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

A 45-min coronary artery occlusion followed by a 120-min reperfusion was performed in rats anesthetized with α-chloralose. The selective κ1-opioid receptor (OR) agonist U-50,488 was administered intravenously in doses of 0.1 or 1 mg/kg. The selective κ2-OR agonist GR-89696 was injected in a dose of 0.1 mg/kg. The selective κ1-OR agonists ICI-199,441 and ICI-204,448 were employed in the doses of 0.1 and 4 mg/kg, respectively. These drugs were injected 5 min prior to reperfusion. U-50,488 exerted the cardioprotective effect in a dose of 1 mg/kg, but it produced no effect on infarct size in a dose of 0.1 mg/kg. ICI-199,441 reduced the reperfusion injury to the heart. The infarct size limiting effects of U-50,488 and ICI-199,441 were prevented by preliminary injection of naltrexone or nor-binaltorphimine. It is concluded that infarct size limiting effects of U-50,488 and ICI-199,441 were mediated via activation of κ1-OR.