Iodine Metabolism in Pregnancy

Abstract

The metabolism of I131 was studied in 6–8, 13–15, and 19–21 day gestating rats. During pregnancy renal excretion of I131 was significantly increased and thyroidal accumulation of the isotope was significantly depressed, compared with control values. Radiochromatographic studies of nonhydrolyzed and hydrolyzed thyroids and of serum from pregnant and control animals revealed no qualitative or quantitative differences among the radioactive compounds isolated. The metabolism of radiothyroxine (Tx*) and radiotriiodothyronine (Trit*) was studied in 10–15 day gestating thyroidectomized and control animals. The disappearance rate of Tx* from serum was significantly faster in pregnant rats than in controls. The disappearance rate of Trit* from serum was the same in pregnant and control animals. During pregnancy in the rat there is a depletion of iodine and iodine-containing compounds and no evidence for enhanced thyroidal function was found to compensate for this depletion. The situation in rat pregnancy is not applicable to that in human pregnancy.