Abstract

Glucose is one of the most important energy sources for the body in general, and the brain in particular. It is essential for survival to keep glucose levels within strict boundaries. Acute disturbances of glucose homeostasis are rapidly corrected by hormonal and neuronal mechanisms. Furthermore, changes in energy expenditure associated with the light-dark cycle induce variations in the plasma glucose concentration that are more gradual. Organisms take advantage of adapting their internal physiology to the predictable daily changes in energy expenditure, because it enables them to anticipate these changes and to prevent unnecessary disturbance of homeostasis. The hypothalamic biological clock, located in the suprachiasmatic nucleus (SCN), receives light information from the eyes and transmits this information to the rest of the body to synchronize physiology to the environment. Here we review several studies providing evidence for biological clock control of the daily variation in several aspects of glucose metabolism. Although both hormones and the autonomic nervous system can stimulate glucose uptake or production by organs in the periphery, we have shown that the biological clock control of glucose metabolism mostly occurs through the autonomic nervous system. The critical involvement of the biological clock is also indicated by several studies, indicating that disturbance of the biological clock is often associated with metabolic diseases, such as obesity, diabetes mellitus and hypertension.

Keywords: Circadian, Rhythms, Metabolism, Autonomic Nervous System, Hypothalamus, Liver