EFFECT OF VARIOUS GOITROGENS AND OF DOSE OF PROPYLTHIOURACIL ON THE RATIO OF RADIOIODIDE CONCENTRATIONS IN THE THYROID GLAND AND SERUM IN MICE

Abstract

Ratio of the radioiodide concentration in the thyroid gland and serum (T/S ratio) was studied in young male mice. As little as 10 [mu]g of propylthiouracil caused a partial inhibition of the binding of radioiodide by the thyroid; this was associated with an increase in the T/S ratio. Between 10 and 60 [mu]g the T/S ratio progressively increased whereas the binding of radioiodide decreased. Between 60 and 2500 [mu]g the binding process was almost completely blocked and the T/S ratio remained almost constant. With 5 mg, however, the T/S ratio was significantly elevated above that with 2.5 mg of propylthiouracil. This was correlated with an unusually high rate of decrease of the blood radioiodide concentration following the larger dose of propylthiouracil. T/S ratio was also measured using thiouracil, 2-mercaptoimidazole, thio-barbital, 2-mercaptothiazoline, sulfadiazine and phloroglucinol to block binding. The T/S ratio was relatively constant and independent of the goitrogen. I131 in the thyroids blocked by the last 3 goitrogens and by propylthiouracil was almost entirely in the form of iodide.