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

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