Measurement of digitalis-like compound in plasma: application in studies of essential hypertension.

A digitalis-like compound was detected in human plasma by tritiated ouabain competition binding to the sodium pump. The study comprised analyses of plasma extracts from 17 normal controls, 17 normotensive subjects with one or both parents hypertensive, and 16 patients with untreated essential hypertension. In two thirds of the untreated hypertensive and several of the normotensive subjects with a family history of hypertension the potency of the digitalis-like compound, as measured by its interference with ouabain binding, was significantly greater than in the controls. In the untreated hypertensive patients the potency of the compound was significantly correlated with the urinary sodium output. Measurement of this salt-related, digitalis-like compound may be useful in clinical studies of hypertension.