THE RATE OF TURNOVER OF PROTEIN-BOUND IODINE IN THE PLASMA OF THE DOG AS MEASURED WITH RADIOACTIVE IODINE1

Abstract

THE METHODS most frequently employed for estimating the rate of thyroid secretion have been based on the replacement of circulating thyroid hormone by the injection of crystalline thyroxine. In the procedure introduced by Dempsey and Astwood (1943), rats were fed thiouracil in order to inhibit the formation of the thyroid hormone and injected simultaneously with graded doses of 1-thyroxine. The minimum quantity of thyroxine necessary to prevent increased thyrotropic activity of the pituitary as judged by thyroid size was taken as equivalent to the rate of secretion of the thyroid hormone. This amounted to 5.2 micrograms of 1-thyroxine per day for 80-120 gm. rats kept at 25°C. The above method was applied to the chick by Mixner et at. (1944), and to the fowl, goat, and cow by Schultze and Turner (1945).