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
Which of the following substance causes retrograde contraction during gut peristalsis? 
Select and explain. 
A. NO, B. Vasoactive Intestinal peptide, C. Substance P, D. None of the above
C: Substance P
Answer: C: Substance P 
Explanation: Retrograde contraction by
Anterograde relaxation by



Acetycholine
Substance P
Serotonin


NO
Vasoactive Intestinal Peptide