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Pharmacology · single question

What is the mechanism of action of acetylcholine in asthma?

  1. Inhibits COX-2 to reduce airway inflammation
  2. Blocks histamine H1 receptors
  3. Beta-2 receptor agonist causing bronchodilation
  4. Binds muscarinic receptors causing bronchoconstriction and increased mucus secretion
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Correct answer: D. Binds muscarinic receptors causing bronchoconstriction and increased mucus secretion

  • A. COX-2 inhibition is the mechanism of selective NSAIDs — not acetylcholine.
  • B. H1 receptor blockade is the mechanism of antihistamines — not acetylcholine.
  • C. Beta-2 agonist activity is the mechanism of bronchodilators like albuterol — not acetylcholine.
  • D. Correct. Acetylcholine (the parasympathetic neurotransmitter) binds MUSCARINIC receptors (M3) in airway smooth muscle, causing: (1) BRONCHOCONSTRICTION (smooth muscle contraction); (2) INCREASED MUCUS SECRETION. In asthma, excessive cholinergic activity contributes to airway obstruction. Anticholinergic drugs (ipratropium/tiotropium) are used to counteract this. Albuterol (beta-2 agonist) opposes this effect.

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