Objectives: Melatonin, a hormonal product of the pineal gland, is now known
to be a multi-faceted free radical scavenger and anti-oxidant, Since littl
e 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 myoc
ytes were preloaded with tetramethylrhodamine (TMRM) in combination with on
e of the following fluorophores: dichlorodihydrofluorescein diacetate (DCDH
F), dihydrorhodamine 123 (DHR) of fluo 3 (Fluo) and then investigated with
confocal laser scanning microscopy. Chemical hypoxia was induced by additio
n 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. Re
sults: Cells subjected to 12.5 min chemical hypoxia showed marked morpholog
ical changes, increased fluorescence intensity of DCDHF, DHR and Flue, sugg
esting Ca2+ accumulation and generation of H2O2 and reactive oxygen species
. The number of cells showing increased fluorescence also increased signifi
cantly. Melatonin (50 and 100 muM) caused a significant reduction in morpho
logical changes, number of cells with increased fluorescence and fluorescen
ce intensity of DHR and Fluo, (but not DUDHF). Conclusion: Melatonin effect
ively reduced damage induced by chemical hypoxia in adult cardiomyocytes, p
robably by virtue of its effects on reactive oxygen species generation and
intracellular Ca2+ accumulation, (C) 2001 Academic Press.