Norepinephrine


Norepinephrine (INN) or noradrenaline (BAN) is a catecholamine and a phenethylamine with chemical formula C<sub>8</sub>H<sub>11</sub>NO<sub>3</sub>. The natural stereoisomer is <small>L</small>-(−)-(R)-norepinephrine. The prefix "nor" stands for the German abbreviation "Nitrogenium Ohne Rest" meaning "Nitrogen without rest" referring to the absence of a methyl group at the N-atom present in epinephrine/adrenaline. It is released from the 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.