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sATP and β-NAD are inhibitory neurotransmitters released by the enteric musculomotorinnervation of the intestinal musculature of humans and guinea pigs. Actions of ATP andβ-NAD are at P2Y1 purinergic receptors with greatest potency for ATP. (Supported by NIHR01DK037238 & R01 DK068258).

Mo1651

Decreased Visceral Sensitivity Produced by a Combination of the 5-HT3Receptor Antagonist Palonosetron and of the NK1 Receptor AntagonistNetupitant in a Rodent Model of Visceral HypersensitivityClaudio Pietra, Karl R. Tyler, Victoria A. Weaver, Ehsan Mohammadi, BeverleyGreenwood-Van Meerveld

Background: Previous studies have shown that 5-HT3 receptor antagonism reduces symptomsin patients with irritable bowel syndrome associated with diarrhea (IBS-D), however anunfavorable side effect profile limits the clinical use of this approach.More recently, synergisticactivity has been observed between serotonergic 5-HT 3 and tachykinergic NK1 responsesIn Vitro and In Vivo. In the current study we tested the hypothesis that a synergistic inhibitoryeffect on visceral hypersensitivity occurs with the concomitant use of 5-HT3 receptor andNK1 receptor antagonists. To address this hypothesis we investigated the efficacy of a 5-HT3 antagonist,Palonosetron and the NK1 antagonist, Netupitant, alone or in combinationin a rodent model of colonic hypersensitivity. Methods: Colonic hypersensitivity was inducedexperimentally in rats by infusing diluted acetic acid (0.6%) into the colon. To assess thelevel of colonic sensitivity we measured a visceromotor behavioral response (VMR) quantifiedas the number of abdominal contractions in response to graded isobaric pressures (0-60mmHg) of colorectal distension (CRD). Palonosetron or Netupitant were administered viaoral gavage. Results: Administration of Palonosetron or Netupitant (0.1-1.0 mg/kg p.o.)when dosed alone resulted in a significant (P<0.05) inhibition of colonic hypersensitivity.Lower doses (0.001 mg/kg p.o.) of either compound were found to be ineffective. However,when non-effective doses (0.001 mg/kg p.o.) of Palonosetron and Netupitant were adminis-tered in combination, a significant (P<0.05) inhibition in colonic hypersensitivity was evidentin all rats. Summary: when combined at low doses, Palonosetron and Netupitant producesynergistic effects manifested by a statistically significant decrease in colonic hypersensitivityto luminal distension. Conclusion: In a rodent model of visceral hypersensitivity a combina-tion of a 5-HT3 receptor antagonist with a NK1 receptor antagonist showed a synergisticanalgesic activity; therefore the combination may prove to be a useful therapeutic approachto treat visceral pain associated with IBS-D.

Mo1652

Imbalanced Sympathetic Receptor Signaling Decreases Ghrelin Production andSecretion in an Urocortin 1-Induced Stress ModelKoji Yakabi, Kiyoshige Takayama, Shoki Ro, Mitsuko Ochiai, Shino Ohno, Yumi Harada,Masamichi Noguchi, Tomohisa Hattori

Background/Aim: Urocortin 1 (UCN), a member of the corticotropin-releasing factor (CRF)family, is an endogenous ligand for CRF receptors, and intracerebroventricular (ICV) UCNadministration results in marked inhibition of feeding behavior. Previously, we demonstratedthat UCN-induced anorexia may be partly caused by a decrease in gastric ghrelin secretionvia central CRF2 receptor activation. However, details of the mechanisms downstream ofCRF2 receptor activation remain unknown. To elucidate the detailed mechanisms of decreas-ing ghrelin secretion during conditions of stress, we examined the role of adrenergic receptorson decreased plasma ghrelin levels in an UCN-induced stress model in rats. Method: Aftera 24-h fast, male Sprague-Dawley rats were given an ICV injection of UCN or phosphate-buffered saline, and blood and brains were collected. The test drugs were administered 15min before UCN injection or simultaneously. After perfusion fixation, the fixed whole brainswere cut in the coronal plane. Central expression of c-fos mRNA and protein was evaluatedby in situ hybridization and immunohistochemical staining, respectively. Plasma acyl anddes-acyl ghrelin levels were measured by enzyme-linked immunosorbent assay. Results:Increased expression of both c-fos mRNA and protein were clearly observed in the solitarytract nucleus of rats under UCN-induced stress. They were also observed in several otherareas, including the supraoptic nucleus, paraventricular nucleus of the hypothalamus, locuscoeruleus, and the ventrolateral medulla. They were barely observed in the dorsal motornucleus of the vagus. Decreased plasma acyl- and desacyl-ghrelin levels in rats underUCN-induced stress were inhibited by treatment with an α-adrenergic receptor antagonist(phentolamine: 5 mg/kg, i.p.), an α2-adrenergic receptor antagonist (yohimbine: 5 mg/kg,i.p.), a β-adrenergic receptor agonist (isoproterenol: 0.2 mg/kg, i.p.) and a β1-adrenergicreceptor agonist (denopamine: 0.1 mg/kg, i.p.). In contrast, treatment with a β-adrenergicreceptor antagonist (propranolol: 3 mg/kg, i.p.), an α1-adrenergic receptor antagonist (prazo-sin: 5 mg/kg, i.p.) and a β2-adrenergic receptor agonist (salbutamol: 0.1 mg/kg, i.p.) failedto inhibit the decrease in ghrelin level. Conclusion: This study demonstrated changes incentral fos expression, suggesting that sympathetic efferent nerves may be involved in theinhibition of gastric ghrelin secretion, and that the reduction in ghrelin secretion in ratsunder UCN-induced stress may be mediated by activation ofα2-adrenergic receptor signalingand a reduction in β1-adrenergic receptor signaling.

S-650AGA Abstracts

Figure 2 : Effect of α and β-adrenergic receptor antagonist on plasma ghrelin levels

Figure1 : Effect of β-adrenergic receptor agonist on plasma ghrelin levels

Mo1653

Differential Expression of Leptin Receptor Isoforms Contribute to AlteredLeptin Signaling and Hyperphagia in Diet-Induced Obesity in RatsMoon Kyung Joo, Il Song, Andrea Heldsinger, Yuanxu Lu, Chung Owyang

Ingestion of fat-enriched diets is associated with hyperphagia and obesity. Recent studiessuggest that altered leptin signaling may be an important contributing factor. Leptin actsby binding to its receptor which is alternatively spliced into several isoforms. Although OB-Rb, the long isoform of the leptin receptor, is assumed to be responsible for transmittingthe signals mediating the central effects of leptin on appetite and energy expenditure, otherreceptor isoforms may be necessary for leptin to exert its full spectrum of In Vivo functions.In this study, we investigated the expression of five leptin receptor isoforms in the hypothal-amus and vagal nodose ganglia (NG), the principle sites for mediating the satiety actionsof leptin, in rats fed with a high fat diet (HFD). Rats fed with HFD gained 12% more weightcompared to controls at 12 wks. In the hypothalamus, there was a 45% reduction in thegene expression of OB-Rb (P<0.05, n=4). This was accompanied by a 70% increase in mRNAexpression of suppressor of cytokine signaling-3 (SOCS-3). In contrast to OB-Rb, the geneexpression of OB-Ra, OB-Rc, OB-Re and OB-Rf were increased by 87%, 21%, 180% and64% compared to age-matched controls. The nodose ganglia showed a similar pattern ofchanges in that the gene expression of OB-Ra, OB-Rc, OB-Re and OB-Rf were increased65%, 57%, 142% and 123% compared to controls (n=4, P<0.05). In contrast to the hypothal-amus, the expression of the long form OB-Rb did not change from controls, although SOCS-3 showed a 400% increase in protein expression. The increased expression of OB-Re (solublereceptor) in the hypothalamus and NG was accompanied by a 2.2-fold increase in the solubleleptin receptor (SLR) in the plasma. SLR is capable of binding leptin in the circulation andCSF. It may delay the clearance of leptin and contribute to the increase in plasma leptinobserved in HFD rats. The increased expression in OB-Ra may enhance transport of leptinacross the blood brain barrier (Peptides 1999;20:1449) and contribute to the developmentof leptin resistance in the hypothalamus. In fact we showed a 75+5% and 83+6% reductionof pSTAT3 in the hypothalamus and NG, respectively, in response to leptin challenge in12 wk HFD rats. In conclusion, we showed that there was a differential expression of thefive splice variants of leptin receptors in rats fed with a HFD. In the hypothalamus thedecreased expression of OB-Rb and the increased expression of SOCS-3 contributed to thedecreased response to leptin signaling. In the NG, there was normal expression of OB-Rb,but the enhanced expression of SOCS-3 led to leptin resistance. These together with theincreased expression of OB-Re which led to delayed clearance of leptin, may all contribute tothe altered leptin signaling resulting in hyperphagia and weight gain in diet-induced obesity.

Mo1654

Decreased Intestinal NHE3 Expression by mTOR Inhibition and ItsImplication in Rapamycin Related Diarrhea in Renal Transplant RecipientsJun Yang, Rachana Potru, Michael Dolinger, David Conti, Mark Donowitz, CatherineBartholomew, Seth Richter, Yunfei Huang, Xinjun Zhu

Background/Aim: The Mammalian target of rapamycin (mTOR) is a serine/threonine kinasethat regulates cell growth and proliferation as well as protein synthesis. The mTOR inhibitorrapamycin, an immunosuppressant, is frequently used in organ transplantation recipients.Chronic diarrhea, weight loss and episodic profound diarrhea requiring multiple hospitaliza-tions are costly, problematic and affect patients' quality of life. The incidence of rapamycinrelated diarrhea varies among different kinds of organ transplantations and is clearly correlatedwith high doses. However, the mechanism underlying rapamycin-induced diarrhea remainsunclear. The brush border Na+/H+ exchangers, such as NHE2 and NHE3, are known to