This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
cAMP is the exclusive second messenger for all the following except 
Select and explain. 
A. Coicotrophin, B. Dopamine, C. Glucagon, D. Vasopressin
D: Vasopressin
Answer: D: Vasopressin 
Explanation: cAMP is the second messenger for dopamine, coicotrophin and glucagon. Vasopressin (ADH) acts on atleast 3 kinds of receptors: V-1A, V-1B, V2. All the 3 are G-protein coupled receptors. V-1A and V-1B receptors (Gq) act through IP3 as a second messenger, to increase the intracellular calcium concentration. V2 receptors (Gs) use cAMP as a second messenger. Dopamine has 5 receptors (D1, D2, D3, D4, D5) All use cAMP as second messengers. D1, D5 act by increasing cAMP. D2, D3, D4 act by decreasing cAMP. Coicotrophin (ACTH) and glucagon use cAMP as a second messenger. Ref: Ganong's Medical physiology 26th edition PGno: 685