Depletion of Thyroid Glandular Iodine After Administration of Thyrotropin

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Abstract
Thyroid content of iodine and of iodoamino acids released by enzymic proteolysis of thyroid tissue was measured before and 3 hr after the intravenous administration of thyrotropin to rats whose glands had been labeled with I131. The thyrotropin-induced loss of radioiodine was considerably greater when animals were given propylthiouracil shortly before injection of thyrotropin than when given saline. In propylthiouraciltreated animals the iodotyrosines and iodothyronines disappeared from the gland in the proportions in which they were present in the gland, while, in animals not given propylthiouracil, thyrotropin induced a relatively greater depletion of iodotyrosines than of iodothyronines. Specific activity data suggested that conversion of iodotyrosines to iodothyronines was accelerated during the 3-hr interval after injecting thyrotropin in control animals while this was probably prevented in the animals given propylthiouracil. Inhibition by propylthiouracil of the conversion of iodotyrosine to iodothyronine and of glandular reutilization of iodide arising from intraglandular deiodination was probably responsible for the quantitative and qualitative differences in the response to thyrotropin of animals given propylthiouracil, as compared with controls.