A hormone found in the pancreas, intestine, and central nervous system. It has many actions in the body, such as helping to control the secretion of water, salts, enzymes, and gastric acid during digestion. It also causes smooth muscles in the digestive tract, the heart, and the blood vessels to relax. It also has effects on the immune system and the central nervous system. Certain tumors in the pancreas make large amounts of VIP hormone. Also called vasoactive intestinal peptide.