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Noradrenaline Receptors — FRCA Primary MCQ

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HardPharmacology - CardiovascularNoradrenaline ReceptorsFRCA Primary

A noradrenaline infusion is started in an anaesthetised patient with vasodilatory hypotension. Blood pressure rises promptly but heart rate falls slightly. Which receptor-level explanation is best?

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Correct answer: E — Alpha-mediated vasoconstriction triggers baroreflex vagal slowing despite beta1 activity

The best answer is “Alpha-mediated vasoconstriction triggers baroreflex vagal slowing despite beta1 activity”. Noradrenaline has potent alpha activity with beta1 activity. Its alpha-mediated rise in arterial pressure activates baroreceptors, increasing vagal tone and potentially producing reflex bradycardia that outweighs direct beta1 chronotropy. It has little clinically useful beta2 vasodilation, is not a muscarinic agonist and does not lower sympathetic outflow by alpha2 blockade.

Reference: RCoA, Primary FRCA syllabus: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf; Cardiovascular Anatomy and Pharmacology: https://pmc.ncbi.nlm.nih.gov/articles/PMC7121118/