Vasoactive intestinal peptide (VIP) is a neuropeptide that functions as both a neuromodulator and neurotransmitter, with a range of physiological and pathological effects on various bodily systems. VIP receptors are found in various tissues, including the gastrointestinal system, pancreas, pituitary, and liver, mediating the physiological effects of VIP. VIP acts through specific high-affinity receptors, which are G protein-coupled receptors (GPCRs). These receptors, known as VIP receptors or VIPRs, share significant sequence homology and are distinct from the rhodopsin/beta-adrenergic family of receptors. It is a potent vasodilator and plays a role in regulating smooth muscle activity, epithelial cell secretion, and blood flow in the gastrointestinal tract. It stimulates intestinal water and electrolyte secretion, vasodilation, liver glycogenolysis, pancreatic secretion of fluid and enzymes, pituitary prolactin secretion, and smooth muscle relaxation. VIP has been shown to be therapeutic in several inflammatory models, including colitis, sepsis, and collagen-induced arthritis, and has demonstrated immunoregulatory effects in patients with pulmonary sarcoidosis. It may also play a role in wound healing and restoration of immune homeostasis in the cornea following infection.
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