THE RENAL REGULATION OF ACID-BASE BALANCE IN MAN. I. THE NATURE OF THE MECHANISM FOR ACIDIFYING THE URINE 1

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Abstract
In a series of 8 expts. on 4 healthy human subjects it was found that the induction of acidosis by the ingestion of ammonium chloride and the promotion of buffer excretion by the infusion of phosphate or creatinine greatly increased the rate of excretion of titratable acid. Simultaneous measurement of the rate of filtration, reabsorption and excretion of mono- and dibasic phosphate and carbonic acid demonstrated that the quantity of acid excreted far exceeded that which entered the urine in the glomerular filtrate. Therefore, acid must have been added to the filtrate as it passed along the nephron by some mechanism of active transport resident in the renal tubular cells. It is suggested that this addition of acid is effected by the exchange of hydrogen ions formed within the tubular tells for ions of fixed base in the tubular urine. Carbonic acid is doubtless the intracellular source of hydrogen ions. This mechanism for acid excretion in the human kidney is qualitatively similar to that previously described in the dog. Quantitatively, the human kidney has a greater acid excretory capacity than the dog kidney.