Physiological and pharmacological effects of melatonin on myocardial ischemic postconditioning protection on infarct size and role of mitochondrial uncoupling protein 2 and 3

Myocardial ischemic postconditioning (PostC) is a strong endogenous cardioprotective phenomenon, which targets the increased tolerance of the myocardium against continuous ischemia when the myocardium is subjected to short intervals of ischemia-reperfusion I/R at the beginning of reperfusion following ischemia. Physiologic and pharmacologic concentrations of melatonin released from the pineal gland has been shown protective effect against I/R injury. It has been reported that protective effects of PostC decreases/disappears with age and chronic heart disease. Similarly in low serum melatonin levels have been reported in the same risk groups. In this study, it was aimed to investigate the physiological and pharmacological role of melatonin in PostC protection. For this purpose, I/R injury induced enfarct size, irisin (is a hormone in charge of energy metabolism) and protect the mitochondria from oxidative stress levels of UCP2 and 3 proteins were examined. Initially rats were divided into 2 groups (control (Non-Px)) or pinealectomized (Px)) 2 months before the I/R studies. 30 min ischemia, 3 cycles of 10 sec of I / R ve120 min of reperfusion applied. Risk areas with evans blue, infarct size with triphenyltetrazoliumchloride were determined and calculated with the ImageJ program. Levels of irisin, UCP 2 and 3 were analyzed by qRT-PCR. In Non-Px groups, infarct size decreased by PostC and melatonin applications (18.83%, 17.53%). İnfarct size in Px rats (33.58%) was significantly higher compared with the control (25.46%). UCP3 level decreased with I/R and Px, increased by PostC and melatonin application. After Px, PostC does not create significant effect on the infarct size and UCP2,3 but protection was provided with melatonin before PostC. İrisin level increased with I/R and Px, decreased by PostC and melatonin applications. These findings showed that UCP 2, 3 and irisin levels could play a role in retention of PostC, protective effect (infarct size, UCP2, 3) disappears with the reduction of physiological melatonin and comes back with melatonin replacement. These results suggest that physiological and pharmacological concentrations of melatonin are important in protection of PostC. Melatonin and PostC are protective with a similar rate and similar parameters, so melatonin may be an agent capable of pharmacological PostC. Keywords: Postconditioning, melatonin, I/R, irisin, UCP 2/3