Intracellular calcium and cAMP mediated effect of opioid receptors on the resistance of the isolated heart

The effect of activation of ƒ1- and ƒ1-opioid receptor (OR) on the tolerance of isolated perfused rat heart to global ischemia and reperfusion were studied. It was established that stimulation of cardiac ƒ1- and ƒ1-OR by adding agonists U-50,488 encourage the decrease of reperfusion release of creatine kinase from heart compared to control group. Occupancy of ƒ1-OR by DPDPE did not affect the cAMP levels in the heart before and after ischemia. Occupancy of ƒ1-OR by U-50,488 had no effect on the cAMP levels in the myocardium pre-ischemia period but reduced the cAMP content in reperfusion period in comparison with control group. The pretreatment with inhibitor of Ca2+-ATPase of sarcoplasmic reticulum cyclopiazonic acid completely abolished the cardioprotective effect of ƒ1-OR agonist DPDPE. It was proposed that cardioprotective effect of ƒ1-OR stimulation is dependent on the decrease in cAMP levels in the heart but Ca2+-ATPase of sarcoplasmic reticulum is involved in the cardioprotective effect of ƒ1-OR activation.