger.com\/Article\/Pdf\/123990","content-type":"application\/pdf","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/karger.com\/article-pdf\/doi\/10.1159\/000123990","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,5,1]],"date-time":"2026-05-01T19:05:55Z","timestamp":1777662355000},"score":1,"resource":{"primary":{"URL":"https:\/\/karger.com\/article\/doi\/10.1159\/000123990"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2008,3,28]]},"references-count":0,"URL":"https:\/\/doi.org\/10.1159\/000123990","archive":["Portico"],"relation":{},"ISSN":["0028-3835","1423-0194"],"issn-type":[{"value":"0028-3835","type":"print"},{"value":"1423-0194","type":"electronic"}],"subject":[],"published":{"date-parts":[[2008,3,28]]}}}