DENOPAMINE (BETA1-SELECTIVE ADRENERGIC-RECEPTOR AGONIST) AND ISOPROTERENOL (NONSELECTIVE BETA-ADRENERGIC-RECEPTOR AGONIST) EQUALLY INCREASE HEART-RATE AND MYOCARDIAL OXYGEN-CONSUMPTION IN DOG HEART

The effects of denopamine (a beta-1-selective adrenergic receptor agonist) and isoproterenol (a non-selective beta-adrenergic receptor agonist) on heart rate, left ventricular contractility, and left ventricular oxygen consumption (Vo2) at the same left ventricular volume were compared in excised cross-circulated dog hearts. Denopamine and isoproterenol increased heart rate and Vo2 to a comparable extent at a comparably increased contractility. Moreover, the oxygen cost of contractility which quantifies Vo2 for excitation-contraction coupling was the same between the two agents. These findings contradict the the previously reported smaller increases in heart rate and Vo2 by denopamine than by isoproterenol in open-chest dog hearts, which have been mainly attributed to the beta-1-selectivity of denopamine. Our results suggest that in isolated and denervated hearts, the degree of beta-1-selectivity of a beta-agonistic agent does not directly determine the relative potencies of its inotropic and chronotropic effects and the oxygen cost of contractility.