A patient on a non-selective β-blocker (propranolol) develops bronchospasm. The bronchoconstriction is due to blockade of which receptor subtype and the resulting decrease in which intracellular messenger?
- A β2 receptors; decrease in cAMP ✓
- B β1 receptors; decrease in cAMP
- C β2 receptors; decrease in cGMP
- D α1 receptors; decrease in IP3
Correct answer: A. β2 receptors; decrease in cAMP
Explanation
Bronchial smooth muscle expresses β2-adrenoceptors coupled to Gs; activation raises cAMP and causes bronchodilation. Propranolol's blockade of β2 receptors removes this bronchodilator tone, precipitating bronchoconstriction in susceptible individuals. The decrease in cAMP — not cGMP — is the key second-messenger change. This is why cardioselective β1-blockers (metoprolol, atenolol) are preferred in asthmatic patients.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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