CORRELATION OF RADIOIODINE UPTAKE WITH THYROID WEIGHT IN THE MOUSE AT VARYING LEVELS OF EXOGENOUS AND ENDOGENOUS THYROTROPIN STIMULATION1

Abstract

Previous studies have shown that transplanting the pituitary to the anterior ocular chamber in mice alters its ability to stimulate the thyroid gland. Radioiodine metabolism is well maintained whereas thyroid weight falls to the hypophysectomy level. Chronic propylthiouracil treatment in such animals causes a marked increase in thyroidal radioiodine uptake but minimal increase in thyroid weight. In similarly treated normal controls both radioiodine metabolism and thyroid weight are greatly increased. These observations provided further evidence that separate “growth” and “metabolic” thyrotropins might exist, the growth factor requiring direct contiguity of the pituitaiy with the hypothalamus for adequate secretion. Since it was possible that radioiodine uptake might be more sensitive to small amountsof a single thyrotropin than thyroid weight, the quantitative response of these two parameters to both exogenous and endogenous thyrotropin was compared. Radioiodine uptake was found to reach a maximum with a considerably smaller dose of TSH than did thyroid weight. The present results indicate that the data previously obtained in mice with heterotopic pituitarics can be explained within the classic framework of a single thyrotropin.