Salt handling in patients with chronic renal insufficiency.

In 7 patients with moderate degrees of renal insufficiency the effect of high and low salt intake on renal NaCl handling was investigated by means of clearance techniques. After a steady state had been reached at low (1 g NaCl daily) and high (10 mmol NaCl daily for every ml X min-1 glomerular filtration rate) salt intake, proximal and distal fractional salt reabsorption (FSRprox and FSRdist) were estimated, maximal free water clearance being taken as an index of distal NaCl reabsorption. Mean FSRprox during low salt intake was 86.7% (range 80-90%) of the filtered load, and decreased to 77.9% (range 70.1-80.5%) during high salt intake. The water-loading procedure in these patients resulted in enhanced NaCl and nonelectrolyte solute excretion, especially during salt restriction. This made certain corrections obligatory for the proper calculation of FSRdist. Mean FSRdist during low salt intake was 96.5% (range 93.1-99.8%) of distal delivery, and decreased to 76.0% (range 68.0-82.1%) during high salt intake. This decrease of FSRdist also existed at comparable levels of distal delivery. It is concluded that renal response to chronic sodium loading in patients with chronic renal insufficiency is similar to that as in normal men, and consists of reduction of both proximal and distal fractional NaCl reabsorption.