Norepinephrine

Norepinephrine is a hormone that regulates blood pressure]] by causing blood vessels to narrow and the heart to beat faster when blood pressure]] drops.

Norepinephrine (also known as noradrenaline) is a naturally occurring catecholamine neurotransmitter and hormone that plays a crucial role in the regulation of various physiological processes, such as the fight-or-flight response, attention, and blood pressure regulation. It is also used as a medication to treat hypotensive emergencies and septic shock.

Biosynthesis and function

Norepinephrine is synthesized from the amino acid tyrosine in a series of enzymatic steps, which involve the conversion of tyrosine to L-DOPA by tyrosine hydroxylase, followed by the conversion of L-DOPA to dopamine by DOPA decarboxylase, and finally, the conversion of dopamine to norepinephrine by dopamine β-hydroxylase.

Norepinephrine acts as both a neurotransmitter and a hormone. As a neurotransmitter, it is involved in regulating attention, alertness, and arousal. As a hormone, it is released by the adrenal medulla and contributes to the fight-or-flight response, increasing heart rate, blood pressure, and blood flow to muscles.

Pharmacology and clinical uses

As a medication, norepinephrine is primarily used as a potent vasoconstrictor to treat hypotensive emergencies and septic shock. It acts on α₁-adrenergic receptors, causing constriction of blood vessels, which increases blood pressure and improves tissue perfusion. Norepinephrine also has β₁-adrenergic receptor agonist activity, which can result in an increased heart rate and contractility.

Side effects

Norepinephrine can cause a range of side effects, including:

• Increased heart rate (tachycardia)
• Irregular heartbeats (arrhythmias)
• High blood pressure (hypertension)
• Anxiety and restlessness
• Headache
• Nausea and vomiting
• Sweating
• Shortness of breath

More severe side effects may include:

• Chest pain (angina)
• Heart attack (myocardial infarction)
• Stroke
• Tissue damage at the injection site (extravasation)

Healthcare professionals should closely monitor patients receiving norepinephrine to minimize the risk of adverse effects.

Contraindications

Norepinephrine should not be used in patients with a known hypersensitivity to norepinephrine or any of its components. It is also contraindicated in patients with uncontrolled hypertension, pheochromocytoma, or certain types of cardiac arrhythmias. Caution should be exercised when using norepinephrine in patients with coronary artery disease, peripheral vascular disease, or hyperthyroidism.

Drug interactions

Norepinephrine may interact with other medications, including:

• Monoamine oxidase inhibitors (MAOIs), which can potentiate the effects of norepinephrine and lead to hypertensive crises
• Tricyclic antidepressants, which may also potentiate the effects of norepinephrine
• α- and β-adrenergic antagonists, which may counteract the effects of norepinephrine
• Ergot alkaloids, which may increase the risk of peripheral ischemia when used concurrently with norepinephrine

See also

• Epinephrine
• Catecholamine
• Adrenergic receptor
• Neurotransmitter

References

• Dailymed label info on Norepinephrine
• FDA Norepinephrine

Norepinephrine Resources
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