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
Mechanism of action of Nitric oxide is through 
Select and explain. 
A. cGMP, B. cAMP, C. Ca++, D. Tyrosine
A: cGMP
Answer: A: cGMP 
Explanation: Nitric oxide is formed from Arginine, released from endothelial cells and acts through cGMP to cause vasodilation.