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
The site of action of vasopressin antagonist in kidney 
Select and explain. 
A. Medullary Collecting duct, B. Coical collecting duct, C. Proximal convoluted tubule, D. Distal convoluted tubule
A: Medullary Collecting duct
Answer: A: Medullary Collecting duct 
Explanation: 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