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 the following mediate their action using cAMP as second messenger except: 
Select and explain. 
A. Coicotropin, B. Dopamine, C. Glucagon, D. Vasopressin
D: Vasopressin
Answer: D: Vasopressin 
Explanation: D i.e. Vasopressin