Shin Tanaka

Dynamic regulation of gastric surface pH by luminal pH

In vivo confocal imaging of the mucosal surface of rat stomach was used to measure pH noninvasively under the mucus gel layer while simultaneously imaging mucus gel thickness and tissue architecture. When tissue was superfused at pH 3, the 25 microm adjacent to the epithelial surface was relatively alkaline (pH 4.1 +/- 0.1), and surface alkalinity was enhanced by topical dimethyl prostaglandin E2 (pH 4.8 +/- 0.2). Luminal pH was changed from pH 3 to pH 5 to mimic the fasted-to-fed transition in intragastric pH in rats. Under pH 5 superfusion, surface pH was relatively acidic (pH 4.2 +/- 0.2). This surface acidity was enhanced by pentagastrin (pH 3.5 +/- 0.2) and eliminated by omeprazole, implicating parietal cell H,K-ATPase as the dominant regulator of surface pH under pH 5 superfusion. With either pH 5 or pH 3 superfusion (a) gastric pit lumens had the most divergent pH from luminal superfusates; (b) qualitatively similar results were observed with and without superfusion flow; (c) local mucus gel thickness was a poor predictor of surface pH values; and (d) no channels carrying primary gastric gland fluid through the mucus were observed. The model of gastric defense that includes an alkaline mucus gel and viscous fingering of secreted acid through the mucus may be appropriate at the intragastric pH of the fasted, but not fed, animal.

Direct measurement of acid permeation into rat oesophagus

Background and aims: The early responses of the oesophageal mucosa to acid perfusion may predict subsequent pathology. Mucosal responses to luminal acid may result either from acid permeating through the mucosa or from other unknown transduction mechanisms. In order to better understand the dynamics of acid permeation into the oesophageal mucosa, we measured interstitial pH (pHint) of the oesophageal basal epithelial layer, pre-epithelial layer thickness, and blood flow in rats in vivo during luminal acid challenge. A novel confocal microscopic technique was used in vitro to measure pHint from defined cellular sites in response to luminal and basolateral acidification. Methods: 5-(and-6)-Carboxyfluorescein (CF) and carboxy-seminapthorhodofluor-1 (SNARF-1) fluorescence was used to measure pHint by conventional and confocal microscopy, respectively, in urethane anaesthetised rats. Pre-epithelial layer thickness was measured optically with carbon particles as markers. Blood flow was measured with laser Doppler flowmetry. Results: Luminal acidification failed to alter pHint in vivo and in vitro, but pHint was lowered by modest serosal acidification. Pre-epithelial layer thickness and blood flow increased significantly during luminal surface acid perfusion. Indomethacin had no effect on any acid related response. Conclusion: In this first dynamic measurement of oesophageal acid permeation and pre-epithelial layer thickness, pHint was preserved in spite of high luminal acidity by two complementary techniques. Despite the apparent permeability barrier to acid permeation, oesophageal blood flow and thickness responded to luminal acid perfusion.

Pentagastrin gastroprotection against acid is related to H2 receptor activation but not acid secretion

Background—Pentagastrin enhances gastric mucosal defence mechanisms against acid and protects the gastric mucosa from experimental injury. Aims—To investigate whether this gastroprotection is mediated by histamine receptors or occurs as a secondary effect of acid secretion stimulation. Methods—The effects of omeprazole (100 μmol/kg), ranitidine (20 mg/kg), and pyrilamine (10 mg/kg) on pentagastrin (80 μg/kg/h) induced gastroprotection against acidified aspirin injury were examined in a luminal pH controlled model. The effects of these compounds on pentagastrin enhanced gastroprotective mechanisms were investigated using intravital microscopy, in which intracellular pH of gastric surface cells (pHi), mucus gel thickness, gastric mucosal blood flow, and acid output were measured simultaneously. Results—Pentagastrin protected rat gastric mucosa from acidified aspirin injury. This gastroprotection was abolished by ranitidine, but not omeprazole or pyrilamine. Pentagastrin induced a hyperaemic response to luminal acid challenge, increased mucus gel thickness, and elevated pHi during acid challenge. Ranitidine reversed these enhanced defence mechanisms, whereas omeprazole and pyrilamine preserved these effects. Conclusions—These data indicate that pentagastrin associated gastroprotection and enhanced defence mechanisms against acid result mainly from activation of histamine H2 receptors, and not as an effect of the stimulation of acid secretion.

Gastroprotective effect of ranitidine bismuth citrate is associated with increased mucus bismuth concentration in rats.

BACKGROUND: Antisecretory and bismuth compounds protect the gastric mucosa from injury resulting from non-steroidal anti-inflammatory drugs. AIM: To study the mechanism underlying the gastroprotective effects of ranitidine bismuth citrate (GG311) in rats. METHODS: Indomethacin rat injury model and in vivo microscopy in which acid output, surface cell intracellular pH (pHi), gastric mucus gel thickness, and mucosal blood flow were measured simultaneously. RESULTS: In injury studies, GG311 dose dependently protected against severe injury induced by indomethacin (60 mg/kg subcutaneously). In in vivo microscopic studies, indomethacin significantly decreased mucus gel thickness and increased the initial rate of acidification of gastric surface cells when the superfusate pH was lowered from 7.4 to 1.0, and impaired pHi during acid exposure. Indomethacin had no effect on mucosal blood flow or acid output. GG311 alone had no effect on gel thickness, blood flow, or pHi homeostasis during acid exposure, but improved the initial acidification rate and pHi during superfusion with pH 1.0 solutions in the presence of indomethacin. In separate experiments, indomethacin pretreatment considerably increased gastric mucus bismuth concentrations in rats given GG311. CONCLUSIONS: The gastroprotective effect of GG311 against indomethacin induced gastric injury is associated with high and prolonged gastric mucus bismuth concentrations, which may impair proton permeation across the mucus gel.

Gastroduodenal Microcirculatory Response to Luminal Acid

The hyperemic response to luminal acid, a key protective mechanism for upper gastrointestinal mucosa, occurs by different mechanisms in the distal esophagus, stomach, and duodenum. The esophagus is a stratified squamous mucosa of high electrical resistance. Although luminal acid permeates only into the superficial epithelial layer, luminal acid induces protective mucosal hyperemia and clinical symptoms. The stomach has a well-studied microcirculatory response to luminal acid. Blood flow is believed to play a prominent role in mucosal protection, since the abolition of the hyperemic response to luminal acid is associated with enhanced mucosal injury susceptibility. Infusion of pentagastrin, mimicking the endogenous secretory gastric response to food, unmasked this hyperemic response in undamaged mucosa and activates neurons in the vagal nucleus. The duodenum is a leaky, low-resistance, columnar epithelium. Unlike the stomach, duodenal hyperemia is readily produced by perfusion with acidic luminal solutions. We further studied the afferent pathways involved with this hyperemic response. The vanilloid receptor (VR) antagonist capsazepine (CPZ) dose-dependently inhibited capsaicin-induced hyperemia. Capsazepine dosedependently inhibited acid-induced hyperemia. The gastric and intestinal mucosae are richly innervated with VR. Each segment of the gastrointestinal tract exposed to gastric acid appears to have a unique protective mechanisms to which regulation of mucosal blood flow plays an important role.

Correlation of surface pH versus mucus gel thickness by in vivo confocal microscopy of rat gastric mucosa

and HM-CAP, but the FLEX PACK assay failed to detect two (33%). Conclusions: (1) The Chiron lysate and HM-CAP are equally sensitive in detecting HP antibody but the lysate assay is twice as specific; (2) the FLEX PACK assay is significantly less sensitive than the other two assays; (3) 29% of pediatric patients with abdominal pain have antibodies to CagA or VacA. These patients are accurately detected by Chiron lysate or HM-CAP assays, but not by FLEX PACK. This study was funded in part by a grant from EPI.