Which is not an effect of atropine ?
**Core Concept**
Atropine is a non-selective anticholinergic agent that blocks the action of acetylcholine at muscarinic receptors in the central and peripheral nervous system. Its effects are mediated through the inhibition of parasympathetic neurotransmission.
**Why the Correct Answer is Right**
Atropine's anticholinergic effects include:
- **Dry mouth and decreased salivation**: Atropine inhibits the muscarinic receptors in the salivary glands, leading to a decrease in salivation.
- **Pupillary dilation**: Atropine blocks the muscarinic receptors in the iris sphincter muscle, resulting in mydriasis (pupillary dilation).
- **Tachycardia**: Atropine inhibits the vagal tone on the heart, leading to an increase in heart rate.
- **Urinary retention**: Atropine blocks the muscarinic receptors in the bladder, leading to a decrease in bladder contractility and urinary retention.
**Why Each Wrong Option is Incorrect**
* **Option A:** Atropine does indeed cause **mydriasis** (pupillary dilation), so this option is incorrect.
* **Option B:** Atropine is known to cause **tachycardia** due to its inhibition of vagal tone on the heart, making this option incorrect.
* **Option C:** Atropine causes **urinary retention** by blocking the muscarinic receptors in the bladder, making this option incorrect.
**Clinical Pearl / High-Yield Fact**
Atropine is often used to treat bradyarrhythmias and as a preanesthetic medication to reduce salivation and bronchial secretions. However, it should be used with caution in patients with glaucoma, as it can worsen intraocular pressure.
**Correct Answer: D.**