ABSTRACT
It is known that the reabsorption of filtered HCO<SUB>3</SUB><SUP>-</SUP>depends on the tubular flowrate in the proximal uniferous tubule. In animal experiments, studies have demonstratedthat, when diuresis was induced, the pH of the collecting duct urine decreased, resulting from the decrease in HCO<SUB>3</SUB><SUP>-</SUP>concentration with no change in the pCO<SUB>2</SUB> level.The present study was designed to examine changes in urine acidification in humansunder a water diuretic state. Urine pH, pCO<SUB>2</SUB> levels, and HCO<SUB>3</SUB><SUP>-</SUP>concentration weremeasured before and after the drinking of water. In 120 minutes after hydration, theurine pH level fell about 0.5 pH unit from that before the intake of water. The urine HCO<SUB>3</SUB><SUP>-</SUP>concentration coincidentally decreased significantly. However, pCO<SUB>2</SUB> values remainedunchanged. These results indicated that also in humans, water diuresis promotesurine acidification, resulting from a decrease in HCO<SUB>3</SUB><SUP>-</SUP>concentration with nochange in the pCO<SUB>2</SUB> level, which may contribute to the prevention of the loss of plasmaHCO<SUB>3</SUB><SUP>-</SUP>into the urine when the urine flow rate increases.