Definition of Norepinephrine

Norepinephrine (INN)(abbr. norepi or NE) or noradrenaline (BAN) is a catecholamine and a phenethylamine with chemical formula C₈H₁₁NO₃. The natural stereoisomer is L-(−)-(R)-norepinephrine. The prefix nor-, short for "normal," might also now be a mnemonic device for the German abbreviation "N (symbol for nitrogen) ohne Radikalen," meaning "Nitrogen without remainder," referring to the absence of a methyl group at the N-atom present in epinephrine/adrenaline. It is released from the adrenal medulla of the adrenal glands as a hormone into the blood, but it is also a neurotransmitter in the central nervous system and sympathetic nervous system where it is released from noradrenergic neurons during synaptic transmission. As a stress hormone, it affects parts of the human brain where attention and responding actions are controlled. Along with epinephrine, norepinephrine underlies the fight-or-flight response, directly increasing heart rate, triggering the release of glucose from energy stores, and increasing skeletal muscle readiness.