VIP

Vasoactive intestinal peptide is a naturally occurring 28-amino-acid neuropeptide found throughout the central and peripheral nervous systems as well as in numerous peripheral tissues. Despite its name, VIP is not limited to the intestine. It functions as a neurotransmitter, neuromodulator, and peptide hormone involved in a wide range of physiological signaling processes.

VIP exerts most of its effects through two receptors known as VPAC1 and VPAC2. Both belong to the class B family of G-protein-coupled receptors and respond with high affinity to VIP. Receptor activation commonly stimulates adenylate cyclase and increases intracellular cyclic AMP, triggering downstream signaling that varies by tissue and cell type. VPAC1 is widely expressed in tissues including the liver, lung, intestine, immune cells, cortex, and hippocampus, while VPAC2 is found in areas including the central nervous system and smooth muscle tissues.

Through these pathways, VIP has been studied for effects on smooth-muscle relaxation, vascular tone, gastrointestinal secretion and motility, pancreatic signaling, immune-cell activity, inflammatory responses, and nervous-system function. Its broad receptor distribution explains why VIP research spans numerous scientific fields rather than being limited to one isolated pathway