Epinephrine (INN) or adrenaline (BAN) is a hormone and a neurotransmitter. Both names mean the same: 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.
Epinephrine plays a central role in the short-term stress reaction—the physiological response to conditions that threaten the physical integrity of the body. 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 muscle. 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 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 diuretic which also promotes peripheral vascular resistance leading to blood shunting via vasoconstriction, but without the attendant increase to myocardial irritability.
Epinephrine is also used as a vasoconstrictor in anaphylactic shock and sepsis, and as a bronchodilator in acute bronchial asthma. Allergy patients undergoing immunotherapy can get an epinephrine rinse before their allergan extract is administered. Adverse reactions include palpitations, tachycardia, anxiety, headache, tremor, hypertension, and acute pulmonary oedema.
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.
Chemically, epinephrine is a catecholamine hormone, a sympathomimetic monoamine derived from the amino acids phenylalanine and tyrosine. The chemical formula of epinephrine is C9H13NO3. Its structure is shown right.
Epinephrine was first isolated and identified in 1897 by John Jacob Abel. Jokichi Takamine discovered the same hormone in 1901, without knowing about the previous discovery, and called it adrenaline. It was first artificially synthesized in 1904 by Friedrich Stolz.
The actions of epinephrine 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, which activates the adenylate cyclase signaling pathway, which will in turn increase glycogenolysis.
Epinephrine versus adrenaline
Whilst epinephrine is the currently accepted International Non-Proprietary Name (INN) and United States Approved Name (USAN), it is widely known as adrenaline in the rest of the world (outside the United States) which followed the British Approved Name (BAN) as listed in the British Pharmacopoeia.
The monograph name in the European Pharmacopoeia remains adrenaline, despite the adoption of INN names for all other agents, and European Union (EU) countries continue to use either adrenaline or dual-labelling of both names on products. This is because of the confusion that the name epinephrine would cause to patients in EU countries, and resistance to the perceived Americanisation of drug names.
The basis for the name epinephrine in the United States was out of necessity - the name adrenalin (without a final "e") was registered as a trademark by Parke, Davis & Co. In other countries where this trademark was not registered, the name adrenaline was adopted at the insistence of the British pharmacologist Henry Hallett Dale. Resistance to the adoption of epinephrine has even resulted in some dispute as to the validity of the name (Aronson, 2000).
- Aronson JK (2000). "Where name and image meet (http://bmj.bmjjournals.com/cgi/content/full/320/7233/506)" - the argument for "adrenaline". British Medical Journal 320, 506-9.