Nóradrenalín

Nóradrenalín, also known as noradrenaline or norepinephrine, is a catecholamine neurotransmitter and hormone of the sympathetic nervous system. It is synthesized from dopamine by dopamine β-hydroxylase in sympathetic neurons and in the adrenal medulla, stored in vesicles, and released during sympathetic activation. Peripherally it acts as a circulating hormone and as a local neurotransmitter at sympathetic nerve endings.

Nóradrenalín exerts its effects by binding to adrenergic receptors, with high affinity for α1 and α2 receptors and significant activity at β1 receptors, while its activity at β2 receptors is comparatively limited. The dominant consequence is increased vascular tone through vasoconstriction (primarily via α1), which raises mean arterial pressure. β1 activation increases heart rate and myocardial contractility, contributing to changes in cardiac output. The net effect is a rise in blood pressure with variable effects on heart rate due to reflex responses.

Physiologically, nóradrenalín is crucial for maintaining blood pressure and regional blood flow during stress. In the central nervous system, it modulates arousal, attention, and the stress response, while peripherally it supports sympathetic cardiovascular function.

Clinical use is primarily as a vasopressor in acute hypotension and septic shock. It is administered intravenously as a continuous infusion and is not effective when given orally. Because it strongly vasoconstricts, extravasation can cause tissue necrosis; careful administration and monitoring are required. It is rapidly metabolized by monoamine oxidase and catechol-O-methyltransferase, with a short plasma half-life, and is taken back up into neurons by the norepinephrine transporter.

Adverse effects include hypertension, tachyarrhythmias, and potential myocardial ischemia, especially in patients with cardiovascular disease.