Characterization of distal hydrogen ion secretion in acute respiratory alkalosis

The effect of acute respiratory alkalosis (ARA) on distal nephron H+ secretion was evaluated by measuring urine-to-blood (U-B) Pco2 in dogs with highly alkaline urine (urine pH greater than 7.8). ARA led to a significant decrease in U-B Pco2 and in urine HCO3 concentration; urine pH, however, increased significantly, indicating that the decrease in urine Pco2 was of greater magnitude than the decrease in urine HCO3 concentration. For any given urine HCO3 concentration urine Pco2 was lower (i.e., urine pH was higher) in ARA than in controls. Administration of tris(hydroxymethyl)aminomethane (Tris) during ARA resulted in a significant increase in U-B Pco2 to control values. In animals with moderately alkaline urine (urine pH 6.4--7.4) and high urine PO4 concentration, ARA resulted in a significant decrease in UB-Pco2 and urine PO4 concentrations. Neutral PO4 infusion in these dogs resulted in an increase in urine PO4 concentration and U-B Pco2 to control levels. These data demonstrate that ARA results in a significant decrease in U-B Pco2 that is not solely attributable to changes in urine HCO3 concentration. The observation that Tris and PO4 infusion during ARA raises U-B Pco2 to control levels suggests that the ability to secrete H+ is intact.