A 35-year-old woman with angle-closure glaucoma is started on a cholinergic drug to lower intraocular pressure. Which receptor subtype mediates the contraction of the ciliary muscle leading to increased aqueous outflow through the trabecular meshwork?
- A M3 muscarinic receptor ✓
- B Nicotinic NM receptor
- C Alpha-1 adrenoceptor
- D Beta-2 adrenoceptor
Correct answer: A. M3 muscarinic receptor
Explanation
Pilocarpine and other miotics act on M3 muscarinic receptors in the ciliary muscle, causing its contraction. This pulls the scleral spur posteriorly, widens the trabecular meshwork spaces, and facilitates conventional aqueous outflow, reducing IOP. In angle-closure glaucoma, miosis from M3 stimulation in the iris sphincter also opens the anterior chamber angle. Nicotinic receptors are absent in smooth muscle; alpha-1 and beta-2 adrenoceptors play roles in uveal blood flow and aqueous production respectively, not trabecular outflow via miosis.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.