Metabolic effects of glucagon in humans.

Diabetes is a common metabolic disorder that involves glucose, amino acids, and fatty acids. Either insulin deficiency or insulin resistance may cause diabetes. Insulin deficiency causes type 1 diabetes and diabetes associated with total pancreatectomy. Glucagon produces insulin resistance. Glucagon-induced insulin resistance promotes type 2 diabetes and diabetes associated with glucagonoma. Further, glucagon-induced insulin resistance aggravates the metabolic consequences of the insulin-deficient state. A major metabolic effect of insulin is the accumulation of glucose as glycogen in the liver. Glucagon opposes hepatic insulin action and enhances the rate of gluconeogenesis, increasing hepatic glucose output. In order to support gluconeogenesis, glucagon promotes skeletal muscle wasting to supply amino acids as gluconeogenic precursors. Glucagon promotes hepatic fatty acid oxidation to supply energy required to sustain gluconeogenesis. Hepatic fatty acid oxidation generates β-hydroxybutyrate and acetoacetate (ketogenesis). Prospective studies reveal that elevated glucagon secretion at baseline occurs in healthy subjects who develop impaired glucose tolerance at follow-up compared with subjects who maintain normal glucose tolerance, suggesting a relationship between elevated glucagon secretion and development of impaired glucose tolerance. Prospective studies have identified animal protein consumption as an independent risk factor for type 2 diabetes and cardiovascular disease. Animal protein intake activates glucagon secretion inducing sustained elevations in plasma glucagon. Glucagon is a major hormone that causes insulin resistance. Insulin resistance is an established cardiovascular risk factor additionally to its pathogenic role in diabetes. Glucagon may be a potential link between animal protein intake and the risk of developing type 2 diabetes and cardiovascular disease.