Effect of sodium intake on the excretion of urinary natriuretic factor in essential hypertensives.

A simplified method for the determination of natriuretic factor in the urine as measured by digoxin-like substance was studied. Digoxin-like substance in the urine was estimated by RIA using anti-digoxin antibody after being extracted by reversed phase cartridge column but without gel filtration. The values found by radioimmunoassay (RIA) yielded a significant correlation with those of the inhibitory effect of Na-K-ATPase activity which was measured by biochemical assay as described by Hamlyn et al. Using this RIA method, the effect of salt intake on natriuretic factor in urine was studied in patients with essential hypertension. The natriuretic factor on a high sodium diet (NaCl 20 g/day for three days) increased approximately 1.5 times, as compared to those on a low sodium diet (NaCl 3 g/day) (p less than 0.05). The Natriuretic factor showed a positive correlation with urinary Na excretion (P less than 0.050) when the patients were placed on ad. lib. sodium diet. From these results, it is suggested that secretion of natriuretic factor in the urine might be regulated in part by salt intake.