THYROXINE UTILIZATION IN NON-PREGNANT, STEROID-INDUCED PSEUDOPREGNANT, AND PREGNANT MONKEYS

ABSTRACT The utilization of thyroxine was studied in pregnant, non-pregnant and steroid-induced pseudopregnant rhesus monkeys. The PBI concentration in the blood serum was found to be higher during pregnancy and pseudopregnancy than in the non-pregnant state. The turn-over rate of radiothyroxine, following its intravenous injection, was found to be higher during and outside of pregnancy than during pseudopregnancy. The extra-thyroidal thyroxine pool was calculated to be more expanded during pregnancy and (probably) pseudopregnancy than in the non-pregnant state. The utilization of thyroxine per unit time proved to be smaller in the non-pregnant monkey than in the pregnant and (probably) greater than in the pseudopregnant animal. It is concluded that thyroxine utilization during pregnancy is higher than during pseudopregnancy. The increased activity of the thyroid of the pregnant monkey, as judged from the increase in thyroxine utilization, is not only caused by the high level of placental steroids that characterize this state.