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

Abstract

The effect of thiouracil on the uptake of injd. radioactive inorganic iodide (I131) by the thyroid gland and its conversion in this tissue to thyroxine and diiodotyrosine was detd. Rats weighing 270-305 gm. were fed 3.4-4.2 mg. of thiouracil daily for 7 days. They were injd. with P131 7 and 14 days after the adm. of thiouracil had been discontinued. The animals were killed 48 hrs. after the inj. of the I131 and the content of total I131, thyroxine V31 and diiodotyrosine I131 of their thyroid glands measured. At the end of the 7-day period of thiouracil feeding, the capacity of the gland to concentrate injd. I131 and the amts. of I131 converted in the gland to thyroxine and diiodotyrosine were depressed. Both the I131-concentrating capacity of the gland and the amts. of radiothyroxine and radiodiiodotyrosine formed in the thyroid were restored to normal 2 wks. after the adm. of thiouracil had been discontinued.