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
Which of the following is involved in peristalsis by causing relaxation 
Select and explain. 
A. Acetyl choline, B. Substance P, C. Noradrenaline, D. Vasoactive Intestinal Polypeptide
D: Vasoactive Intestinal Polypeptide
Answer: D: Vasoactive Intestinal Polypeptide 
Explanation: The release of NO and VIP (Vasoactive intestinal polypeptide) from the cholinergic neurons passing in an anterograde direction relaxes the segment of the intestine ahead of the stimulus. Peristalsis involves the contraction of a segment of intestine behind the bolus of food and relaxation of a segment behind the bolus of food and relaxation of a segment of the intestine in front of the bolus of food. Cholinergic neurons passing in retrograde direction produce substance P and acetylcholine which cause contraction of a segment of intestine. Cholinergic neurons passing in anterograde direction produce NO and VIp which causes relaxation of a segment of the intestine in front of a bolus of food. Ref: Ganong&;s Review of medical physiology 26th edition Pgno: 495