norepinefriini

Norepinefriini, also known as norepinephrine or noradrenaline, is a catecholamine that functions as a neurotransmitter in the central and peripheral nervous systems and as a circulating hormone in the bloodstream. It is the principal neurotransmitter of the sympathetic nervous system and contributes to the body’s “fight-or-flight” response. Its chemical identity is C8H11NO3, and its IUPAC name is 4-(2-aminoethyl)benzene-1,2-diol.

Norepinefriini is synthesized from the amino acid tyrosine through a pathway that includes tyrosine hydroxylase, DOPA decarboxylase, and dopamine beta-hydroxylase, primarily in sympathetic neurons and the adrenal medulla. After synthesis, it is stored in synaptic vesicles and released in response to action potentials. In the adrenal medulla, it is released into the bloodstream as a hormone alongside epinephrine.

Released norepinefriini acts on adrenergic receptors, especially alpha-1 and beta-1 receptors. Activation increases vascular tone and blood pressure, raises heart rate and myocardial contractility, and can influence pupil dilation and bronchodilation. In the central nervous system, it modulates attention, arousal, mood, and the response to stress. Its effects are modulated by the local receptor distribution and by interactions with other neurotransmitter systems.

After release, norepinefriini is cleared from the synapse by reuptake into neurons via the norepinephrine transporter or metabolized by enzymes such as monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT). Metabolites including normetanephrine, metanephrine, and vanillylmandelic acid can be measured in plasma or urine for diagnostic purposes in certain disorders.

Clinically, norepinefriini is used as a vasopressor to treat acute hypotension, including septic shock, by rapidly increasing vascular tone. It is distinct from epinephrine in its receptor activity profile and is not typically employed as a long-term antidepressant agent; instead, noradrenergic signaling is targeted by various antidepressants and related drugs.