Glucagon

Glucagon is derived from the Greek words gluco (glucose) and agon (agonist). It is a single-chain polypeptide with 29 amino acids, produced in the α-cells of the islets of Langerhans, located in the endocrine portion of the pancreas. This protein is important in the metabolism of carbohydrates. Its function is to increase glycemia by acting as an insulin antagonist. In a hypoglycaemia, glucagon is released into the bloodstream and acts mainly in the liver, where it binds to specific receptors on hepatocytes (which store glycogen), stimulating them to produce and then release glucose. This mechanism is called glycogenolysis. After glycogen stores cease, the liver synthesizes glucose through gluconeogenesis.Thus, under normal conditions, glucose ingestion inhibits glucagon secretion. During fasting, there is a decrease in hepatic glycogen, a decrease in glycolysis in the liver, a stimulation of gluconeogenesis, a stimulation of fatty acid oxidation in adipocytes and increase of serum levels of this protein. An important function of glucagon is to maintain the concentration of glucose high enough for the normal functioning of neurons, preventing seizures or hyporglycemic coma in normal fasting situations, such as in nighttime sleep.
Glucagon secretion is controlled physiologically not only by the hypoglycemia, but also by low levels of fatty acids, hyperaminoacidemia, vagal stimulation and adrenal system stimuli, such as stress or physical exercise. Increased glucagon in the blood will activate lipase from fat cells, inhibit the storage of triglycerides in the liver, inhibit the reabsorption of sodium by the kidneys, increase cardiac output, increase the secretion of bile and inhibit the secretion of gastric acid.
In the cases of pathology, high levels of glucagon in the blood may be present related to glucagonoma, a rare neoplasm of the α-cells of the pancreas, causing increased glucose and lipid levels, decreased levels of amino acids, anemia, diarrhea and weight loss. It is also observed the appearance of migratory erythema, characterized by the presence of erythematous blisters in the lower abdomen, buttocks, perineum and groin. Diabetes mellitus often results from the imbalance between the hormones insulin and glucagon present in this neoplasm.
Glucagon can be used in dental emergencies as in severe hypoglycemia, common in an uncontrolled diabetic. It can be administered intramuscularly, causing the rapid increase of glucose levels in the
blood.

Text written by:

- Catarina Capelo

- Dina Nair

- Marta Santos

- Samyra Matni