Effects of endogenous cardioprotective mechanisms on ischemia-reperfusion injury.

Ischemic heart disease have been remarked as a leading cause of morbidity and mortality in adults. Early restoration of cardiac perfusion is necessary to restore perfusion of ischemic heart muscle. Effective revascularization reduce mortality by limiting myocardial necrosis at the acute phase of the cardiac infarction. However, reperfusion may induce a cascade of pathophysiological reactions causing the increase of the infarct area of the myocardium This phenomenon known as ischemia-reperfusion injury is responsible for up to 50% of the final infarct size. Sequences of brief episodes of nonlethal ischemia and reperfusion applied before (preconditioning - IPC) or after (postconditioning - POC) the coronary occlusion are well documented to reduce the ischemiareperfusion injury. These phenomena improve cardiac function by mobilizing the molecular and cellular mechanisms limiting reperfusion injury. The mechanisms underlying IPC or POC are still not clarified, but strong experimental evidence suggests that opioids may be the part of the endogenous cardioprotective response to I/R injury. Stimulation of opioid receptors activates related to POC mechanisms affecting protection to the ischemic myocardium, while the use of non-selective opioid receptor antagonist - naloxone reduces this effect. There is no consensus that the subtype of opioid receptor is responsible for the protection of the human heart muscle. Morphine may reduce cardiac preload by peripheral vasodilatation. Numerous studies show a direct cardioprotective effect of the opioid pathway in ischemic conditions. Opioids act via membrane receptors: μ, δ, κ. The predominant subtype in the human cardiac cells are μ- and δ - opioid receptors. It has been hypothetized that opioid receptor activation exerts cardioprotection in human heart muscle pathway what may give insight into the explanation of the protective mechanisms in the acute myocardial infarction.