Chemical, experimental, and clinical studies on endogenous ouabain-like substance in hypertension

A heat-stable, low molecular weight, anionic substance(s) capable of inhibiting 3H-ouabain binding and Na+-K+-ATPase activity could be extracted from human urine and plasma. The level of the inhibitor was elevated in 40%-50% of essential hypertensives, compared to controls, and also in some of the offspring of hypertensive parents. Higher levels of the inhibitor were measured in patients treated with beta-blocking agents than in those treated with diuretics. The inhibitor extracted from plasma also appeared capable of (1) inhibiting the uptake of serotonin in human platelets, an Na+-dependent mechanism, and (2) inducing an increase in blood pressure when injected intracerebroventricularly. From these various data, we propose that the increase in the endogenous inhibitor may play a role in essential hypertension and may modulate, at least partially, some of the various cell functions that depend on a transmembrane Na+ gradient, including cellular excitability.