This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Vasopressin antagonist acts on which pa of the nephron? 
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: Answer- D (Medullary collecting duct)'The mechanism by which vasopressin exes its anti-diuretic effect is activated by V2 receptors and involves the inseion of aquaporin-2 into the apical (luminal) membranes at the principle cells of the collecting duct.'