Some effects of protein deficiency on the rat thyroid

The response of the thyroid of young growing rats exposed to protein deficiency was studied, and the effects of prolonged administration of propylthiouracil were measured. Control animals received a normal protein diet isocaloric with the average amount of food consumed by the deficient rats. The growth response was measured by gland weight, percentage of nuclei labeled with 3Hthymidine, and mitotic counts. Thyroid to serum radioiodide concentration ratios (T/S) were also determined as a functional index. A marked reduction in the growth response of the thyroid was observed in protein-deficient animals in comparison with the controls. This was associated with a striking 2- to 3-fold increase in the iodide concentrating ability of the thyroids in the deficient group as measured by the T/S ratio. No consistent changes were found in the distribution of labeled iodine or in the ratios of the iodinated amino acids among the thyroid cell particles and the soluble component