Vasoactive intestinal peptide (VIP) is a peptide that acts as a neurotransmitter and hormone.[1],[2] It is found in the brain and peripheral nervous system and binds to VPAC1 and VPAC2 receptors (Kis = 0.15-3.16 and 1.58-15.8 nM, respectively).[1] VIP is involved in vasodilation, bronchodilation, and regulating circadian rhythm.[1],[2],[3] It also has actions in the immune system where it inhibits the production of cytokines and chemokines involved in inflammation.[2]
Reference:
[1]. Harmar, A.J., Fahrenkrug, J., Gozes, I., et al. Pharmacology and functions of receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide: IUPHAR review 1. Br. J. Pharmacol. 166(1), 4-17 (2012).
[2]. Delgado, M., and Ganea, D. Vasoactive intestinal peptide: A neuropeptide with pleiotropic immune functions. Amino Acids 45(1), 25-39 (2013).
[3]. Wu, D., Lee, D., and Sung, Y.K. Prospect of vasoactive intestinal peptide therapy for COPD/PAH and asthma: A review. Respir. Res. 12:45, (2011).