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Little or no ability of obestatin to interact with ghrelin or modify motility in the rat gastrointestinal tract.

ABSTRACT: BACKGROUND AND PURPOSE: Obestatin, encoded by the ghrelin gene may inhibit gastrointestinal (GI) motility. This activity was re-investigated. EXPERIMENTAL APPROACH: Rat GI motility was studied in vitro (jejunum contractility and cholinergically-mediated contractions of forestomach evoked by electrical field stimulation; EFS) and in vivo (gastric emptying and intestinal myoelectrical activity). Ghrelin receptor function was studied using a GTPgammaS assay and transfected cells. KEY RESULTS: Contractions of the jejunum or forestomach were unaffected by obestatin 100 nM or 0.01-1000 nM, respectively (P>0.05 each; n=4-18). Obestatin (0.1-1 nM) reduced the ability of ghrelin 1 microM to facilitate EFS-evoked contractions of the stomach (increases were 42.7+/-7.8% and 21.2+/-5.0 % in the absence and presence of obestatin 1 nM; P<0.05; n=12); higher concentrations (10-1000 nM) tended to reduce the response to ghrelin but changes were not statistically significant. Similar concentrations of obestatin did not significantly reduce a facilitation of contractions caused by the 5-HT(4) receptor agonist prucalopride, although an inhibitory trend occurred at the higher concentrations (increases were 69.3+/-14.0% and 42.6+/-8.7% in the absence and presence of 1000 nM obestatin; n=10). Obestatin (up to 10 microM) did not modulate recombinant ghrelin receptor function. Ghrelin increased gastric emptying and reduced MMC cycle time; obestatin (1000 and 30,000 pmol kg(-1) min(-1)) had no effects. Obestatin (2500 pmol kg(-1) min(-1), starting 10 min before ghrelin) did not prevent the ability of ghrelin (500 pmol kg(-1) min(-1)) to shorten MMC cycle time. CONCLUSIONS AND IMPLICATIONS: Obestatin has little ability to modulate rat GI motility.

SUBMITTER: Bassil AK

PROVIDER: S-EPMC2013842 | biostudies-other | 2007 Jan

REPOSITORIES: biostudies-other

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Project description:Background: The molecular basis of segment specific epithelial functions of the stomach and bowel has not been established. Regionally unique molecular properties of epithelial cells can be identified using cell-specific gene expression in each epithelial region by comparative mRNA analysis. Aim: To describe segment-specific epithelial mRNA content by comparative mRNA analysis of purified epithelial cell suspensions of stomach, small and large bowel. Results: 12% of all annotated genes show segment specific enrichment. The gastric (>3000 genes) and ileal (519 genes) mucosa show the most diverse expression profile. (a) Stomach: The gastric mucosa expresses the machinery for acid secretion, digestive enzyme release, and hormone release by gastric enteroendocrine cells. Associated with acid secretion is a specific set of K+, Cl-, and bicarbonate channels. Novel is a pathway for glucose and fatty acid sensing, iodine and glutamate uptake, and taurine synthesis. Specific sets of transcription factors control epithelial (Barx1, Runx) and enteroendocrine (FoxA2/N4) cell differentiation. (b) Small Bowel: This epithelium expresses genes coding for a unique fructose/glucose uptake and utilization mechanism. Enteroendocrine signalling to the gastric function is present. The upper portion expresses genes for iron uptake, bicarbonate secretion, and detoxification of food contents. Epithelial differentiation is transcriptionally controlled by Meis2/Pdx1 and Onecut 2. Expression of digestive enzymes, lipid/bile acid uptake and utilization increases distally. The ileal epithelium is also involved in innate and acquired immune defence, regulation of motility, and electrolyte and water re-absorption. Transcriptional regulation of enterocyte and goblet cell differentiation is mainly controlled by increasing expression of Cdx1 and 2. (c) Colon: This epithelium is mainly involved in Ca++-, K+, and water re-absorption, fatty acid uptake and sensing, and innate and acquired immune defence. Epithelial differentiation is controlled by Hox transcription factors in addition to Cdx1/2. Conclusion: This regional survey of gene expression by the GI tract epithelium reveals unique epithelial properties, raising several important questions as to the role of the proteins encoded in gut physiology.

Project description:Ghrelin is a gut-brain peptide hormone, which binds to the growth hormone secretagogue receptor (GHS-R) to regulate a wide variety of biological processes in fish. Despite these prominent physiological roles, no studies have reported the anatomical distribution of preproghrelin transcripts using in situ hybridization in a non-mammalian vertebrate, and its mapping within the different encephalic areas remains unknown. Similarly, no information is available on the possible 24-h variations in the expression of preproghrelin and its receptor in any vertebrate species. The first aim of this study was to investigate the anatomical distribution of ghrelin and GHS-R1a ghrelin receptor subtype in brain and gastrointestinal tract of goldfish (Carassius auratus) using immunohistochemistry and in situ hybridization. Our second aim was to characterize possible daily variations of preproghrelin and ghs-r1 mRNA expression in central and peripheral tissues using real-time reverse transcription-quantitative PCR. Results show ghrelin expression and immunoreactivity in the gastrointestinal tract, with the most abundant signal observed in the mucosal epithelium. These are in agreement with previous findings on mucosal cells as the primary synthesizing site of ghrelin in goldfish. Ghrelin receptor was observed mainly in the hypothalamus with low expression in telencephalon, pineal and cerebellum, and in the same gastrointestinal areas as ghrelin. Daily rhythms in mRNA expression were found for preproghrelin and ghs-r1 in hypothalamus and pituitary with the acrophase occurring at nighttime. Preproghrelin, but not ghs-r1a, displayed a similar daily expression rhythm in the gastrointestinal tract with an amplitude 3-fold higher than the rest of tissues. Together, these results described for the first time in fish the mapping of preproghrelin and ghrelin receptor ghs-r1a in brain and gastrointestinal tract of goldfish, and provide the first evidence for a daily regulation of both genes expression in such locations, suggesting a possible connection between the ghrelinergic and circadian systems in teleosts.

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Little or no ability of obestatin to interact with ghrelin or modify motility in the rat gastrointestinal tract.

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