Thyroid Function in Female Rats Severely Depleted of Body Protein

The effect of protein depletion on thyroid function was studied in growing female rats fed low iodine diets. Severe protein depletion caused a marked reduction in thyroid growth; this reduction was accompanied by an apparent suppression of thyroidal activity as indicated by thyroid to serum radioiodide concentration ratios (T/S). Upon repletion of protein-starved animals, thyroid size and function returned to normal. Treatment of iodine-deficient, proteindepleted animals with thyroid-stimulating hormone (TSH) failed to increase thyroidal activity over that observed in iodine-deficient controls. In protein-depleted animals, there was no relative impairment of thyroxine synthesis as indicated by the distribution of radioiodide among the iodinated amino acids of thyroid digests. (Endocrinology79:1023,1966)