Renal water handling in minimal change nephrotic syndrome

Renal water handling was studied in proteinuric and non-proteinuric phase in 25 children with minimal change nephrotic syndrome. Clearance of inulin was determined during water diuresis and in hypodropenia followed by intravenous saline infusion. The diluting capacity, evaluated both as minimal urinary osmolality and as free water clearance did not differ from that in controls. An inverse correlation was found between distal tubular sodium delivery and serum albumin concentration during proteinuric phase. The concentrating capacity, evaluated as maximal urinary osmolality did not differ in proteinuric and non-proteinuric phase. Free water reabsorption, however, was significantly lower in proteinuric phase than in remission. The correlation of severe hypoalbuminemia with high distal tubular sodium delivery indicates a decrease in proximal sodium reabsorption in proteinuric phase, and the normal diluting capacity supports an intact, probably increased, distal tubular sodium reabsorption. The normal ability to excrete a water load suggests that the water retention in the nephrotic syndrome is secondary to sodium retention.