Effect of Antithyroid Compounds on the Deiodination of Thyroxine in the Rat

Sixty compounds were tested for their capacity to inhibit the deiodination of thyroxine. Most of these compounds had antithyroid activity and others were structurally related. Estradiol, testosterone, cortisone and salicylate were tested because of their possible importance in deiodination. Sixteen compounds were found to inhibit the deiodination of thyroxine, and 5-n-propyl-2- thiouracil was the most effective of all. Sodium salicylate increased the deiodination of thyroxine. The effectiveness in inhibiting deiodination of thyroxine did not correlate with antithyroid activity.