Myocardial resistance to ischemic and reperfusion injuries under conditions of chronic administration of opioid receptor agonists and antagonists.

Chronic treatment with opioid receptor ligands: nonselective peptide opioid receptor agonist dalargin (intraperitoneally in a dose of 1 mg/kg), selective nonpeptide kappa-receptor agonist GR 89696 (subcutaneously in a dose of 0.03 mg/kg), nonselectrive nonpeptide antagonist quadazocine (subcutaneously in a dose of 3 mg/kg) or naltrexone (subcutaneously in a dose of 10 mg/kg) for 20 day had no effect of the incidence of ischemic ventricular arrhythmias and the size of necrotic zone after coronary occlusion and reperfusion in rats in vivo.