Circulating Digitalis-Like Compounds in Essential Hypertension

Inhibitors of the Na+ pump have been proposed as participating in sodium excretion, extracellular fluid regulation, and in the rise of blood pressure. The presence of digitalis-like compounds in human plasma has been investigated by comparing the effects of plasma extracts to those of ouabain in 4 tests. - competition with ouabain for binding to the Na+ pump, - inhibition of Na+ and K+ dependent hydrolysis - inhibition of serotonin uptake by human platelets - central hypertensive effect Plasma fractions exhibited digitalis-like properties in the 4 tests. The effects of plasma extracts of 42 normotensive subjects (21 with family history of hypertension) and 38 patients with essential hypertension (15 with antihypertensive treatment) and 9 patients with chronic renal failure were compared. Plasma from Forty per cent of untreated hypertensive patients and normotensives with hypertensive heredity had a high inhibition level. Inhibition was enhanced in beta-blocker treated patients and decreased in those on diuretics. No digitalis-like activity was observed in uremic plasma. These observations strongly suggest the presence of digitalis-like compound(s) in human plasma and point to its possible association with hypertension.