Thyroid Function in Chickens and Rats Effect of Iodine Content of the Diet and Hypophysectomy on Iodine Metabolism in White Leghorn Cockerels and Long-Evans Rats

Abstract

Some aspects of the thyroidal metabolism of iodine (I¹²⁷ and I¹³¹) were studied in intact and hypophysectomized White Leghorn cockerels maintained on a low iodine diet, and on the diet supplemented with iodide. Thyroid glands of intact chickens on low iodine dist were hyperactive, as judged by I¹³¹ uptake, thyroid/serum radioiodide concentration ratios and histology of the gland; however, a long retention of thyroidal I¹³¹ and a low level of circulating thyroid hormone were found. Supplementation of the diet with iodide strikingly reduced the thyroidal activity and altered the distribution of I¹²⁷ and I¹³¹ in the iodoamino acids of the thyroglobulin. When the cockerels were hypophysectomized, although the target organs atrophied, an unusually high thyroidal activity remained a month and a half later; nevertheless, there was a severe deficiency in the labeling of the thyroxine of the thyroglobulin following injection of radioiodide. It is postulated that the high residuum of activity is attributable to dietary iodine insufficiency prior to removal of the pituitary. Similar results, in some respects, were obtained with hypophyssctomized rats maintained on a diet with low iodine content.