Effect of melatonin on ischemia reperfusion injury induced by middle cerebral artery occlusion in rats

Free radicals have been implicated in neuronal injury during ischemia reperfusion in stroke. Therefore, in the present study, melatonin, a potent antioxidant, was studied in male Wistar rats subjected to 2 h of transient middle cerebral artery occlusion. Melatonin (10, 20 and 40 mg/kg i.p.) was administered four times in an animal at the time of middle cerebral artery occlusion, 1 h after middle cerebral artery occlusion, at the time of reperfusion and 1 h after reperfusion. Two hours after reperfusion, rats were euthanized for estimation of oxidative stress markers (malondialdehyde and reduced glutathione). The doses of 20 and 40 mg/kg of melatonin significantly attenuated the raised level of malondialdehyde (287±28, 279±52 nmol/g wet tissue, respectively) as compared to the levels (420±61 nmol/g wet tissue) in vehicle-treated middle cerebral artery-occluded rats. There was an insignificant change in levels of reduced glutathione at these doses (95±42, 88.7±36 μg/g wet tissue, respectively) as compared to those in the vehicle-treated middle cerebral artery-occluded rats (108.21±21 μg/g wet tissue). However, there was an insignificant difference between 20 and 40 mg/kg treated rats. Therefore, the dose of 20 mg/kg i.p. was used to evaluate the neuroprotective effect by using diffusion-weighted imaging (30 min after reperfusion), assessing the neurological deficit (24 h after middle cerebral artery occlusion) and estimating oxidative stress markers (72 h after middle cerebral artery occlusion). In the 20 mg/kg melatonin-treated group, percent ischemic lesion volume on diffusion-weighted imaging was significantly attenuated (9.8±3.9) as compared to that in the vehicle-treated group (21.4±4.7). The neurological deficit was significantly improved in the melatonin group (1.8±0.06) as compared to that in the vehicle-treated (2.9±0.38) group. The level of malondialdehyde (321.4±31 nmol/g wet tissue) and reduced glutathione (142.6±13 μg/g wet tissue) in the melatonin-treated group was also significantly decreased as compared to the level of malondialdehyde (623±22 nmol/g wet tissue) and reduced glutathione (226.6±19 μg/wet tissue) in the vehicle-treated group. The present study indicates that melatonin has a neuroprotective action in focal ischemia, which may be attributed to its antioxidant property