Abstract. Insulin controls hepatic glucose production (HGP) and maintains glucose homeostasis through the direct action of hepatic insulin receptors, as well as the indirect action of insulin receptors in the central nervous system. Insulin acts on insulin receptors in the hypothalamic arcuate nucleus, activates ATP-sensitive potassium channels in a phosphoinositide 3-kinase (PI3K)-dependent manner, induces hyperpolarization of the hypothalamic neurons, and regulates HGP via the vagus nerve. In the liver, central insulin action augments IL-6 expression in Kupffer cells and activates STAT3 transcription factors in hepatocytes. Activated STAT3 suppresses the gene expression of gluconeogenic enzymes, thereby reducing HGP. It has become evident that nutrients such as glucose, fatty acids, and amino acids act upon the hypothalamus together with insulin, affecting HGP. On the other hand, HGP control by central insulin action is impeded in obesity and impeded by insulin resistance due to disturbance of PI3K signaling and inflammation in the hypothalamus or inhibition of STAT3 signaling in the liver. Although the mechanism of control of hepatic gluconeogenic gene expression by central insulin action is conserved across species, its importance in human glucose metabolism has not been made entirely clear and its elucidation is anticipated in the future.Key words: Hypothalamus, Insulin, Liver, Vagus nerve, STAT3 THE LIVER plays a central role in the maintenance of whole-body glucose homeostasis, by adjusting glucose production according to the energy balance. The master regulator of hepatic glucose production (HGP) is insulin, as the liver is exposed to portal blood, which displays high insulin concentrations of approximately three times that in venous blood [1]. Indeed, in diabetes mellitus, the increase of HGP is closely related to the rise of fasting blood level [2]. HGP is strongly controlled by direct actions of insulin on hepatocytes [3]. When bound to its receptor, insulin suppresses HGP via the activation of phosphoinositide 3-kinase (PI3K) signal transduction pathway consisting of insulin receptor substrate (IRS), PI3K, phosphoinositide-dependent kinase 1 (PDK1) and Akt [4]. Thus, liver-specific insulin receptor knockout mice or impaired PI3K signal transduction exhibit hyperinsulinemia and glucose intolerance with impaired insulin-dependent suppression of HGP [5][6][7][8]. Meanwhile, insulin is known to control HGP not only by direct mechanisms via hepatic insulin receptors, but also by indirect mechanisms mediated by insulin actions on other organs (Fig.1). It has been reported that insulin still suppresses HGP partially even in mice with PI3K signal transduction inhibition in the liver [8,9]. Further, in an investigation of the changes in HGP after intravenous and intraportal insulin administration, it was shown that the differences in portal blood insulin level, that is, the direct insulin action on hepatocytes, do not necessarily correlate with the effect of insulin on HGP suppression [10].Indirect suppressio...