Some Effects of Protein Deficiency on the Rat Thyroid1

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Abstract
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 H3-thymidine, 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.