This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anti-Emetic, Subject name: Pharmacology
Antiemetic effect of metoclopramide is mainly due to its action as: 
Select and explain. 
A. 5HT3 antagonist, B. D2 antagonist, C. M3 antagonist, D. 5HT4 agonist
B: D2 antagonist
Answer: B: D2 antagonist 
Explanation: Ans. (B) D2 antagonist(Ref: Katzung 13th/1070, KDT 8th/e p713)Metoclopramide has action on several receptors.Main action as anti-emetic is because of D2 receptor antagonism.Main action as prokinetic is because of 5HT4 agonism.Mechanism of actions of metoclopramideReceptorActionClinical effectD2AntagonismAnti-emetic5HT3AntagonismAnti-emeticProkinetic5HT4AgonismProkinetic