Acute hypercapnic acidosis diminishes renal water excretion in conscious dogs

The effects of acute hypercapnic acidosis (PaCO2 = 52 +/- 2 mm Hg, pH = 7.23 +/- 0.01) of 40-80 min duration on renal water excretion and circulating vasopressin were examined in conscious dogs during stable diuresis in protocols either with hypotonic water loading (n = 6) or in the euvolemic state (n = 7). The mean arterial pressure increased (p less than 0.05) during acute hypercapnic acidosis in euvolemic dogs, but was unchanged in the dogs given a water load. However, the free water clearance decreased (p less than 0.05), and urine osmolality increased during acute hypercapnic acidosis in both water-loaded and euvolemic dogs despite stable renal hemodynamic function and osmolar clearance. Plasma vasopressin concentrations increased (p less than 0.05) during hypercapnic acidosis in euvolemic but not in water-loaded dogs. The plasma renin activity increased with hypercapnic acidosis in both water loaded and euvolemic dogs. These observations indicate that acute hypercapnic acidosis results in diminished renal water excretion and increased urine osmolality in conscious dogs.