Effect of glucose infusion on muscle malonyl-CoA during exercise

Previous work in this laboratory has shown that muscle malonyl-CoA, the inhibitor of carnitine palmitoyltransferase I (CPT I), decreased during exercise. Hepatic malonyl-CoA content decreases when glucose availability decreases such as during fasting or when the glucagon-to-insulin ratio increases such as during prolonged exercise or in response to insulin deficiency. To investigate the effect of glucose infusion on muscle malonyl-CoA during exercise, male rats were anesthetized (pentobarbital via venous catheters) at rest or after running (21 m/min, 15% grade) for 30 or 60 min. During exercise rats were infused with either glucose (0.625 g/ml) or saline at a rate of 1.5 ml/h. Gastrocnemius muscles and liver samples were frozen at liquid nitrogen temperature. Muscle malonyl-CoA decreased from 1.24 +/- 0.06 to 0.69 +/- 0.05 nmol/g with glucose infusion and to 0.43 +/- 0.04 nmol/g with saline infusion during 60 min of exercise. In the liver, glucose infusion prevented the drop in malonyl-CoA. This indicates that glucose infusion attenuates the progressive decline in muscle malonyl-CoA and prevents the decline in liver malonyl-CoA during prolonged exercise.