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 o f peptide hormones, either alone or in cominations, and intravenously administered provocative agents have been used to stimulate hormone re lease to aid in the diagnosis and localization in suspected cases. The se features of PETs led us to perform detailed biochemical investigati ons and provocative testing in a 26-year-old man with a 5 cm vasoactiv e intestinal peptide (VIP)-secreting tumor of the head of the pancreas Methods. Plasma hormone radioimmunoassays and immunohistochemical stu dies were performed for a panel of peptide hormones, including VIP, ne urotensin, and pancreatic polypeptide (PP). Acid alcohol extracts of t umor specimens were analyzed for these peptide hormones as well. Befor e operation, four provocative test regimens were administered intraven ously 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 extr action studies indicated secretion of VIP, neurotensin, and PP by the tumor. Coexpression of VIP and neurotensin was seen immunohistochemica lly, within some individual tumor cells. Provocative testing resulted in maximal stimulation of VIP and neurotensin secretion with pentagast rin administration, which produced increases in plasma levels of VIP a nd neurotensin over basal levels of 81% and 87%, respectively. After o peration, plasma bevels of VIP, neurotensin, and PP were undetectable before and after administration of pentagastrin. Conclusions. The resu lts emphasize the importance of comprehensive biochemical evaluation i n 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 t hese tumors.