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: Physiology
All of the following use c-AMP as a second messenger except: 
Select and explain. 
A. Corticotropin, B. Dopamine, C. Glucagon, D. Vasopressin
D: Vasopressin
Answer: D: Vasopressin 
Explanation: Vasopressin receptor  V1 and V3 acts via IP3/calcium pathway. V2 acts via cAMP.