Renal tubular sodium and water excretion were evaluated in 5 patients in the recovery stage of acute tubular necrosis (ATN) by means of clearance technique. During the period of maximal hydration, urine osmolality in these patients remained high compared to control group despite same level of plasma osmolality in both groups. The values of maximal urine flow rate (V/Ccr), free water excretion rate (CHH2OO/Ccr) and (CNa+CH2O)/Ccr in patients with ATN were not significantly different from those in control group, indicating that proximal tubules in patients with ATN had already recovered function in terms of sodium and water excretion. However, CH2O/(CNa+CH2O), an index of sodium reabsorption rate in distal tubule, was significantly lower in patients with ATN than in control group. These results suggest that proximal tubules can recover function earlier than distal tubules in terms of sodium and water excretion in ATN.
