Insulin regulates blood glucose primarily by two mechanisms:
Suppressing glucose production by the liver
Enhancing glucose uptake by other tissues, particularly muscle and liver
Since the cells contained in liver, muscle and other tissues respond directly to insulin stimulation, most people don't think about the role of the brain in this process. An interesting paper just published in Diabetes reminds us of the central role of the brain in glucose metabolism as well as body fat regulation (1). Investigators showed that by inhibiting insulin signaling in the brains of mice, they could diminish insulin's ability to suppress liver glucose production by 20%, and its ability to promote glucose uptake by muscle tissue by 59%. In other words, the majority of insulin's ability to cause muscle to take up glucose is mediated by its effect on the brain.