Renal function during recovery from minimal lesions nephrotic syndrome.

We followed renal function through the natriuretic phase of 6 occasions of drug-induced recovery from minimal lesions nephrotic syndrome (MLNS). Protein excretion started to fall 1-3 days prior to the start of the natriuresis. The natriuresis was accompanied by a rise in glomerular filtration rate (GFR, inulin clearance). The filtration fraction, calculated from the GFR and the p-aminohippurate clearance, rose steadily in 5 subjects in whom it was low before therapy. Proximal and distal sodium reabsorption fractions, estimated from the changes in maximum free water clearance, fell, and fractional sodium, lithium, uric acid and free water clearance rose. At the time of these changes plasma protein had hardly risen, whereas renin activity was down. These results are in agreement with the notion that the sodium retention of MLNS is due to a renal defect. Repair of the glomerular filter, evident from the disappearance of proteinuria and the rise in filtration fraction, apparently normalizes the elevated tubular sodium reabsorption proximal to the macula densa, which leads to a fall in renin release.