This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidney, Subject name: Pharmacology
[{'content': 'The site of action of vasopressin antagonist in kidney \nSelect and explain. \nA. Medullary Collecting duct, B. Coical collecting duct, C. Proximal convoluted tubule, D. Distal convoluted tubule', 'role': 'user'}, {'content': 'Answer: A \nExplanation: V2 receptors are located on medullary collecting ducts. drugs acting on V2 receptor antagonists are vaptans like convivaptan and tolvaptan Ref: Goodman Gillman 12th ed pg 707', 'role': 'assistant'}]