THE TIME COURSE CHANGE AFTER CASTRATION IN SHORT-LOOP NEGATIVE FEEDBACK CONTROL OF LH BY HCG IN WOMEN

Abstract

The time course of change in the suppressive effect of human chorionic gonadotropin (HCG) on luteinizing hormone (LH) and/or LH-.beta. following castration was studied by a specific LH-.beta. radioimmunoassay. At 14-50 days after castration 8 women were given 10,000 IU of HCG in a simple i.m. injection (group 1), 5 women were given 2000 IU of HCG in the same way (group 2), and 5 were injected with saline as controls (group 5). In addition, 5 women 6-15 mo. (group 3) and 7 women 3-8 yr (group 4) after castration were given 10,000 IU of HCG. The serum concentrations of HCG in groups 1, 2, 3 and 4 reached peak levels of 209.4, 44.1, 210.6 and 238.6 mU[milliunits]/ml, respectively, 4 h after the HCG injection. The serum LH concentration in group 1 was reduced significantly (P < 0.01) by HCG administration, but the reductions in the LH levels in groups 2, 3 and 4 after HCG injection were not significantly different from that of the controls. These findings suggest that the threshold of the short-loop negative feedback control of LH in women changes with time after castration.