All of the following are actions of muscarinic antogonists, except :
💡 Explanation
## **Core Concept**
Muscarinic antagonists, also known as antimuscarinics or anticholinergics, are drugs that block the action of acetylcholine at muscarinic receptors. These receptors are part of the parasympathetic nervous system and are involved in various physiological functions such as smooth muscle contraction, heart rate reduction, and glandular secretion.
## **Why the Correct Answer is Right**
The correct answer, , is an action that is not typically associated with muscarinic antagonists. Muscarinic antagonists generally cause effects that are opposite to those of muscarinic agonists, including relaxation of smooth muscles, increase in heart rate, and reduction in glandular secretions.
## **Why Each Wrong Option is Incorrect**
* **Option A:** - This is an action of muscarinic antagonists. They can cause mydriasis (pupil dilation) by blocking the muscarinic receptors in the eye that are responsible for pupil constriction.
* **Option B:** - This is an action of muscarinic antagonists. They can decrease salivation and other glandular secretions by blocking muscarinic receptors in the glands.
* **Option D:** - This is an action of muscarinic antagonists. They can increase heart rate (tachycardia) by blocking the muscarinic receptors in the heart that slow down the heart rate when stimulated.
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that muscarinic antagonists can cause significant side effects, including dry mouth, blurred vision, constipation, urinary retention, and confusion, especially in the elderly. These side effects are due to their blockade of muscarinic receptors in various parts of the body.