NaHCO3 therapy corrects the increased urinary Na, K, Cl and H2O excretion induced by NH4Cl

Micropuncture studies conflict as to whether the proximal volume reabsorptive defect of acute hyperchloremic metabolic acidosis corrects when the acidosis is repaired with NaHCO3. Whether NaHCO3 improves the elevation in urinary solute and water excretion rates induced by acidosis in euvolemic animals, reflecting normalization of proximal reabsorption, has not been previously examined. In these studies in awake rats, NH4Cl caused the plasma bicarbonate concentration to fall from 22 to 11 mEq/l concomitantly with a 1 1/2- to 3-fold increase in sodium, potassium, chloride and volume urinary excretion rates. Isotonic NaHCO3 (5% body weight) infusion restored the plasma bicarbonate concentration to 21 mEq/l and urinary electrolyte and volume excretion rates returned to control values. Comparable volume expansion with NaCl did not correct the acidosis or improve urinary excretion rates. We conclude that correction of acute metabolic acidosis by NaHCO3 therapy repairs the natriuresis, kaluresis, chloruresis and diuresis, presumably by improving proximal reabsorption.