Effects of Perchlorate and Other Anions on Thyroxine Metabolism in the Rat

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Abstract
Effects of perchlorate and other anions on thyroxine metabolism were studied in the rat. When perchlorate was given to animals treated with methima-zole and graded doses of thyroxine, the increase in serum PBI [protein-bound iodine] was markedly depressed. In thyroidectomized, thyroxine -maintained and perchlorate-fed animals, a significant decrease of serum PBI was also shown by radioisotopic technique and by chemical determination. The smallest amount of perchlorate necessary to reduce serum PBI was about 50 [mu]moles/g diet. Perrhenate depressed serum PBI at a lower concentration (25 [mu]moles/g diet) than perchlorate. Thiocyanate, chlorate and fluoborate slightly reduced serum PBL but nitrate had no effect. In thyroidectomized and thyroxine-maintained animals, perchlorate produced an increase of urinary excretion of 131I-iodide after a single injection of 131I-thyroxine. Muscle uptake of 131I-thyroxine significantly increased in the presence of plasma obtained from perchlorate-fed animals. Perchlorate and other anions may interfere with thyraxine-plasma protein interaction in vivo and thus augment the turnover rate of thyroxine.