The effect of melatonin on blood pressure and myocardial ischemia-reperfusion induced infarct size in chronic nitric oxide synthase inhibited rats

2. ABSTRACTReduced nitric oxide synthesis or bioavailability would lead to vasoconstriction,increased peripheral vascular resistance and may cause to hypertension. Hypertension,atherosclerosis and endothelial dysfunction are the major risk factors increasing morbidity andmortality of cardiovascular origin and worsen the prognosis of myocardial infarction.Melatonin is a potent free radical scavenger, has antioxidant effect and may decreasethe intracellular calcium overload. Furthermore, melatonin can suppress sympathetic nervefunction and decrease catecholamine release so it can exhibit antihypertensive effect. Thereare many studies associated with the protective effects of melatonin on myocardial ischemia-reperfusion injury.This study was designed to investigate the effects of exogenous administration ofmelatonin on blood pressure and ischemia-reperfusion-induced infarct size in chronic nitricoxide synthase (NOS) inhibition with Nω-Nitro-L-arginine methyl ester (L-NAME) in rats.The experimental animals were divided into three groups: control, L-NAME (40mg/kg for 15days) and L-NAME+Melatonin (10 mg/kg for last 5 days, i.p.) groups. To produce cardiacdamage the left main coronary artery was occluded for 30 minutes followed by 120 minutesreperfusion in rats. Blood pressure and ECG changes were recorded during experiments.While L-NAME administration significantly increased blood pressure compared withcontrol group, melatonin administration significantly reduced blood pressure. Infarct size inL-NAME group was higher than control group but melatonin treatment significantlyattenuated the infarct size compared with L-NAME group. While the death ratio resulted frommyocardial ischemia-reperfusion increased in L-NAME group, melatonin administrationdecreased but this changes was not statistically significant.According to our knowledges, this study which was demonstrated the activity ofmelatonin treatment on the ischemia-reperfusion injury in chronic NOS inhibition by L-NAME in rats is the first study and the results have been suggested that melatonin may bealso effective to prevent reduce ischemia-reperfusion injury in hypertensive individuals.Keywords: L-NAME, melatonin, blood pressure, ischemia-reperfusion, infarct size, heart