STIMULATION OF VASOACTIVE-INTESTINAL-PEPTIDE AND NEUROTENSIN SECRETION BY PENTAGASTRIN IN A PATIENT WITH VIPOMA SYNDROME

Background. Pancreatic endocrine tumors (PETs) may secrete a variety of peptide hormones, either alone or in cominations, and intravenously administered provocative agents have been used to stimulate hormone release to aid in the diagnosis and localization in suspected cases. These features of PETs led us to perform detailed biochemical investigations and provocative testing in a 26-year-old man with a 5 cm vasoactive intestinal peptide (VIP)-secreting tumor of the head of the pancreas Methods. Plasma hormone radioimmunoassays and immunohistochemical studies were performed for a panel of peptide hormones, including VIP, neurotensin, and pancreatic polypeptide (PP). Acid alcohol extracts of tumor specimens were analyzed for these peptide hormones as well. Before operation, four provocative test regimens were administered intravenously after an overnight fast: pentagastrin (0.5 mu g/kg/5 sec); rapid calcium infusion (2 mg/kg/min); a combination of calcium (2 mg/kg/min) followed by pentagastrin (0.5 mu g/kg/min); and secretin (2 clinical units/kg bolus). Blood samples were collected before each test and 1, 2, 3, 5, and 10 minutes after the infusions. Results. Measurement of plasma hormone levels and tumor immunohistochemistry and hormonal extraction studies indicated secretion of VIP, neurotensin, and PP by the tumor. Coexpression of VIP and neurotensin was seen immunohistochemically, within some individual tumor cells. Provocative testing resulted in maximal stimulation of VIP and neurotensin secretion with pentagastrin administration, which produced increases in plasma levels of VIP and neurotensin over basal levels of 81% and 87%, respectively. After operation, plasma bevels of VIP, neurotensin, and PP were undetectable before and after administration of pentagastrin. Conclusions. The results emphasize the importance of comprehensive biochemical evaluation in patients with VIPoma syndrome to detect the production of a range of peptide hormones. Administration of intravenous pentagastrin appears to stimulate release of VIP and NT and should be evaluated further as a provocative agent for the diagnosis and follow-up of patients with these tumors.