1. Stepwise increases of oral doses of propranolol produced both a significant lowering of blood pressure and suppression of plasma renin activity in sixteen patients with mild or moderate normal-renin essential hypertension.
2. The hypotensive and the renin-suppressive actions of propranolol were differently related to plasma propranolol concentrations. At the lowest propranolol concentrations (15–40 nmol/l), there was almost no decrease in blood pressure whereas plasma renin activity and responsiveness to renin-releasing stimuli (standing, intravenous frusemide) were already strongly depressed (greater than 50%). Therefore in a large number of normal-renin hypertensive patients under small doses of propranolol, the renin-suppressive action of the drug can be dissociated from the hypotensive effect. Dissociation of the two effects, though in the opposite way, was also observed in three of four low-renin hypertensive patients, whose blood pressure was decreased by propranolol without further reduction of the already suppressed plasma renin activity.
3. It is concluded that in patients with mild and moderate hypertension and low or normal plasma renin activity, the hypotensive effect of propranolol cannot be attributed to suppression of renin activity. These conclusions do not necessarily apply to high-renin hypertensive patients.