Inhibition of implantation and termination of pregnancy in the rat by a human chorionic gonadotropin antagonist.

Administration of varying doses (10-50 micrograms) of deglycosylated human CG (DG-hCG) which was previously shown to be a potent hormonal antagonist in vitro, to pregnant rats inhibited implantation and terminated gestation. When administered between days 1-5 implantation was inhibited as seen on day 10. Serum progesterone levels were also suppressed. Similar doses administered between days 8 and 11 resulted in complete fetal resorption when examined on day 16. This was also accompanied by a dramatic reduction in serum progesterone. A dose of 50 micrograms DG-hCG given during the second half of pregnancy between days 13 and 16 had no deleterious effect on pregnancy including the day of parturition but the number of pups delivered was reduced by 26% as compared to 3% loss in control groups. It is concluded that DG-hCG can successfully antagonize hormone action in vivo by blockade of ovarian receptor sites for LH in the pregnant rat.