The pathophysiological role of digitalis-like substance in essential hypertension

In order to investigate the role of digitalis-like substance in patients with essential hypertension, levels of plasma digitalis-like substance were measured in nine normotensive, 12 normal-renin and seven low-renin essential hypertensive subjects. The level of plasma digitalis-like substance was determined by using two different methods, the digoxin radio-immunoassay established by our laboratory and Na+,K+-ATPase inhibitory activity (modified Hamlyn's method). There was a significant positive correlation between plasma immunoreactive digitalis-like substance and Na+,K+-ATPase inhibitory activity in plasma samples. Both values were significantly higher in hypertensives than in normotensives. Moreover, Na+,K+-ATPase inhibitory activity was significantly higher in low-renin hypertensives than in normal-renin hypertensives or normotensives. These findings suggest (1) digoxin radio-immunoassay may be able to determine the level of plasma digitalis-like substance; (2) digitalis-like substance is increased in essential hypertensives, especially in low-renin hypertensives; (3) the level of digitalis-like substance might be related to plasma renin activity, and mediated by a change in plasma volume; and (4) the activity of the digitalis-like substance may contribute to the pathophysiology of essential hypertension.