Does the circadian rhythm of melatonin affect ischemia-reperfusion injury after coronary artery bypass grafting?

BACKGROUND Melatonin is a potent scavenger of free radicals and an antioxidant. We studied the relationship between the protective effect of melatonin against ischemia-reperfusion injury (IRI) during cardiopulmonary bypass, the plasma level of melatonin, and the time of surgery. METHODS Forty patients who were to undergo elective coronary artery bypass grafting (CABG) were divided into 2 groups, those who underwent their operations at 8 AM (group I; n = 20) and those who underwent their operations at 1 PM (group II; n = 20). The operations were carried out by the same surgical team and with the same standard surgical technique. Blood samples were collected before the operation (T1), when the aortic cross-clamp was removed (T2), and at 4 hours (T3) and 24 hours (T4) after the operation. RESULTS Preoperative plasma levels of melatonin were substantially higher in group I than in group II. Intraoperative and postoperative melatonin levels were also significantly higher in patients who underwent their operations in the morning. The 2 groups had similar preoperative levels of intercellular adhesion molecule 1 and interleukin 8; however, intraoperative and postoperative values were lower in group I for all samples. This difference was statistically significant for both markers. Plasma levels of lactate dehydrogenase were significantly lower in group I. The 2 groups had similar aortic cross-clamp and cardiopulmonary bypass times. Preoperative and postoperative troponin I levels were lower in group I than in group II, but these differences were not statistically significant. The 2 groups showed no significant differences in plasma creatine kinase MB levels for either preoperative or postoperative measurements. CONCLUSION High plasma levels of melatonin may be directly related to low levels of IRI markers. Melatonin may have a protective effect against IRI in CABG. This effect seems to be directly correlated with the plasma levels of melatonin and inversely related with light. If melatonin protects myocardium from IRI, additional studies may be planned for the preoperative use of melatonin in patients with coronary artery disease to improve myocardial protection.