Evaluation of practolol in hypertension. Effects on sympathetic nervous system and renin responsiveness.

The ,B-adrenergic blocker, practolol, proved to be an effective antihypertensive agent in a single-blind crossover trial, involving I7 patients with essential hypertension of mild to moderate severity.After a 2-month placebo period, dosage was begun at IOO mg twice a day, and titrated against blood pressure response up to a maximum dose of 400 mg twice a day, leading to an average reduction in blood pressure of 20/18 mmHg, and satisfactory control in I4 of I6 patients (one defaulter).The clinical and physiological data were analysedfor prediction of response to practolol.The urinary noradrenaline response to head-up tilt, an index of the responsiveness of the sympathetic nervous system, correlated significantly with subsequent blood pressure reduction with practolol IOO mg twice a day (r=0-62, P< O.OI).In 8 patients, responsiveness to tilt was retested after control of blood pressure: changes in diastolic blood pressure and pulse rate while on practolol were both significantly less than pretreatment responses.The urinary noradrenaline response was also reduced (+o -o 5,tg/hr vs. pretreatment mean of + i *64,tg/hr; P< o oI), a finding not explicable in terms of known receptor-blocking properties of the drug.It is suggested that the antihypertensive action of /3-adrenergic blockers may be related to a reduction in the reflex activity of the sympathetic nervous system.Plasma renin activity, which was normal in the recumbent state, rose with tilting.The response with tilt was significantly reduced with practolol, though plasma renin activity during recumbency was only marginally lowered by the drug.Although fl-adrenergic blocking drugs are finding increasing application in the treatment of hyper- tension, the mechanism by which they lower blood pressure remains uncertain.The antihypertensive