Glycine-extended gastrin enhances somatostatin release from cultured rabbit fundic D-cells

The role of the peptide hormone gastrin in stimulating gastric acid secretion is well established. Mature amidated gastrin is processed from larger peptide precursor forms. Increasingly these processing intermediates, such as glycine-extended gastrin (G-Gly) and progastrin, have been shown to have biological activities of their own, often separate and complementary to gastrin. Although G-Gly is synthesized and secreted by gastric antral G-cells, the physiological functions of this putative mediator are unclear. Gastrin and cholecystokinin (CCK) stimulate the secretion of somatostatin from gastric D-cells as part of the feedback control of gastric acid. In this study the effect of G-Gly and gastrin on the release of somatostatin from rabbit fundic D-cells was examined. D-cells were obtained by collagenase-EDTA digestion and elutriation and cultured for 48 hours. With a 2 hour exposure to the peptides, gastrin but not G-Gly stimulated somatostatin release. Treatment of D-cells for 24 hours with gastrin or G-Gly individually, significantly enhanced subsequent basal as well as CCK- and GLP-1-stimulated somatostatin release. Twenty four hours exposure to gastrin combined with G-Gly synergistically enhanced basal and agonist-stimulated somatostatin release and cellular somatostatin content. Gastrin and G-Gly may be important in the longer term regulation of D-cell function.