Vasoactive intestinal peptide (VIP) is a linear 28-residue neuropeptide, HSDAVFTDNYTRLRKQMAVKKYLNSILN-NH₂, with a C-terminal asparagine amide and no non-natural residues. The sequence is identical in human, porcine and rat. VIP is processed from a precursor that also yields the related peptide PHM-27, and it belongs to the secretin/glucagon superfamily alongside PACAP. It was isolated from porcine small intestine in 1970 and sequenced in 1974.

VIP is reported to bind with high and similar affinity to two class B G-protein-coupled receptors, VPAC1 and VPAC2, which it shares with PACAP; its affinity for the PACAP-preferring PAC1 receptor is much lower. VPAC receptors couple principally to Gs, increasing adenylyl cyclase activity and cyclic AMP, with additional reported coupling to Gq and phospholipase C. Binding follows the class B two-domain model, in which the peptide C-terminal region engages the receptor's N-terminal extracellular domain.

VIP is used as a reference agonist in VPAC receptor binding and cAMP assays, in class B GPCR structural studies, and in selectivity work with PACAP and synthetic analogues. Other research areas include neuropeptide signalling in enteric and central neurons, suprachiasmatic nucleus circadian models, and immune-cell signalling in culture. Like other methionine-containing peptides, it is susceptible to oxidation.

Research use only. This material is sold for in-vitro laboratory research and development purposes exclusively. It is not a drug, food, or dietary supplement, has not been evaluated by the FDA, and must not be used in humans or animals.