VASOACTIVE INTESTINAL PEPTIDE - A peptide that is found in highest concentration in the nervous system and gut. Vasoactive intestinal peptide, or VIP, may be a type of neurotransmitter or neuromodulator. VIP increases the electrolyte and water secretion from the pancreas and intestines. It also increases the release of hormones from the pancreas, gut, and hypothalamus. VIP stimulates the breakdown of fat and glycogen, stimulates bile flow, and inhibits gastrin and gastric acid secretion. Greater than normal values of VIP in the bloodstream can indicate a VIP-secreting tumor.