Pre- and Post-Treatment of Streptozocin Administered Rats with Melatonin: Effects on Some Hepatic Enzymes of Carbohydrate Metabolism

Background: Melatonin, found in high concentrations in the pineal gland, organs within the digestive system and in some plants and fungi, acts as an antioxidant which decreases reactive oxygen species in streptozocin-induced diabetic rats, raises insulin secretion by the pancreatic β- cells and increases the number of insulin receptors on hepatocyte membranes. Materials and Methods: The protective and therapeutic effects of melatonin feeding in streptozocin-induced diabetic rats were studied. Streptozocin administered rats were gavaged with melatonin, pre- and post-treatment, at a level of 5 mg/kg body weight daily for a period of 15 days. Levels of plasma glucose, cholesterol, triacylglycerol, oral glucose tolerance test, and some hepatic enzymes of carbohydrate metabolism including insulin inducible glucokinase, hexokinase and glucose 6-P dehydrogenase were measured using standard methods and compared with the values in normoglycemic and diabetic control groups. Results: Both pre- and post-treatment of the streptozocin administered rats with melatonin normalized plasma glucose, cholesterol, and triacylglycerol, improved oral glucose tolerance test and increased hepatic glucokinase, hexokinase and glucose 6-P dehydrogenase specific activities to the levels seen in normal rats. Conclusion: Melatonin pre-treatment prevents the injurious effects of streptozocin in rats. In streptozocin induced diabetic animals, post-treatment with this antioxidant normalizes both blood and liver constituents which were ameliorated by streptozocin.