Adrenaline in Local Anaesthesia — MFDS Part 1 MCQ

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ModeratePharmacologyAdrenaline in Local AnaesthesiaMFDS Part 1

In a dental local anaesthetic solution, adrenaline is added to cause local vasoconstriction and reduce absorption of the local anaesthetic from the injection site. Which receptor principally mediates this intended local vascular effect?

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Correct answer: E — Alpha-1 adrenergic receptors

Adrenaline's intended effect in a local anaesthetic solution is vasoconstriction, principally mediated by alpha-1 adrenergic receptors on vascular smooth muscle. Reduced local blood flow slows removal of the anaesthetic from the injection site, prolongs anaesthesia and improves haemostasis. Adrenaline is not alpha-1 selective and also stimulates other adrenoceptors. Alpha-2 receptors can contribute to vascular regulation but are not the principal mediator tested here. Beta-1 stimulation increases cardiac rate and contractility, whereas beta-2 stimulation produces bronchodilation and can cause vasodilation in some vascular beds. Muscarinic M3 receptors are cholinergic rather than adrenergic receptors.

Reference: Electronic Medicines Compendium. Adrenaline (Epinephrine) Injection BP 1 in 1000, SmPC, section 5.1 Pharmacodynamic properties. Updated 23 June 2026. https://www.medicines.org.uk/emc/product/6284/smpc