A plasma inhibitor of sodium and potassium activated adenosine triphosphatase in patients with essential hypertension.

The purpose of this study is to evaluate the plasma Na, K-ATPase inhibitor (NKI) in patients with essential hypertension and to compare the mode of its biochemical actions on the Na, K-ATPase with that of ouabain. Plasma NKI was extracted through a reversed-phase cartridge column and its inhibitory action on hog brain Na, K-ATPase was measured in vitro. Plasma NKI activity was significantly greater in patients with essential hypertension (44 +/- 2.8% (S.E.), n = 28, p less than 0.01) than in normotensive controls (25 +/- 2.4%, n = 21). No significant correlation was demonstrated between the values of plasma NKI and mean arterial pressure in either group. Both plasma NKI and ouabain showed a dose-dependent inhibition on the Na, K-ATPase reaction. An action of ouabain was competitively antagonized by increased concentration of potassium in the reaction mixture, while plasma NKI showed a constant inhibition on the Na, K-ATPase independently of potassium concentrations. The action of plasma NKI was of rapid onset and linear with time, while ouabain showed a delayed onset of the reaction over 30 sec, followed by a progressively increasing inhibition on the enzyme reaction. Finally, the inhibitory action of plasma NKI on Na, K-ATPase was completely abolished in the presence of bovine serum albumin even at the concentration of 500 micrograms/ml in the reaction mixture, which did not have any influence on the actions of ouabain. To sum up, the results showed a markedly different nature of plasma NKI from ouabain in the mode of biochemical actions on the Na, K-ATPase in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)