Distribution of somatostatin-14 and somatostatin-28 gastrointestinal-pancreatic cells of rats and humans.

Somatostatin-14 and somatostatin-28 are biologically active peptides derived from the posttranslational cleavage of prosomatostatin. Because both peptides are found in variable concentrations in the gastrointestinal (GI) tract and pancreas, it has been contended that somatostatin-28 is either an intermediate in the processing to somatostatin-14 or a terminal product derived from prosomatostatin. To address this question, two antisera were used to recognize epitopes in two regions of somatostatin-14; one with high specificity for somatostatin-14 and the other interacting with prosomatostatin, somatostatin-28, and somatostatin-14. Distribution of these peptides was measured in extracts of pancreas and mucosa and submucosa/muscularis from the rat and human GI mucosal biopsies; the antisera were used to immunostain cells in these tissues. Extracts of human and rat intestinal mucosa contained both somatostatin-28 and somatostatin-14. By immunocytochemistry, D cells in stomach and pancreas and neural processes in the intestine, extending into the mucosal villi adjacent to endocrine cells, stained with both antisera indicating the presence of somatostatin-14, prosomatostatin, and possibly somatostatin-28. In contrast, endocrine cells in the gut reacting with antisera against somatostatin-28 did not immunostain with somatostatin-14-specific antisera. Thus, these data suggest that somatostatin-28 is the terminal peptide processed from prosomatostatin in intestinal mucosal cells, whereas somatostatin-14 is the major final product in gastric and pancreatic D cells and neurons. The localization of somatostatin-28 and somatostatin-14 in different cells in the pancreas and GI tract implies that they serve different functions.