ANALYSIS OF THE MODIFYING EFFECT OF DIETARY IODINE LEVELS ON THE THYROIDAL RESPONSE OF HYPOPHYSECTOMIZED RATS TO THYROTROPHIN1

Abstract

In hypophysectomized rats treated with a standard dose of thyro-tropin (TSH) the response of the thyroidal iodide concentrating mechanism was inversely proportional to the dietary I levels. Variations in I intake, however, failed to affect the reaction of the iodide concentrating mechanism to TSH when propylthiouracil was also given. These findings suggest that an organic I-con-taining compound within the thyroid, possibly thyroid hormone itself, antagonizes the stimulating action of TSH on thyroidal iodide collection.