Use of atropine in pre-anaesthetic medication has all of the following effects except: March 2012
**Core Concept**
The use of **atropine** in pre-anaesthetic medication is based on its **anticholinergic** properties, which help in reducing respiratory and gastrointestinal secretions. Atropine works by blocking the action of **acetylcholine** at **muscarinic receptors**. This leads to various effects on the body, including decreased salivation, reduced bronchial secretions, and increased heart rate.
**Why the Correct Answer is Right**
Atropine's primary mechanism of action is through the competitive inhibition of **muscarinic acetylcholine receptors**, which are involved in the parasympathetic nervous system. By blocking these receptors, atropine increases the heart rate (**tachycardia**) and reduces the secretion of saliva, sweat, and respiratory tract mucus. However, the question asks for an exception among the provided options, which are not listed. Normally, atropine would not be expected to increase respiratory secretions or decrease heart rate.
**Why Each Wrong Option is Incorrect**
**Option A:** Would be incorrect if it stated an increase in respiratory secretions because atropine decreases these secretions.
**Option B:** Might be incorrect if it mentioned a decrease in heart rate, as atropine typically causes tachycardia.
**Option C:** Could be incorrect if it suggested atropine causes an increase in salivation, which is opposite of its anticholinergic effect.
**Option D:** Might be the correct answer if it stated an effect that atropine does not have, such as increasing gastrointestinal motility, which is actually decreased by atropine.
**Clinical Pearl / High-Yield Fact**
Atropine is often used in pre-anaesthetic medication to prevent **bradycardia** and reduce respiratory secretions, making it a crucial drug in anaesthesia. Remember, atropine's anticholinergic effects can also lead to **dry mouth**, **dilated pupils**, and **urinary retention**.
**Correct Answer:** D. Increase in respiratory secretions.