Effect of Iodide on Recovery of Function of Rat Thyroid Gland After Administration of Antithyroid Agents

Iodide-deficient female rats were fed propylthiouracil (PTU) or dl-5-vinyl-oxazolidinethione mixed into a low-iodide diet for 10 days and then were either maintained on a low-iodide diet or given iodide supplements. Recovery of thyroid function after withdrawal of the antithyroid agents was markedly affected by the iodide supplementation. Without the iodide supplement 1) there was no regression of goiter or increase in serum PBI concentration; 2) the uptake of 131I by the thyroid was rapid and the 4-hr uptakes showed the expected ‘rebound’ phenomenon; 3) the 131I which was accumulatedby the 4th hr after administration was rapidly lost from the gland so that the 24-hr values were low and did not show the “rebound” phenomenon; 4) the ratios of radioactive DIT%MIT and T4%T3 were reversed; 5) there was a rapid loss of 131I-labeled MIT and DIT from the thyroid between the 4th and 24th hr after isotope administration, commencing 1 day after withdrawal of the drug, and a rapid loss of radioactive T4 and T3, comm...