Mo2040

Emergence of Circumferential Slow Wave Propagation During GastricDysrhythmias in Diabetic GastroparesisGregory O'Grady, Timothy R. Angeli, Leo K. Cheng, Christopher J. Lahr, NiranchanPaskaranandavadivel, Peng Du, Wim J. Lammers, David Midgley, Gianrico Farrugia,Thomas L. Abell, Andrew J. Pullan

Introduction Gastric smooth muscle layers are electrically excited by slow waves. In thenormal stomach, slow waves propagate longitudinally in ring wavefronts from the uppercorpus to the distal antrum. Circumferential propagation does not appear to occur, likelybecause there is no excitable tissue available circumferentially in these rings. However, rapidcircumferential propagation has been observed in isolated gastric tissues and during gastricpacing. In this study, the propagation profiles of slow wave behaviors in diabetic gastroparesiswere defined at high resolution (HR). The hypothesis was that circumferential propagationoccurs during dysrhythmia, presenting a novel marker of gastric electrical dysfunction.Methods HR (multi-electrode) mapping was performed in 7 patients with diabetic gastropar-esis undergoing laparotomy for stimulator implantation. Anterior serosal recordings weretaken using flexible PCB arrays (256 electrodes; 4 mm spacing; 36cm2), and activationmapping was performed. Velocity fields were calculated using a finite difference approachincorporating a Gaussian filter smoothing function. Amplitudes were calculated using apeak-trough detection algorithm. Longitudinal and circumferential propagation data fromcorpus recordings were compared with Student's t-test. Means±SEM are reported. ResultsAtypical or dysrhythmic propagation was observed in 6/7 patients, including incompleteconduction block, complete block with escape, ectopic pacemaking in the corpus and antraltachygastria (freq range: 2.7-4.2 cpm). Circumferential propagation was associated with allof these events (circumferential velocity 6.6 ± 0.9 mm/s vs longitudinal velocity 2.9 ±0.2 mm/s; p<0.01). Extracellular slow wave amplitudes were also ~2.5x higher duringcircumferential propagation (411±66 uV vs 170±27 uV; p<0.01). Isochronalmapping demon-strated that circumferential propagation led to the rapid restoration of a normal longitudinalwavefront distal to the source of the dysrhythmia. However, circumferential propagation alsopromoted organized retrograde propagation in the case of antral tachygastria. ConclusionsPropagation abnormalities in diabetic gastroparesis include conduction blocks, escape, andectopic events, potentially as a consequence of known ICC network degradation. Circumfer-ential propagation emerges in many of these abnormal patterns because excitable tissuebecomes available in the circumferential direction. Circumferential conduction is found tobe associated with high velocities and high amplitudes, which could therefore serve as usefulclinical indicators for abnormal slow wave propagation. Functionally, rapid circumferentialpropagation serves to restore normal slow wave propagation distal to conduction defects,however it can also promote organized retrograde tachygastria.

Mo2041

A Novel Phenotype of Glycogen Storage Disease Presenting as GastrointestinalNeuromuscular DiseaseJoanne E. Martin, ATMDilshad H. Chowdhury, Suzanne McElwaine, Asma Fikree, JohnBroad, Charles H. Knowles, Liz Allen, Shaun Bevan, Emma Burt, Austin J. Hymas, PhilipJ. Rowburrey, Gareth J. Sanger, Mohammed M. Rahman, Alice A. Thomas, YanYiannakou, Sheldon C. Cooper, Christopher A. Evagora, Pauline M. Levey, Finbarr E.Cotter, Qasim Aziz, Murphy Elaine, Richard W. Pickersgill, Katie Bainbridge, David B.Silk

BACKGROUND Patients with gastrointestinal neuromuscular disease can present with pain,vomiting, and pseudo-obstruction and develop intestinal failure. There are typically multipleinteractions with clinicians and investigations, often without diagnostic resolution. We haveidentified a specific histological phenotype in a significant subset of these patients andinvestigated the associated biochemical and genetic defects, testing the hypothesis that theyhave a disorder of glycogen storage. METHODS We collated patients with GI neuromusculardisease with polyglucosan bodies of the small bowel, and examined a subset case series of11, including clinical details with ROME II questionnaires in 10, quantitative histologicalanalysis and immunohistochemical studies of full thick bowel biopsies together with biochem-ical assay, RNA and DNA genetic studies of glycogen branching enzyme (GBE) in blood inall 11. We calculated the minimum phenotype prevalence in a separate well characterisedclinical series of 67 patients with pseudo-obstruction who had undergone full thicknesssmall bowel biopsy. RESULTS All 11 patients had polyglucosan bodies in the muscularispropria of the bowel wall with no fibrosis or inflammation. 6 had low or very low GBEactivity in blood, 2 borderline low, and 3 normal range. Mean GBE activity was 28.7 (range8-51) compared with control mean 74 (range 32-116). One had a novel pathogenic mutationin the active site of GBE at Y329, and three others low levels (mean 57%, range 55-60%)of GBE RNA in blood compared with controls (p<0.000054). Mean age of onset was 45(n=9, range 29-66). One patient had small bowel transplant for intestinal failure and wasunwell. 10 others completed the questionnaire, 9 had frequent or almost constant abdominalpain, 5 recurrent vomiting and 6 nausea. One was on TPN, two others had had PEGs andfour others bowel resection. Of a separate series of 67 patients with pseudoobstruction atleast 6.7% have the polyglucosan body phenotype. CONCLUSIONS Our findings indicatethat a significant proportion of patients with gastrointestinal neuromuscular disease have adisorder of glycogen storage. Intestinal glycogen storage disease (IGSD) may arise from arange of molecular mechanisms, including mutation similar to that seen in type IV glycogenstorage disease (GSD4). GSD4 is described in hepatic, neuromuscular and cardiac forms,but a specific primary gastrointestinal phenotype has not previously been described.

S-705 AGA Abstracts

Figure 1. Cartoon representation of the active centre of GBE1 (PDB code 1M7X; Abad etal, 2002). The active centre is at the C-terminal end of the (beta/alpha)8-barrel and theeight beta -strands (represented as arrows) are labelled beta1 through 8. Some of the aminoacid residues implicated in activity are shown clustered around the C-terminal end of the(beta/alpha)8-barrel including: Y251, H291, R355, D357, E412, D481 (human numbering.Also conserved is Y329 which can be seen to reside in the beta3 alpha3 loop adjacent tothe active centre. Substitution of this tyrosine by cysteine would reduce the hydrophobicburial in this region; also a hydrogen bond from the tyrosine hydroxyl to the main-chaincarbonyl of residue 290 would be lost. Both these changes are likely to reduce the stabilityof this loop region and affect the position of H291 and environment of D357 at the activecentre resulting in a reduction of GBE1 activity. This Figure was made using PYMOL.

Mo2042

Increased Dopamine and DA2 Receptor Expression in the Gastric MyentericPlexus (MP) is Responsible for Gastroparesis in Parkinson's Disease RatModel Treated With 6-OhdaLifei Zheng, Jin Song, Zhiyong Wang, Chung Owyang, Jinxia Zhu

Gastroparesis is reported in up to 100% of Parkinson's disease (PD). However the responsiblemechanism(s) is not well understood. Dopamine (DA) and its receptors are present in thegastric MP. DA administration inhibits gastric motility. It is conceivable that enhancedproduction of DA and/or an upregulation of its receptors in the MP may be responsible fordelayed gastric emptying in PD. To test this hypothesis, we used a PD rat model which wastreated with bilateral microinjection of 6-hydroxydopamine (6-OHDA) in the substantianigra (SN). In Vivo gastric motility studies performed 6 wks following 6-OHDA treatmentshowed reduced frequency of migrating motor complex (6.0±0.3/hr vs 9.4±0.5/hr, P<0.001)and decreased amplitude of contraction (1.3±0.2 g vs 3.2±0.3 g, P<0.001). This was accom-panied by a 28% reduction in gastric emptying (P<0.05). Organ bath gastric muscle stripstudies showed a 66+5% reduction in motility index (P<0.001). These motility changeswere accompanied by a 46% increase in DA contents (from 7.8±0.9 to 11.4+±1.4 nmol/g,P<0.05) and a 2-3 fold increase in gene expression and protein level of DA2 but not DA1receptor. IV infusion of domperidone (2 μg/kg DA2 receptor antagonist) but not SCH2390(14 μg/kg DA1 receptor antagonist) increased the frequency and amplitude of contractionsby 50%. To confirm that the increased production of DA and expression of DA2 receptorsin the gastric MP is responsible for delayed gastric emptying in the 6-OHDA rats, weperformed motility studies in another rodent PD model which was treated with systemicadministration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP caused asimilar degree loss of dopaminergic neurons in the SN but in contrast to 6-OHDA, it alsoproduced a 60% reduction in DA contents in the gastric MP. The MPTP animals showedno significant change in frequency and amplitude of concentrations compared to controls.To investigate the mechanism responsible for the enhanced production of DA contents andDA2 receptors in the stomach, we demonstrated that tyrosine hydroxylase (TH) expressionin DMV neurons was increased from 0.61±0.05 to 0.89±0.06 ng/g (P<0.05) by Westernblot analysis. This was confirmed by immunocytochemistry studies. Subdiaphragmatic vago-tomy at the time of 6-OHDA treatment prevented increase in DA contents and DA2 receptorexpression in the MP and reduction in gastric motility in 6-OHDA rats. In conclusion, wedemonstrated that delayed gastric emptying in PD is due to increased DA content andupregulation of DA2 receptors in the gastric MP. This motility abnormality can be amelioratedby the administration of domperidone. It is conceivable that dopaminergic deficiency in theSN may result in enhanced production of DA in the DMV. This in turn modulates theexpression of DA and DA2 receptors in the gastric MP resulting in reduced gastric motilityin PD.

Mo2043

Aberrant Initiation and Conduction of Slow Wave Activity in Diabetic andIdiopathic GastroparesisGregory O'Grady, Timothy R. Angeli, Leo K. Cheng, Christopher J. Lahr, Peng Du, WimJ. Lammers, David Midgley, Michelle Deacon, Gianrico Farrugia, Thomas L. Abell,Andrew J. Pullan

Introduction: Gastric motility is coordinated by slow wave activity, which is generated andpropagated by the interstitial cells of Cajal (ICC). ICC loss is now recognized to be themajor histological hallmark of diabetic gastroparesis and idiopathic gastroparesis. ICC loss

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