Which of the following regulators would MOST likely inhibit the lower esophageal sphincter in normal individuals?

Physiologically impoant inhibitors of the lower esophageal sphincter include nitric oxide and vasoactive intestinal polypeptide. Physiologically impoant substances that stimulate the lower esophageal sphincter include acetylcholine and substance P. Also Know: VIP contains 28 amino acid residues. It is found in nerves in the gastrointestinal tract and thus is not itself a hormone, despite its similarities to secretin. VIP is, however, found in blood, in which it has a half-life of about 2 min. GIP contains 42 amino acid residues and is produced by K cells in the mucosa of the duodenum and jejunum. Its secretion is stimulated by glucose and fat in the duodenum, and because in large doses it inhibits gastric secretion and motility, it was named gastric inhibitory peptide. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 25. Overview of Gastrointestinal Function & Regulation. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.