Influence of propranolol on catecholamine concentration in blood of normotensive man during physical exercise and dependence of the drug effect on dosage intervals.

Physical exercise on a bicycle ergometer caused in normotensive subjects an overshooting increase of plasma noradrenaline and adrenaline concentration, when exercise test was performed during acute or chronic treatment with propranolol both 2 hours after the last intake of the beta receptor blocking agent. At the same time heart rate and blood pressure during exercise were significantly reduced by the drug. But 8 hours after intake of the drug there was a dissociation between the drug effect on plasma catecholamine concentration and its effect on heart rate and blood pressure. While heart rate and blood pressure still were effectively lowered, the influence on plasma catecholamine concentration had already disappeared. The results demonstrate that an increase of plasma catecholamine concentration caused by the adrenergic beta receptor blocking agent propranolol, is strongly dependent on the time interval between measurement of drug effect and the last intake of the drug.