Acute Effects of Hypophysectomy and Injection of Stable Iodide on Iodothyronine Synthesis in Iodine-Depleted Rats 1

Summary

The hypothesis was examined that one reason severely iodine-deficient rats have a lower thyroidal labeled iodothyronine content than iodine-replete rats after ¹³¹I administration may be because thyroid iodine turnover is too rapid in the iodine-deficient rats to permit maximal labeled iodothyronine accumulation. Thyroid radioiodine accumulation and relative labeled amino acid distribution was examined between 3 and 24 hr after ¹³¹I administration to iodine-deficient rats. Half the animals were hypophysectomized to inhibit thyroid secretion 30 min before giving ¹³¹I. No increase in the proportion of thyroid ¹³¹I present as iodothyronines was produced by thus acutely inhibiting secretion. Our data therefore do not support the hypothesis. Addition of 1 μg ¹²⁷I- to the ¹³¹I injection increased labeled iodothyronine synthesis (primarily as T₄) in both intact and hypophysectomized iodine-deficient rats.