Renal Excretion of Radioiodide in Rats

¹ From the Department of Anatomy, State University of Iowa, Iowa City, Iowa

Elimination of radioiodide by the kidney of adult male rats pretreated with a single dose of propylthiouracil was measured. Rats given water or isotonic saccharose served as controls. Renal clearance of radioiodide (C_I¹³¹) was greatly enhanced (up to 100-fold) by the sodium salts of chloride, perchlorate, stable iodide, bromide and bicarbonate, and by choline iodide, but not by sodium thiosulfate. Under most conditions C_I¹³¹ markedly exceeded the C_Cl and C_Na of the same animals, which suggest that renal tubules are less permeable to iodide than to chloride or sodium. C_I¹³¹/C_Na varied greatly, its magnitude being dependent on the loading solution used. C_I¹³¹ showed no correlation with urine flow or excretion of endogenous creatinine-like chromogen (U_CrV) when groups receiving different treatments were compared. Both urine flow and U_CrV showed only minor variations among these groups. Our findings are most easily explained by the hypothesis that tubular reabsorption of iodide filtered by the glomeruli involves, possibly in addition to a passive process, an active transport mechanism capable of saturation by iodide and (competitive?) inhibition by other anions.