Effect of Eight Weeks of Endurance Training in Light and Dark Phases of Circadian Rhythm on the Oxidative Stress Index in Pancreas of Diabetic Mice

Introduction: Chronic hyperglycemia is associated with an increase in cellular damage due to oxidative stress in pancreatic tissue. The effect of exercise in different phases of the circadian cycle on protecting pancreatic tissue from oxidative stress in diabetic patients is unknown. The aim of this study was to investigate the effect of eight weeks of endurance training in light and dark phases of circadian rhythm on the oxidative stress index in pancreas of diabetic mice. Methods: In this study, 18 mice from the Naval Medical Research Institute  (26.3±3.22 gr) were selected and after inducing diabetes through high-fat food and Streptozotocin injection (20 mg/kg), randomly divided into 6 groups: light phase healthy control, dark phase healthy control, light phase diabetic control, dark phase diabetic control, light phase diabetic training and dark phase diabetic training. The endurance training protocol (50-60 %Vmax) was performed 5 d/w for 8 weeks. After anesthesia, blood samples and pancreatic tissues were removed. Insulin resistance markers, oxidative stress index and expression of Brain and Muscle ARNT-Like1 protein expression were measured in pancreas of diabetic rats. Data were analyzed by one way analysis of variance at the significance level of p <0.05. Results: The eight weeks of endurance training significantly decreased insulin resistance markers (p= 0.005), oxidative stress index (p ˂0.05) and significantly increased the Bmal1 protein expression (p = 0.009). The mean values of all variables showed significant differences between light and dark phases. Conclusion: Endurance training may improve insulin sensitivity and oxidant damage in diabetic conditions by increasing the function of the antioxidant system and the expression of Circadian regulation proteins. Activity in the dark phase causes further increases the metabolism of cells. As a result, performing these types of exercises in the dark phase is recommended to these patients as a new treatment strategy.