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(nôr'ĕpīnĕf`rən), a neurotransmitterneurotransmitter,
chemical that transmits information across the junction (synapse) that separates one nerve cell (neuron) from another nerve cell or a muscle. Neurotransmitters are stored in the nerve cell's bulbous end (axon).
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 in the catecholaminecatecholamine
, any of several compounds occurring naturally in the body that serve as hormones or as neurotransmitters in the sympathetic nervous system. The catecholamines include such compounds as epinephrine, or adrenaline, norepinephrine, and dopamine.
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 family that mediates chemical communication in the sympathetic nervous system, a branch of the autonomic nervous system. Like other neurotransmitters, it is released at synaptic nerve endings to transmit the signal from a nerve cell to other cells. Norepinephrine is almost identical in structure to epinephrineepinephrine
, hormone important to the body's metabolism, also known as adrenaline. Epinephrine, a catecholamine, together with norepinephrine, is secreted principally by the medulla of the adrenal gland.
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, which is released into the bloodstream from the adrenal medulla under sympathetic activation. The sympathetic nervous system functions in response to short-term stress; hence norepinephrine and epinephrine increase the heart rate as well as blood pressure. Other actions of norepinephrine include increased glycogenolysis (the conversion of glycogenglycogen
, starchlike polysaccharide (see carbohydrate) that is found in the liver and muscles of humans and the higher animals and in the cells of the lower animals. Chemically it is a highly branched condensation polymer of glucose; it is readily hydrolyzed to glucose.
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 to glucoseglucose,
or grape sugar,
monosaccharide sugar with the empirical formula C6H12O6 . This carbohydrate occurs in the sap of most plants and in the juice of grapes and other fruits.
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) in the liver, increased lipolysis (the conversion of fats to fatty acids; see fats and oilsfats and oils,
group of organic substances that form an important part of the diet and also are useful in many industries. The fats are usually solid, the oils generally liquid at ordinary room temperatures.
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) in adipose (fat) tissue, and relaxation of bronchial smooth muscle to open up the air passages to the lungs. All of these actions represent a mobilization of the body's resources in order to meet the stressful challenge—such a response is often termed the "flight or fight" syndrome.



(also noradrenaline, arterenol, 3,4-dihydroxyphenylethanolamine), a biologically active catecholamine. Norepinephrine has the following structure:

In animals and man, norepinephrine is in part produced by the chromaffin cells of the adrenal medulla, but it is mostly secreted by the adrenergic nerve elements of the sympathetic nervous system, where it serves as a chemical transmitter, or mediator substance, in nerve excitation. Judging by its action on the heart, blood vessels, smooth muscles, and carbohydrate metabolism, norepinephrine possesses the properties of hormones and is similar to its N-methyl derivative—adrenaline. The level of norepinephrine in the blood, organs, and excretions of the body is an indicator of the tone and reactivity of the sympathetic nervous system.

Norepinephrine can be produced synthetically. It is used in medicine to treat such conditions as low blood pressure, collapse, shock, and hemorrhage.


C8H11O3N A hormone produced by chromaffin cells of the adrenal medulla; acts as a vasoconstrictor and mediates transmission of sympathetic nerve impulses. Also known as noradrenaline.