Direct examination of chloride transport across papillary collecting duct of the rat

Abstract

The role of the collecting duct (CD) in the regulation of salt excretion remains controversial. The reabsorptive characteristics of Cl beyond the superficial late distal tubule was examined indirectly by comparing the fraction of Cl remaining at the superficial late distal tubule with that fraction at the base of the collecting duct and directly by similar comparisons in the papillary collecting duct at 2 levels (base and tip CD) in young Munich-Wistar rats. Volume expansion to 10% body weight with Ringer bicarbonate resulted in a greater fraction of Cl remaining at the base CD (11.9 .+-. 0.8%) than the fraction remaining at the superficial late distal tubule (6.8 .+-. 0.6%). Fractional Cl reabsorption by the collecting duct increased from 0.44 .+-. 0.08 during hydropenia to 2.1 .+-. 0.6%/mm CD after Ringer loading. In contrast, the fraction of chloride remaining at the base CD was significantly less than that at the superficial late distal tubule after infusion of hyperoncotic albumin to 0.6% body weight. Furosemide abolished the difference in Cl remaining at the superficial late distal tubule and base CD. Net addition of Cl occurs between the superficial late distal tubule and the base collecting duct during acute isotonic volume expansion and fractional Cl reabsorption increases across the papillary collecting duct after Ringer loading as fractional delivery increases. The data are compatible with the view that the chloruresis associated with isotonic volume expansion is a result of greater chloride delivery out of the deeper nephrons.