Measurement of circulating sodium-pump inhibitory activity in uraemia and essential hypertension

By measuring in vitro the effect of deproteinized plasma on canine kidney Na+K+-ATPase activity, evidence was sought for the presence of a circulating inhibitor of the enzyme in 31 patients with end-stage renal failure, 10 patients treated with digoxin, and 22 patients with untreated essential hypertension. In the renal failure group, mean Na+K+-ATPase activity with plasma samples taken just before a regular haemodialysis was 88% of that obtained with plasma from a normotensive control group (P less than 0.001). In digoxin-treated patients, the result was 94% of that obtained in control subjects (P less than 0.005). There was no significant difference in mean Na+K+-ATPase activity with plasma, between the hypertensive and control groups, or between age- and sex-matched subsets of these groups. The hypertensive group did not differ significantly from the control group in plasma renin activity or erythrocyte Na+ concentration. It was concluded that a circulating digitalis-like sodium-pump inhibitor was readily detectable in volume-expanded renal failure, but not in normal-renin essential hypertension.