| Abstrakt: |
The effect of combined alpha- and beta-adrenergic blockade with phenoxybenzamine and propranolol, respectively, on changes in left ventricular myocardial oxygen consumption and blood flow during nicotine administrations (36 micrograms/kg/min, i.v.) was evaluated in anesthetized, open-chest dogs. Myocardial blood flow was estimated by injection of 8 to 10 micrometers diameter radioactive microspheres into the left atrium, and myocardial oxygen consumption was computed from the Fick principle. Before adrenergic blockade, nicotine caused a market (+151%) elevation in myocardial oxygen consumption and a parallel increase in myocardial blood flow. The increase in myocardial blood flow was uniform transmurally. These cardiac changes were accompanied by elevations in systemic arterial and left atrial pressures, peripheral vascular resistance, and heart rate, but by no change in aortic flow or in myocardial contractility. After adrenergic blockade, nicotine caused somewhat lesser, though still marked, elevations in myocardial oxygen consumption (+60%) and blood flow (+43%). Again, myocardial blood flow increases were uniform transmurally. Also, nicotine-induced increases in systemic arterial and left atrial pressure and in peripheral vascular resistance persisted after adrenergic blockade, whereas heart rate remained constant and aortic flow and myocardial contractility declined. The results indicate that nonadrenergic mechanisms contribute significantly to the increase in myocardial oxygen demand during nicotine infusion. |
