Vasoactive Intestinal Peptide

Discovery and Nomenclature

Vasoactive intestinal peptide was isolated in 1970 by Said and Mutt from porcine duodenum as a factor producing profound vasodilation and hypotension when administered intravenously. The name reflects its original functional characterization, though subsequent research revealed pleiotropic biological activities extending far beyond vascular effects. VIP is a member of the secretin-glucagon family of peptides and shares approximately 70% sequence homology with pituitary adenylate cyclase-activating polypeptide (PACAP).

Structure and Receptor Pharmacology

VIP consists of 28 amino acids with the sequence: His-Ser-Asp-Ala-Val-Phe-Thr-Asp-Asn-Tyr-Thr-Arg-Leu-Arg-Lys-Gln-Met-Ala-Val-Lys-Lys-Tyr-Leu-Ala-Ala-Ser-Ile-Leu-NH2. The peptide adopts an alpha-helical conformation in solution, with the N-terminal region critical for receptor activation and the C-terminal segment mediating binding affinity. VIP acts through two high-affinity Gs-coupled receptors: VPAC1 (广泛 expressed in peripheral tissues) and VPAC2 (predominantly in brain, immune cells, and endocrine tissues). Both receptors activate adenylyl cyclase, elevating intracellular cAMP.

Cardiovascular and Respiratory Functions

VIP is one of the most potent endogenous vasodilators known, producing relaxation of arterial smooth muscle through both endothelium-dependent nitric oxide release and direct smooth muscle relaxation. VIP-containing nerves innervate cerebral, pulmonary, and mesenteric vasculature. In the airways, VIP mediates bronchodilation and inhibits mucus secretion, leading to its investigation as a therapeutic agent for asthma. Pulmonary VIP deficiency has been implicated in the pathogenesis of sarcoidosis and asthma.

Gastrointestinal Actions

VIP regulates intestinal fluid and electrolyte secretion, functioning as the primary mediator of secretory diarrhea in conditions such as VIPoma (Verner-Morrison syndrome). Tumors secreting excessive VIP cause profuse watery diarrhea, hypokalemia, and achlorhydria (WDHA syndrome). In the enteric nervous system, VIP acts as a non-adrenergic non-cholinergic inhibitory neurotransmitter, mediating relaxation of gastrointestinal smooth muscle.

Neuroimmunomodulatory Roles

VIP is a potent immunomodulator, suppressing pro-inflammatory cytokine production and promoting anti-inflammatory macrophage polarization. VIP neurons infiltrate inflamed tissues, and the peptide inhibits NF-kappaB activation in immune cells. These properties have generated interest in VIP-based therapeutic strategies for autoimmune diseases, including rheumatoid arthritis and inflammatory bowel disease.

References

1. Said SI, Mutt V. Polypeptide with broad biological activity: isolation from small intestine. Science. 1970;169:1217-1218.
2. Vaudry D, Falluel-Morel A, Bourgault S, et al. Pituitary adenylate cyclase-activating polypeptide and VIP receptors. Pharmacological Reviews. 2009;61:263-319.
3. Gomazkov OA. Vasoactive intestinal peptide as a neuroimmunomodulator. Neuroscience and Behavioral Physiology. 2003;33:859-866.