Differential energetic response of brain vs. skeletal muscle upon hyperglycemia in humans

Objectives: The brain aims to maintain its energy content at a highly stable level. During acute hypoglycemia, high energy phosphate concentrations of the brain remain constant while there is a decrease in skeletal muscle. Accordingly, we assumed a differential energetic response of brain and skeletal muscle under conditions of excess energy supply, i.e. during acute hyperglycemia.

Methods: We investigated the key metabolites of energy metabolism which are ATP and phosphocreatine (PCr) as rapidly available energy stores by 31P magnetic resonance spectroscopy in brain and skeletal muscle of 17 healthy men. Measurements were performed at baseline and during dextrose induced hyperglycemia.

Results: During hyperglycemia, PCr concentrations increased significantly in the brain (P=0.013) whereas skeletal muscle content remained constant (P=0.149). Analyses of the PCr changes from baseline revealed significantly different energetic responses of the brain as compared to skeletal muscle (p=0.005). This effect was reflected by ATP concentrations (P=0.018).

Conclusion: Our results confirm previous data suggesting that the brain regulates its energy metabolism by a mechanism independent from that of the periphery. A disturbance of these mechanisms may have far reaching implications for diabetic features such as hypoglycemia unawareness or body weight regulation.