Effect of Stress and Cortisone on Plasma Protein-Bound Iodine and Thyroxine Metabolism in Rats

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Abstract
Plasma protein-bound I (PBI) is depressed after exposing rats to 4[degree] C or to 2 hrs. of violent exercise (swimming). Prolonged fasting (72 hrs.) also depresses the PBI. In thyroidectomized rats maintained on daily doses of DL-thyroxine, swimming and cold also depressed the PBI. Cortisone (12.5 mg./day (3 times)) depressed the PBI of intact rats, but thyroidectomized, thyroxine-maintained rats had elevated PBI after 3 days of cortisone. The stresses studied,therefore, increase the rate of disposal (catabolism or excretion) of thyroxine, without any necessary effect on thyroid function. Since the PBI depression was greater in thyroidectomized than intact rats after exposure to cold, presumably increased thyroidisecretion occurred at 4[degree]. Cortisone decreased the disposal of thyroxine, and the depressed PBI in intact rats given this steroid must have been due to reduced thyroid function. Cortisone also blocked the effects of cold-stress upon the PBI of thyroidectomized, thyroxine maintained rats.