Glucagon

Glucagon is a peptide hormone consisting of 29 amino acids with a molecular mass of 3483 Da. Glucagon is an antagonist of insulin in its effect on glucose, protein and fatty acid metabolism. Glucagon and insulin are produced by different cells in the islets of Langerhans of the pancreas:

β-cells (70% of islet cells) produce insulin.

α-cells (20% of islet cells) produce glucagon from its precursors preglucagon and preproglucagon.

With normal nutrition, the secretion of glucagon remains constant in relation to the secretion of insulin. In this coordinated control loop, hypoglycemia leads to a rapid increase in glucagon. In this case, glucagon secretion can be increased up to fourfold. The blood sugar rises again. At the same time, glucagon promotes the uptake of amino acids into the hepatocytes, which are used for gluconeogenesis when energy requirements are high and glycogen stores are depleted.

Other secretory stimuli of glucagon include high-protein meals, infusion of amino acids (e.g., arginine, alanine), prolonged vigorous exercise, and stress.

Insulin, somatostatin, and GLP-1 inhibit the secretion of glucagon, as does high blood glucose. Amino acid-stimulated glucagon synthesis is inhibited by amylin, which is formed reactively during food intake and causes a feeling of satiety in the brain.

In the liver, glucagon binds to a receptor on the liver cell membrane. Here, the peptide hormone regulates transcription factors and signal transduction processes that control the metabolism of amino acids, lipids and carbohydrates. Glucagon is metabolized in the liver and inactivated by cleavage.

Glucagon, like insulin, can be produced synthetically and is used therapeutically in hypoglycemic shock as an immediate glucagon injection set.

Glucagon test (C-peptide): This is a rarely used test procedure that can be used to test the stimulability of pancreatic β-cells (functional reserve) to differentiate between type I and type II diabetes.

Glucagonom, a glucagon-producing neuroendocrine tumor of the gastroentero-pancreatic system (GEP-NET), is usually a malignant islet cell tumor of the pancreatic α-cells with increased glucagon production. Frequently suggestive is a recurrent dermatitis(migratory necrolytic erythema).