Postnidatory effects of luteinizing hormone releasing hormone (LHRH) in hamsters.

Whereas the administration of LHRH to pregnant hamsters has no effect during the prenidatory period, the hormone is effective in terminating pregnancy when given after implantation (days 6-10). The ED50 for pregnancy termination over this period approximates a dose of 0.35-0.4 mg b.i.d. When given to pregnant females in a second study, the effects of LHRH at this dose were completely reverse by minute doses of progesterone (30 microgram and above). Finally, administration of LHRH at 1.5 mg b.i.d., from days 6-10 was followed by daily sacrifice through day 12; bloods were sampled at autopsy for progesterone evaluation. Autopsies on days 7 and 8 showed few differences between controls and LHRH-treated hamsters, although decreased weights of the uterine/conceptus units signaled the initation of resorption. Significant LHRH-induced decreases in circulating progesterone were seen by day 9. Fetal resorption continued and was essentially complete by day 11, while progesterone levels continued depressed through the end of the study.