Biological activity of oxidized and reduced iodinated bombesins

A method is reported for preparing oxidized and reduced iodinated Tyr4-bombesin. Iodogen was used to iodinate Tyr4-bombesin and the reaction products were separated by reverse-phase HPLC. The peak of oxidized label was then reduced by incubation with 725 mM dithiothreitol at 80 degrees C (pH 8.0) for one hour and the reaction products separated by HPLC as before. The reduced but not oxidized peaks of 125I-Tyr4-bombesin stimulated amylase release from rat pancreatic acini in vitro. We conclude that oxidation of bombesin producing C-terminal methionine sulfoxide destroys the biological activity of the peptide and that this form of oxidation can be reversed.

Localization of specific binding sites for bombesin in the canine gastrointestinal tract

The goal of these studies was to determine the tissue and cell types possessing specific binding sites for bombesin/gastrin-releasing peptide in the canine gastrointestinal tract. Monoiodinated, biologically active (Tyr-4)-bombesin 14 (100 pM) was applied to sections of canine gut and localized using quantitative autoradiography. The highest density of bombesin/gastrin-releasing peptide specific binding sites occurred over endocrine cells in the antral mucosa. Specific binding sites were also found on the circular muscle layer of the gastric fundus, gastric antrum, and ileum, on longitudinal muscle of the gastric fundus and antrum, and on neuronal elements in the myenteric plexus in the gastric fundus, antrum, and small intestine. No evidence for specific binding of 125I-(Tyr-4)-bombesin 14 was found in sections of canine esophagus, gastric cardia, gallbladder, pancreas, or colon. These results suggest sites of direct action of bombesin and endogenous gastrin-releasing peptide for gastrin release and gastrointestinal motility.

Distribution and molecular forms of immunoreactive bombesin in the ovine median eminence

The distribution and molecular forms of bombesin-like immunoreactivity (BLI) were determined in the ovine median eminence using a new, C-terminally directed antiserum. BLI was confined to neurons of the external zone of the median eminence, near small blood vessels, many of which also were immunoreactive for CRF. Each median eminence contained about 10 pmol of BLI (533 pmol/g tissue). Gel filtration and reverse-phase high pressure liquid chromatography (HPLC) demonstrated the existence of two molecular forms of BLI, which co-eluted with porcine gastrin releasing peptide (GRP)1-27 and GRP18-27 in a molar ratio of 1:2. The presence of BLI in the ovine median eminence and its co-localization in some neurons with CRF, suggest a possible role for peptides of the bombesin family in the regulation of pituitary function.

Bombesin stimulation of gastrin release from canine gastrin cells in primary culture

A method is described for the isolation and short-term culture of canine antral gastrin (G) cells. Tissue was dispersed by enzymes and G cells enriched by elutriation and cultured for 40 h. These cultures contained 12% G cells and less than 2% somatostatin- or serotonin-containing cells. Bombesin (0.001-100 pM) potently stimulated gastrin release from cell cultures in a linear fashion over 2 h. The bombesin-specific monoclonal antibody 2A11 dose-dependently blocked bombesin stimulation. Somatostatin (0.001-1,000 nM) inhibited bombesin-stimulated gastrin release. Antibody to somatostatin (Mab S8) prevented the inhibition by exogenous somatostatin but did not alter bombesin-stimulated or basal gastrin release. The substance P (SP) analogue spantide (1 nM-1 microM) did not inhibit bombesin-stimulated gastrin release. Postreceptor activation of adenylate cyclase by forskolin and of protein kinase C by the phorbol ester, beta-TPA, caused gastrin release. The calcium ionophore A23187 also released gastrin in a dose-dependent fashion. This methodology allows enrichment and short-term culture of antral G cells; these cells have stimulatory bombesin and inhibitory somatostatin receptors, suggesting that these peptides have a direct action on antral G cells. Furthermore, G cells are activated by cAMP and calcium/phosphatidylinositol-dependent mechanisms.

Immunoreactive Met-enkephalin Arg6 in rat brain, and bovine brain, gut, and adrenal

Antibodies directed against the Met-enkephalin-related hexapeptide, Met-enk Arg6, have been used in radioimmunoassays in the characterization of material in rat brain, and bovine striatum, colon, and adrenal medulla. Met-enk Lys6 reacted 0.27 relative to Met-enk Arg6, but Leu-enk Arg6 and C-terminal extensions or deletions of Met-enk Arg6 showed less than 0.02 immunoreactivity. In rat brain, the concentration of Met-enk Arg6-like immunoreactivity was less than 20 pmol X g-1 in all regions, but after trypsinization of tissue extracts there were up to 80-fold increases in immunoreactivity as a result of cleavage of C-terminally extended forms. The tryptic product eluted as Met-enk Arg6 on gel filtration. In control extracts of rat brain there were at least three immunoreactive forms of Met-enk Arg6; one eluted in the position of the hexapeptide standard on gel filtration and HPLC while the others had properties of N-terminally extended forms. In bovine striatum and colon the hexapeptide-like material predominated; but in bovine adrenal extracts, there were relatively low concentrations of the hexapeptide and, instead, the dominant immunoreactive forms corresponded to two components that were probably N-terminally extended variants. Trypsin again produced marked increases in immunoreactivity. HPLC studies indicated that Met-enk Arg6Phe7- and Met-enk Arg6Gly7Leu8-like immunoreactive peptides were important substrates in bovine brain for the production of hexapeptide immunoreactivity after trypsin. The differences in the patterns of immunoreactive forms in bovine adrenal, colon, and brain are consistent with tissue variations in the pathways of posttranslational processing of the precursor molecules.

Evidence for different patterns of post-translational processing of pro-enkephalin in the bovine adrenal, colon and striatum indicated by radioimmunoassay using region-specific antisera to Met-Enk-Arg6-Phe7 and Met-Enk-Arg6-Gly7-Leu8

Specific antisera to two opioid peptides, Met-Enk-Arg6-Phe7 and Met-Enk-Arg6-Gly7-Leu8, were used in radioimmunoassay to study molecular forms in extracts of bovine adrenal, striatum and colon. The antisera to Met-Enk-Arg6-Phe7 and Met-Enk-Arg6-Gly7-Leu8 were each highly specific for the C-terminus of their respective haptens and showed less than 1% cross-reactivity with related enkephalins and their variants. In adrenal extracts, gel filtration on Sephadex G-50 indicated N-terminally extended forms of Met-Enk-Arg6-Phe7 and Met-Enk-Arg6-Gly7-Leu8 as the predominating immunoreactive species, whereas in the striatum and colon the main immunoreactive forms were compatible with the hepta- and octapeptides. The results suggest different patterns of post-translational processing of precursors in the adrenal medulla compared with striatal and colonic neurones.

Fine structure of the gastric mucous and endocrine cells of the toad, Bufo marinus

The ultrastructure of the mucous and endocrine cells of the gastric mucosa of the cane toad (Bufo marinus) has been examined. Surface mucous cells line the entire gastric mucosa and pits. Many of their secretory granules contain an electro-dense core that remains unreactive after cytochemical testing for glycoproteins. A second spatially and structurally discrete population of mucous cells is present in the gastric glands. These glandular mucous cells are probably homologous with the antral gland and mucous neck cells of mammals; their secretory granules also contain non-glycoprotein cores. Three distinct populations of endocrine cells show structural homologies with gastric hormone-storing cells of higher vertebrates.

Ultrastructure and cytochemistry of the gastric mucosa of a reptile, Tiliqua scincoides

The gastric mucosa of a reptile, the lizard Tiliqua scincoides, has been examined by light and electron microscopy. The gastric pits lead into glands that are extensively coiled in the proximal stomach but become progressively shorter and straighter in the distal stomach. The following epithelial cell types have been identified: (i) Surface mucous cells (SMC) line the entire lumenal surface as well as the pits. They contain mucus granules that stain with periodic acid-Schiff and, like the granules of mammalian SMC, commonly contain an electron dense core that appears not to be mucus (periodic acid-chromic acid-silver methenamine nonreactive). (ii) Glandular mucous cells are present in glands throughout the mucosa. They are probably homologous with the mucous neck and antral gland cells of mammals; like SMC their mucus granules contain nonglycoprotein cores. (iii) Oxynticopeptic cells (OPC) are the predominant cell type in the proximal gland but become infrequent distally. Their fine structure resembles that of OPC in other nonmammalian vertebrates, with features like those of both parietal cells and zymogen cells of mammals. (iv) Endocrine cells of three different types have been identified. Two of these show close similarities to the EC and ECL cells of mammals.

Epithelial surfaces of the upper gastrointestinal tract of the blue-tongues lizard, Tiliqua scincoides: a scanning electron microscope study

The surface epithelium of the oesophagus, stomach and small intestine of healty T. scincoides was examined by scanning electron microscopy and the findings confirmed by both light and transmission microscopy. The oesophagus was lined by ciliated, goblet and microvillous cells. Its topography appeared similar to the trachea and major bronchi of a number of mammals and birds. Throughout the length of the stomach microvillous cells were uniformly arranged on the gastric rugae. The cells were slightly convex and sparsely populated by microvilli, which appeared more numerous at intercellular margins. Swollen epithelial cells, approximately twice the size of the adjacent cells, were scattered throughout the gastric epithelium. Cells with focal apical erosions were found in isolated regions, being relatively more numerous in the distal stomach. The openings of the gastric glands were observed as invaginations of the epithelial surface and were most prominent near the tops of the gastric rugae. The small intestine was lined by epithelial cells covered by long, densely packed microvilli. Goblet cells were interspersed along the surface of the intestinal villi. Except for the oesophagus, the topography of the upper gastrointestinal tract of T. scincoides closely resembles that of homologous regions of the mammalian gut.