Vasointestinal peptide (VIP) and pituitary adenylate cyclase–activating peptide (PACAP) belong to the glucagon hormone superfamily, which includes secretin, growth hormone–releasing hormone (GHRH), glucagon, glucagon-like peptides 1 and 2 (GLP-1 and GLP-2), peptide histidine methionine (PHM), and glucose-dependent insulinotropic polypeptide (GIP). PACAP and VIP effects have been described in the digestive tract, cardiovascular system, airways, reproductive system, immune system, endocrine glands, and brain. VIP and PACAP share a common G-protein coupled receptor, VPAC1.