VIP (Vasoactive intestinal peptide) is a 28 amino acid peptide originally isolated from swine intestines and found to be vasoactive by dilating arterioles. VIP is widely distributed in both the central and peripheral nervous system and is released by both neurons and immune cells. VIP has pleiotropic effects as a neurotransmitter, immune regulator, vasodilator and secretagogue. VIP is a master circadian regulator, as its deletion in mice causes a cycling shift in wake/sleep duration with reduced food intake and body weight.
