1. Acebutolol, a β1-receptor blocker, has, at a daily dose of 800 mg, a mild but significant anti-hypertensive effect in moderate sustained essential hypertension with normal or low plasma renin activity.
2. Prediction of its anti-hypertensive effect is better based on the evaluation of the sympathetic nervous system responsiveness to head-up tilt than on the evaluation of plasma renin activity or dopamine-β-hydroxylase.
3. The anti-hypertensive effect of acebutolol is better explained on the basis of inhibition of the sympathetic nervous system activity than on the basis of suppression of plasma renin activity.
4. A positive correlation between plasma renin activity and dopamine-β-hydroxylase in patients on diuretics suggests the common dependence of these two variables on sympathetic overactivity.