This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Pharmacology
Vasopressin antagonist acts on 
Select and explain. 
A. Proximal convoluted tubule, B. Distal convoluted tubule, C. Coical collecting tubule, D. Medullary collecting duct
D: Medullary collecting duct
Answer: D: Medullary collecting duct 
Explanation: Vaspression receptors(V2) are present on principal cells of inner medullary collecting tubule. The antagonist like Conivaptan and Tolvaptan may be used in conditions like SIADH and CHF.