Further Studies on Anti-Thyroxine Effects of Various Compounds.

Summary (1) The study of compouds inhibiting the peripheral metabolic action of thyroxine in thyroidectomized rats has been extended to such substances as vit. A, vit. B12, cholesterol and a series of aliphatics and aromatics carrying the 3,5-diiodo-4-hydroxyphenyl grouping. (2) The compounds found capable of producing approximately 50% inhibition were vit. A, β-carotene, cholesterol, butyl-3,5-diiodo-4-hydroxybenzoic acid, and x-methyl-β-(3,5-diiodo-4-hydroxyphenyl) -propionic acid. Several other substances were found to be less active than these. No compound tested was found clearly active as a thyroxine antagonist at an inhibitor: thyroxine ratio of less than 300.