VIP (Vasoactive intestinal peptide) is a 28 amino acid peptide hormone, a member of the secretin/glucagon superfamily, and evolutionarily well conserved. It is synthesized as part of a larger propeptide which is proteolytically processed to release bioactive VIP as well as two other neuropeptides.
VIP is expressed in gastrointestinal tissues and in the central and peripheral nervous system. It is released from neurons upon depolarization and is known to stimulate adenylyl cyclase.
In the brain, VIP acts as a neurotransmitter and is involved in rhythm generation in the suprachiasmatic nucleus, the regulation of neuroendocrine secretions in the hypothalamus and energy metabolism of glial cells.
Peripherally, VIP influences many functions including blood flow and cardiac output, smooth muscle activity, secretion in the digestive tract, gastric motility, bronchodilation and activity within the hypothalamic-pituitary-adrenal axis.
The Verner-Morrison or Watery Diarrhea Hypokalemia and Achlorhydria (WDHA) syndrome is a characteristic clinical syndrome associated with overproduction of VIP from endocrine tumors.