A 65-year-old man on prazosin for BPH develops postural hypotension. The mechanism is best explained by blockade of which receptor subtype at vascular smooth muscle?
- A Alpha-2 adrenoceptors
- B Alpha-1 adrenoceptors ✓
- C Beta-1 adrenoceptors
- D Beta-2 adrenoceptors
Correct answer: B. Alpha-1 adrenoceptors
Explanation
Prazosin is a selective alpha-1 adrenoceptor antagonist. Alpha-1 receptors on arteriolar and venous smooth muscle mediate norepinephrine-induced vasoconstriction. Blockade dilates both arterioles and veins, reducing preload and afterload, causing postural hypotension especially after the first dose. Alpha-2 blockade would increase norepinephrine release; beta blockade affects heart rate and contractility rather than peripheral resistance.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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