Norepinefryna

Norepinefryna, also known as norepinephrine or noradrenaline, is a catecholamine that functions as both a neurotransmitter in the central and peripheral nervous systems and a hormone released by the adrenal medulla. In humans, it is produced primarily by sympathetic neurons and, to a lesser extent, by the adrenal medulla, and it plays a key role in the body's fight-or-flight response.

Biosynthesis and storage occur from the amino acid tyrosine through the intermediates DOPA and dopamine, with dopamine beta-hydroxylase converting dopamine to norepinephrine. It is stored in synaptic vesicles and released into the synaptic cleft in response to nerve impulses. After release, norepinephrine binds to adrenergic receptors, predominantly alpha-1, alpha-2, and beta-1 receptors, producing a range of physiological effects.

Physiologically, norepinephrine increases peripheral vascular resistance and blood pressure through vasoconstriction, while beta-1 receptor activation enhances cardiac contractility and, to a lesser extent, heart rate. Its central actions, especially within the locus coeruleus, influence arousal, attention, and stress responses. Metabolic effects include glycogenolysis and lipolysis in response to acute stress.

In clinical practice, norepinephrine is used as a vasopressor to treat life-threatening hypotension and septic shock. It is typically administered intravenously and requires careful monitoring due to risks such as tissue necrosis from extravasation and potential cardiovascular side effects. Its activity is largely terminated by reuptake via the norepinephrine transporter and by enzymatic breakdown through monoamine oxidase and catechol-O-methyltransferase, producing metanephrines that can be measured in plasma or urine for diagnostic purposes.