Epinephrine is a hormone secreted by the adrenal glands, located near the kidneys. Naturally released in high-stress, “fight or flight” moments, epinephrine (also known as adrenaline) speeds breathing and heart rate, constricts blood vessels, and affects a wide range of other body tissues. Once released as a reaction to stresses, epinephrine enters the bloodstream and acts on the body tissues. Because of its effects, epinephrine is also used to treat asthma and severe allergic reactions.
The hormone epinephrine is a neurotransmitter able to bind to a variety of cell receptors. This ability is what enables epinephrine to act on nearly all body tissues, as many types of cells have these receptors. The different adrenergic receptors trigger different metabolic changes. The binding of epinephrine generally causes a sympathetic (or 'fight-or-flight') response.
There are two main groups of adrenergic cell receptors (? and ?), each with several subtypes. Epinephrine binds to several types of adrenergic receptors, including ?1, ?2, ?1, ?2, and ?3 receptors.
When epinephrine binds to ?-adrenergic receptors, insulin secretion by the pancreas is reduced. Meanwhile, gycolysis is stimulated in muscle tissue, preparing the muscles for action. When epinephrine reacts with ?-adrenergic receptors, it causes vasoconstriction, or the constricting of blood vessels. This leads to increased heart rate, one of the most noticeable results of the release of epinephrine. At the same time, epinephrine also binds to ?-adrenergic cell receptors. ?-Adrenergic receptor binding triggers secretion of hormones and glucagon that serve to increase blood glucose levels, providing increased energy for cells throughout the body.