This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Physiology
Tone of LES is maintained by 
Select and explain. 
A. Acetyl choline, B. Dopamine, C. Serotonine, D. VIP
A: Acetyl choline
Answer: A: Acetyl choline 
Explanation: Acetylcholine and tachykinins are involved in the LOS contraction acting through acetylcholine M3 and tachykinin NK2 receptors. Nitric oxide can also be involved in the regulation of LOS contraction. Ref: guyton and hall textbook of medical physiology 12 edition page number:443,444,445