Effect of estradiol on the pituitary response to intravenous stimulation with luteinizing hormone-releasing hormone in menopausal women.

Five menopausal patients were submitted to stimulation with 100-micrograms doses of luteinizing hormone-releasing hormone (LH-RH) administered 120 minutes apart under three different types of conditions: (1) in a hypoestrogenic state (test 1); (2) in a hyperestrogenic state after acute intravenous bolus injection of 400 micrograms 17 beta-estradiol (E2) (test 2); (3) in a hyperestrogenic state after daily oral administration of 50 micrograms ethinyl E2 for 3 to 4 weeks (test 3). The results of the three tests showed that (1) the time needed to reach maximum LH values after LH-RH injection was longest in test 3; (2) the hormonal production rate (HPR) in test 1 was greatest after the first stimulus with LH-RH. In test 2, the two stimulations with LH-RH induced an equivalent HPR, whereas in test 3, the HPR was greatest after the second stimulation; (3) the correlation between basal LH values before LH-RH injection and the maximal values of the responses obtained after each injection changed throughout the experiment. In all three tests, the slope of the line (significant positive correlation) was always greater after the second stimulation. When the three tests were compared, the slope in test 3 was greater than in test 2, and the slope in test 2 greater than in test 1. These results clearly suggest the important role of estrogens in the regulation of LH release in women by acting not only at the hypothalamus but also at the pituitary level, and demonstrate a correlation between basal LH levels and the maximum response to LH-RH stimulation. This correlation is more marked during estrogen treatment and depends on the time of exposure to estrogen.