MECHANISM OF ANTITHYROID EFFECTS OF A SULFONYLUREA IN THE RAT1

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Abstract
In studies designed to elucidate the mechanism of antithyroid effects of carbutamide, an hypoglycemic sulfonylurea, rats were fed a synthetic low iodine diet with carbutamide, sulfaguanidine, propylthiouracil and iodide added in various concentrations. Carbutamide (0.125 to 1.0%) reduced I131 uptake, increased thyroid weight and depleted glandular iodine. It was found to be 13 times as potent as sulfaguanidine and l/200th of propylthiouracil. In contrast to sulfaguanidine and like propylthiouracil the goiters produced by carbutamide were inhibited by excess iodide. In rats fed carbutamide, I131 accumulated in the thyroid but was promptly discharged by thiocyanate. Except for a delay of 3 days in maximum activity the antithyroid effects of carbutamide were indistinguishable from propylthiouracil.