Direct pituitary effects of estrogen and progesterone on gonadotropin secretion in the ovariectomized ewe.

摘要: The direct pituitary effects of estrogen and progesterone on the secretion luteinizing hormone (LH) follicle-stimulating (FSH) were studied in ovariectomized (OVX) ewes which had been disconnected surgically from hypothalamus (hypothalamo-pituitary disconnection, HPD). Gonadotropin was restored with hourly pulses 500 ng gonadotropin-releasing (GnRH) via intra-atrial cannulae. Intramuscular injections 50 micrograms estradiol benzoate (EB) to 5 sheep initially caused reductions (approximately 50%) plasma LH baseline, peak values pulse amplitude. Thereafter all parameters concentration increased 2- 3-fold above starting values. After these received 2 subcutaneous implants (mean +/- SEM levels 5.3 1.5 nmol/l), biphasic response EB still apparent increases (267 19%) amplitudes (262 23%) greater (p less than 0.05) those seen alone (195 11 172 14%, respectively). presence did not change or amplitude, FSH In second experiment, where 4 OVX-HPD given (plasma 27.7 3.4 there no basal responses more marked animals alone. Also, estrogen-induced surge occurred earlier alone.(ABSTRACT TRUNCATED AT 250 WORDS)