EXTRA-THYROIDAL IODIDE METABOLISM IN THE RAT

Abstract

Inorganic iodide is distributed in a volume equivalent to about 50% of the weight of the rat. Injection of 10 mg of potassium thiocyanate reduced the iodide space to about 40% apparently by a reduction of secretion of iodide into the gastrointestinal tract. The combined salivary and gastric secretions contained a total of about 70% of an injected dose of radioiodine, the salivary glands contributing about one-fifth of this. Administration or inhibition of secretion of thyrotropin did not appear to affect these values; nor did 100 [mu]g of carrier iodide. Amounts of carrier iodide up to 200 [mu]g did not change the distribution space, renal clearance, or rate of loss of I131 from the blood. The renal clearance of iodide was found to be about 0.1 ml per minute, one-sixth to one-eighth of the filtration rate. Administration of propylthiouracil (5 or 10 mg/100 g body weight) substantially increased iodide clearance by the kidney. This finding may have implication in studies of thyroid function using propylthiouracil and suggests the presence of an active tubular transport mechanism for iodide.