SUPPRESSION OF SERUM LEVELS OF LUTEINIZING-HORMONE BY SHORT-LOOP AND LONG-LOOP NEGATIVE FEEDBACK IN OVARIECTOMIZED WOMEN

The suppressive effects of short- and long-loop negative feedback on serum levels of LH [luteinizing hormone] were assessed after administration of human chorionic gonadotrophin (hCG) and conjugated estrogens. Fourteen ovariectomized women were injected i.v. with 5 mg conjugated estrogens, 8 of these patients were also given an i.m. injection of 10,000 IU hCG 8 h later, while the other 6 patients were given a control injection of 0.9% saline. The serum levels of LH decreased by similar amounts in both groups of women. Thirteen other ovariectomized women were initially injected with 10,000 IU hCG, i.m., 7 of these patients were also given an i.v. injection of 5 mg conjugated estrogens 8 h later, while the remaining 6 patients received a control injection of 0.9% saline. Conjugated estrogens could further suppress the serum level of LH which had been reduced by prior hCG treatment. In 6 ovariectomized women who received i.m. saline injections at the start of the experiment and 8 h later, the serum levels of LH did not change significantly. The suppression of the serum concentrations of LH by long-loop negative feedback after administration of 5 mg conjugated estrogens is greater than that by short-loop negative feedback after treatment with 10,000 IU hCG.