Hemodynamic effects of beta adrenergic receptor stimulant and blockade. Hemodynamic effects of isoproterenol after propranolol..

The effects of isoproterenol and propranolol on the hemodynamics were evaluated in dogs for the purpose of their clinical application in the management of cardiovascular surgical patients. In dogs receiving 0.002 mgjkg of isoproterenol intravenously with one shot, marked positive inotropic and chronotropic responses were achieved in 5 seconds and returned to the control values in 5 minutes. Heart rate, myocardial contractility, coronary blood flow and cardiac output increased markedly, but blood pressure decreased by about 50%. In dogs receiving the same dose of isoproterenol infusion over 15 minutes, similar changes were achieved, though milder. The effect remained stable during infusion. Isoproterenol iufusion was thought to be superior to injection as one shot in clinical application. In dogs receiving 0.2 m/kg of propranolol intravenously, depressing inotropic and chronotropic effects appeared in a few minutes. Myocardial contractility, cardiac output and heart rate decreased, but stroke volume increased. When 0.002 mg/kg of isoproterenol was injected after propranolol, the effects of isoproterenol were milder. The effect of isoproterenol to decrease blood pressure was prevented by propranolol. Isoproterenol infusion after propranolol injection resulted in a significant increase in myocardial contractility and a less in heart rate by overcoming the effects of propranolol with a far less increase in myocardial oxygen consumption.