THE EFFECT OF THIOURACIL ON THE FORMATION OF THYROXINE AND DIIODOTYROSINE BY THE THYROID GLAND OF THE RAT WITH RADIOACTIVE IODINE AS INDICATOR¹

Abstract

IT HAS BEEN repeatedly shown during the last few years that the administration of thiourea and of a number of its derivatives produces hyperplasia and hypertrophy of the thyroid gland (MacKenzie and MacKenzie, 1943; Astwood, Sullivan, Bissell and Tyslowitz, 1943; Astwood, 1943; Kennedy, 1942; Richter and Clisby, 1942). The evidence obtained in the intact animal indicates that these compounds depress the activity of the thyroid gland (MacKenzie and MacKenzie, 1943; Astwood, Sullivan, Bissell and Tyslowitz, 1943). Recent investigations in this laboratory have demonstrated that these compounds inhibit the conversion of inorganic iodide to thyroxine and diiodotyrosine by the thyroid gland (Franklin and Chaikoff, in press). This was shown by an in vitro procedure in which surviving thyroid slices were incubated in a Ringer's medium containing radioactive inorganic iodide. The addition of thiourea, allylthiourea and thiouracil strongly retarded the formation of thyroxine and diiodotyrosine. Allylthiourea markedly depressed this formation at a concentration as low as 10-4 M.