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
Relaxation of mesangial cells of kidney is brought about by ? 
Select and explain. 
A. cAMP, B. Endothelin, C. PGF2, D. Vasopressin
A: cAMP
Answer: A: cAMP 
Explanation: A i.e. C-Amp