Acid Back-diffusion Research Articles

Concentration of Sulfuric Acid from Spent Acidic Liquor by Cascaded Electrodialysis Using an Interpolymer Anion Exchange Membrane

Cascaded electrodialysis system has been developed for increasing the concentration of sulfuric acid from aqueous solution using an interpolymer anion exchange (IPA) membrane. Enrichment process was carried out in a cascade of six electrodialyzers at 20.2 mA/cm2 current density. The performance of the process was evaluated rigorously in terms of current efficiency, voltage requirements and processability to enrich the acid concentration. The bench-scale experimental results exhibited the ability of membrane to perform as a low proton leakage membrane and to enrich the sulfuric acid concentration up to 27.93 wt. %. The higher values of current efficiencies were reported to be in the range of 50 to 60 %. Proton leakage through the membrane, acid back diffusion, concentration polarization and solution conductivity were considered to be the limiting factors for acid enrichment and their effects were found significant on current efficiency and voltage requirement.

Regulatory mechanism of the gastric hyperemic response following barrier disruption: roles of cyclooxygenase-1, the prostaglandin E2/EP1 receptor and sensory neurons.

We herein reviewed the mechanism underlying the gastric hyperemic response following barrier disruption, with a focus on cyclooxygenase (COX) isozymes, prostaglandin (PG) E2, and capsaicin-sensitive afferent neurons. Mucosal damage was induced by exposing the stomach to 20 mM taurocholate (TC) with 50 mM HCl. The TC treatment disrupted surface epithelial cells, and then increased acid back-diffusion and mucosal blood flow (GMBF) in the stomachs of rats or wild-type mice. This hyperemic response in the rat stomach was inhibited by indomethacin without affecting acid back-diffusion, which resulted in the aggravation of lesions. The effect of indomethacin was mimicked by loxoprofen and the selective COX-1 inhibitor, SC-560, but not by the selective COX-2 inhibitor, celecoxib. The GMBF responses induced by TC were similarly observed in the stomachs of wild-type mice and EP3 receptor knockout mice, but not in mice lacking the EP1 receptor or pretreated with an EP1 antagonist. The increase in the GMBF response associated with acid back-diffusion after the TC treatment was also inhibited by the chemical ablation of capsaicin-sensitive afferent neurons, but not capsazepine, a TRPV1 antagonist. Thus, endogenous PGE2 produced by COX-1 plays a role in the gastric hyperemic response following barrier disruption of the stomach by interacting with capsaicin-sensitive afferent neurons, mainly through EP1 receptors, and facilitating the GMBF response to acid back-diffusion. These findings have also contributed to a deeper understanding of mucosal defensive mechanisms following barrier disruption and the development of new strategies for the treatment of gastrointestinal diseases.

Capsaicin receptor as target of calcitonin gene-related peptide in the gut.

Calcitonin gene-related peptide (CGRP), a 37 aminoacid-residue peptide, is a marker of afferent fibers in the upper gastrointestinal tract, being almost completely depleted following treatment with the selective neurotoxin capsaicin that targets these fibers via transient receptor potential vanilloid type-1 (TRPV-1). It is widely distributed in the peripheral nervous system of mammals where it is present as alpha isoform, while intrinsic neurons of the enteric nervous systems express predominantly CGRP-beta. Many gastrointestinal functions involve CGRP-containing afferent fibers of the enteric nervous system such as defense against irritants, intestinal nociception, modulation of gastrointestinal motility and secretion, and healing of gastric ulcers. The main effects on stomach homeostasis rely on local vasodilator actions during increased acid-back diffusion. In humans, release of CGRP through the activation of TRPV-1 has been shown to protect from gastric damage induced by several stimuli and to be involved in gastritis. In both dyspepsia and irritable bowel syndrome the repeated stimulation of TRPV-1 induced an improvement in epigastric pain of these patients. The TRPV-1/CGRP pathway might be a novel target for therapeutics in gastric mucosal injury and visceral sensitivity.

Role of Calcitonin Gene-Related Peptide in Gastric Mucosal Defence and Healing

Calcitonin gene-related peptide (CGRP) is a polypeptide produced by alternative processing of calcitonin gene transcripts and is endowed with important systemic physiological effects. The recent characterization of its receptor and the discovery of stable antagonists has addressed them in the indication migraine. Beside this, several studies have been focused on role of CGRP at gastric level. CGRP is considered a marker of afferent fibers in the upper gastrointestinal tract being almost completely depleted following treatment with the selective neurotoxin capsaicin that targets these fibers via transient receptor potential vanilloid of type-1. The exogenous administration of the peptide was able to afford protection against experimental ulcers induced by an increase in gastric secretion. The use of CGRP knockout mice has let to characterize the endogenous role of CGRP showing that the local release of this neuropeptide protects from ethanol injury and favours ulcer healing. Decreased levels of gastric CGRP-like immunoreactivity (li) were observed during acetic acid-, cysteamine-, concentrated ethanol- or water immersion stress-ulcers. Restoration of CGRP-li was found in animals bearing ulcers in healing status and delayed healing in mice knockout to CGRP. CGRP was able to release somatostatin from gastric D cells but its main effects on the stomach homeostasis rely on local vasodilator action during increased acid-back diffusion.

Ablation of primary afferent neurons by neonatal capsaicin treatment reduces the susceptibility of the portal hypertensive gastric mucosa to ethanol-induced injury in cirrhotic rats

Primary sensory afferent neurons modulate the hyperdynamic circulation in cirrhotic rats with portal hypertension. The stomach of cirrhotic rats is prone to damage induced by ethanol, a phenomenon associated with reduced gastric hyperemic response to acid-back diffusion. The aim of this study was to examine the impact of ablation of capsaicin-sensitive neurons and the tachykinin NK1 receptor antagonist A5330 on the susceptibility of the portal hypertensive gastric mucosa to ethanol-induced injury and its effects on gastric cyclooxygenase (COX) and nitric oxide synthase (NOS) mRNA expression. Capsaicin was administered to neonatal, male, Wistar rats and the animals were allowed to grow. Cirrhosis was then induced by bile duct ligation in adult rats while controls had sham operation. Ethanol-induced gastric damage was assessed using ex vivo gastric chamber experiments. Gastric blood flow was measured as well as COX/NOS mRNA expression. Topical application of ethanol produced significant gastric damage in cirrhotic rats compared to controls, which was reversed in capsaicin- and A5330-treated animals. Mean arterial and portal pressure was normalized in capsaicin-treated cirrhotic rats. Capsaicin and A5330 administration restored gastric blood flow responses to topical application of ethanol followed by acid in cirrhotic rats. Differential COX and NOS mRNA expression was noted in bile duct ligated rats relative to controls. Capsaicin treatment significantly modified gastric eNOS/iNOS/COX-2 mRNA expression in cirrhotic rats. Capsaicin-sensitive neurons modulate the susceptibility of the portal hypertensive gastric mucosa to injury induced by ethanol via tachykinin NK1 receptors and signalling of prostaglandin and NO production/release.

Pathogenic importance of pepsin in ischemia/reperfusion-induced gastric injury

We investigated the role of pepsin in the development of ischemia/reperfusion (I/R)-induced gastric lesions in rats. Under urethane anesthesia, the pylorus was ligated, the celiac artery was clamped, and 1 ml of HCl (50–150 mM) was instilled in the stomach. Then, reperfusion was established 15 min later by removing the clamp, and 2 h later the stomach was assessed for gross mucosal damage. Pepstatin (a specific pepsin inhibitor) or pepsin was given i.g. after the pylorus was ligated while cimetidine, omeprazole, or atropine was given s.c. 30 min before the ligation. I/R produced hemorrhagic gastric injury, with a concomitant increase in the amount of pepsin secreted, and the degree of both these responses was dependent on the concentration of HCl. The formation of lesions by IR in the presence of 100 mM HCl was significantly prevented by atropine or bilateral vagotomy, but neither omeprazole nor cimetidine had any effect. Intragastric administration of pepstatin dose-dependently reduced the severity of the I/R-induced gastric lesions, the effect being significant even at 0.1 mg/kg, while that of pepsin markedly aggravated these lesions. The increased pepsin output during I/R was associated with luminal acid loss and significantly inhibited by bilateral vagotomy or pretreatment with atropine but not cimetidine or omeprazole, while pepstatin significantly inhibited the pepsin activity. In conclusion, we suggest that pepsin plays a pivotal role in the pathogenesis of I/R-induced gastric lesions, and pepsin secretion is increased during I/R, the process being associated with acid back-diffusion and mediated through a vagal-cholinergic pathway.

NSAID injury to the gastrointestinal tract: evidence that NSAIDs interact with phospholipids to weaken the hydrophobic surface barrier and induce the formation of unstable pores in membranes

In this review, we have discussed our current understanding of the barrier properties that are in place to protect the upper gastrointestinal mucosa from luminal acid, and the pathogenic mechanism by which nonsteroidal anti-inflammatory drugs (NSAIDs) induce injury to the gastrointestinal tract. The changes in our view of the importance of NSAID-induced cyclo-oxygenase (COX) inhibition on the pathogenesis and prevention of NSAID-induced gastrointestinal injury is presented. The focus of this paper has been placed on the effects of NSAIDs on the mucosal surface, and specifically the effect of these powerful drugs in inducing changes in the hydrophobicity, fluidity, biomechanical and permeability properties of extracellular and membrane phospholipids. Lastly, recent evidence is presented that salicylic acid and related NSAIDs may alter the stability of membranes, inducing the formation of unstable pores that may lead to back-diffusion of luminal acid and membrane rupture. This understanding of the interaction of NSAIDs with membrane phospholipids may prove valuable in the design of novel NSAID formulations with reduced gastrointestinal side-effects.

Role of gastric oxidative stress and nitric oxide in formation of hemorrhagic erosion in rats with ischemic brain

To investigate the role of gastric oxidative stress and nitric oxide (NO) in the formation of gastric hemorrhagic erosion and their protection by drugs in rats with ischemic brain. Male Wistar rats were deprived of food for 24 h. Under chloral hydrate (300 mg/kg) anesthesia, bilateral carotid artery ligation was performed. The pylorus and carotid esophagus of the rats were also ligated. The stomachs were then irrigated for 3 h with either normal saline or simulated gastric juice containing 100 mmol/L HCl plus 17.4 mmol/L pepsin and 54 mmol/L NaCl. Rats were killed and stomachs were dissected. Gastric mucosa and gastric contents were harvested. The rat brain was dissected for the examination of ischemia by triphenyltetrazolium chloride staining method. Changes in gastric ulcerogenic parameters, such as decreased mucosal glutathione level as well as enhanced gastric acid back-diffusion, mucosal lipid peroxide generation, histamine concentration, luminal hemoglobin content and mucosal erosion in gastric samples, were measured. Bilateral carotid artery ligation produced severe brain ischemia (BI) in rats. An exacerbation of various ulcerogenic parameters and mucosal hemorrhagic erosions were observed in these rats. The exacerbated ulcerogenic parameters were significantly (P<0.05) attenuated by antioxidants, such as exogenous glutathione and allopurinol. These gastric parameters were also improved by intraperitoneal aminoguanidine (100mg/kg) but were aggravated by N(G)-nitro-L-arginine-methyl ester (L-NAME: 25 mg/kg). Intraperitoneal L-arginine (0-500 mg/kg) dose-dependently attenuated BI-induced aggravation of ulcerogenic parameters and hemorrhagic erosions that were reversed by L-NAME. BI could produce hemorrhagic erosions through gastric oxidative stress and activation of arginine-nitric oxide pathway.

Modulation of gastric hemorrhage and ulceration by oxidative stress and histamine release in Salmonella typhimurium-infected rats

Infection with Salmonella typhimurium can produce multiple organ dysfunctions. However, document concerning with gastric hemorrhagic ulcers occur in this infectious disease is lacking. The aim was to study modulation of gastric hemorrhagic ulcer by oxidative stress and mast cell histamine in S. typhimurium-infected rats. Additionally, the protective effects of drugs, such as ofloxacin, lysozyme chloride, ketotifen, ranitidine, and several antioxidants, including exogenous glutathione (GSH), allopurinol and dimethylsulfoxide (DMSO) were evaluated. Male Wistar rats were injected intrajejunally with a live culture of S. typhimurium (1 x 10(10) colony-forming units/rat) and followed by deprivation of food for 36 h. Age-matched control rats received sterilized vehicle only. Rat stomachs were irrigated for 3 h with either normal saline or a simulated gastric juice containing 100 mM HCl, 17.4 mM pepsin and 54 mM NaCl. S. typhimurium caused aggravation of offensive factors, including enhancing gastric acid back-diffusion, mucosal lipid peroxide generation, histamine release, microvascular permeability and hemorrhagic ulcer, as well as an attenuation of defensive substances, such as mucosal GSH and mucus level. Intragastric irrigation of gastric juice caused further aggravation of these gastric biochemical parameters. This exacerbation of ulcerogenic factors was abolished by pretreatment of ofloxacin and lysozyme chloride. Antioxidants, such as reduced GSH, allopurinol and DMSO also produced significant (P < 0.05) amelioration of gastric damage in S. typhimurium infected rats. In conclusion, gastric oxidative stress and histamine play pivotal roles in the formation of hemorrhagic ulcers that were effectively ameliorated by ofloxacin, lysozyme chloride, ketotifen, ranitidine, diamine oxidase and various antioxidants in S. typhimurium-infected rats.

Effect of lysozyme chloride on betel quid chewing aggravated gastric oxidative stress and hemorrhagic ulcer in diabetic rats

To evaluate the protective effect of lysozyme chloride on betel quid chewing (BQC) aggravated gastric oxidative stress and hemorrhagic ulcer in rats with diabetes mellitus (DM). Male Wistar rats were challenged intravenously with streptozotocin (65 mg/kg) to induce DM. Rats were fed with regular pellet food or BQC-containing diets. After 90 d, rats were deprived of food for 24 h. Rat stomachs were irrigated for 3 h with normal saline or simulated gastric juice. Rats were killed and gastric specimens were harvested. An enhancement of various gastric ulcerogenic parameters, including acid back-diffusion, mucosal lipid peroxide generation, as well as decreased glutathione levels and mucus content, were observed in DM rats. After feeding DM rats with BQC, an exacerbation of these ulcero-genic parameters was achieved. Gastric juice caused a further aggravation of these ulcerogenic parameters. Daily intragastric lysozyme chloride dose-dependently inhibited exacerbation of various ulcerogenic parameters in those BQC-fed DM rats. (1) Gastric juice could aggravate both DM and BQC-fed DM rat hemorrhagic ulcer; (2) BQC exacerbated gastric hemorrhagic ulcer in DM rats via enhancing oxidative stress and reducing defensive factors; (3) lysozyme chloride effectively protected BQC aggravated gastric damage in DM rats.

Cystic fibrosis gene mutation reduces epithelial cell acidification and injury in acid-perfused mouse duodenum

Dysfunction of the cystic fibrosis transmembrane regulator (CFTR) is associated with diminished duodenal HCO3- secretion, despite a reported lack of clinical duodenal ulceration in affected subjects. We hypothesized that duodenal epithelial cells expressing a mutant CFTR have enhanced resistance to acid-induced injury. To test this hypothesis, we measured duodenal epithelial cell intracellular pH (pHi), injury, and acid back-diffusion in response to a luminal acid challenge in transgenic mice. A murine colony was established for the CFTR DeltaF508 (DeltaF) mutation. Epithelial cell pH i was measured by microscopy with a trapped, fluorescent pH-sensitive dye in living C57BL/6 and DeltaF/DeltaF, +/DeltaF, and +/+ mice. In vivo confocal microscopy confirmed the localization of the dye in the cytoplasm of the epithelial cells. Epithelial injury was measured fluorometrically using propidium iodide. Duodenal epithelial bicarbonate secretion and proton permeability were measured by back-titration. Bicarbonate secretion and acid back-diffusion were measured in a perfused duodenal loop. Basal and post-acid exposure bicarbonate secretion were reduced in DeltaF/DeltaF mice, although acid back-diffusion was similar to controls. Epithelial pHi of CFTR DeltaF/DeltaF mice during luminal acid exposure was significantly higher than pHi in +/DeltaF, +/+, or C57BL/6 mice. Acid-related epithelial injury was markedly less in DeltaF/DeltaF mice in comparison with the other groups. Increased cellular buffering power of the epithelial cells of DeltaF/DeltaF mice likely protects against acidification and injury during acid exposure. We speculate that this protective mechanism partially underlies the perceived relative lack of peptic ulceration in patients affected by cystic fibrosis.

Role of histamine and acid back-diffusion in modulation of gastric microvascular permeability and haemorrhagic ulcers in betel-quid-fed rats

Evidence concerning the pathogenesis of gastric haemorrhagic ulcer produced by betel quid chewing (BQC) is lacking. This research first proposes that alterations of mast cell histamine release and gastric acid back-diffusion are important in modulating gastric microvascular permeability and mucosal haemorrhagic ulcer in BQC-fed rats. The effects of several histamine receptor antagonists on this ulcer model also were evaluated. Male Wistar rats were fed with BQC diet or normal pellet diet. After 1, 30 and 90 day(s), rat stomachs were irrigated for 3 h with either normal saline or simulated gastric juice. Gastric acid back-diffusion, mucosal histamine concentration, microvascular permeability, as well as luminal haemoglobin content and ulcer areas were determined. Severe gastric haemorrhage and mucosal ulcerations, particularly in acidic stomachs, were observed in BQC-fed rats. A high correlation was observed between histamine and gastric haemorrhage, as well as between acid back-diffusion and mucosal ulceration was found in rats fed with BQC. This haemorrhagic ulcer in BQC-fed rats was effectively ameliorated by intragastric ketotifen, ranitidine or their combination. In conclusion, enhancement of acid back-diffusion, mast cell histamine release and microvascular permeability is important in modulating gastric haemorrhage and ulcer in BQC-fed rats.

Protective effects of lysozyme chloride and reduced glutathione on betel quid chewing-produced gastric oxidative stress and haemorrhagic ulcer in rats

The pathogenic mechanisms underlying betel quid chewing (BQC)-induced gastric haemorrhagic ulcer are totally unknown. This study first demonstrated that BQC produced gastric haemorrhagic ulcer via oxidative stress that could be protected by lysozyme chloride and glutathione in rats. Male Wistar rats were fed with regular pellet food or BQC-containing diets. After 1-90 days rats were deprived of food for 24 h. Rat stomachs were irrigated for 3 h with normal saline or simulated gastric juice. Rats were killed and gastric specimens were harvested. A BQC-feeding period-dependent exacerbation of gastric parameters, such as enhanced acid back-diffusion, mucosal lipid peroxide generation, as well as related decreased glutathione levels and mucus content, were observed. Gastric juice caused a further aggravation of these ulcerogenic parameters. Daily intragastric lysozyme chloride or glutathione dose-dependently inhibited exacerbation of various ulcerogenic parameters in those BQC-fed rats. In conclusion, BQC can produce gastric haemorrhagic ulcer in rats via oxidative stress that could be ameliorated by lysozyme chloride and glutathione.

Gastric oxidative stress and hemorrhagic ulcer in Salmonella typhimurium-infected rats

Infection of Salmonella typhimurium ( Salmonella typhi) can lead to various organ diseases. This research first proposed that Salmonella typhi-infection could result in gastric oxidative stress and hemorrhagic ulcers that were ameliorated by ofloxacin, lysozyme chloride and several antioxidants, including exogenous glutathione (GSH), allopurinol and dimethylsulfoxide (DMSO). Male Wistar rats were given intrajejunally the live culture of Salmonella typhi [1×10 10 colony-forming unit (CFU)/rat] and followed by deprivation of food for 36 h. Age-matched control rats received vehicle only. Rat stomachs were irrigated for 3 h with either normal saline or a simulated gastric juice containing 100 mM HCl, 17.4 mM pepsin and 54 mM NaCl. Infection of Salmonella typhi produced an aggravation of ulcerogenic factors, including enhancing gastric acid back-diffusion, mucosal lipid peroxide generation and hemorrhagic ulcer as well as an attenuation of mucosal GSH level. Intragastric irrigation of gastric juice caused further aggravation of these gastric biochemical parameters. This exacerbation of ulcerogenic factors was abolished by pretreatment of ofloxacin and lysozyme chloride. Antioxidants, such as reduced GSH, allopurinol and DMSO also produced significant ( P<0.05) amelioration of gastric damage in Salmonella typhi-infected rats. In conclusion, infection of Salmonella typhi substantially caused gastric oxidative stress and disruption of gastric mucosal barriers, consequently resulted in gastric hemorrhagic ulcerations that were effectively ameliorated by ofloxacin, lysozyme chloride and various antioxidants.

Role of bradykinin in gastric vasodilation caused by hypertonic saline and acid back diffusion

Protective vasodilation in response to tissue injury and acid back diffusion is associated with release of bradykinin in the rat stomach. We hypothesized that bradykinin might be involved in mechanisms behind such vasodilation via influence on mast cells and sensory neurons. Acid back diffusion after mucosal barrier disruption with hypertonic saline evoked degranulation of mast cells in the rat stomach wall. Acid back diffusion was also associated with increased luminal release of histamine and gastric blood flow in normal rats, but not in mast cell-deficient rats. Bradykinin (BK 2) receptor blockade inhibited degranulation of submucosal mast cells in the stomach and attenuated gastric vasodilation both in response to acid back diffusion and after stimulation of sensory neurons with capsaicin. Gastric vasodilation caused by mucosal injury with hypertonic saline alone was associated with degranulation of mucosal mast cells. These events were unaffected by inhibition of prostaglandin synthesis, whereas bradykinin (BK 2) receptor blockade was associated with abolished vasodilation and inhibition of mucosal mast cell degranulation. We conclude that bradykinin is involved in gastric vasodilation caused by hypertonic injury alone via influence on mast cells, and by acid back diffusion via influence on both sensory neurons and mast cells.

Role of histamine and acid back-diffusion in modulation of gastric microvascular permeability and hemorrhagic ulcers in Salmonella typhimurium-infected rats

Documentation concerning the pathogenesis of gastric hemorrhagic ulcer in Salmonella typhimurium ( Salmonella typhi)-infective disease is lacking. This research first proposed that alterations of mast cell histamine release, gastric acid back-diffusion and mucosal microvascular permeability are important in modulating gastric ulcer and hemorrhage in Salmonella typhi-infected rats. Additionally, effects of several histamine-related drugs on this ulcer model were evaluated. Male Wistar rats were deprived food for 36 h. Live cultures of Salmonella typhi (OU 5045, 1 × 10 10 CFU in 1.0 mL of sterilized phosphate buffer saline) were challenged, intrajejunally to rats just before withdrawal of food. Control rats received the same volume of sterilized vehicle only. Rat stomachs were irrigated for 3 h with either normal saline or simulated gastric juice. Gastric acid back-diffusion, mucosal histamine concentration, microvascular permeability as well as luminal hemoglobin content and ulcer areas were determined. Severe gastric hemorrhage and mucosal ulcerations, particularly in acidic stomachs, were observed in Salmonella typhi-infected rats. A positive correlation of histamine to gastric hemorrhage and ulcer was found in those rats with Salmonella typhi-infection. This hemorrhagic ulcer in Salmonella typhi-infected rats was effectively ameliorated by intraperitoneal ketotifen, diphenhydramine and ranitidine but was worsen by exogenous histamine or diamine oxidase. In conclusion, enhancement of acid back-diffusion, mast cell histamine release and microvascular permeability is important in modulating gastric hemorrhage and ulcer in Salmonella typhi-infected rats.

Acid Transport through Gastric Mucus

The gastric mucosa is frequently exposed to endogenously secreted hydrochloric acid of high acidity. Gastric mucosal defense mechanisms are arranged at different levels of the gastric mucosa and must work in unison to maintain its integrity. In this work, several mechanisms underlying gastric mucosal resistance to strong acid were investigated in anesthetized rats and mice. The main findings were as follows:Only when acid secretion occurred did the pH gradient in the mucus gel withstand back-diffusion of luminal acid (100 mM or 155 mM HCl), and keep the juxtamucosal pH (pH(jm)) neutral. Thus, with no on-going acid secretion and low luminal pH, the pH gradient was destroyed.Bicarbonate ions, produced concomitant with hydrogen ions in the parietal cells during acid secretion and transported by the blood to the surface epithelium, were carried transepithelially through a DIDS-sensitive transport. Prostaglandin-dependent bicarbonate secretion seemed to be less important in maintaining a neutral pH(jm).Removal of the loosely adherent mucus layer did not influence the maintenance of the pH(jm). Hence, only the firmly adherent mucus gel layer, approximately 80 microm thick, seemed to be important for the pH(jm). Staining of the mucus gel with a pH-sensitive dye revealed that secreted acid penetrated the mucus gel from the crypt openings toward the gastric lumen only in restricted paths (channels). One crypt opening was attached to one channel, and the channel was irreversibly formed during acid secretion. Gastric mucosal blood flow increased on application of strong luminal acid (155 mM HCl). This acid-induced hyperemia involved the inducible but not the neural isoform of nitric oxide synthase. These results suggest a novel role for iNOS in gastric mucosal protection and indicate that iNOS is constitutively expressed in the gastric mucosa.

Role of prostaglandins in maintaining gastric mucus-cell permeability against acid exposure

Regulation of gastric epithelial permeability is important in the protection of the gastric mucosa from secreted acid. However, the mechanism(s) for this regulation in gastric mucus cells remains unknown. In this study, we evaluated gastric epithelial-cell permeability in response to acid exposure by monitoring trans-epithelial electrical resistance (TEER) and paracellular permeability with carbon 14–labeled mannitol. We also examined the role of prostaglandins on gastric epithelial permeability. Rat gastric epithelial cells (RGM-1) were plated on 8-μm-pore tissue-culture inserts. Cells were exposed to solutions of differing pH (3–7.4), with and without the nonsteroidal antiinflammatory drug (NSAID) indomethacin (10 −7 mol/L), for 60 to 120 minutes. Transepithelial permeability was measured on the basis of TEER and the diffusion rate of [ 14C]mannitol. Prostaglandin E 2 (PGE 2) was administered in some experiments with NSAIDs. After acid exposure (pH 3.0–5.0), TEER rapidly and significantly increased, peaking in 5 minutes. Diffusion of [ 14C]mannitol was blocked during the period when TEER increased. Pretreatment with the cyclooxygenase (COX) inhibitor indomethacin blocked the rapid acid-induced increase in TEER. A specific COX-2 inhibitor had no effect on this rapid increase in TEER. The blockade by indomethacin was eliminated by the addition of PGE 2. These findings suggest that when gastric-surface mucus cells are exposed to acid, gastric epithelial permeability decreases rapidly to inhibit acid back-diffusion. Prostaglandins play an important role in this protective response to acid exposure. COX inhibitors such as indomethacin may inhibit the regulation of epithelial permeability by reducing the concentration of PGE 2.

Stomach-brain communication by vagal afferents in response to luminal acid backdiffusion, gastrin, and gastric acid secretion

Vagal afferents play a role in gut-brain signaling of physiological and pathological stimuli. Here, we investigated how backdiffusion of luminal HCl or NH(4)OH and pentagastrin-stimulated acid secretion interact in the communication between rat stomach and brain stem. Rats were pretreated intraperitoneally with vehicle or appropriate doses of cimetidine, omeprazole, pentagastrin, dexloxiglumide (CCK(1) receptor antagonist), and itriglumide (CCK(2) receptor antagonist) before intragastric administration of saline or backdiffusing concentrations of HCl or NH(4)OH. Two hours later, neuronal activation in the nucleus of the solitary tract (NTS) and area postrema was visualized by c-Fos immunohistochemistry. Exposure of the rat gastric mucosa to HCl (0.15-0.5 M) or NH(4)OH (0.1-0.3 M) led to a concentration-dependent expression of c-Fos in the NTS, which was not related to gender, gastric mucosal injury, or gastropyloric motor alterations. The c-Fos response to HCl was diminished by cimetidine and omeprazole, enhanced by pentagastrin, and left unchanged by dexloxiglumide and itriglumide. Pentagastrin alone caused an omeprazole-resistant expression of c-fos, which in the NTS was attenuated by itriglumide and prevented by dexloxiglumide but in the area postrema was reduced by dexloxiglumide and abolished by itriglumide. We conclude that vagal afferents transmit physiological stimuli (gastrin) and pathological events (backdiffusion of luminal HCl or NH(4)OH) from the stomach to the brain stem. These communication modalities interact because, firstly, acid secretion enhances afferent signaling of gastric acid backdiffusion and, secondly, gastrin activates NTS neurons through stimulation of CCK(1) receptors on vagal afferents and of CCK(2) receptors on area postrema neurons projecting to the NTS.

The protective effect of rebamipide on paracellular permeability of rat gastric epithelial cells.

Barrier function in gastric epithelial cells is essential for the gastric defence mechanism against acid back-diffusion into the mucosal layer. Our previous study indicated that trans-epithelial resistance (TER) of rat gastric epithelial cells was rapidly increased when the cells were exposed to acid. This response to acid was diminished by indometacin. Evaluate the effects of a mucoprotective agent, rebamipide, on the nonsteroidal anti-inflammatory drug (NSAID)-induced increase of gastric epithelial permeability. Rat gastric epithelial cells were plated on tissue culture inserts. Cells were exposed to a NSAID (indometacin, 10-7 M). Trans-epithelial permeability was measured by TER and diffusion rate of 14C-mannitol. The effect of rebamipide was evaluated by measuring TER. Endogenous prostaglandin E2 (PGE2) production in culture medium was also measured. Indometacin gradually and significantly decreased TER and increased 14C-manitol permeability. Rebamipide reversed the indometacin-induced changes in epithelial permeability and induced PGE2 synthesis. This induction was blocked by either indometacin or a Cyclooxygenase (COX)-2 specific inhibitor. COX inhibitors such as indometacin inhibit regulation of epithelial permeability by reducing PGE2. COX-1 has an important role in the gastric defense mechanism. Rebamipide suppressed an indometacin-induced increase in gastric epithelial permeability by increasing PGE2 levels in a COX-2 dependent manner.