There has been increased interest in
melatonin recently, since it was shown to be a potent scavenger of toxic
free radicals.
Melatonin has been found to be effective in protecting against pathological states due to
reactive oxygen species release. The present study was performed in order to determine whether
melatonin or 5-methoxy-carbonylamino-N-acetyl-tryptamine (5-MCA-NAT), a structurally related
indole compound, protect against
ischemia-reperfusion injury in the isolated rat heart. Wistar rats were treated in vivo with either
melatonin (1 or 10 mg/kg, i.p.) or
5-MCA-NAT (10 mg/kg, i.p.) or their vehicle, 30 min before their hearts were excised and perfused according to the Langendorff technique. Two different protocols were then applied. In the first one, a regional
ischemia (5 min)-reperfusion (30 min) sequence was performed in order to record incidence and duration of reperfusion arrhythmias. In the second one,
infarct size was assessed after a regional
ischemia (30 min)-reperfusion (120 min) sequence. Results show a spectacular protection against
ischemia-reperfusion injuries (on arrhythmias as well as on
infarct size) in rats pre-treated with 10 mg/kg of
melatonin or
5-MCA-NAT. In conclusion, both
melatonin and its structural analog,
5-MCA-NAT, appear to confer protection against
ischemia-reperfusion injury in the isolated rat heart. This observation suggests that
melatonin could have a potential clinical application in the treatment of
myocardial ischemia, even if the mechanisms underlying this protection remain to be determined.