Metoclopramide is a dopamine receptor antagonist and has been approved by the FDA to treat nausea and vomiting in patients with gastroesophageal reflux disease or diabetic gastroparesis by increasing gastric motility.. Metoclopramide works by antagonizing central and peripheral dopamine-two receptors (D2) in the medullary chemoreceptor trigger zone in the area postrema, usually stimulated by levodopa or apomorphine. It achieves this by decreasing the sensitivity of visceral afferent nerves that transmit from the gastrointestinal system to the vomiting center in the area postrema in the chemoreceptor trigger zone. In addition to antagonizing dopamine receptors, metoclopramide is an antagonist at 5HT3 (type 3 serotonin receptors) and an agonist at 5HT4 receptors. Metoclopramide also blocks the antiperistaltic effects of apomorphine, allowing metoclopramide to slow apomorphine's inhibition of gastric emptying, thereby accelerating gastric emptying by increasing the amplitude and duration of esophageal contractions. Consequently, it increases the resting tone of the lower esophageal sphincter while simultaneously relaxing the duodenal bulb and pyloric sphincter, thereby increasing the peristalsis of the duodenum and jejunum.

Metoclopramide - Dopamine Antagonist Pathway References