Vasoactive Intestinal Peptide (VIP) is found in nerve fibers throughout the central and peripheral nervous systems, likely functioning as a neurotransmitter. It induces smooth muscle relaxation, vasodilation, and secretion from exocrine glands. Excess VIP production, often due to neuroblastomas or endocrine tumors in the pancreas, results in the Verner-Morrison or Watery Diarrhea Hypokaliemia and Achlorhydria (WDHA) syndrome.
