INI-CET 2014 — Pharmacology

Q: Methacholine acts primarily at which receptor?

M3. ***M3*** - **Methacholine** is a non-selective muscarinic agonist that acts at all muscarinic receptors, but its **primary clinically relevant effects**, particularly in the airways (e.g., bronchoconstriction in asthma challenge tests), are mediated through **M3 receptors**. - **M3 receptors** are Gq-coupled and lead to **smooth muscle contraction**, glandular secretion, and vasodilation via nitric oxide release. *M1* - **M1 receptors** are primarily found in the central nervous system and autonomic ganglia, playing a role in **neuronal excitation** and **autonomic transmission**. - While methacholine can activate M1 receptors, this is not its predominant site of action for clinical uses. *M2* - **M2 receptors** are found in the heart and are Gi-coupled, leading to a **decrease in heart rate** and contractility. - While methacholine acts on M2 receptors, its most notable effects (like bronchoconstriction) are not primarily mediated through M2. *M4* - **M4 receptors** are primarily located in the central nervous system, where they modulate neurotransmitter release and contribute to **motor control** and cognition. - Methacholine has some affinity for M4, but it is not the primary receptor responsible for its clinically relevant effects. [Practice more Pharmacology PYQs on OnCourse]

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Methacholine acts primarily at which receptor?

Q2Easy

Which of the following conditions is NOT treated with a cholinomimetic agent?