Quantitative measurement of the influence of plasma sodium concentration on the overall tubular reabsorption of sodium.

Comparative experiments on isolated dog kidneys perfused with heparinized blood with or without dilution of the blood by isotonic or hypotonic saline demonstrated that the fractional excretion of sodium is modulated positively by plasma sodium concentration. This relationship was evaluated quantitatively and corresponded to the values found in the whole animal. The renal response to the variations of plasma sodium concentration is therefore autonomous and its mediation by extrarenal natriuretic or antinatriuretic factors cannot be demonstrated in the narcotized animal.