SOME FACTORS THAT INFLUENCE THE RELEASE OF IODINE FROM THE THYROID GLAND

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Abstract
A newer method, the application of external gamma-ray counting to rats in which each animal serves as its own control was used under a number of exptl. conditions. In most cases I131 was injd. 40 hrs. before the 1st count was made and propylthiouracil treatment was then instituted to block further synthesis of organic I. Control rats lost I131 from the thyroid with a biological half-life of 3.3 days. Addition of 0.03% propylthiouracil to the diet accelerated release to a half-life of 1.6 days. Hypophysectomy prolonged the I131 half-life to 24 days and subsequent thyroid treatments of operated rats led to a rapid recovery of the I131 release to normal in 24 hrs. Treatment with thyroxine had an effect similar to hypophysectomy, whereas thyrotropin treatment markedly accelerated the release of I131 from the thyroid. Large doses of iodide failed to influence the release of previously injd. I131 from the gland shown both in the thyroxine and non-thyroxine organic I fractions of the thyroid. Furthermore, iodide did not alter appreciably the accelerated release of I131 resulting from simultaneously admd. thyrotropin.