Vasoactive intestinal polypeptide (VIP) as a mediator of the watery diarrhea syndrome.

Evidence that VIP is the principal humoral mediator of the watery diarrhea syndrome includes: (a) actions of VIP in experimental anaimals parallel the clinical manifestations of the syndrome; (b) infusions of VIP induce watery diarrhea in intestinal loops of dogs and a picture resembling the clinical syndrome in pigs, at circulating levels of the peptide similar to those observed in human disease; (c) most patients with the watery diarrhea syndrome and underlying tumors have elevated plasma levels of VIP; (d) in those patients in whom pre- and postoperative measurements were made, plasma VIP levels fell to the normal range with removal of the tumor and relief of the diarrhea; and (e) extracts of such tumors are rich in VIP-immunoreactivity and VIP-like biologic activity. A few patients with the syndrome have been reported to have normal plasma VIP levels, and it is possible that other humoral agents (such as pancreatic polypeptide, prostaglandins) may contribute to the production of the diarrhea.