[Glucagon and glucagon-like peptides the role in control glucose homeostasis. Part I]

Glucose homeostasis is controlled primarily by the opposing actions of insulin and glucagon, hormones that are secreted by the islets of Langerhans from β-cells and α-cells and Δ-cells, their role in glucose homeostasis still needs identifying. Insulin secretion is increased in response to elevated blood glucose to maintain normoglycemia by stimulating glucose transport in muscles and adipocytes and reducing glucose production by inhibiting gluconeogenesis in the liver. Whereas glucagon secretion is suppressed by hyperglycemia, it is stimulated during hypoglycemia, promoting hepatic glucose production and ultimately raising blood glucose levels. Glucagon secretion from pancreatic α-cells is regulated by various mechanisms including glycemia, neural input, and secretion from neighboring β-cells. Glucagon primarily acts on liver to initiate glycogenolysis and gluconeogenesis, resulting in a rapid increase in endogenous production of glucose. With longer stimulation, glucagon action on the liver results in a glucose-sparing activation of free fatty acid oxidation and production of ketones.