Efficacy of HCG and ovarian steroids in the maintenance/interruption of pregnancy in-albino rats.

We investigated the efficacy of human chorionic gonadotrophin (HCG) and ovarian steroids in the maintenance/interruption of pregnancy in normal pregnant rats. Holtzman's strain rats were laparotomized to observe the number of implantations. In this study, continuous administration of HCG (5 IU) to normal pregnant rats, from day 8 through days 14 or 19, interrupted gestation, resulting in fetal resorption with many placentomas and placental scars. By contrast, a single injection of HCG (5 IU or 1 IU) on day 8 had no deleterious effect on pregnancy, except that the percent fetal survival was slightly reduced, attributable to a slight hyperstimulation of the ovaries of the pregnant rats. One possibility is that prolonged treatment with HCG might have caused progesterone/luteal hormone deficiency with a concomitant increase in estrogen secretion, resulting in the interruption of pregnancy. Hence, here we tested whether progesterone (5 mg) or estradiol-17beta (1 microg) administered to HCG treated rats could compensate this deficiency and maintain pregnancy. The results indicate that these steroids cannot prevent the interruption of pregnancy induced by the continuous administration of HCG, possibly due to an overstimulation of the ovaries by gonadotrophin.