Which muscarinic receptor subtype predominantly mediates the relaxation of the detrusor muscle of the urinary bladder, making it the target of drugs used in overactive bladder?

• A M1 (neural)
• B M2 (cardiac/smooth muscle)
• C M4 (CNS)
• D M3 (exocrine glands/smooth muscle) ✓

Explanation

M3 receptors mediate detrusor contraction through Gq-coupled phospholipase C activation, so selective M3 antagonists such as solifenacin and darifenacin are used for overactive bladder. Although M2 receptors are numerically predominant on detrusor smooth muscle (~80%), they serve a modulatory role rather than directly causing contraction. M1 receptors are mainly neural and M4 is primarily a CNS subtype.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.