Renal Tubular Reabsorption of Iodide as Compared with Chloride*

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Abstract
Simultaneous clearances of inulin, chloride, and radioiodide, during constant infusion of the latter, were measured in dogs salt depleted or infused with solutions of glucose, mannitol, NaCl, Na2SO4, NaHCO3, HCl, NaI, NaBr, NaSCN, NaNO3, NaClO4, or combinations of these. The data were examined to determine whether they were consistent with the possibility that iodide and chloride are passively and coextensively reabsorbed, with the ratio of the tubular permeabilities to the 2 ions unchanging along the length of the tubule. If this were the case, log (excreted/filtered I)/ log (excreted/filtered Cl) = k should be nearly constant, at least in individual experiments. The calculated discrimination factor k was independent of plasma chloride or iodide levels, filtration rate, or the administration of these infusions. Increasing flow decreased k indicating that iodide clearance varies slightly with flow independently of chloride clearance. For all of the experiments, k = 0. 468 - 0. 7x(flow/glomerular filtration rate). In individual experiments, values of iodide clearance predicted in this manner from chloride clearance and urine flow were closely correlated with observed iodide clearance. These results are thus consistent with the hypothesis. However, at very low excretion fractions of chloride (< 0. 002), active transport of iodide became apparent, and iodide reabsorption in some instances was more nearly complete than chloride reabsorption.

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