Depressed distal tubule acidification corrects chloride-deplete alkalosis in rats

We investigated the relative contributions made by the proximal and distal tubule to the correction of Cl-deplete metabolic alkalosis induced by systemic administration of NaCl. Free-flow micropuncture was used to examine net bicarbonate reabsorption in superficial proximal and distal tubules of anesthetized Munich-Wistar rats during maintenance and correction of chronic furosemide-induced Cl-deplete metabolic alkalosis. The distal tubule of animals with correcting vs. maintained alkalosis had a lower fractional reabsorption of bicarbonate (38 vs. 75%, P less than 0.001) and a lower slope of the linear regression comparing absorption to delivered load (0.48 vs. 0.99, P less than 0.02). By contrast, proximal tubule of animals with correcting vs. maintained alkalosis had fractional reabsorption (85 vs. 90%, P = 0.07) and slopes of the regression comparing reabsorption to filtered load (1.09 vs. 0.98, P = 0.48) that were not different. The data indicate that correction of Cl-deplete metabolic alkalosis induced by NaCl administration involves a qualitative decreased in bicarbonate reabsorption in distal tubule with maintenance of the same load-dependent relationship for bicarbonate reabsorption in proximal tubule.