Beta-2 Agonist Bronchodilation — FRCA Primary MCQ
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Correct answer: B — Beta-2 adrenergic
Explanation lettering: D = shown as A · C = shown as B · E = shown as C · B = shown as D · A = shown as E
C is correct. Salbutamol is a selective beta-2 adrenoceptor agonist. Beta-2 receptor activation in bronchial smooth muscle is coupled through Gs proteins to adenylyl cyclase, increasing intracellular cyclic AMP and promoting smooth-muscle relaxation and bronchodilation. Beta-1 receptors principally mediate cardiac chronotropic and inotropic effects and may be stimulated less selectively at higher salbutamol doses. Alpha-1 receptor activation causes smooth-muscle contraction and vasoconstriction, while alpha-2 receptors mainly reduce presynaptic noradrenaline release. Airway M3 receptor activation promotes bronchoconstriction and secretion; muscarinic antagonists such as ipratropium produce bronchodilation by blocking this pathway. Beta-2 stimulation also accounts for adverse effects including tremor, peripheral vasodilatation and hypokalaemia.
Reference: Orion Pharma (UK) Limited. Easyhaler Salbutamol 100mcg, Summary of Product Characteristics, section 5.1 Pharmacodynamic properties, revised October 2025. https://www.medicines.org.uk/emc/product/6339/smpc