Circulating Digitalis-Like Compounds in Essential Hypertension

Inhibitors of the Na⁺ pump have been proposed as participating in sodium excretion, xtracellular 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.