The role of melatonin in acute myocardial infarction.

Melatonin, a circadian hormone with marked antioxidant properties, has been shown to protect against ischemia-reperfusion myocardial damage, especially when administered during reperfusion period. Melatonin has cardioprotective properties via its direct free radical scavenging and its indirect antioxidant activity. Melatonin efficiently interacts with various reactive oxygen and reactive nitrogen species and it also upregulates antioxidant enzymes and downregulates pro-oxidant enzymes. In addition, melatonin demonstrated blood pressure lowering, lipid profile normalizing and anti-inflammatory properties. The lack of these cardioprotective effects due to insufficient melatonin levels might be associated with several cardiovascular pathologies including ischemic heart disease. Patients with acute coronary syndrome or after myocardial infarction were shown to have reduced nighttime melatonin levels and 6-sulfatoxymelatonin urinary excretion. These alterations might translate to increased cardiovascular risk observed in acute myocardial infarction patients with low melatonin levels; and a mutation in melatonin receptors might augment the risk for acute myocardial infarction. Therefore, it is expected that melatonin administration could play a clinically relevant role in the pharmacotherapy of ischemic heart disease; an assumption supported by low toxicity and high safety of melatonin.