A 72-year-old man with BPH is prescribed tamsulosin for urinary outflow obstruction. Tamsulosin's selectivity for alpha-1A receptors (over alpha-1B) explains why it causes less orthostatic hypotension. Where are alpha-1A receptors predominantly located?
- A Vascular smooth muscle of systemic arteries (predominant vascular receptor subtype)
- B Urethral sphincter and prostate smooth muscle ✓
- C Cardiac pacemaker cells regulating heart rate
- D Renal juxtaglomerular cells controlling renin secretion
Explanation
Alpha-1A receptors are predominantly expressed in prostate smooth muscle and the internal urethral sphincter. Blocking alpha-1A reduces prostate/sphincter tone, improving urinary flow in BPH. Alpha-1B receptors are predominant in vascular smooth muscle of systemic arteries; non-selective alpha-1 blockers (e.g., prazosin, doxazosin) block both subtypes, causing significant vascular dilation and orthostatic hypotension. Tamsulosin's alpha-1A selectivity spares vascular alpha-1B to a greater degree, minimising postural hypotension. Cardiac rate regulation involves beta-1 receptors; renin secretion is controlled by beta-1 receptors on juxtaglomerular cells.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.