Effects of structure and iodine content of the rat thyroid on the distribution of 127-I and 131-I between particulate and soluble thyroidal protein-bound iodine.

Abstract

The distribution of 127I between particulate and soluble iodoproteins and the labeling of these 2 PBI fractions with 131I were studied in rat thyroids whose structure, function and iodine content were manipulated by hypophysectomy, feeding of a low iodine diet, administration of goitrogens such as propylthiouracil (PTU) or NaClO4, and feeding of diets rich or poor in iodine during recovery from NaClO4 treatment. The percentage of thyroidal PB127I in particulate form, which is around 10 in normal rats on an iodine-sufficient or iodine-deficient diet, was lowered to 2.6 in the iodine-rich, atrophic glands of hypophysectomized rats; in hyperplastic glands, whose iodine concentration was low, it ranged from 5.5 to 17.4, showing no correlation with the degree of hyperplasia or the iodine content. Both in hypophysectomized and in iodine-deficient intact rats, the percentage of thyroidal PB131I in the particulate fraction leveled off at 5-7 within 4 hr after 131I injection, in spite of marked differences in thyr...