Henri Duboc1,2,3, Ganna Tolstanova1,2,4, Pu-Qing Yuan1,2, Vincent Wu1,2, Izumi Kaji5,6, Mandy Biraud1,2, Yasutada Akiba2,5,6, Jonathan Kaunitz2,5,7,6, Mulugeta Million1,2, Yvette Tache1,2, Muriel Larauche1,2. 1. CURE: Digestive Diseases Research Center and Center for Neurobiology of Stress, Department of Medicine, Division of Digestive Diseases, David Geffen School of Medicine at UCLA. 2. VA Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA. 3. DHU UNITY, Inserm UMR 1149, and Louis Mourier Hospital, Department of Gastroenterology and Hepatology, AP-HP, University Paris Diderot Sorbonne Paris Cité, Paris, France. 4. Educational-Scientific Center "Institute of Biology" Taras Shevchenko National University of Kyiv, Kyiv, Ukraine. 5. Department of Medicine, School of Medicine, UCLA. 6. Brentwood Biomedical Research Institute, Los Angeles, California, USA. 7. Department of Surgery, School of Medicine, UCLA.
Abstract
BACKGROUND: Recent evidence from rat neuron-free mucosa study suggests that the membrane bile acid receptor TGR5 decreases colonic secretion under basal and stimulated conditions. As submucosal neurons are key players in secretory processes and highly express TGR5, we investigated their role in TGR5 agonist-induced inhibition of secretion and the pathways recruited. METHODS: TGR5 expression and localization were assessed in rat proximal (pC) and distal (dC) colon by qPCR and immunohistochemistry with double labeling for cholinergic neurons in whole-mount preparations. The influence of a selective (INT-777) or weak (ursodeoxycholic acid, UDCA) TGR5 agonist on colonic secretion was assessed in Ussing chambers, in dC preparation removing seromuscular ± submucosal tissues, in the presence of different inhibitors of secretion pathways. KEY RESULTS: TGR5 mRNA is expressed in full thickness dC and pC and immunoreactivity is located in colonocytes and pChAT-positive neurons. Addition of INT-777, and less potently UDCA, decreased colonic secretion in seromuscular stripped dC by -58.17± 2.6%. INT-777 effect on basal secretion was reduced in neuron-free and TTX-treated mucosal-submucosal preparations. Atropine, hexamethonium, indomethacin, and L-NAME all reduced significantly INT-777's inhibitory effect while the 5-HT4 antagonist, RS-39604, and lidocaine abolished it. INT-777 inhibited stimulated colonic secretion induced by nicotine, but not cisapride, carbachol or PGE2. CONCLUSIONS & INFERENCES: TGR5 activation inhibits basal and stimulated distal colonic secretion in rats by acting directly on epithelial cells and also inhibiting submucosal neurons. This could represent a counter-regulatory mechanism, at the submucosal level, of the known prosecretory effect of bile acids in the colon.
BACKGROUND: Recent evidence from rat neuron-free mucosa study suggests that the membrane bile acid receptor TGR5decreases colonic secretion under basal and stimulated conditions. As submucosal neurons are key players in secretory processes and highly express TGR5, we investigated their role in TGR5 agonist-induced inhibition of secretion and the pathways recruited. METHODS:TGR5 expression and localization were assessed in rat proximal (pC) and distal (dC) colon by qPCR and immunohistochemistry with double labeling for cholinergic neurons in whole-mount preparations. The influence of a selective (INT-777) or weak (ursodeoxycholic acid, UDCA) TGR5 agonist on colonic secretion was assessed in Ussing chambers, in dC preparation removing seromuscular ± submucosal tissues, in the presence of different inhibitors of secretion pathways. KEY RESULTS:TGR5 mRNA is expressed in full thickness dC and pC and immunoreactivity is located in colonocytes and pChAT-positive neurons. Addition of INT-777, and less potently UDCA, decreased colonic secretion in seromuscular stripped dC by -58.17± 2.6%. INT-777 effect on basal secretion was reduced in neuron-free and TTX-treated mucosal-submucosal preparations. Atropine, hexamethonium, indomethacin, and L-NAME all reduced significantly INT-777's inhibitory effect while the 5-HT4 antagonist, RS-39604, and lidocaine abolished it. INT-777 inhibited stimulated colonic secretion induced by nicotine, but not cisapride, carbachol or PGE2. CONCLUSIONS & INFERENCES: TGR5 activation inhibits basal and stimulated distal colonic secretion in rats by acting directly on epithelial cells and also inhibiting submucosal neurons. This could represent a counter-regulatory mechanism, at the submucosal level, of the known prosecretory effect of bile acids in the colon.
Authors: Roberto Berni Canani; Pia Cirillo; Giuseppe Mallardo; Vittoria Buccigrossi; Annalisa Passariello; Serena Ruotolo; Giulio De Marco; Francesco Porcaro; Alfredo Guarino Journal: World J Gastroenterol Date: 2006-08-07 Impact factor: 5.742
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