title: Food-induced expression of orexin receptors in rat duodenal mucosa regulates the bicarbonate secretory response to orexin-A.
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.
authors.affiliation: Dept. of Neuroscience, Division of Physiology, Uppsala University, BMC, PO Box 572, SE-751 23 Uppsala, Sweden.
authors.forename: Magnus W
authors.initials: MW
authors.lastname: Bengtsson
authors.forename: Kari
authors.initials: K
authors.lastname: Mäkelä
authors.forename: Markus
authors.initials: M
authors.lastname: Sjöblom
authors.forename: Sanna
authors.initials: S
authors.lastname: Uotila
authors.forename: Karl E O
authors.initials: KE
authors.lastname: Akerman
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Herzig
authors.forename: Gunnar
authors.initials: G
authors.lastname: Flemström
mesh_terms: D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001583:Benzoxazoles / Q000008:administration & dosage; D018723:Bethanechol / Q000494:pharmacology; D001639:Bicarbonates / Q000378:metabolism*; D002552:Cerebral Ventricles / Q000187:drug effects / Q000378:metabolism; D003433:Crosses, Genetic; D004305:Dose-Response Relationship, Drug; D004386:Duodenum / Q000187:drug effects / Q000378:metabolism*; D004435:Eating / Q000502:physiology*; D005508:Food Deprivation; D006863:Hydrogen-Ion Concentration; D007261:Infusions, Intra-Arterial; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D007419:Intestinal Secretions / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000008:administration & dosage / Q000378:metabolism*; D008297:Male; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009287:Naphthyridines; D009479:Neuropeptides / Q000008:administration & dosage / Q000378:metabolism*; D064446:Orexin Receptors; D000068797:Orexins; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011917:Rats, Inbred Lew; D043562:Receptors, G-Protein-Coupled / Q000096:biosynthesis* / Q000187:drug effects / Q000235:genetics; D018013:Receptors, Neuropeptide / Q000096:biosynthesis* / Q000187:drug effects / Q000235:genetics; D013997:Time Factors; D015854:Up-Regulation; D014508:Urea / Q000008:administration & dosage / Q000031:analogs & derivatives
chemical_list: C420062:1-(2-methylbenzoxazol-6-yl)-3-(1,5)naphthyridin-4-yl urea; D001583:Benzoxazoles; D001639:Bicarbonates; D047908:Intracellular Signaling Peptides and Proteins; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D009287:Naphthyridines; D009479:Neuropeptides; D064446:Orexin Receptors; D000068797:Orexins; D012333:RNA, Messenger; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide; D018723:Bethanechol; D001285:Atropine; D014508:Urea