DIFFERENTIATION OF THE ANTITHYROID ACTION OF THIOURACIL, THIOUREA AND PABA FROM SULFONAMIDES BY IODIDE ADMINISTRATION

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Abstract
Iodide exerts different and opposite effects on the response of the rat to the antithyroid drugs, thiouracil, and sulfaguanidine. Small amts. of iodide inhibit the goiterogenic action of thiouracil by 50-100%, depending on the level of the goiterogen employed. Higher levels of iodide, while not increasing this inhibition, suppress the thyroid hyperplasia. The goiterogenic effect of low levels of sulfaguanidine is augmented by a high level of iodide. With either low levels of iodide or a high level of sulfaguanidine, this synergistic action is not observed. However, iodide appears to increase the degree of thyroid hyperplasia under all of the conditions studied. p-Aminoben-zoic acid resembles thiouracil rather than sulfaguanidine in so far as both its goiterogenic and hyperplastic actions are inhibited by iodide. It is concluded that thiouracil, thiourea, and p-aminobenzoic acid differ from sulfaguanidine in the primary biochemical reactions responsible for their effects on the thyroid.