Comparative Analysis of Infarct Size Limiting Activity of δ-Opioid Receptor Agonists in Reperfused Heart In Vivo

The study examined the effects of δ-opioid receptor (OR) agonists on infarct size on cardiac ischemia (45 min) and reperfusion (120 min) in vivo model in rats narcotized with α-chloralose. The OR agonists were injected intravenously 5 min prior to reperfusion, OR antagonists were administered 10 min before reperfusion. A selective δ-OR agonist BW373U86 (1 mg/kg) reduced the infarct size/area at risk ratio. A selective δ₁-OR agonist DPDPE injected in the doses of 0.1 or 0.969 mg/kg produced no effect on infarct size. The selective δ₂-OR agonist deltorphin II (0.12 mg/kg) reduced infarct size/area at risk ratio by 2 times. The δ-OR agonist p-Cl-Phe-DPDPE (1 mg/kg) reduced infarct size/area at risk ratio by 40%. Naltrexone and naloxone methiodide, the peripheral OR antagonists, and selective δ₂-OR antagonist naltriben prevented the infarct size limiting effect of deltorphin II. Therefore, activation of peripheral δ₂-OR enhanced cardiac resistance against toxic action of reperfusion. During reperfusion, deltorphin II demonstrated the most pronounced cardioprotective activity.