Thyroid Hormone-Catecholamine Interrelationships

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Abstract
Experiments were performed to investigate the role of cateholamines in the peripheral deiodination of thyroxine (T4). Deiodination was studied in vivo in rats maintained with I131-labeled T4, by measuring the daily urinary excretion of I131. Thyroid function was blocked with potassium perchlorate. When isotopic equilibrium was obtained, approximately 50% of the daily dose of I131 was excreted in the urine. Urinary I131 was increased following administration of epinephrine and was decreased by reserpine. Furthermore, in both normal and thyroidectomized rats, the urinary excretion of I131 in the 24-hr period following a single injection of I131-labeled T4 was increased by epinephrine. However, the increase was statistically significant only in the thyroidectomized rats. Epinephrine, and sometimes norepinephrine, when administered to mice in vivo for 4 days, induced a significant increase in the deio-dinating activity of homogenates of mouse liver. The effect was not due solely to the hyperglycemic or hypermetabolic actions of the catecholamines, since the increase was not observed following administration of glucose or 2,4-dinitrophenol. Deiodinating activity was greatly decreased in tissues obtained from mice pretreated with reserpine.