Free water reabsorption during saline diuresis in experimental enterococcal pyelonephritis in rats

Inability to attain Umax after overnight dehydration is the earliest functional abnormality in human and experimental pyelonephritis caused by diverse microorganisms. In order to characterize the defect in Umax in experimental enterococcal pyelonephritis, another index of renal concentrating ability. TcH2O, was determined during saline loading. Normal TcH2O depends on adequate sodium chloride delivery and reabsorption in the ascending limb of Henle's loop and water reabsorption from the collecting duct. Rats with early pyelonephritis, 3 days after intravenous injection of enterococci, were compared with normal rats in studies of Umax during hydropenia and TcH2O during 1.2% saline infusion. Mean Umax in infected rats was significantly lower than in uninfected rats (1120 vs. 2767 mOsm/kg H2O) (p less than 0.01), but CIn in infected rats was not significantly different from that in uninfected rats (0.96 vs. 0.89 ml/min per 100 gm) (p less than 0.05). During saline diuresis, maximal Cosm/CIn was more than 35% in both the normal and infected rats. The relationship between TcH2O/CIn and Cosm/CIn was linear in both groups, and the r, slope, any y intercept of the regression equation of TcH2O/CIn vs. Cosm/CIn in infected rats were not significantly different from those in normal rats. During saline diuresis the regression of sodium excretion UNaV/CIn) vs. Cosm in infected rats was not significantly different from that in control rats. The finding of normal TcH2O during saline loading suggests that reabsorption of increasing amounts of sodium chloride from the ascending limb of Henle's loop and reabsorption of water in the collecting duct are normal in early pyelonephritis.