RENAL TUBULAR SODIUM AND WATER REABSORPTION IN ISOTONIC SODIUM CHLORIDE-LOADED RAT

Renal tubular sodium and water reabsorption were studied in rats undergoing isotonic saline diuresis. Fluid was collected by micropuncture and analyzed for sodium and inulin-14 C. Increased excretion of salt and water was due to a decrease in proximal reabsorption which was only partially compensated for by enhanced transport out of loops of Henle. Inhibition of proximal reabsorption was due solely to a decrease in the inherent transport capacity of proximal epithelium. The distal tubule was unable to lower the sodium concentration of tubular fluid under free -flow conditions to the same extent as in nondiuretic conditions. This failure was not due to a change in the apparent electromotive force of the sodium pump but is probably related to a diminished distal load of urea.