Epinephrine

Epinephrine or adrenaline, sometimes spelled "epinephrin" or "adrenalin" respectively, is a hormone and a neurotransmitter. Epinephrine is a catecholamine, a sympathomimetic monoamine derived from the amino acids phenylalanine and tyrosine. The Latin roots ad-+renes and the Greek roots epi-+nephros both literally mean "on/to the kidney" (referring to the adrenal gland, which secretes epinephrine). Epinephrine is sometimes shortened to epi in medical jargon.

In May 1886, William Bates reported the discovery of a substance produced by the suprarenal gland in the New York Medical Journal. Epinephrine was isolated and identified in 1895 by Napoleon Cybulski, Polish physiologist. The discovery was repeated in 1897 by John Jacob Abel. Jokichi Takamine discovered the same hormone in 1900, without knowing about the previous discovery; but, in later years, counterevidence is shown from the experiment note that Kaminaka leaves that the Takamine team is the discoverer of first adrenaline. It was first artificially synthesized in 1904 by Friedrich Stolz.


The chemical formula of epinephrine, a.k.a. 4-(1-hydroxy- 2-(methylamino)ethyl)benzene-1,2-diol, is C9H13NO3

Actions in the body

Epinephrine plays a central role in the short-term stress reaction—the physiological response to threatening, exciting or environmental stressor conditions such as high noise levels or bright light. It is secreted by the adrenal medulla. When released into the bloodstream, epinephrine binds to multiple receptors and has numerous effects throughout the body. It increases heart rate and stroke volume, dilates the pupils, and constricts arterioles in the skin and gut while dilating arterioles in leg muscles. It elevates the blood sugar level by increasing hydrolysis of glycogen to glucose in the liver, and at the same time begins the breakdown of lipids in fat cells. Epinephrine has a suppressive effect on the adaptive immune system.

Epinephrine is used as a drug to promote peripheral vascular resistance via alpha-stimulated vasoconstriction in cardiac arrest and other cardiac disrhythmias resulting in diminished or absent cardiac output, such that blood is shunted to the body's core. This beneficial action comes with a significant negative consequence, increased cardiac irritability, which may lead to additional complications immediately following an otherwise successful resuscitation. Alternatives to this treatment include vasopressin, a powerful antidiuretic which also promotes peripheral vascular resistance leading to blood shunting via vasoconstriction, but without the attendant increase to myocardial irritability.

Because of its suppressive effect on the adaptive immune system, epinephrine is used to treat anaphylaxis and sepsis. Allergy patients undergoing immunotherapy can get an epinephrine rinse before the allergen extract is administered, thus reducing the immune response to the administered allergen. It is also used as a bronchodilator for asthma if specific beta-2-adrenergic agonists are unavailable or ineffective. Adverse reactions to epinephrine include palpitations, tachycardia, anxiety, headache, tremor, hypertension, and acute pulmonary edema.

A pheochromocytoma is a tumor of the adrenal gland (or, rarely, the ganglia of the sympathetic nervous system), which secretes excessive amounts of catecholamines, usually epinephrine.

Pharmacology

Epinephrine's actions are mediated through adrenergic receptors (sometimes referred to as adrenoceptors).

It binds to α1 receptors of liver cells, which activate inositol-phospholipid signaling pathway, signaling the phosphorylation of insulin, leading to reduced ability of insulin to bind to its receptors.

Epinephrine also activates β-adrenergic receptors of the liver and muscle cells, thereby activating the adenylate cyclase signaling pathway, which will in turn increase glycogenolysis. Specifically, β2 receptors exist on many blood vessels. Activation of the adenylate cyclase pathway on this tissue causes inhibition of myosin light chain kinase which, in turn, relaxes the smooth muscle cells of the blood vessel walls to bring about vasodilation.

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