EXTRATHYROIDAL EFFECT OF THIOCYANATE AND PROPYLTHIOURACIL: THE DEPRESSION OF THE PROTEIN-BOUND IODINE LEVEL IN INTACT AND THYROIDECTOMIZED RATS

Abstract

SUMMARY In rats to which 125I was administered for 28 days, the level of protein-bound 125I (PB125I) (estimated by trichloroacetic acid precipitation or filtration on a Sephadex G-25 column) was measured. In intact animals, after a single dose of 16 mg thiocyanate ion, a significant decrease of PB125I was found, which was inversely related to the level of thiocyanate in plasma. The decrease was much faster than that in rats after thyroidectomy. From these findings an extrathyroidal effect of thiocyanate was postulated and tested in rats fed 125I− for 28 days and then thyroidectomized immediately before the administration of a single dose of 16 mg thiocyanate ion or 15 mg propylthiouracil. The level of PB125I in most of the latter animals 4, 8, 18 and 24 h after the administration of the drugs was significantly lower than that in thyroidectomized controls.