A 70-year-old woman develops urinary retention after abdominal surgery. Bethanecol is prescribed to stimulate bladder emptying. Its selective action on the detrusor muscle is mediated through which receptor subtype?

• A Muscarinic M1
• B Muscarinic M3 ✓
• C Muscarinic M2
• D Nicotinic neuronal (Nn)

Explanation

Bethanecol stimulates muscarinic receptors on the detrusor muscle of the bladder, causing contraction and urine voiding. The muscarinic receptor subtype predominantly mediating smooth muscle contraction (including bladder, gut, and exocrine glands) is M3, which signals through Gq and phospholipase B. M2 receptors are also present in the bladder but primarily mediate direct inhibition of relaxation. M1 receptors are mainly in ganglia and gastric parietal cells.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.