Humoral sodium transport inhibitor in acute volume expansion and low renin hypertension

This review summarizes our bioassay methods for determining the level of humoral sodium pump inhibiting factor after acute volume expansion in experimental animals and humans, and in low renin experimental and human essential hypertension. In brief, ouabain-sensitive ⁸⁶Rb uptake and membrane potential in blood vessels from normal animals are measured after incubation in plasma supernate from experimental subjects and animals and their respective controls. The data show that humoral sodium pump inhibitor is elevated after acute volume expansion in normal animals (dogs and rats) and in normal humans. The level of inhibitor is also elevated in patients with low renin essential hypertension and in experimental animals with low renin, volume-dependent types of hypertension, namely, one-kidney, one wrapped hypertension in dogs, and one-kidney, one clip and reduced renal mass-saline hypertension in rats. Humoral sodium pump inhibiting factor inhibits the Na⁺-K⁺ pump in the cardiovascular system. Such inhibition by other means (hypokalemia, cardiac glycosides) activates the system. Therefore, we also discuss the possible role of humoral sodium pump inhibitor in low renin volume-dependent hypertension.