All of the following are actions of muscarinic antagonist except
**Core Concept**
Muscarinic antagonists, also known as antimuscarinics, are a class of medications that block the action of acetylcholine at muscarinic receptors in the central and peripheral nervous system. This leads to a decrease in parasympathetic activity, resulting in various physiological effects.
**Why the Correct Answer is Right**
Muscarinic antagonists are used to treat various conditions, including bradycardia, gastrointestinal disorders, and respiratory diseases. They work by blocking the action of acetylcholine at muscarinic receptors, which leads to an increase in heart rate, reduction in gastrointestinal motility, and dilation of the pupils. The mechanism of action involves the inhibition of muscarinic receptors, specifically M1, M2, M3, M4, and M5 subtypes.
**Why Each Wrong Option is Incorrect**
**Option A:**
This option is incorrect because muscarinic antagonists can indeed decrease salivation and perspiration, as they block the action of acetylcholine at muscarinic receptors in the salivary and sweat glands.
**Option B:**
This option is incorrect because muscarinic antagonists can increase heart rate, as they block the action of acetylcholine at muscarinic receptors in the sinoatrial node, leading to an increase in sympathetic tone.
**Option C:**
This option is incorrect because muscarinic antagonists can indeed reduce gastrointestinal motility, as they block the action of acetylcholine at muscarinic receptors in the gastrointestinal tract, leading to a decrease in peristalsis.
**Clinical Pearl / High-Yield Fact**
One important clinical consideration when using muscarinic antagonists is the potential for anticholinergic side effects, such as dry mouth, blurred vision, and constipation. These side effects can be minimized by selecting the appropriate muscarinic receptor subtype to target.
**Correct Answer:** A.