Melatonin protects against ischaemic-reperfusion myocardial damage

Objectives: Melatonin, a hormonal product of the pineal gland, is now known to be a multi-faceted free radical scavenger and anti-oxidant, Since little information is available regarding the action of melatonin on the heart, we studied the effects of melatonin on adult ventricular myocytes subjected to chemical hypoxia and reoxygenation. Methods: Adult rat ventricular myocytes were preloaded with tetramethylrhodamine (TMRM) in combination with one of the following fluorophores: dichlorodihydrofluorescein diacetate (DCDHF), dihydrorhodamine 123 (DHR) of fluo 3 (Fluo) and then investigated with confocal laser scanning microscopy. Chemical hypoxia was induced by addition of 1.5 mM KCN and 20 mM deoxyglucose to the superfusion buffer. Melatonin (50-100 muM) was added at different time intervals during the protocol. Results: Cells subjected to 12.5 min chemical hypoxia showed marked morphological changes, increased fluorescence intensity of DCDHF, DHR and Flue, suggesting Ca2+ accumulation and generation of H2O2 and reactive oxygen species. The number of cells showing increased fluorescence also increased significantly. Melatonin (50 and 100 muM) caused a significant reduction in morphological changes, number of cells with increased fluorescence and fluorescence intensity of DHR and Fluo, (but not DUDHF). Conclusion: Melatonin effectively reduced damage induced by chemical hypoxia in adult cardiomyocytes, probably by virtue of its effects on reactive oxygen species generation and intracellular Ca2+ accumulation, (C) 2001 Academic Press.