Glucagon Physiology

Glucagon is a peptide hormone secreted from the alpha cells of the pancreatic islets of Langerhans. Hypoglycemia is physiologically the most potent secretory stimulus and the best known action of glucagon is to stimulate glucose production in the liver and thereby to maintain adequate plasma glucose concentrations. However, glucagon is also involved in hepatic lipid and amino acid metabolism and may increase resting energy expenditure. Based on satiety-inducing and food intake-lowering effects of exogenous glucagon, a role for glucagon in the regulation of appetite has also been proposed. This chapter provides an overview of the structure, secretion, degradation and elimination of glucagon, and reviews the actions of glucagon including its role in glucose metabolism and its effects on lipolysis, ketogenesis, energy expenditure, appetite and food intake. Finally, the role of glucagon in the pathophysiology of diabetes, obesity and hepatic steatosis is discussed and emerging glucagon-based therapies for these conditions are outlined.