The Role of Reactive Oxygen Species and Opioid Receptors in the Infarct‐Reducing Effect of Hypoxic Preconditioning

Abstract

An increase in cardiac resistance to ischemia/reperfusion (I/R) is an urgent aim of physiology, pharmacology, and cardiac surgery, since I/R injury of the heart is often the cause of cardiogenic shock and subsequent death of patients in the postoperative period. We have previously established that early hypoxic preconditioning has the infarct-limiting effect in rats. We hypothesized that reactive oxygen species (ROS) and opioid receptors (ORs) can be involved in this protective effect. The study was carried out in male Wistar rats which were subjected to coronary artery occlusion (45 min) and reperfusion (2 h). Before coronary occlusion, early hypoxic preconditioning (HP) was modeled. The rats were exposed to six sessions of hypoxia (8% O2, 10 min) and reoxygenation (21% O2, 10 min) 30 min before ischemia. The total duration of HP was 2 h. 2′,7′-dichlorodihydrofluorescein diacetate was used for the detection of free radicals in myocardial homogenates. Amplex Red was used for the detection of H2O2 in myocardial tissue. The rats were injected with the following compounds: a hydroxyl radical (OH•) scavenger 1,3-dimethylthiourea (DMTM), a non-selective OH• scavenger 2-mercaptopropionyl glycine (2-MPG), a Fe2+ chelator deferoxamine and the OR antagonist naltrexone. It was found that HP contributes to infarct size reduction by 30%. Preliminary administration of DMTM, 2-MPG, deferoxamine eliminated the infarction-limiting effect of HP. Naltrexone did not abolish the infarct-sparing effect of HP. These compounds did not affect the infarct size/area at risk ratio in non-preconditioned rats. The total ROS level was increased in the myocardium after HP by 2-fold. The H2O2 level was increased by about 10%. These data indicate that ROS are involved in the cardioprotective effect of HP. Opioid receptors are not involved in the infarct-limiting effect of HP.