Gastric Mucosal Blood Flow Response Research Articles

Allyl isothiocyanate, an activator of TRPA1, increases gastric mucosal blood flow through calcitonin gene-related peptide and adrenomedullin in anesthetized rats

Allyl isothiocyanate (AITC) activates transient receptor potential ankyrin 1 (TRPA1) channel, which is involved in the control of intestinal mucosal blood flow. However, the mechanism underlying the increased gastric mucosal blood flow (GMBF) in response to AITC remains unknown. We examined the effect of AITC on GMBF in the ex vivo stomachs of normal and sensory deafferented rats using a laser Doppler flowmeter. Mucosal application of AITC increased GMBF in a concentration-dependent manner. Repeated AITC exposure resulted in a marked desensitization. The increased GMBF response induced by AITC was entirely blocked by co-application of TRPA1 channel blockers HC-030031 or AP-18. Increased GMBF in response to AITC was significantly attenuated by chemical deafferentation following systemic capsaicin injections (total dose: 100 mg/kg). In contrast, increased GMBF responses to capsaicin, a transient receptor potential vanilloid 1 (TRPV1) activator, were completely abolished by chemical deafferentation. The increased GMBF response to AITC was markedly inhibited by BIBN 4096, a calcitonin gene-related peptide receptor (CGRP) antagonist, or AGP-8412, an adrenomedullin receptor antagonist. These results suggest that AITC-stimulated TRPA1 activation results in the increased GMBF through the release of CGRP and adrenomedullin.

Neuronal Nitric Oxide Synthase-Derived Nitric Oxide Is Involved in Gastric Mucosal Hyperemic Response to Capsaicin in Rats

Background and Aims: Activation of transient receptor potential vanilloid type 1 (TRPV1) by capsaicin leads to gastric hyperemic response through capsaicin-sensitive sensory nerves and nitric oxide (NO). The aim of the present study is to examine which isoform of nitric oxide synthase (NOS)/NO is involved in the hyperemic response to capsaicin in the rat stomach. Methods: Gastric mucosal blood flow (GMBF) was measured by laser Doppler flowmetry in rats. The localizations of TRPV1 and neuronal NOS (nNOS) in the rat gastric mucosa were detected by immunohistochemical staining. Results: The nNOS inhibitor N⁵-[imino(propylamino)methyl]-<smlcap>L</smlcap>-ornithine substantially reduced GMBF during capsaicin application, whereas the endothelial NOS (eNOS) inhibitor N⁵-(1-iminomethyl)-<smlcap>L</smlcap>-ornithine did not affect the effect of capsaicin during the application. The nonselective NOS inhibitor N^G-nitro-<smlcap>L</smlcap>-arginine methyl ester apparently inhibited the capsaicin-induced GMBF, while the inducible NOS inhibitor 1400W did not affect GMBF response to capsaicin. The immunohistochemical studies revealed nerve fibers coexpressing TRPV1 and nNOS around blood vessels in the gastric submucosa. Conclusion: We demonstrated for the first time that nNOS/NO is involved in gastric hyperemic responses to capsaicin.

Irsogladine : Overview of the Mechanisms of Mucosal Protective and Healing- Promoting Actions in the Gastrointestinal Tract

Irsogladine, a mucosal protective drug, was developed in Japan for the treatment of peptic ulcer disease and acute gastritis. This drug is superior to gefarnate, the same therapeutic category drug, in a randomized, controlled and double-blind clinical study in 1987. The mechanisms of irsogladine's actions are apparently different from those of antisecretory drugs. Irsogladine increases intracellular cyclic adenosine 3',5'-monophosphate content via non-selective inhibition of phosphodiesterase isozymes and exhibits gastric cytoprotection partly mediated by endogenous nitric oxide. These effects may account for a variety of actions of irsogladine in the gastrointestinal tract, including facilitation of gap junctional intercellular communication, inhibition of the reduced gastric mucosal blood flow response, suppression of reactive oxygen generation and so on. Since 1984, more than 60 papers have been published to further verify the effects of irsogladine on gap junctional intercellular communication, tight junction, nitric oxide production and neutrophil migration as well as Helicobacter pylori-related pathological changes in the stomach as well as the adverse reactions induced in the stomach or the small intestine by various drugs, including nonsteroidal anti-inflammatory drugs, bisphosphonates or selective serotonin re-uptake inhibitors. In this article, we review recent advances in understanding the mechanisms of irsogladine's actions and the most recent data in experimental as well as clinical studies.

Assessment of Mucosal Movement in the Gastroesophageal Junction High-Pressure Zone During Swallowing Using Simultaneous Endoluminal Ultrasound and Manometry

BACKGROUND & AIM: Allyl isothiocyanate, the pungent ingredient of wasabi and mustard oil, is known to activate transient receptor potential (TRP) cation channels TRPA1. TRPA1 was recently shown to be functionally expressed in the gastrointestinal tract, whose ion channel presents in a subpopulation of primary sensory neurons that coexpressed with TRPV1. Previously, we also reported (1) that TRPV1-expressing sensory nerve fivers abundantly exist around blood vessels in the submucosa in the rat stomach, suggesting that TRPV1 plays an important role in control of local blood flow (Scand J. Gastroenterol. 39, 303-312, 2004), and (2) that allyl isothiocyanate facilitates to increase gastric mucosal blood flow (GMBF) in the rat stomach (Gastroenterology 138 (Suppl.1) S-721, 2010). However, the mechanism for the increased GMBF in response to allyl isothiocyanate remains unknown. In the present studies, we examined the effect of a TRPA1 activator allyl isothiocyanate on GMBF in the ex-vivo stomach of normal and sensory deafferented rats. METHODS: Male SD rats (160-200 g) were used after 18 hr-fasting. GMBFwasmeasured in the ex-vivo stomach of urethane-anesthetized rats by using the laser Doppler flowmeter. Allyl isothiocyanate (0.3310 mM) or a TRPV1 channel activator capsaicin (3.3 mM) was topically applied for 10 min to the rat stomach, and changes in GMBF were monitored. Either a TRPA1 channel blocker HC-030031 (14.1 mM) or a TRPV1 channel blocker BCTC (0.8 mM) was co-applied with allyl isothiocyanate (10 mM) for 10 min to the stomach. RESULTS: Mucosal application of allyl isothiocyanate increased GMBF in a concentration-dependentmanner.When themucosa was exposed to allyl isothiocyanate (10 mM) repeatedly, this response showed a marked desensitization. The increased GMBF response caused by allyl isothiocyanate was entirely blocked by co-application with HC-030031, but not BCTC. Interestingly, the increased GMBF in response to allyl isothiocyanate was significantly attenuated, but not completely disappear, by chemical deafferentation following systemic capsaicin injections (total dose: 100 mg/kg), although the increased GMBF in response to capsaicin was completely abolished by chemical deafferentation. The increased GMBF response to capsaicin was also significantly decreased in allyl isothiocyanate-desensitized preparation of the ex-vivo stomach. CONCLUSION: These results suggested that allyl isothiocyanate increases GMBF through activation of TRPA1, but not TRPV1. It is assumed that the increased GMBF in response to allyl isothiocyanate is mediated by TRPA1 located on both TRPV1-expresseing and TRPV1 nonexpressing sensory nerves.

Impairment by 5-Fluorouracil of the Healing of Gastric Lesions in Rats: Effect of Lafutidine, a Histamine H2 Receptor Antagonist, Mediated by Capsaicin-Sensitive Afferent Neurons

We investigated the influence of 5-fluorouracil (5-FU), an anti-tumor agent, on the healing of gastric lesions generated by 0.6 M HCl in rats and the effect of lafutidine, a histamine H(2) receptor antagonist, on the impaired healing. Animals fasted for 18 h were given 1 ml of 0.6 M HCl p.o., fed normally from 1 h later, and killed 1-96 h thereafter. 5-FU was given i.v. twice, 1 h and 24 h after the HCl. The gastric lesions healed spontaneously within 96 h. Although it decreased acid secretion, 5-FU markedly delayed the healing. Lafutidine, but not cimetidine, given p.o. immediately after each dosing of 5-FU significantly reversed the delay in healing by 5-FU, and this effect was attenuated by the chemical ablation of capsaicin-sensitive afferent neurons. Capsaicin also significantly reversed the delay in healing. The mucosal application of 50 mM HCl did not affect gastric mucosal blood flow (GMBF) in the normal stomach, but significantly increased it in the stomach damaged by 0.6 M HCl. The increases in GMBF were attenuated by 5-FU; however, the co-administration of lafutidine significantly restored the response. In addition, 5-FU inhibited both cell proliferation and migration in rat gastric epithelial cells (RGM1) in vitro. These results suggest that 5-FU delayed the healing of gastric lesions generated by 0.6 M HCl, probably through the inhibition of cell migration and proliferation, as well as the impairment of GMBF, and lafutidine reversed the delay in healing, mainly through the amelioration of the GMBF response mediated by capsaicin-sensitive afferent neurons.

Prophylactic effect of lafutidine against the adverse reaction induced in rat stomach by repeated administration of 5-fluorouracil

We examined the prophylactic effect of lafutidine, a histamine H2 receptor antagonist, on the morphological and functional derangement of the rat stomach after the administration of 5-fluorouracil (5-FU) in the absence or presence of taurocholate Na (TC). Rats were given 5-FU p. o. once daily for 5 days. After 18 hr fasting, the animals were given omeprazole to inhibit acid secretion. Under urethane anesthesia, the stomach was mounted on an ex-vivo chamber, perfused with 100 mM HCl, and both the transmucosal potential difference (PD) and gastric mucosal blood flow (GMBF) were simultaneously measured before and after exposure of the mucosa to 20 mM TC for 30 min. The 5-FU treatment lowered the basal PD with a decrease in the mucosal height and caused few haemorrhagic lesions in the stomach when perfused with 100 mM HCl for 2 hr. The 5-FU treatment had no influence on the reduced PD response caused by TC, but significantly impaired the increase in GMBF after exposure to TC, resulting a marked aggravation of gastric lesions. Lafutidine, given together with 5-FU for 5 days, significantly antagonized the deleterious effect of 5-FU on the basal PD and the GMBF response to TC, and prevented the aggravation of gastric lesions. These effects of lafutidine were not mimicked by cimetidine and disappeared due to the chemical ablation of capsaicin-sensitive afferent neurons. We conclude that 1) 5-FU treatment caused the morphological and functional derangement of the stomach and increased the mucosal vulnerability against acid, and 2) lafutidine prevents such changes caused by 5-FU treatment, probably mediated through capsaicin-sensitive afferent neurons.

Effect of lafutidine, a histamine H2-receptor antagonist, on gastric mucosal blood flow and duodenal HCO3- secretion in rats: relation to capsaicin-sensitive afferent neurons.

Lafutidine is a new type of antiulcer drug, possessing both an antisecretory effect, exerted via a blockade of the histamine H2 receptor, and gastroprotective activity, mediated by capsaicin-sensitive afferent nerves (CSN). In the present study, we examined the effect of lafutidine on gastric mucosal blood flow (GMBF) and duodenal HCO3- secretion (DAS) under basal and acid-stimulated conditions in rats. Under urethane anesthesia, GMBF was measured using a laser Doppler flowmeter in a chambered stomach before and after exposure to 20 mM taurocholate (TC) plus 50 mM HCl, while DAS was measured in a proximal duodenal loop before and after mucosal acidification (10 mM HCl for 10 min) by titrating the perfusate at pH 7.0 using a pH-stat method and by adding 10 mM HCl. Lafutidine given intraperitoneally affected neither GMBF nor DAS under basal conditions, but augmented an increase in both GMBF and DAS induced by mucosal acidification. Although the acid-induced GMBF and DAS responses were significantly mitigated by both indomethacin and sensory deafferentation but not by ruthenium red (RT), the vanilloid receptor (VR)-1 antagonist, the responses were preserved in lafutidine-treated animals, even in the presence of indomethacin. Both GMBF and DAS were significantly increased by local application of capsaicin, the responses being attenuated by indomethacin and RT as well as sensory deafferentation. Lafutidine augmented the GMBF and DAS responses to capsaicin and preserved the responses, even in the presence of indomethacin. Capsaicin evoked an increase in [Ca2+]i in rat VR1-transfected HEK293 cells, while lafutidine had no effect by itself on [Ca2+]i in these cells and did not affect the increase in [Ca2+]i evoked by capsaicin. In conclusion, these results suggest that lafutidine mimics endogenous effects of prostaglandins to augment the GMBF and DAS responses to acid or capsaicin, probably by sensitizing CSN through an unknown site other than VR1. The luminal H+ itself is not a ligand for the RT-sensitive site of VR1 but plays a modulator role in the CSN-mediated physiological responses.

Effects of tidal volume reduction in acute respiratory distress syndrome on gastric mucosal perfusion

This study was conducted with the aim of testing the effects of a reduction in tidal volume (V(T)) on gastric mucosal perfusion using laser-Doppler flowmetry in patients with acute respiratory distress syndrome (ARDS). It was designed as a prospective study. Seventeen patients with ARDS were enrolled in the study. All patients were mechanically ventilated in volume-controlled mode. Before the start of the protocol, V(T) was set at 9 ml/kg body weight. V(T) was reduced to 6 ml/kg body weight. Measurements of systemic hemodynamic parameters and gastric mucosal blood flow (GMBF) were obtained before and after reduction of V(T). Cardiac index, heaart rate and pulmonary arterial pressure increased significantly after V(T) reduction. The increase in cardiac output was observed in all patients. However, despite a mean 25% increase in cardiac output after V(T) reduction, no significant increase in mean GMBF was observed, and individual GMBF responses were heterogeneous. V(T) reduction in patients with ARDS, despite resulting in an increase in cardiac output, did not change gastric mucosal perfusion. The heterogeneity in the individual response of GMBF to V(T) reduction could be due to opposite direct (i.e., local vasodilatory effect) and indirect (i.e., global sympathetic stimulation) effects of hypercapnia on gut vessels.

Monochloramine impairs mucosal blood flow response and healing of gastric lesions in rats: relation to capsaicin-sensitive sensory neurons.

We examined the effects of monochloramine (NH2Cl) on the gastric mucosal blood flow (GMBF) response and the healing of ethanol-induced gastric lesions in rats. Rats fasted for 18 h were given the 99% ethanol p.o. for induction of gastric lesions, and were fed normally from 1 h later onwards. Monochloramine, at non-ulcerogenic doses (5 to approximately 20 mmol/L), was given p.o. twice daily for 7 days, starting 2 h after ethanol treatment. Gastric lesions caused by ethanol healed almost completely within 7 days with re-epithelialization. The repeated administration of NH2Cl significantly delayed the healing of ethanol-induced gastric lesions in a dose-dependent manner. The damaged mucosa showed a marked rise in H+ permeability, resulting in luminal acid loss, but this process was accompanied by an increase of mucosal blood flow. Monochloramine did not affect the increased mucosal H+ permeability observed in the stomach after damage by ethanol, but significantly inhibited the mucosal hyperemic response associated with luminal acid loss. Prior exposure of the mucosa to NH2Cl (20 mmol/L) did not affect the gastric hyperemic response caused by mucosal application of misoprostol (a prostaglandin E1 derivative) or NOR-3 (a nitric oxide donor), but totally attenuated the increase of GMBF in response to intragastric capsaicin. Impaired healing and GMBF responses were also observed in rats following chemical ablation of capsaicin-sensitive sensory neurons. These results suggest that NH2Cl impaired the healing of acute gastric mucosal lesions at low concentrations, and this action may be attributable, at least partly, to the impairment of gastric hyperemic response caused by the dysfunction of capsaicin-sensitive sensory neurons.

Effect of monochloramine on recovery of gastric mucosal integrity and blood flow response in rat stomachs — Relation to capsaicin-sensitive sensory neurons

Gastric mucosal blood flow (GMBF) response and the recovery of gastric mucosal integrity were investigated in anesthetized rat stomachs after damage by monochloramine (NH2C1), in comparison with 20 mM taurocholate Na (TC). A rat stomach was mounted in an ex-vivo chamber, and the mucosa was exposed to 50 mM HCl during a test period. Mucosal application of 20 mM TC for 10 min caused a marked reduction of transmucosal potential difference (PD), but the PD recovered rapidly without development of gross lesions 90 min later. In contrast, the exposure of the mucosa to NH 2Cl (5~20 mM) produced a concentration-dependent decrease in gastric PD, and the values remained lowered even 90 min after removal of the agent, resulting in severe hemorrhagic damage in the stomach. TC caused a considerable H + back-diffusion, followed by an increase in the GMBF. In the mucosa damaged by NH 2Cl, such GMBF responses were not observed, except for the temporal increase during the exposure, although similar degrees of H + back-diffusion were observed following NH 2Cl treatment. In addition, the prior exposure of the mucosa to NH 2Cl significantly attenuated gastric hyperemic response induced by capsaicin but not by misoprostol (a PGE 1 derivative) or NOR-3 (a NO donor). Chemical ablation of capsaicin-sensitive sensory neurons had no effect on the PD reduction caused by TC but totally attenuated the GMBF response, resulting in hemorrhagic damage in the stomach. These results suggest that NH 2Cl delayed the recovery of the mucosal integrity in the stomach after damage, and this effect may be attributable, at least partly, to the impairment of gastric hyperemic response associated with H + back-diffusion, probably due to dysfunction of capsaicin-sensitive sensory neurons.

Epalrestat prevents the decrease in gastric mucosal blood flow and protects the gastric mucosa in streptozotocin diabetic rats.

We have recently reported that steady-state gastric mucosal blood flow (GMBF) is decreased in streptozotocin (STZ) diabetic rats, and that their GMBF response to burn-stress is impaired, probably via a nitric oxide (NO)-mediated mechanism. Accordingly, this study was designed to investigate the relation of aldose reductase (AR) and NO synthase to the regulation of GMBF during chronic hyperglycemia. STZ rats were treated with or without chronic oral administration of an AR inhibitor, epalrestat (EPA) and/or an NO synthase inhibitor, N-nitro-L-arginine methyl ester (L-NAME). GMBF was measured by laser-Doppler velocimetry (LDV). In the STZ rats, GMBF after a 24-h fasting period was decreased significantly 4 weeks after the onset of diabetes and this was accompanied by an increase in the gastric ulcer index (UI) (a measure of the length of gastric erosions and ulcers). Chronic oral administration of EPA to the STZ rats dose-dependently inhibited the increased UI and the decreased GMBF after the fasting stress, whereas chronic oral administration of L-NAME further increased the UI and further decreased the GMBF. EPA administered in combination with L-NAME to the STZ rats reduced the effects of L-NAME, but the effects did not reach significance. These results suggest that EPA protects the gastric mucosa of diabetic rats, by preventing the decrease in GMBF that is, at least in part, caused by NO-related mechanisms.

Increased susceptibility of gastric mucosa to ulcerogenic stimulation in diabetic rats--role of capsaicin-sensitive sensory neurons.

1. We examined the gastric mucosal blood flow (GMBF) and ulcerogenic responses following barrier disruption induced by sodium taurocholate (TC) in diabetic rats and investigated the role of capsaicin-sensitive sensory neurons in these responses. 2. Animals were injected streptozotocin (STZ: 70 mg kg(-1), i.p.) and used after 5, 10 and 15 weeks of diabetes with blood glucose levels of > 350 mg dl(-1). The stomach was mounted on an ex-vivo chamber under urethane anaesthesia and exposed to 20 mM TC plus 50 mM HCl for 30 min in the presence of omeprazole. Gastric transmucosal potential difference (PD), GMBF, and luminal acid loss (H+ back-diffusion) were measured before and after exposure to 20 mM TC, and the mucosa was examined for lesions 90 min after TC treatment. 3. Mucosal application of TC caused PD reduction in all groups; the degree of PD reduction was similar between normal and diabetic rats, although basal PD values were lower in diabetic rats. In normal rats, TC treatment caused luminal acid loss, followed by an increase of GMBF, resulting in minimal damage in the mucosa. 4. The increased GMBF responses associated with H+ back-diffusion were mitigated in STZ-treated rats, depending on the duration of diabetes, and severe haemorrhagic lesions occurred in the stomach after 10 weeks of diabetes. 5. Intragastric application of capsaicin increased GMBF in normal rats, but such responses were mitigated in STZ diabetic rats. The amount of CGRP released in the isolated stomach in response to capsaicin was significantly lower in diabetic rats when compared to controls. 6. The deleterious influences on GMBF and mucosal ulcerogenic responses in STZ-diabetic rats were partially but significantly antagonized by daily insulin (4 units rat(-1)) treatment. 7. These results suggest that the gastric mucosa of diabetic rats is more vulnerable to acid injury following barrier disruption, and this change is insulin-sensitive and may be partly accounted for by the impairment of GMBF response associated with acid back-diffusion and mediated by capsaicin-sensitive sensory neurons.

Inhibition of gastric acid secretion by galanin in rats: Relation to endogenous histamine release

Inhibitory effect of galanin on basal and secretagogs-stimulated gastric acid secretion was investigated in urethane-anesthetized rats. A rat stomach was mounted in an ex-vivo chamber, perfused with saline, and either gastric acid or alkaline secretion was determined by titrating the perfusate. Gastric mucosal blood flow (GMBF) was measured by a laser Doppler flowmeter. Intravenous infusion of galanin dose-dependently inhibited the increase of acid secretion induced by pentagastrin and carbachol but not by histamine, without any influence on the GMBF response. Galanin also reduced basal acid secretion while increasing GMBF, but did not evoke any change in basal gastric alkaline secretion. M15, which is a galanin receptor antagonist in the central nervous system but acts as a full agonist in the gastrointestinal smooth muscle, also suppressed pentagastrin-induced acid secretion, similar to galanin. In addition, pentagastrin increased the release of histamine into the gastric lumen, and this response was significantly inhibited by galanin. These results suggest that the inhibitory effect of galanin on acid secretion is mediated by suppression of endogenous histamine release from enterochromaffin-like cells and that the process may be related to the activation of the same subtype of galanin receptors as in the central nervous system and pancreatic β-cells.

Gastric mucosal blood flow response to stress in streptozotocin diabetic rats: regulatory role of nitric oxide.

To investigate cytoprotection against mucosal injuries of the stomach in patients with diabetes, we investigated gastric mucosal blood flow (GMBF), its response to a burn stress, and the involvement of nitric oxide (NO) in streptozotocin (STZ) diabetic rats. GMBF was measured by laser-Doppler velocimetry (LDV) and by the hydrogen gas clearance technique (HGC). The steady-state GMBF of STZ rats decreased according to the duration of diabetes, and insulin treatment blocked this decrease. Burn stress caused a rapid decrease in the GMBF. Reduction of the GMBF and gastric mucosal leakage of Evans blue (EB) after the burn stress were greater in the STZ rats than in the controls, but insulin treatment completely blocked this increase in EB leakage in the STZ rats. There was a significant negative correlation between the percent GMBF 3 h after the burn stress and EB leakage at the same time point. In the controls and the insulin-treated STZ rats, N-nitro-L-arginine (L-NNA), an NO synthase inhibitor, enhanced the decrease in postburn GMBF and EB leakage, but was without effect in the STZ rats. These results suggest that NO may be involved in the regulation of GMBF, and that persistent hyperglycemia may impair this regulation. These findings suggest that patients with diabetes have reduced cytoprotection against a variety of gastric mucosal injuries.

Nitric oxide, prostaglandin, and sensory neurons in gastric mucosal blood flow response during acid secretion in rats

1. 1. The mechanism underlying the increase of gastric mucosal blood flow (GMBF) during acid secretion induced by pentagastrin was investigated in anesthetized rats, in relation to nitric oxide (NO), prostaglandin (PG), and sensory neurons. 2. 2. An intravenous infusion of pentagastrin at 60 μg/kg/h (submaximal dose) produced an increase of acid secretion and GMBF as determined by laser Doppler flowmetry, and the GMBF response was totally attenuated when the acid secretion was inhibited by omeprazole or when the luminal H + was removed by mucosal perfusion with glycine (200 mM). 3. 3. Prior administration of N G-nitro-L-arginine methyl ester (L-NAME, 5 mg/kg, IV), a NO synthase inhibitor, significantly mitigated the GMBF response to pentagastrin, without any influence on acid secretion, and this effect was antagonized by coadministration of L-arginine (500 mg/kg IP). 4. 4. The increase of GMBF during pentagastrin infusion also was significantly mitigated by indomethacin (5 mg/kg, SC) or sensory deafferentation following capsaicin pretreatment, had no effect on the acid secretion, and was totally inhibited by the combined treatments with indomethacin plus L-NAME in addition to sensory deafferentation. 5. 5. Pentagastrin infusion for 8 hr did not by itself cause any macroscopic damage in the stomach, but additional treatments with L-NAME, and indomethacin plus sensory deafferentation provoked severe lesions in the gastric mucosa. 6. 6. These results suggest that the increase of GMBF induced by submaximal dose of pentagastrin totally depends on luminal H +. This process seems to be mediated by endogenous NO and PGs, as well as capsaicin-sensitive sensory neurons, and to play a pivotal role in maintaining mucosal integrity during acid secretion.

Role of nitric oxide in mucosal blood flow response and the healing of HCl-induced lesions in the rat stomach.

The role of nitric oxide (NO) in the gastric mucosal blood flow response and the healing of HCl-induced gastric lesions was investigated in rats. After 18 h fasting rats were given 0.6 N HCl p.o. for the induction of gastric lesions, and 1 h later they were fed normally. After induction of gastric lesions, they were repeatedly administered the NO synthase inhibitors NG-nitro-L-arginine methyl ester (L-NAME 5-20 mg/kg p.o. twice daily) or aminoguanidine (20 mg/kg s.c. once daily) for 7 days. Gastric lesions caused by HCl healed almost completely within 5 days with granulation and to an extent with re-epithelialization. Repeated administration of L-NAME but not aminoguanidine significantly delayed the healing of gastric lesions in a dose-dependent manner. The damaged mucosa secreted less acid, but showed a marked rise in H+ permeability, resulting in luminal acid loss accompanied by an increase of mucosal blood flow. Aminoguanidine did not significantly affect any of these functional changes observed in the stomach after damage by HCl, whereas L-NAME treatment slightly reversed the decreased acid response, increased the luminal H+ loss, and totally inhibited the mucosal hyperemic response associated with luminal acid loss in the damaged mucosa. In addition, the deleterious influences of L-NAME on the mucosal blood flow response and the healing of gastric lesions were significantly antagonized by co-administration of L-arginine but not of D-arginine (500 mg/kg x 2, i.p.). Luminal output of NO2-/NO3- was significantly increased in pylorus-ligated stomachs in control rats on days 3 and 5 after damage, and such increases in gastric NO output were completely attenuated by L-NAME treatment. These results suggest that endogenous NO may contribute to the healing of acute gastric injury by mediating the mucosal hyperemic responses associated with acid back-diffusion and by facilitating acid disposal in the damaged mucosa. NO mediating such responses and participating in the healing aspect of gastric lesions may be produced by the constitutive type of NO synthase.

Increased susceptibility of rat gastric mucosa to ulcerogenic stimulation with aging

We examined the influences of aging on gastric damage and gastric mucosal blood flow (GMBF) responses induced by acid back-diffusion, following the barrier disruption, and investigated the relation of capsaicin-sensitive sensory nerves to these changes. Male Fischer rats 3, 13, and 24 months old were used. Under urethane anesthesia, a rat stomach was mounted on a chamber, and gastric potential difference (PD), luminal H+ loss, and GMBF were measured before, during, and after exposure to 20 mM sodium taurocholate (TC) for 30 min, in the presence of 50 mM HCl. Mucosal exposure to TC caused surface cell damage, PD reduction, and acid back-diffusion (luminal H+ loss) in all groups of rats; delta PD reduction and the amount of H+ loss were not significantly different between young and aged rats. In young rats, a marked increase of GMBF was observed with luminal acid loss following TC treatment, yet it resulted in less damage in the gastric mucosa. In aged rats, however, such GMBF responses were apparently mitigated, leading to a significant worsening of gastric mucosal lesions induced by TC. Mucosal application of capsaicin (0.1 mg/ml) caused an increase of GMBF in young rats, but this response was significantly attenuated in aged rats. In addition, the amount of calcitonin gene-related peptide (CGRP) released in the isolated stomach in response to capsaicin (1 X 10(-5) M) was significantly lower in aged animals when compared to young rats. These findings suggest that the gastric mucosa of aged rats is more vulnerable to acid back-diffusion following the barrier disruption, partly because of dysfunction of GMBF responses mediated by capsaicin-sensitive sensory neurons in the acidic conditions.

Mechanism by which histamine increases gastric mucosal blood flow in the rat

The mechanism by which histamine increases gastric mucosal blood flow (GMBF) was investigated in the anesthetized rat. The experiment was performed in the presence of tripelennamine, an H1 antagonist, to focus on the relationship between acid secretion (H2-receptor-mediated response) and GMBF. The stomach was mounted on a Lucite chamber, perfused with saline, and GMBF was measured by laser Doppler flowmetry simultaneously with acid secretion. Under these conditions, histamine at the submaximal dose significantly increased GMBF as well as acid secretion, and this increase of GMBF was completely blocked when acid secretion was inhibited by cimetidine or omeprazole. The elevation of GMBF caused by histamine was also significantly attenuated when luminal H+ was removed by intraluminal perfusion with NaHCO3 or glycine. Glycine by itself did not affect the increase of acid secretion induced by histamine and the increase of GMBF caused by isoproterenol, yet significantly inhibited the GMBF response induced by pentagastrin. Intraluminal perfusion with HCl also produced an increase of GMBF in a concentration-related manner, even in the presence of omeprazole during histamine infusion. Pretreatment of the animals with indomethacin significantly blocked the GMBF responses induced by either histamine or luminal HCl. These results suggest that the increase of GMBF during acid secretion induced by histamine may be caused by luminal H+ and involve endogenous prostaglandins in its mechanism.

Capsaicin-Sensitive Sensory Nerves in Recovery of Gastric Mucosal Integrity after Damage by Sodium Taurocholate in Rats

We compared the recovery process of gastric mucosal integrity after damage by 20 mM sodium taurocholate (TC) in control, sensory deafferented and indomethacin-treated rats. Under anesthetized conditions, the stomach was mounted on a chamber and perfused with saline or 50 mM HCl. Application of TC (30 min) to the saline-perfused stomach produced a marked reduction in the potential difference (PD) (surface epithelial damage), followed by increases of gastric mucosal blood flow (GMBF) and luminal pH (alkalinization), but there was a rapid recovery of PD without development of gross lesions. Chemical ablation of capsaicin-sensitive sensory nerves had no influence on the PD reduction and luminal alkalinization, but significantly inhibited the rise in GMBF and the PD recovery. Indomethacin pretreatment (5 mg/kg, s.c.) significantly inhibited these changes seen after exposure to TC, except for PD reduction. In contrast, TC caused a sizable amount of H+ back-diffusion and a more pronounced and persistent rise in GMBF in the stomach perfused with 50 mM HCl, yet only minimal damage was observed in the control animals. Under these conditions, both sensory deafferentation and indomethacin inhibited such GMBF responses, leading to hemorrhagic damage without affecting the degree of H+ back-diffusion. These results suggest that capsaicin-sensitive sensory nerves contribute to the recovery of gastric mucosal integrity after damage, probably by maintaining GMBF responses associated with H+ back-diffusion and preventing the later extension to gross damage in the presence of acid.

Role of capsaicin-sensitive afferent neurons in mucosal blood flow response of rat stomach induced by mild irritants.

The role of capsaicin-sensitive sensory nerves in gastric mucosal blood flow (GMBF) responses to mild irritants was investigated in the rat stomach mounted on a lucite chamber using hypertonic NaCl and 0.2 N HCl. Exposure of the mucosa to hypertonic NaCl (0.5, 0.75, 1 M) for 10 min caused a reduction in the transmucosal potential difference (PD) in a concentration-related manner, followed by an increase of luminal pH and GMBF. In contrast, mucosal application of 0.2 N HCl caused no or little change in PD and pH, but increased GMBF significantly. Functional ablation of capsaicin-sensitive sensory nerves significantly inhibited the increase of GMBF after exposure to these irritants, although the PD and pH responses induced by 1 M NaCl remained unaltered by this treatment. Pretreatment with indomethacin (5 mg/kg, subcutaneously) significantly attenuated the GMBF responses to 1 M NaCl and 0.2 N HCl and inhibited the increase of pH caused by 1 M NaCl. Mucosal application of capsaicin (0.1 mg/ml for 10 min) produced an increase of GMBF without being accompanied by change in PD and pH, and this effect was significantly blocked by either indomethacin or chemical deafferentation. These results suggest that capsaicin-sensitive sensory nerves as well as endogenous prostaglandins may be involved in the mechanism of GMBF responses induced by mild irritants, and the latter might sensitize these nerves to mucosal irritation. PD reduction may be obligatory for pH but not GMBF responses.