THE NATURE OF THE RENAL TUBULAR MECHANISM FOR ACIDIFYING THE URINE

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Abstract
A series of 18 expts. on 4 trained unanesthetized [female]5 dogs were designed to test critically the several current hypotheses concerning the renal mechanism for the excretion of an acid urine. Animals rendered acido-tic by the feeding of HC1 and infused intravenously with neutral Na phosphate and creatinine excreted as much as 0.380 m. eq. of titratable acid/min. The quantity of acid excreted far exceded the quantity of acid filtered through the glomeruli. Therefore acid must have been added to the urine by some secretory mechanism as the urine passed through the renal tubules. Expts. designed to elucidate the nature of this mechanism suggested that the urine is acidified by a process involving the exchange of H+ ions formed withm the cells of the distal tubule for Na+ ions present within the tubular urine. Renal carbonic anhydrase plays a role in this tubular mechanism by catalyzing the hydration of carbon dioxide to carbonic acid within the tubular cells. The carbonic acid so formed serves both as the intracellular source of H+ ions exchanged for Na+ ions, and as the source of HC03- ions in combination with which the Na+ ions are absorbed into the peritubular blood.

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