Termination of early pregnancy in the rat by a single dose of human menopausal gonadotropin.

Human menopausal gonadotropin (hMG) is commonly used to induce ovarian follicular development and ovulation in infertile women. This report is a preliminary analysis of the ability of hMG to cause folliculogenesis and ovulation in pregnant laboratory animals. Wistar rats were injected subcutaneously with 0.5 mg of hMG on selected days of pregnancy. In addition, 2 days after receiving hMG, one group of animals was injected with 50 IU of human chorionic gonadotropin (hCG) as a substitute for an ovulation-inducing dose of luteinizing hormone. A single dose of hMG caused follicular development and ovulation in the pregnant animals. Furthermore, the results show that such hormone treatment usually terminated the gravid state of the animals. The frequency of pregnancy termination was greater (1) When hMG was administered during the first quarter of the 21-day gestation period; (2) When higher doses of hMG were used; and (3) When the hMG injection was followed 2 days later by hCG. In conclusion, hMG can terminate early pregnancy in a laboratory animal like the rat, and this observation raises the possibility that it may also act as an abortifacient agent in humans. Therefore, a more extensive analysis of the effects of hMG on pregnancy is warranted.