Peripheral concentrations of gonadotropins and progestins during pregnancy in rabbits after active immunization against testosterone.

The effects of active immunization of female rabbits against testosterone on various endocrine parameters during pregnancy were examined. Peripheral blood samples were obtained from immunized rabbits at timed intervals after mating up to the 29th day of pregnancy, when the rabbits were killed and various tissues were analyzed. Progesterone concentrations were higher in testosterone-immunized rabbits (TIR) than in controls during pregnancy. Luteinizing hormone (LH) and follicle-stimulating hormone concentrations were not significantly different in controls and TIR during pregnancy. Both progestins and gonadotropins showed the expected coitus-induced increases, but LH levels were higher in TIR. The binding of testosterone in fetal plasma and amniotic fluid was higher in TIR than in controls. Weights of fetuses and litter size were not significantly different in TIR and controls. These data suggest that testosterone may play a role during pregnancy in the rabbit.