Superficial distal and deep nephrons in correction of metabolic alkalosis.

Chloride is necessary and sufficient to correct alkalosis induced by dialysis vs. 0.15 M NaHCO3. To determine the contribution of the cortical (SC) distal convolution (DCT) and juxtamedullary (JM) nephrons to correction, we examined Cl and total CO2 (tCO2) transport in alkalotic Sprague-Dawley rats infused with 5% dextrose (group DM) or with 5% dextrose and 80 mM Cl (group CC); in papillary studies in alkalotic Munich-Wistar rats, 6% albumin was added to the infusate. In cortical studies, changes in plasma Cl and tCO2 were 4.9 +/- 0.7 vs. 0.7 +/- 0.9 and -6.0 +/- 0.8 vs. 0.4 +/- 0.9 meq/l and in tCO2 excretion (133 +/- 28 vs. -8 +/- 10 mueq/min) in groups CC and DM, respectively; results in papillary studies were similar. Delivery of tCO2 out of late SC DCT (CC 146 +/- 20 and DM 146 +/- 23 pmol/min) and Henle's loop (CC 145 +/- 18 and DM 202 +/- 56 pmol/min) and reabsorption within DCT (CC 15 +/- 24 and DM 45 +/- 19 pmol/min) did not differ. During correction of chloride-depletion alkalosis, the increment in bicarbonate excretion does not emanate from DCT of SC nephrons or JM nephrons but rather from the collecting duct.