Effect of Estrogen on Iodinated Amino Acids of the Thyroid and Serum

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

A chromatographic analysis of hydrolyzed and nonhydrolyzed thyroid tissue and of serum was made 6 and 24 hours after the administration of I¹³¹ to estrogen-treated and control castrate male rats. No consistent significant differences were noted between the thyroids and sera of experimental and control animals. Triiodothyronine was released more rapidly from the thyroids of all animals than was thyroxine. Thyroidal accumulation and renal excretion of I¹³¹ was also studied. When 10,000 iu of estrogen (1.0 mg estrone) were administered over 4 days, 24-hour renal excretion of I¹³¹ was significantly depressed. When 1000 iu of estrogen (0.1 mg estrone) were administered over 4 days, 24 hour renal excretion of I¹³¹ was depressed to a lesser degree. It was concluded that the action of estrogen on thyroidal uptake was twofold; indirect, by suppression of I¹³¹ urinary excretion and, most likely direct, from the evidence cited, by enhancing the iodide trapping mechanism.