Melatonin affords protection against gastric lesions induced by ischemia-reperfusion possibly due to its antioxidant and mucosal microcirculatory effects. 
Melatonin, a pineal hormone, is known to scavenge oxygen free radicals and to be present in the gut but little is known about its role in the protection of gastric mucosa against the damage accompanied by a marked increase in these radicals.  This study was designed to determine the effects of melatonin on the formation of acute gastric lesions induced by ischemia-reperfusion and, for comparison, by a topical irritant such as 100% ethanol.  It was found that pretreatment with melatonin at a dose of 5 mg/kg given intragastrically reduced significantly gastric lesions induced by ischemia-reperfusion and this was accompanied by a reduction in free radicals in the blood and by attenuation of the fall in gastric blood flow.  In contrast, melatonin failed to affect acute gastric lesions induced by 100% ethanol.  We conclude that melatonin is capable of protecting gastric mucosa from the damage caused by ischemia-reperfusion and that this action is mediated, at least in part, by limitation of the generation of free radicals and by attenuation of the fall in gastric blood flow.