OPIOIDS POTENTIATE CONTRACTILE RESPONSE OF RABBIT MYOCARDIUM TO THE BETA ADRENERGIC AGONIST ISOPROTERENOL

Opioid agonists and antagonists have both been reported to augment myocardial contractile force in vitro. We report that the strong opioid agonists morphine and levorphanol, the weak agonist dextrorphan (an optical isomer of levorphanol), and the opioid antagonist naloxone all potentiate the stimulatory effects of the beta-adrenergic agonist isoproterenol on isometric tension generated by isolated rabbit right ventricular myocardium.