norepinefryny

Norepinephrine, also known as noradrenaline, is a catecholamine that acts as both a neurotransmitter in the central nervous system and a hormone in the peripheral nervous system. It is produced from dopamine by the enzyme dopamine beta-hydroxylase, stored in secretory vesicles, and released upon sympathetic nerve activation or adrenal medulla stimulation. In the bloodstream it functions as a circulating hormone that helps regulate vascular tone and blood pressure.

Norepinephrine acts primarily on adrenergic receptors, including alpha1, alpha2, beta1, and beta2 subtypes. Through alpha1 receptors it produces vasoconstriction, increasing peripheral vascular resistance and blood pressure. Beta1 receptor activation increases heart rate and myocardial contractility, while beta2 effects are comparatively modest with respect to norepinephrine. The net cardiovascular response is influenced by receptor distribution and reflex mechanisms such as baroreceptor activity.

In the brain, norepinephrine is released from neurons in regions like the locus coeruleus and modulates arousal, attention, mood, and the stress response. Although it does not cross the blood-brain barrier easily, its central actions are significant for cognitive function and emotional regulation.

Clinically, norepinephrine is used as a vasopressor to treat hypotension and shock, especially septic shock, due to its potent vasoconstrictive effects. It is typically given intravenously and requires careful monitoring because extravasation can cause tissue necrosis. It is metabolized by monoamine oxidase and catechol-O-methyltransferase and is taken back up into neurons via the norepinephrine transporter.