gastrins and xenopsin

Distribution and association of neurotensin (NT)- and xenopsin (XP)-like peptides were investigated using immunocytochemical techniques in the amphibian gut. Antisera against both groups of peptides showed an identical distribution pattern of NT- and XP-positive cells in Xenopus laevis gastrointestinal tract. Immunolabeling of consecutive semithin sections revealed the coexistence of NT- and XP-like substances within cells of the stomach and small intestine. Recent reports of the colocalization of XP-like material with gastrin in mammalian G cells led us to study the association of NT/XP-like peptides with members of the gastrin/cholecystokinin (CCK)/caerulein (G/C) family in amphibians. The data obtained from immunolabeling serial sections with NT/XP-specific and G/C-specific antisera show that in some intestine NT/XP- and G/C-like peptides do exist in the same cells. In the stomach, however, G/C-like material is confined to endocrine cells of the antral region, while NT/XP-like substances occur in distinct cells accumulating in cardial glands but absent in the pyloric glands. Our findings thus indicate that in amphibian gastrointestinal tract there is some association between the regulatory peptide families NT/XP and G/C, similar to mammals. The regional distribution of both hormone families, however, is different from that in mammals.

Topics: Animals; Ceruletide; Cholecystokinin; Digestive System; Gastrins; Immunologic Techniques; Neuropeptides; Neurotensin; Oligopeptides; Pentagastrin; Peptides; Xenopus laevis; Xenopus Proteins

The nature of xenopsin immunoreactivity in mammalian antral G-cells has been reassessed. Xenopsin immunostaining was most intense in human antral G-cells, present in those of the dog and pig and not detected in guinea pig or rat tissues. Rigorous specificity controls for ionic binding of immunoglobulins to antral G-cell granules indicated that this mechanism was not responsible for xenopsin immunostaining. Preincubation of the xenopsin antiserum with xenopsin, human gastrin 1-13 and gastrin 2-17 completely abolished immunostaining at similar molar concentrations. Gastrin 34 was ineffective at much higher concentrations. These results infer that xenopsin-immunoreactivity in antral G-cells resides in the N-terminal region of gastrin 17. Examination of the primary structures of xenopsin and the N-terminal regions of some mammalian gastrins reveals a hitherto unrecognized homology.

Topics: Amino Acid Sequence; Animals; Dogs; Gastric Mucosa; Gastrins; Guinea Pigs; Hormones; Humans; Immunohistochemistry; Molecular Sequence Data; Oligopeptides; Peptides; Rats; Swine; Xenopus Proteins

Studies indicating evidence for the presence of the amphibian octapeptide xenopsin in gastric mucosa of mammals prompted us to investigate the cellular localization of this peptide. Using the peroxidase-antiperoxidase method and a specific antiserum to xenopsin (Xen-7) on paraffin and adjacent semithin sections of gastric antral mucosa from man, dog, and Tupaia belangeri, we found numerous epithelial cells showing a specific positive immunoreaction. These cells were of typical pyramidal shape and could be classified as of the "open" type. Cell quantification in serial sections processed for xenopsin and gastrin immunoreactivity, respectively, revealed an identical number of cells per section and an identical distribution of these cells in the middle zone of the antral mucosa. Furthermore, adjacent semithin sections demonstrated the colocalization of xenopsin and gastrin immunoreactivity within the same G-cell. The xenopsin antiserum could be completely absorbed with synthetic xenopsin but not with gastrin. Preabsorption tests with neurotensin, a xenopsin related peptide, or with somatostatin, glucagon, and enkephalins gave no evidence for crossreactivity of the xenopsin antiserum with these peptides. It is concluded that gastric antral G-cells in addition to gastrin also contain the amphibian peptide xenopsin.

Topics: Animals; Dogs; Gastric Mucosa; Gastrins; Humans; Immunoenzyme Techniques; Oligopeptides; Peptides; Tupaia; Xenopus Proteins

Effects of synthetic xenopsin on endocrine pancreas and gastric antrum in anesthetized dogs were studied. Synthetic xenopsin was administered into the superior pancreaticoduodenal artery and plasma insulin, glucagon and gastrin in the superior pancreaticoduodenal vein and gastrin in the right gastroepiploic vein were measured radioimmunologically. Administration of 10 microgram of xenopsin per kg of body weight brought about a hyperglycemic response and rapid and sharp elevations of the hormones in the pancreatic vein. Plasma gastrin level in the gastric vein also showed an immediate and sharp increase following xenopsin administration. Xenopsin appeared more potent inducer of the glucagon. It is concluded that xenopsin acts directly on endocrine pancreas and gastric antrum to secrete their hormones.

Topics: Animals; Dogs; Gastrins; Glucagon; Insulin; Islets of Langerhans; Oligopeptides; Peptides; Pyloric Antrum; Radioimmunoassay; Xenopus; Xenopus Proteins