Effects of acute increases in the excretion of solute and water on renal acid excretion in man.

It is well established that renal acid excretion can be influenced by certain tubular mechanisms that operate independently of systemic acid-base equilibrium. Thus, the stimulus for sodium reabsorption (1, 2), the competition between potassium and hydrogen ions for secretion (3), and the penetrating ability of anions present in the glomerular filtrate (4-6) are factors known to affect acid excretion. It is not clear, however, whether the process of urine acidification is influenced by the quantities of solute and water being excreted by the kidney. Although acid excretion has been measured during various types of diuresis (7-11), most studies were not specifically designed to answer this question. In the present study, the effects of acute increases in either solute or water excretion on the simultaneous excretion of acid were examined in man. To investigate the effects of solute and water separately, water excretion was limited as much as possible during solute diuresis, and changes in solute excretion were avoided during water diuresis. Control observations on acid excretion were made in nondiuretic subjects in the recumbent position. The results indicate that diuresis induced by nonelectrolyte solutes (hypertonic urea or mannitol) causes a significant fall in urine pH and an increase in ammonium and titratable acid excretion in recumbent subjects. In contrast, water diuresis had no consistent effect on over-all acid ex-