VIP and Substance P are both small peptides with significant autocrine and paracrine signaling ability. The role of VIP in controlling gut protein and solute secretion has been understood for approximately 20 years. The clinical entity where this has been best described are in rare "VIP-omas" and some other chromophore secreting gut tumors where massive amounts of VIP are secreted by the tumor and overwhelm the body's normal ability to clear VIP through cleavage by neutral endopeptidases in the pulmonary endothelium.