EFFECT OF 5-HALOGENO-2-THIOURACIL AND OF 6-METHYL-5-IODO-2-THIOURACIL ON OXYGEN CONSUMPTION IN RATS*

Abstract

Oral admn. of equimolar amts. of thiouracil, thiouracil-KI and of the 5-halogeno-2-thiouracils (Cl, Br, I) for 58 days produced about the same lowering of oxygen consumption in young rats (-18%). None of these compounds, up to 78[mu] [image]/day, were as effective as thyroidectomy, while the effect of KI alone or of 6-methyl-5-iodo-2-thiouracil was slight. In this expt. none of the halogenated derivatives produced gross thyroid hyperplasia and only the bromo derivative produced toxicity. Animals receiving either the iodinated compounds or KI alone showed an increased growth rate. In addition to its antimetabolic potency, 5-iodo-2-thiouracil was unique in producing a marked depletion of thyroid I without disturbing thyroid histology, and a prolonged metabolic depression following cessation of treatment. It is suggested that the unique action of this compound should be ascribed to the entire molecule rather than to any particular moiety.