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Food-induced expression of orexin receptors in rat duodenal mucosa regulates the bicarbonate secretory response to orexin-A

Food-induced expression of orexin receptors in rat duodenal mucosa regulates the bicarbonate... Presence of appetite-regulating peptides orexin-A and orexin-B in mucosal endocrine cells suggests a role in physiological control of the intestine. Our aim was to characterize orexin-induced stimulation of duodenal bicarbonate secretion and modulation of secretory responses and mucosal orexin receptors by overnight food deprivation. Lewis x Dark Agouti rats were anesthetized and proximal duodenum cannulated in situ. Mucosal bicarbonate secretion (pH stat) and mean arterial blood pressure were continuously recorded. Orexin-A was administered intra-arterially close to the duodenum, intraluminally, or into the brain ventricles. Total RNA was extracted from mucosal specimens, reverse transcribed to cDNA and expression of orexin receptors 1 and 2 (OX1 and OX2) measured by quantitative real-time PCR. OX1 protein was measured by Western blot. Intra-arterial orexin-A (60–600 nmol·h –1 ·kg –1 ) increased ( P < 0.01) the duodenal secretion in fed but not in fasted animals. The OX1 receptor antagonist SB-334867, which was also found to have a partial agonist action, abolished the orexin-induced secretory response but did not affect secretion induced by the muscarinic agonist bethanechol. Atropine, in contrast, inhibited bethanechol but not orexin-induced secretion. Orexin-A infused into the brain ventricles (2–20 nmol·kg –1 ·h –1 ) or added to luminal perfusate (1.0–100 nM) did not affect secretion, indicating that orexin-A acts peripherally and at basolateral receptors. Overnight fasting decreased mucosal OX1 and OX2 mRNA expression ( P < 0.01) as well as OX1 protein expression ( P < 0.05). We conclude that stimulation of secretion by orexin-A may involve both receptor types and is independent of cholinergic pathways. Intestinal OX receptors and secretory responses are markedly related to food intake. bicarbonate secretion; enteroendocrine cells; fed and fasting state; perfused duodenum in situ; TRH Address for reprint requests and other correspondence: G. Flemström, Dept. of Neuroscience, Division of Physiology, Uppsala Univ., BMC, PO Box 572, SE-751 23 Uppsala, Sweden (e-mail: gunnar.flemstrom@neuro.uu.se ) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png AJP - Gastrointestinal and Liver Physiology The American Physiological Society

Food-induced expression of orexin receptors in rat duodenal mucosa regulates the bicarbonate secretory response to orexin-A

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Publisher
The American Physiological Society
Copyright
Copyright © 2011 the American Physiological Society
ISSN
0193-1857
eISSN
1522-1547
DOI
10.1152/ajpgi.00514.2006
pmid
17585016
Publisher site
See Article on Publisher Site

Abstract

Presence of appetite-regulating peptides orexin-A and orexin-B in mucosal endocrine cells suggests a role in physiological control of the intestine. Our aim was to characterize orexin-induced stimulation of duodenal bicarbonate secretion and modulation of secretory responses and mucosal orexin receptors by overnight food deprivation. Lewis x Dark Agouti rats were anesthetized and proximal duodenum cannulated in situ. Mucosal bicarbonate secretion (pH stat) and mean arterial blood pressure were continuously recorded. Orexin-A was administered intra-arterially close to the duodenum, intraluminally, or into the brain ventricles. Total RNA was extracted from mucosal specimens, reverse transcribed to cDNA and expression of orexin receptors 1 and 2 (OX1 and OX2) measured by quantitative real-time PCR. OX1 protein was measured by Western blot. Intra-arterial orexin-A (60–600 nmol·h –1 ·kg –1 ) increased ( P < 0.01) the duodenal secretion in fed but not in fasted animals. The OX1 receptor antagonist SB-334867, which was also found to have a partial agonist action, abolished the orexin-induced secretory response but did not affect secretion induced by the muscarinic agonist bethanechol. Atropine, in contrast, inhibited bethanechol but not orexin-induced secretion. Orexin-A infused into the brain ventricles (2–20 nmol·kg –1 ·h –1 ) or added to luminal perfusate (1.0–100 nM) did not affect secretion, indicating that orexin-A acts peripherally and at basolateral receptors. Overnight fasting decreased mucosal OX1 and OX2 mRNA expression ( P < 0.01) as well as OX1 protein expression ( P < 0.05). We conclude that stimulation of secretion by orexin-A may involve both receptor types and is independent of cholinergic pathways. Intestinal OX receptors and secretory responses are markedly related to food intake. bicarbonate secretion; enteroendocrine cells; fed and fasting state; perfused duodenum in situ; TRH Address for reprint requests and other correspondence: G. Flemström, Dept. of Neuroscience, Division of Physiology, Uppsala Univ., BMC, PO Box 572, SE-751 23 Uppsala, Sweden (e-mail: gunnar.flemstrom@neuro.uu.se )

Journal

AJP - Gastrointestinal and Liver Physiology – The American Physiological Society

Published: Aug 1, 2007

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