Effect of beta adrenergic blockade on the hemodynamic responses to epinephrine in man

Abstract

The effects of beta adrenergic receptor blockade by propranolol on the hemodynamic responses to isoproterenol and epinephrine were investigated in 10 supine normal volunteers. Intravenous propranolol (10 mg.) lowered heart rate, cardiac output and stroke volume, raised mean right atrial pressure and total peripheral resistance without affecting arterial pressure, and blocked almost completely the hemodynamic responses to 2 or 2.5 μg./min. of isoproterenol. An infusion of isoproterenol at 12.5 μg./min. partially overcame the beta blockade. During beta blockade most of the responses to an infusion of epinephrine at 5 μg./min. were reversed, with heart rate, cardiac output and stroke volume decreasing, and arterial and mean right atrial pressures and total peripheral resistance increasing. Before beta blockade the isometric period of left ventricular systole was shortened by isoproterenol and epinephrine. After beta blockade it was unaffected by isoproterenol but lengthened by epinephrine.The changes in control data produced by propranolol are consistent either with the blockade of pre-existing beta adrenergic activity or with a nonspecific direct, possibly depressant, action on the heart. The data demonstrate that beta adrenergic receptor blockade by propranolol may be used to unmask the potent alpha (vasoconstrictive) action of epinephrine in man.