Clinical relevance of regulatory gastrointestinal peptides

The application of radioimmunoassay of insulin, C-peptide, gastrin, glucagon, vasoactive intestinal polypeptides (VIP), somatostatin, human pancreatic polypeptides (hPP), substance P and neurotensin to detect endocrine tumors of the pancreas and other organ systems is undoubtedly important in the clinical management of patients suspected of having tumors that secrete these hormones. Radioimmunoassays of the above gut peptides have certain degrees of specificity and sensitivity; however, there are several factors that need to be considered in the interpretation of results since heterogeneity of molecular forms does occur and the varied radioimmunoassay techniques use different antibodies that may yield different results. It is, therefore, important that each laboratory establish its own normal values, determine the molecular species that each assay is detecting, and also determine the false positivity of the methodology. The same endocrine tumor may contain and secrete several detectable peptides, but the syndrome may relate to only one peptide. Although the simultaneous measurement of multiple peptides in patients with benign gastrointestinal disease has yielded information that contributes to our understanding of the complexities of gut neuroendocrine interaction, the pathophysiological role of gut peptides and their clinical relevance need further evaluation.