The vasoactive intestinal polypeptide (VIP) is a peptide of 28 amino acid residues that belongs to the glucagon/secretin superfamily of peptides. It is distributed in different regions of the nervous system, including several autonomic ganglia and the brain. Once released from neurons, it acts on the vasoactive intestinal peptide receptor 1 (VPAC1), the vasoactive intestinal peptide receptor 2 (VPAC2) and the pituitary adenylate cyclase-activating polypeptide type I receptor (PAC1). All three belong to a family of G-protein coupled receptors, sharing the activation of adenylate cyclase and the increase in intracellular cyclic adenosine monophosphate (cAMP). The three receptors are involved in many physiological functions, among them the vasodilating and parasympathetic responses. VPAC1 and VPAC2 are expressed in dura mater vessels and are primarily responsible for the relaxation of arteries. PAC1 is located in the trigemino-autonomic system, but not in blood vessels. VIP shares the binding to the three aforementioned receptors with other peptides, including the pituitary adenylate cyclase-activating polypeptide-38 (PACAP38), and the pituitary adenylate cyclase-activating polypeptide-27 (PACAP27).~20-minute infusion of VIP and PACAPs in patients with migraine dilated cranial arteries. However, only PACAP27 and PACAP38 induced a sustained cranial vasodilation, and migraine like-attacks. VIP-induced cranial vasodilation was of short duration, and patients did not report migraine-like attacks. The discrepancy was ascribed to the preferential activation of the PAC1 receptor by PACAPs, but a monoclonal antibody against PAC1 receptor recently failed in migraine prevention. Currently, it is unknown whether the prolonged cranial vasodilation related with the appearance of migraine-like attacks. More recently, a two-hour infusion of VIP promoted a long-lasting cranial vasodilation and delayed headache in healthy volunteers, resembling the effect of PACAP27 and PACAP38, two closely related peptides causing migraine. Whether a long-lasting infusion of VIP may induce a sustained cranial vasodilation and migraine-like attacks in migraine patients, as a twenty-minute infusion of PACAP27 and PACAP38, is unknown.
Vasoactive intestinal peptide (VIP) is a peptide of 28 amino acid residues that belongs to the glucagon/secretin superfamily of peptides. Along with other neuropeptides, such as calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase-activating polypeptide (PACAP), it is released from the trigeminal afferents and exerts a strong vasodilating activity on the cranial vasculature. Especially, it shares 70% structure with PACAP and acts on the same receptors. But, unlike it, VIP cannot induce a long-lasting vasodilation and has a modest capability to induce migraine attacks. Whether it may induce migraine-like attacks in migraine patients, as a twenty-minute infusion of PACAP, is unknown.