Abstract
Introduction: A single exercise session releases opioid peptides considered to be associated to cardioprotection. However, the link between exercise-induced cardioprotection and the opioid system remains unclear. Therefore, the study aims to investigate the involvement of opioid receptors in exercise-induced cardioprotection in rats submitted to myocardial injury by ischemia/reperfusion (I/R) in vitro . Methods: Male Wistar rats (250-300g) were randomly divided into 3 groups submitted to I/R: control (CTR; n=5), exercised (EX; n=5) and exercised treated by naloxone, a non-selective opioid receptor antagonist (EX+NAL; n=5). The exercised groups underwent 4 consecutive days of treadmill training (60 min at 70% of maximal oxygen consumption). After the last exercise session (24h), the hearts were removed and immediately installed on a modified Langendorff apparatus. A latex balloon was inserted in the left ventricle (LV) to monitor the LV developed pressure (%LVDP). All hearts underwent a period of 30 min of sustained global ischemia followed by 1 h of reperfusion. After reperfusion, LV was sliced and incubated 20 min in triphenyltetrazolium to measure infarct size. Results: Anova two-way showed that CTR group presented a larger infarct area when compared to EXE group (32.9±9.2% vs 11.3±4.0% respectively; p<0.05). Naloxone treatment completely blocked the exercise-induced cardioprotection (28.1±8.0%). In respect to %LVDP, CTR and EXE+NAL showed significantly lower results compared to EXE group from 25 min of reperfusion. Conclusions: Our results indicate that opioid system is involved, at least in part, in cardioprotective effects of aerobic exercise in rats.
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