REVIEW Metoclopramide inhibits gastric smooth muscle relaxation produced by dopamine, therefore increasing cholinergic response of the gastrointestinal smooth muscle. It accelerates intestinal transit and gastric emptying by preventing relaxation of gastric body and increasing the phasic activity of antrum. Simultaneously, this action is accompanied by relaxation of the upper small intestine, resulting in an improved coordination between the body and antrum of the stomach and the upper small intestine. Metoclopramide also decreases reflux into the esophagus by increasing the resting pressure of the lower esophageal sphincter and improves acid clearance from the esophagus by increasing amplitude of esophageal peristaltic contractions. Metoclopramide''s dopamine antagonist action raises the threshold of activity in the chemoreceptor trigger zone and decreases the input from afferent visceral nerves. Studies have also shown that high doses of metoclopramide can antagonize 5-hydroxytryptamine (5-HT) receptors in the peripheral nervous system in animals.
REFERENCES
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Justin-Besancon L, Laville C: [Antiemetic action of metoclopramide with respect to apomorphine and hydergine.] C R Seances Soc Biol Fil. 1964;158:723-7.
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Tonini M, Candura SM, Messori E, Rizzi CA: Therapeutic potential of drugs with mixed 5-HT4 agonist/5-HT3 antagonist action in the control of emesis. Pharmacol Res. 1995 May;31(5):257-60.
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