THE EFFECT OF PROPYLTHIOURACIL, METHYLTHIOURACIL AND THIOURACIL ON THE PERIPHERAL METABOLISM OFl-THYROXINE IN THYROIDECTOMIZED,l-THYROXINE MAINTAINED RATS

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Abstract
Thyroidcctomized, l-thyroxine maintained rats were equilibrated isotopically with exogenous I131 labeled l-thyroxine and later treated with propylthiouracil, methylthiouracil or thiouracil. The ensuing alterations in the distribution of radioactive compounds were determined. The results obtained showed that these goitrogens depress extrathyroidal deiodination of l-thyroxine to about half its normal amount; subsequently a larger fraction of the hormone is excreted via the fecal route. Concentration of labeled compounds in the peripheral tissues is not greatly influenced, whereas the level of circulating hormone is usualty increased above normal values. It is concluded that these “antithyroid” drugs have also a very rapid and intense action on the peripheral metabolism of l-thyroxine.