In vivo and in situ action of melatonin on insulin secretion and some metabolic implications in the rat

Introduction: The role of melatonin in human insulin regulation is poorly understood. Aim: To investigate the influence of melatonin supplementation on glucose and insulin levels and on lipid metabolism in blood serum and the liver. Methodology: The acute melatonin effects on insulin secretion in male Wistar rats were investigated. In addition, carbohydrate and lipid metabolism was studied. In in vivo experiments, melatonin was administered subcutaneously in two different doses (0.5 and 1.0 mg/kg body weight, respectively), and animals were decapitated after I hour. Results: The hi-her dose of the hormone increased insulin level in blood. The applied pancreas perfusion technique allowed us to confirm a direct mechanism of melatonin action on the pancreas. The ability of melatonin to stimulate insulin output was dose dependent. The highest effect was noticed for 100 nmol/L, whereas I nmol/L did not influence this process. Conclusion: Melatonin treatment in vivo caused many biochemical consequences. The hormone augmented significantly the concentrations of total, free, and esterified cholesterol. as well as high-density lipoprotein cholesterol in blood. Together with the enhanced insulin secretion observed in the in vivo experiment, the level of free fatty acids in blood decreased and. surprisingly. glucose concentration was significantly elevated.