Epinephrine

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Epinephrine (also adrenaline, epi in medical jargon) is a hormone and acts as 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 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 causes many diverse occurrences by binding to multiple receptors in the body. It acts to increase heart rate and strength of contractions, dilate the pupils and constriction of blood flow restricts blood flow in arterioles in the skin and gut. Vessels dialate in the arterioles of the leg muscle. It breaks down glycogen and synthesizes glucose in the liver cells for energy, and at the same time, begins the breakdown of lipids in fat cells. It also elevates the blood sugar level (by increased hydrolysis of glycogen to glucose), and redistribute blood flow away from the skin and inner organs.

Epinephrine is used as a drug in order to stimulate cardiac action in cardiac arrest, 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 C₉H₁₃N O₃. 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.

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Epinephrine binds to the beta-adrenergic receptors of the liver and muscle cells, which activates the adenylate cyclase signaling pathway, which will in turn increase glycogen breakdown.

It also binds to alpha-1 receptors of liver cells, which activate inositol-phospholipid signaling pathway, signaling the phosphorylation of insulin, leading to reduced ability of insulin to bind to bodily receptors.

Epinephrine

See also