The presence of a natriuretic factor in urine of patients with chronic uremia. The absence of the factor in nephrotic uremic patients.

A gel filtration fraction of serum from chronically uremic patients has been shown previously to produce natriuresis in the rat. In the present studies, the same fraction from urine of uremic patients and normal subjects was studied for its natriuretic activity. Urine samples were obtained from 17 chronically uremic patients (mean glomerular filtration rate [GFR], 8.7 ml/min; mean fractional sodium excretion [FE(Na)], 5.7%), and 14 normal subjects. The fraction from the uremic patients produced a significant increase in absolute sodium excretion (U(Na)V) and FE(Na); the fraction from normal subjects had no statistically significant effect on either U(Na)V or FE(Na); and the difference between the response to the uremic vs. normal fractions was highly significant for both parameters of sodium excretion. When a more concentrated urine fraction from uremic patients was administered, a striking natriuresis was observed with values for FE(Na) rising to levels as high as 12%. Studies also were performed on eight patients with far advanced chronic renal insufficiency and the nephrotic syndrome. The serum fraction was studied in each of these patients and the urine fraction in three. For the group, U(Na)V in the assay rats decreased by 0.87 mueq/min and FE(Na) decreased by 1.35% after infusion of the serum fraction. These results differ significantly from those of patients with chronic uremia without the nephrotic syndrome. The data are consistent with the view that the increased activity of the natriuretic factor in the serum of chronically uremic patients is not due to failure of excretion; rather it relates either to an increased rate of production and/or a decreased rate of degradation. The data also show that the inhibitor is detectable when FE(Na) is increased, but not when uremia is associated with a sodium-retaining state.