Increase in plasma ouabainlike inhibitor of Na+, K+-ATPase with high sodium intake in patients with essential hypertension.

Abstract

Changes in plasma levels of Na+, K+-ATPase inhibitors with salt loading were studied in eight patients with essential hypertension. By improving the assay method of Na+, K+-ATPase inhibitors to distinguish ouabain and vanadate, two types of inhibitors were detected in the plasma of patients with essential hypertension: One was ouabainlike and the other was nonouabainlike. The ouabainlike inhibitor was detected at low KCl concentrations (0.1 mM) in the assay buffer, and the nonouabainlike inhibitor was detected at a high KCl concentration (10 mM). By increasing dietary sodium chloride from 2 g/day for 5 days to 20 g/day for 6 days, systolic blood pressure increased significantly from 122 +/- 3.9 to 138 +/- 3.8 mmHg (p less than 0.005), whereas plasma renin activity decreased significantly from 3.9 +/- 0.8 to 0.8 +/- 0.3 ng/ml/hr (p less than 0.002). Under these conditions, the ouabainlike inhibitor increased significantly from 6.2 +/- 3.9% to 30.5 +/- 5.9% inhibition (p less than 0.005), after increasing dietary sodium. Furthermore, plasma level of the ouabainlike inhibitor correlated significantly with both systolic blood pressure (p less than 0.05) and daily urinary sodium excretion (p less than 0.01). In contrast, the plasma nonouabainlike inhibitor did not change with high sodium intake and did not correlate with blood pressure and daily urinary sodium excretion. These findings suggest that a ouabainlike inhibitor is involved in the maintenance of high blood pressure induced by high sodium intake in patients with essential hypertension. The role of the nonouabainlike inhibitor in blood pressure regulation is still unknown.