Vasoactive intestinal peptide (VIP) is a peptide of 28 amino acid residues that belongs to the glucagon/secretin superfamily of peptides. It is produced in different regions of the nervous system, including the brain, trigeminovascular system and several autonomic nerves. Once released from neurons, it acts on vasoactive intestinal peptide receptor 1 (VPAC1), vasoactive intestinal peptide receptor 2 (VPAC2) and pituitary adenylate cyclase-activating polypeptide type I receptor (PAC1), by mediating smooth muscle relaxation, vasodilation and water secretion. 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, sharing the activation of adenylate cyclase. 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 a long-lasting infusion of VIP may induce a prolonged vasodilation in the cerebral vessels and migraine, as a twenty-minute infusion of PACAP, is unknown.

Inclusion Criteria:

18-60 years. 50-90 kg. Women of childbearing potential must use adequate contraception.

Exclusion Criteria:

Headache less than 48 hours before the tests start All primary headaches Daily consumption of drugs of any kind other than oral contraceptives Pregnant or nursing women. A cardiovascular disease of any kind, including cerebrovascular diseases.