Melatonin increases muscle and liver glycogen content in nonexercised and exercised rats

The effects of melatonin on several parameters of carbohydrate and lipid metabolism were investigated in exercised and nonexercised rats. Animals were run to exhaustion on a rodent treadmill at 24 m/min and a 12% slope. Exercise resulted in a significant hypoglycemia and increased plasma levels of lactate and beta-hydroxybutyrate, together with a significant reduction of glycogen in muscle and liver. Muscle and liver glycogen content was elevated and plasma free fatty acid decreased in nonexercised animals receiving melatonin (0.5 or 2.0 mg/kg i.p). Melatonin at 2.0 mg/kg reduced plasma lactate and increased lactate concentration in liver. When compared to untreated exercised animals glycemia and muscle and liver glycogen content were significantly higher in melatonin-treated exercised animals, while plasma and liver lactate and plasma beta-hydroxybutyrate were significantly reduced. Our data indicate that melatonin preserves glycogen stores in exercised rats through changes in carbohydrate and lipid utilization.