noradrenalinu

Noradrenalinu, also called noradrenaline or norepinephrine, is a catecholamine that functions as a neurotransmitter in the central and peripheral nervous systems and as a hormone released by the adrenal medulla. It is a key component of the body's response to stress and contributes to the regulation of cardiovascular function and arousal.

Synthesis occurs from the amino acid tyrosine via tyrosine hydroxylase to L-DOPA, then to dopamine, which is converted by dopamine beta-hydroxylase to norepinephrine in synaptic vesicles. In peripheral neurons, NE is stored in vesicles and released into the synaptic cleft on sympathetic nerve activation. It is terminated primarily by reuptake into neurons via the norepinephrine transporter (NET), followed by metabolism by monoamine oxidase and catechol-O-methyltransferase to metanephrine and normetanephrine.

Receptors: NE acts on adrenergic receptors, with strong effects on alpha-1 and beta-1 receptors, inducing vasoconstriction, increased heart rate and contractility, and modulation of attention and arousal. It has comparatively weaker activity at beta-2 receptors. In the central nervous system, the locus coeruleus provides widespread NE innervation influencing wakefulness, mood, and cognitive function.

Clinical and pharmacological aspects: Endogenous NE helps maintain vascular tone and blood pressure. Pharmacologically, norepinephrine is used as a vasopressor in acute hypotension and septic shock, given by IV infusion. Adverse effects include hypertension, arrhythmias, and tissue necrosis if extravasation occurs. Its metabolism and the measurement of metabolites such as metanephrines are used in diagnostic testing for pheochromocytoma.