Which one of the following drugs increases gastrointestinal motility?
**Core Concept**
The question is testing the student's knowledge of drugs that affect gastrointestinal motility. Gastrointestinal motility refers to the movement of food, fluid, and gas through the digestive system. Certain drugs can either stimulate or inhibit this process.
**Why the Correct Answer is Right**
The correct answer is a drug that stimulates acetylcholine release, which in turn activates muscarinic receptors in the gastrointestinal tract. This activation increases the contraction of smooth muscles in the gastrointestinal tract, leading to increased motility. The drug works by inhibiting the reuptake of acetylcholine, thereby increasing its concentration and stimulating muscarinic receptors.
**Option A:** Metoclopramide is incorrect because it is a dopamine antagonist that also blocks serotonin 5-HT4 receptors, which actually decreases gastrointestinal motility.
**Option B:** Ondansetron is incorrect because it is a serotonin 5-HT3 receptor antagonist that also decreases gastrointestinal motility.
**Option C:** Chlorpropamide is incorrect because it is an oral antidiabetic drug that does not have a significant effect on gastrointestinal motility.
**Clinical Pearl / High-Yield Fact**
The mnemonic "4 D's" can help remember the drugs that decrease gastrointestinal motility: Dopamine antagonists (e.g., metoclopramide), Dopamine agonists (e.g., apomorphine), Drugs that increase serotonin levels (e.g., ondansetron), and Drugs that block serotonin receptors (e.g., chlorpropamide).
**Correct Answer:** C. Domperidone.