Effect of Estrogen on the Peripheral Utilization of Thyroid Hormones

¹ From the Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania

The effect of estrogen on the peripheral utilization of exogenous and endogenous radiothyroxine and exogenous radiotriiodothyronine was studied in thyroidectomized castrate and in castrate rats. Estrogen did not affect the disappearance rate of these hormones from serum nor their space of distribution. Estrogen increased urinary excretion and decreased fecal excretion of radioactive products compared with controls following the administration of radiotriiodothyronine, but it did not influence the excretion of radioactive products after the injection of radiothyroxine or I¹³¹. Radiotriiodothyronine was utilized more rapidly than radiothyroxine.