| 1. |
- Flemström, Gunnar, 1941-, et al.
(författare)
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Apelin stimulation of duodenal bicarbonate secretion : feeding-dependent and mediated via apelin-induced release of enteric cholecystokinin
- 2011
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Ingår i: Acta Physiologica. - Oxford : Wiley-Blackwell. - 1748-1708 .- 1748-1716. ; 201:1, s. 141-150
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Tidskriftsartikel (refereegranskat)abstract
- Aim: Apelin peptides is the endogenous ligand of the G protein-coupled receptor APJ. Proposed actions include involvement in control of cardiovascular functions, appetite and body metabolism. We have investigated effects of apelin peptides on duodenal bicarbonate secretion in vivo and the release of cholecystokinin (CCK) from acutely isolated mucosal cells and the neuroendocrine cell line STC-1. Methods: Lewis x Dark Agouti rats had free access to water and, unless fasted overnight, free access to food. A segment of proximal duodenum was cannulated in situ in anesthetized animals. Mucosal bicarbonate secretion was titrated (pH stat) and apelin was administered to the duodenum by close intra-arterial infusion. Total RNA was extracted from mucosal specimens, reverse transcripted to cDNA and expression of the APJ receptor measured by quantitative real-time PCR. Apelin-induced release of CCK was measured using (i) cells prepared from proximal small intestine, and (ii) STC-1 cells. Results: Even the lowest dose of apelin-13 (6 pmol kg-1 h-1) caused a significant rise in bicarbonate secretion. Stimulation occurred only in continuously fed animals and even a 100-fold greater dose (600 pmol kg-1 h-1) of apelin was without effect in overnight food deprived animals. Fasting also induced a 8-fold decrease in the expression of APJ receptor mRNA. Apelin induced significant release of CCK from both mucosal and STC-1 cells, and the CCKA receptor antagonist devazepide abolished bicarbonate secretory responses to apelin. Conclusions: Apelin-induced stimulation of duodenal electrolyte secretion is feeding dependent and mediated by local mucosal release of CCK
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| 2. |
- Flemström, Gunnar, 1941-, et al.
(författare)
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Effects of short-term food deprivation on orexin-A-induced intestinal bicarbonate secretion in comparison with related secretagogues
- 2010
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Ingår i: Acta Physiologica. - Oxford : Wiley-Blackwell. - 1748-1708 .- 1748-1716. ; 198:3, s. 373-380
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Forskningsöversikt (refereegranskat)abstract
- Studies of gastrointestinal physiology in humans and intact animals are usually conducted after overnight fast. We have compared effects of orexin-A, vasoactive intestinal polypeptide (VIP), melatonin, serotonin, uroguanylin, ghrelin and prostaglandin E2 (PGE2) on duodenal bicarbonate secretion in fed and overnight fasted animals. This review is a summary of our findings. Secretagogues were administered by intra-arterial infusion or luminally (PGE2) Enterocyte intracellular calcium ([Ca2+]i) signaling was studied by fluorescence imaging. Total RNA was extracted, reverse transcripted to cDNA and expression of orexin receptors measured by quantitative real-time PCR. Orexin-A stimulates the duodenal secretion in continuously fed animals but not in food deprived animals. Similarly, short fasting causes a 100-fold decrease of the amount of the muscarinic agonist bethanechol required for stimulation of secretion. In contrast, fasting does not affect secretory responses to intra-arterial VIP, melatonin, serotonin, uroguanylin and ghrelin, or that to luminal PGE2. Orexin-A induces [Ca2+]i signaling in enterocytes from fed rats but no significant [Ca2+]i responses occurs in enterocytes from fasted animals. In addition, overnight fasting decreases the expression of mucosal and enterocyte orexin receptors. Short food deprivation thus decreases duodenal expression of orexin receptors and abolishes the secretory response to orexin-A as well as orexin-A induced [Ca2+]i signaling. Fasting, furthermore, decreases mucosal sensitivity to bethanechol. The absence of declines in secretory responses to other secretagogues tested is strong evidence that short fasting does affect not the secretory capacity of the duodenal mucosa in general. Studies of intestinal secretion require particular evaluation with respect to feeding status.
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| 3. |
- Sjöblom, Markus, et al.
(författare)
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Cholecystokinin but not ghrelin stimulates mucosal bicarbonate secretion in rat duodenum : Independence of feeding status and cholinergic stimuli
- 2013
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Ingår i: Regulatory Peptides. - : Elsevier BV. - 0167-0115 .- 1873-1686. ; 183, s. 46-53
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Tidskriftsartikel (refereegranskat)abstract
- Cholecystokinin (CCK) is an important regulator of food digestion but its influence on small intestinal secretion has received little attention. We characterized effects of CCK-8, ghrelin and some related peptides on duodenal HCO3- secretion in vivo and demonstrated CCK-induced calcium signaling in acutely isolated enterocytes. A segment of proximal duodenum with intact blood supply was cannulated in situ in anaesthetized rats. Mucosal HCO3- secretion was continuously recorded (pH-stat). Peptides were administrated to the duodenum by close intra-arterial infusion. Clusters of duodenal enterocytes were attached to the bottom of a perfusion chamber. The intracellular calcium concentration ([Ca2+](i)) was examined by dual-wavelength imaging. CCK-8 (3.0, 15 and 60 pmol/kg,h) caused dose-dependent increases (p < 0.01) in duodenal alkaline secretion in both overnight fasted and continuously fed animals. The CCK1R-antagonist devazepide but neither the CCK2R-antagonist YMM022 nor the melatonin MT2-selective antagonist luzindole inhibited the rise in secretion. Atropine decreased sensitivity to CCK-8. The appetite-related peptide ghrelin was without effect on the duodenal secretion in fasted as well as fed animals. Superfusion with CCK-8 (1.0-50 nM) induced [Ca2+](i) signaling in acutely isolated duodenal enterocytes. After an initial peak response, [Ca2+](i) returned to near basal values within 3-5 min. Devazepide but not YMM022 inhibited this [Ca2+](i) response. Low doses of CCK-8 stimulate duodenal alkaline secretion and induce enterocyte [Ca2+](i) signaling by an action at CCK1 receptors. The results point to importance of CCK in the rapid postprandial rise in mucosa-protective duodenal secretion.
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