Studies on the effects of propanolol on plasma catecholamine levels in patients with essential hypertension

The influence of the beta receptor blocking agent propranolol on plasma catecholamine concentrations was studied in eight patients with essential hypertension. The study was of single blind crossover design. Propranolol given in oral doses ranging from 60 to 240 mg daily for a period of 3 weeks decreased blood pressure and heart rate. The beta-adrenergic blocking agent caused plasma catecholamine levels to increase both at rest and during bicycle exercise. Chromatographical analysis showed that concentrations of noradrenaline as well as of adrenaline rose during treatment with propranolol. However, dopamine-beta-hydroxylase activity in plasma was not altered. Furthermore, the urinary excretion of noradrenaline, adrenaline and 4-hydroxy-3-methoxy mandelic acid did not change during beta receptor blockade. The results are compatible with the assumption that antihypertensive doses of propranolol by decreasing cardiac output cause an activation of the sympatho-adrenal system.