Melatonin is assumed to confer cardioprotective action via antioxidative properties. We evaluated the association between ventricular tachycardia and/or ventricular fibrillation (VT/VF) incidence, oxidative stress, and myocardial electrophysiological parameters in experimental ischemia/reperfusion under melatonin treatment. Melatonin was given to 28 rats (10 mg/kg/day, orally, for 7 days) and 13 animals received placebo. In the anesthetized animals, coronary occlusion was induced for 5 min followed by reperfusion with recording of unipolar electrograms from ventricular epicardium with a 64-lead array. Effects of melatonin on transmembrane potentials were studied in ventricular preparations of 7 rats in normal and "ischemic" conditions. Melatonin treatment was associated with lower VT/VF incidence at reperfusion, shorter baseline activation times (ATs), and activation-repolarization intervals and more complete recovery of repolarization times (RTs) at reperfusion (less baseline-reperfusion difference, ΔRT) (p < 0.05). Superoxide dismutase (SOD) activity was higher in the treated animals and associated with ΔRT (p = 0.001), whereas VT/VF incidence was associated with baseline ATs (p = 0.020). In vitro, melatonin led to a more complete restoration of action potential durations and resting membrane potentials at reoxygenation (p < 0.05). Thus, the antioxidative properties of melatonin were associated with its influence on repolarization duration, whereas the melatonin-related antiarrhythmic effect was associated with its oxidative stress-independent action on ventricular activation.

• Keywords
• arrhythmia, depolarization, ischemia, melatonin, oxidative stress, reperfusion, repolarization,
• MeSH
• Anti-Arrhythmia Agents pharmacology   MeSH
• Antioxidants pharmacology   MeSH
• Electrophysiological Phenomena drug effects   MeSH
• Electrocardiography drug effects   MeSH
• Ventricular Fibrillation drug therapy   MeSH
• Rats MeSH
• Melatonin pharmacology   MeSH
• Rats, Wistar MeSH
• Myocardial Reperfusion Injury drug therapy   MeSH
• Reperfusion Injury drug therapy   MeSH
• Arrhythmias, Cardiac drug therapy   MeSH
• Cardiac Electrophysiology methods   MeSH
• Heart Ventricles drug effects   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Anti-Arrhythmia Agents MeSH
• Antioxidants MeSH
• Melatonin MeSH