Cardioprotective Effect of Selective μ₂-Opioid Receptor Agonist Endomorphin-1 in Cardiac Reperfusion In Vivo and In Vitro

The effect of the selective μ₂-opioid receptor agonist endomorphin-1 in reperfusion injury in male Wistar rats was studied in vivo and in vitro. The in vivo experiment included coronary artery occlusion (45 min) and reperfusion (120 min); in in vitro experiments, 45-min global ischemia of the isolated rat heart was followed by 30-min reperfusion. Endomorphin-1 was administered intravenously 5 min before in vivo reperfusion (at a dose 50 μg/kg) or added to the perfusion solution at the onset of reperfusion of the isolated heart (in a concentration of 152 nmol/liter). In vivo endomorphin-1 reduced the infarct size by 33% compared to the control group. In experiments on isolated heart, endomorphin-1 improved the contractile function during reperfusion and reduced the creatine kinase level in the coronary effluent. Hence, stimulation of cardiac μ₂-opioid receptors increases heart tolerance to the pathogenic effects of reperfusion.