Analysis of the relative magnitude of the positive inotropic and chronotropic effects and the coronary vasodilating effects of amrinone conducted in the canine heart-lung preparation with a support dog in comparison with those of dobutamine demonstrated that amrinone was a preferential coronary vasodilator rather than a selective positive inotropic agent. An in vitro experiment in the canine papillary muscle suggested the initiation of the slow response action potential as a mechanism of the positive inotropic effect of amrinone.
To elucidate the role played by catecholamines in the early phase of ischemic derangement of the myocardial energy metabolism, effects of β-blockers (propranolol, pindolol, and celiprolol) and isoprolerenol, and of pretreatment with reserpine and 6-hydroxydopamine (6-OHDA), were studied using the isolated perfused rat heart. β-Blockers and isoproterenol were infused for 12 min prior to induction of global ischemia. The myocardial energy consumption rate was assessed by calculating the product of left ventricular pressure and heart rate (LVP × HR). The myocardial cell creatine phosphate (CP), ATP and pH were determined with 31P nuclear magnetic resonance (31P-NMR). Global ischemia induced by cross-clamping of the aortic inflow line for 15 min resulted in falls in CP, ATP, and pH. Propranolol (6 × 10−8 and 1.8 × 10−7 mol/min) and pindolol (6 × 10-mol/min) produced a decrease in LVP × HR and surpressed the pH fall during ischemia. Celiprolol wa without significant effects on these two parameters. Isc proterenol (6 × 10−12 mol/min) produced an increase i LVP × HR and tended to accelerate the pH fall. Cate cholamine depletion with reserpine or 6-OHDA produce no beneficial effects on the pH fall. It was concluded the the beneficial effects of β-blockers on the pH fall durin early ischemia were not due to the specific β-blockin action but to the nonspecific cardiodepressant effects c these compounds.
