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; 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 × 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.     

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.     

Role of capsaicin-sensitive sensory nerves in acid-induced bicarbonate secretion in rat stomach

The effect of capsaicin-sensitive afferent nerves on the alkaline secretory response induced by mucosal acidification was investigated in theex vivo stomachs of anesthetized rats. The stomach was mounted on a Lucite chamber and perfused with saline (pH 4.5) in the absence of acid secretion (omeprazole pretreatment: 60 mg/kg, intraperitoneal), and luminal pH and transmucosal potential difference (PD) were monitored simultaneously. Under these conditions the gastric mucosa responded to intravenous infection of prostaglandin E₂ (PGE₂: 300 g/kg) and mucosal acidification (0.2 N HCl for 10 min) by a significant increase of pH with a slight decrease of PD; the HCO₃ ^– output was 9.2±0.7 mol and 8.4±0.8 mol, respectively. The increased pH and HCO₃ ^– responses were significantly inhibited by prior administration of indomethacin (5 mg/kg, subcutaneously) or chemical deafferentation following capsaicin injections (total dose: 100 mg/kg, subcutaneously), whereas those induced by PGE₂ remained unchanged after either treatment. On the other hand, the mucosal application of capsaicin (0.3–6 mg/ml) increased the luminal pH and HCO₃ ^– output in a concentration-related manner, and this action was also significantly attenuated by either indomethacin or chemical deafferentation of capsaicin-sensitive sensory neurons. These results suggest that capsaicin-sensitive sensory nerves may be involved in the mechanism of acid-induced HCO₃ ^– secretion in the stomach, in addition to endogenous PGs, and these two pathways may interact somewhere in the stimulatory process.     

Possible role of endogenous prostaglandins in alkaline response in rat gastric mucosa damaged by hypertonic NaCl

Changes in gastric potential difference (PD) and luminal pH of gastric perfusate were studied in anesthetized rats before and after application of hypertonic NaCl to the stomach for 10 min. There was a concentration-dependent reduction of PD and an increase in luminal pH after exposure to NaCl. In the stomach exposed to NaCl over 0.75 M, a significant amount of HCO₃ ^– (0.5–1.5 mol/10min) was titrated in the lumen at pH 7.4 under cimetidine infusion (8 mg/kg/hr). After removal of hypertonic NaCl, the PD returned completely or partially to the basal values within 1 hr. Pretreatment of the rats with subcutaneously administered indomethacin (3 mg/kg) or aspirin (100 mg/kg) significantly inhibited the recovery of PD in the 1 M Nacl-treated stomach. Gastric alkaline response in the damaged mucosa was significantly attenuated in rats pretreated with indomethacin or aspirin. Intravenously administered cimetidine (8 mg/kg/hr) or subcutaneously administered 16,16-dimethyl prostaglandin E₂ (3 g/kg) abolished the inhibitory effect of indomethacin on gastric alkaline response caused by 1 M NaCl, and partially restored the PD recovery. These results indicate that endogenous prostaglandins released in the injured mucosa are probably responsible for the luminal alkalinization noted after exposure to 1 M NaCl. This process would lead to a protection against further damage and accelerate reestablishment of the mucosal integrity.     

Capsaicin-sensitive sensory neurons in healing gastric lesions induced by HCl in rats

The role of capsaicin-sensitive sensory neurons in the healing of HCl-induced gastric lesions was investigated in rats. Rats fasted for 18 hr were given 0.6 N HCl orally for induction of gastric lesions, and they were fed normally from 1 hr later. On various days after HCl treatment, area of lesions, acid secretion, mucosal H⁺ permeability, and blood flow responses were measured. Functional ablation of capsaicin-sensitive sensory neurons was performed two weeks before the experiment by subcutaneous injections of high-dose capsaicin. Sensory deafferentation did not affect the development of gastric damage in response to HCl but significantly delayed the healing of these lesions. The mucosa damaged by HCl secreted less acid but showed significant rise in H⁺ permeability, resulting in acid back-diffusion accompanied by an increase of mucosal blood flow. Sensory deafferentation had no effect on acid secretion and mucosal permeability changes in the damaged stomach but completely blocked the hyperemic response caused by acid back-diffusion. Capsaicin-sensitive sensory neurons may contribute to healing of gastric lesions, probably by mediating the mucosal hyperemic responses associated with acid back-diffusion and by facilitating acid disposal in the mucosa.     

Prostaglandin E receptor EP1 subtype but not prostacyclin IP receptor involved in mucosal blood flow response of mouse stomachs following barrier disruption

AIM: We investigated the role of prostacyclin IP receptors in gastric mucosal protection as well as functional responses induced by taurocholate Na (TC) as a mild irritant using IP receptor knockout mice, in comparison with prostaglandin (PG) E receptor EP1 subtype knockout animals. METHODS: Male C57/BL6 mice fasted for 18 h were used under urethane anesthesia. The stomach mounted on an ex vivo chamber was perfused with 20 mM HCl, and the transmucosal potential difference (PD), luminal acid loss, and gastric blood flow (GMBF) were simultaneously measured before and after exposure of the stomach to 20 mM TC for 20 min. RESULTS: Mucosal exposure to TC in wild-type mice caused a marked decrease in PD, followed by an increase in H(+) loss and GMBF. The PD gradually normalized after removal of TC from the chamber, with minimal damage in the mucosa 1 h later. The increase of GMBF following TC treatment was inhibited by indomethacin with no change in PD reduction or H(+) loss, resulting in severe lesions in the mucosa. None of these responses induced by TC were significantly altered in IP receptor knockout mice. However, in mice lacking EP1 receptors, TC did not increase GMBF, despite causing PD reduction and acid loss, and resulted in severe damage in the mucosa. Mucosal PGE(2) levels were significantly increased after TC, similarly, in all groups of mice, while levels of 6-keto-PGF(1alpha) showed a slight but not significant increase in all groups. CONCLUSION: We confirmed the importance of endogenous PGs and EP1 receptors in the adaptive protection and functional responses induced by a mild irritant in mouse stomach and further suggested that IP receptors are not actively involved in maintaining the gastric mucosal integrity under adverse 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.     

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

AIMS: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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.     

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 H₂ 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.     

Protection against necrotizing agents-induced gastric lesions in rats

Effects of necrotizing agents, blockers of gastric motility, and mild irritants on gastric mucosa and gastric motility were investigated in conscious rats. Gastric motor activity was recorded using a miniature balloon placed in the glandular part of the stomach, which was connected to a pressure transducer and polygraph. Necrotizing agents, such as 96% ethanol, 0.6 N hydrochloric acid, 0.2 N sodium hydroxide, or 4 M sodium chloride, were given intragastrically through a fistula on the forestomach. One milliliter of these agents produced hemorrhagic bandlike lesions in the corpus mucosa along the long axis of the stomach with the occurrence of a complete inhibition of gastric motility (smooth muscle relaxation). Blockers of gastric motility alone, such as subcutaneous papaverine HCl (50 mg/kg), and intraperitoneal verapamil (20 mg/kg), or mild irritants (1 ml/rat, orally) such as 20% ethanol or 1 M NaCl, which by themselves suppressed gastric motility, have no effect on gastric mucosa and on the inhibited gastric motility induced by necrotizing agents. Bandlike lesions were significantly prevented by pretreatment with 20% ethanol or 1 M NaCl but not with papaverine HCl or verapamil administered 30 min before necrotizing agents. The gastroprotection offered by 20% ethanol or 1 M NaCl was significantly diminished by pretreatment with subcutaneous indomethacin (30 mg/kg), but the inhibited gastric motility was not reversed by indomethacin. These results indicate that it seems unlikely that gastric contractile activity would play a major role in the development and prevention of gastric lesions after the administration of necrotizing agents.     

Effect of ecabet disodium, a novel locally-acting antiulcer drug, on epithelial restitution following injury by hypertonic NaCl in bullfrog stomach in vitro

BACKGROUND: The antiulcer drug ecabet 2Na (12-sulfodehydroabietic acid disodium salt) exhibits a gastroprotective activity, mainly through a local action, involving endogenous prostaglandins (PGs) and nitric oxide (NO). In the present study, we examined the effect of ecabet on the epithelial restitution of the bullfrog gastric mucosa in vitro following injury by hypertonic NaCl. METHODS: Bullfrog fundic mucosa was mounted in an Ussing chamber. The tissue injury was induced by exposure of the mucosa to 1.25 M NaCl for 5 min, and transmucosal potential difference (PD) and electrical resistance (R) were measured during a 4-hour test period. Ecabet (3-30 mg/ml) was added to the luminal solution for 10 min before or after NaCl, while 16,16-dimethyl PGE(2) (dmPGE(2): 1x 10(-6) M) or NOR-3 (a NO donor: 1 x 10(-4) M) was added to the nutrient solution 10 min before NaCl. RESULTS: Mucosal application of 1.25 M NaCl caused an immediate reduction of PD and R, followed by a gradual normalization, reaching about 70% of the pre-exposure levels within 4 h. Ecabet, added before NaCl, significantly expedited the recovery of PD and R in a concentration-dependent manner; this effect was mimicked by posttreatment with ecabet and significantly mitigated by prior addition of indomethacin (1 x 10(-5) M) or N(G)-nitro-L-arginine methyl ester (L-NAME: 1 x 10(-3) M). The epithelial restitution was also significantly promoted by serosal application of either dmPGE(2) or NOR-3. The mucosal exposure to ecabet significantly increased the luminal release of PGE(2) and NO metabolites, the effects being attenuated by indomethacin and L-NAME, respectively. The mucous secretion was increased by ecabet as well as dmPGE(2) and NOR-3, and the effect of ecabet was significantly suppressed by both indomethacin and L-NAME. The inhibitory effects of L-NAME on the ecabet action were all significantly antagonized by concurrent addition of L-arginine. CONCLUSION: These results suggest that ecabet significantly expedited the restitution following gastric surface cell injury, and this action is mediated by endogenous NO as well as PGs and may be functionally associated with an increase of mucous secretion.     

Lack of correlation between mucus gel thickness and gastric cytoprotection in rats

The effect of various cytoprotective agents on the thickness of gastric mucus gel layer in rats was studied. It was hypothesized that an increase in the mucus gel layer might be involved in cytoprotection. The results show that this is not the case. Neither prostaglandin E2, 16,16-dimethyl prostaglandin E2, nor mild irritants (20% ethanol, 0.35 M HCl, 20% glucose, 20% mannitol), all given orally, altered the thickness of the mucus gel layer, although these agents were found to be cytoprotective, i.e., inhibiting the formation of gastric mucosal necrotic lesions caused by oral administration of absolute ethanol. The only agents that significantly increased the thickness of the mucus gel layer were a hypertonic solution (4% NaCl) and sodium salicylate. We conclude that if mucus plays a role in cytoprotection, it is not by virtue of an increase in thickness of the gel layer adherent to the gastric mucosa.     

Mucosal irritative and healing impairment action of risedronate in rat stomachs: comparison with alendronate

BACKGROUND AND AIM: We used alendronate and risedronate as bisphosphonates and examined whether or not these agents have a mucosal irritative action in the stomach and impair the healing of pre-existing gastric ulcers in rats. METHODS: Male Sprague Dawley (SD) rats were used in the following two studies: (i) the effects of risedronate and alendronate on gastric potential difference (PD), gastric mucosal blood flow (GMBF) and acid back-diffusion in the stomach mounted on ex vivo chamber under urethane anesthesia and; (ii) the influence of daily treatment with these drugs on the healing of acetic acid-induced gastric ulcers was examined. RESULTS: Mucosal application of risedronate produced PD reduction in the saline-perfused stomachs in a dose-dependent manner. Alendronate also produced a marked PD reduction, the effect being more potent than that of risedronate. In the stomach exposed to acid (100 mM HCl), both drugs produced a marked reduction in PD, followed by acid back-diffusion and a small increase in GMBF, resulting in hemorrhagic lesions, and the effects again were more pronounced with alendronate. These irritative effects were dependent on the pH of drug solution and the action was more potent at pH 7 than pH 4. Conversely, the healing of acetic acid-induced gastric ulcers was significantly delayed by daily administration of these drugs, yet this effect was less pronounced in the case of risedronate. The healing impairing effect of these bisphosphonates was potentiated by coadministration of indomethacin. CONCLUSION: Both alendronate and risedronate have mucosal irritative and healing impairing effects in the stomach, yet the effect of risedronate was much less pronounced compared to alendronate. It is assumed that risedronate is safer than alendronate as the antiresorptive agent in patients with diseases related to bone remodeling.     

Role of leukotriene C4 in mucosal damage caused by necrotizing agents and indomethacin in the rat stomach

Intragastric ethanol stimulates mucosal formation of leukotriene C4 in the rat stomach. The present study demonstrates that the increase in leukotriene C4 formation begins within 30 seconds and is maximal within 5 minutes, closely paralleled by the appearance of hemorrhagic lesions. Leukotriene C4 formation returns to prechallenge levels within 3 hours, although erosions still persist. Intragastric 0.2N NaOH, acidified 100 mmol/L taurocholate, 25% NaCl, or 0.6N HCl did not consistently increase leukotriene C4 formation despite severe mucosal injury. A number of sulfhydryl-containing or sulfhydryl-blocking agents as well as metals protected against mucosal damage and simultaneously prevented the stimulation of leukotriene C4 formation induced by ethanol. None of the agents increased and some virtually abolished mucosal formation of prostaglandin E2, indicating that gastroprotection can occur completely independently of the endogenous prostaglandin system. The leukotriene biosynthesis inhibitor MK-886 markedly suppressed gastric leukotriene C4 formation but did not protect against damage caused by ethanol, NaOH, NaCl, or acidified taurocholate. Oral indomethacin reduced the ex vivo formation of both prostaglandin E2 and, to a lesser extent, leukotriene C4 in the gastric mucosa, inducing a shift in the balance from protective prostaglandins to proulcerogenic leukotriene C4. Pretreatment with MK-886, however, did not significantly diminish indomethacin-induced lesions. These data suggest that leukotriene C4 is not the exclusive mediator of gastric injury caused by necrotizing agents or indomethacin. On the other hand, certain protective compounds exhibit a striking parallelism between protection and inhibition of ethanol-induced leukotriene C4 formation, suggesting that they may affect a target crucial for both mucosal injury and stimulation of 5-lipoxygenase.     

Pathways mediating pentagastrin-induced mucosal blood flow response in rat stomachs

The mechanisms of pentagastrin-induced gastric mucosal blood flow (GMBF) response were investigated in anesthetized rats. A rat stomach was mounted on anex vivo chamber, perfused with saline, and GMBF was measured by a laser Doppler flowmetry simultaneously with acid secretion. Pentagastrin infused intravenously produced a dose-dependent increase of GMBF as well as acid secretion, and its effect reached a maximum at 120 µg/kg/hr (maximal dose). Pretreatment with omeprazole (60 mg/kg, intraperitoneally) completely inhibited the acid secretory response and the enhancement of GMBF induced by both submaximal (60 µg/kg/hr) and maximal doses of pentagastrin. In contrast, the luminal perfusion with glycine (200 mM) to remove luminal H⁺ almost totally attenuated the increase of GMBF caused by the submaximal dose of pentagastrin, without any effect on acid secretion, but partially suppressed such GMBF responses caused by the maximal dose. Subcutaneous pretreatment with indomethacin, a cyclooxygenase inhibitor, significantly mitigated GMBF response caused by both submaximal and maximal doses of pentagastrin, whereas 8-phenyltheophylline (8-PT), an adenosine antagonist, showed a significant inhibition of GMBF response caused by only the maximal dose. However, the combined administration of 8-PT with glycine perfusion further attenuated GMBF response caused by the maximal dose of pentagastrin, and the additional treatment with indomethacin completely blocked this GMBF response. We conclude that pentagastrin-induced GMBF responses are mediated by at least two different pathways; one is related to luminal H⁺ and the other to the parietal cell activity, depending on the dose of pentagastrin. In addition, the latter pathway may be mediated by adenosine, while endogenous prostaglandins may be involved in both pathways.     

Gastric adaptation to injury by repeated doses of aspirin strengthens mucosal defence against subsequent exposure to various strong irritants in rats.

Gastric adaptation to injury during repeated doses of acetyl salicylic acid (ASA) is a well documented finding but it is not known whether this adaptation affects the tolerance of the mucosa to other strong irritants. Gastric adaptation was induced by repeated daily doses of acidified ASA (100 mg/kg in 1.5 ml of 0.2 N HCl) given intragastrically (series A rats). Control rats with an intact stomach were given daily intragastric vehicle only (1.5 ml of 0.2 N HCl) (series B). After full adaptation to ASA (5 days), rats were challenged again with acidified ASA or, for comparison, with strong irritants such as 100% ethanol, 200 mM acidified taurocholate, or 25% NaCl for 1 hour or with water immersion and restraint for 3.5 hours. The first dose of ASA produced numerous gastric lesions and deep histological necrosis accompanied by a fall in the gastric blood flow, negligible expression of epidermal growth factor (EGF) and transforming growth factor alpha (TGF alpha) or their receptors, and no evidence of mucosal proliferation. As adaptation to ASA developed, however, the areas of gastric lesions were reduced by more than 80% and there was a noticeable decrease in deep necrosis, a partial restoration of gastric blood flow, an approximately four-fold increase in EGF expression (but not in TGF alpha) and its receptors, and an appreciable increase in mucosal cell proliferation compared with vehicle treated rats. Increases in the mucosal expression of EGF receptors and the luminal content of EGF were also found in ASA adapted animals. In ASA adapted rats subsequently challenged with 100% ethanol, 200 mM TC, 25% NaCl, or stress, the area of the gastric lesions and deep histological necrosis were appreciably reduced compared with values in vehicle treated rats. This increased mucosal tolerance to strong irritants was also accompanied by the return of the gastric blood flow towards control levels and further significant increases in the mucosal expression of EGF receptors and mucosal cell proliferation. Gastric adaptation to ASA enhances the mucosal resistance to injury by strong irritants probably as a result of the restoration of the gastric blood flow and increased cell proliferation that may result from increased mucosal expression of EGF and its receptors.     

Adaptive cytoprotection mediated by prostaglandin I(2) is attributable to sensitization of CRGP-containing sensory nerves

BACKGROUND & AIMS: The phenomenon by which the gastric mucosa is protected in response to mild irritants has been called adaptive cytoprotection, a mechanism believed to be related to production of endogenous prostaglandins (PGs). We tested whether PGs generated by mild irritant prevent injury through the release of calcitonin gene-related peptide (CGRP) from the sensory nerves using prostanoid receptor-knockout mice. METHODS: The stomach was doubly cannulated and perfused with 1 mol/L NaCl or 50% ethanol. CGRP levels in the perfusate were determined by enzyme immunoassay, and the injured area was estimated at the end of perfusion. RESULTS: Preperfusion with mildly hypertonic saline (1 mol/L NaCl) increased generation of gastric PGE(2) and PGI(2) and reduced ethanol-induced mucosal damage. Exposure of ethanol after 1 mol/L NaCl increased intragastric CGRP levels from 166 +/- 27 to 713 +/- 55 pg/2 min (n = 4, P < 0.05), and the protective action of 1 mol/L NaCl was inhibited by indomethacin treatment. CGRP antagonist blocked 1 mol/L NaCl-induced protective effect. Intragastric perfusion of 50% ethanol after administration of PGI(2), but not of PGE(2), increased CGRP levels. Application of 1 mol/L NaCl to IP receptor-knockout mice (IP(-/-)) did not elicit the protective effects seen in the wild-type on ethanol-induced gastric mucosal lesions. Protective effect of 1 mol/L NaCl was observed in EP3 receptor-knockout mice (EP3(-/-)). CGRP level during ethanol perfusion was not increased in IP(-/-) but was increased in EP3(-/-) and wild-type counterparts after preperfusion of 1 mol/L NaCl. CONCLUSIONS: These results indicate that the endogenous PGI(2) generated by 1 mol/L NaCl may have a protective role in gastric mucosal injury through enhancement of CGRP release from gastric mucosa. This mechanism may explain the adaptive cytoprotection observed after treatment with mild irritants.     

Sensory neurons signal for an increase in rat gastric mucosal blood flow in the face of pending acid injury

Disruption of the gastric mucosal barrier is quickly followed by an increase in gastric mucosal blood flow, which is thought to be a defensive reaction to prevent further injury. This study examined how this increase in blood flow is brought about. When the stomach of urethane-anesthetized rats was perfused with 0.15N HCl, disruption of the gastric mucosal barrier with 15% ethanol increased the disappearance of acid from the gastric lumen and enhanced gastric mucosal blood flow. This increase in blood flow was blocked by local arterial infusion of tetrodotoxin (60 ng/min) to the stomach and by chemical ablation of capsaicin-sensitive sensory neurons. Inhibition of the blood flow increase was associated with exaggeration of gross and histological injury to the mucosa. IV injection of atropine (0.2 mg/kg) or pyrilamine (2 mg/kg) did not affect blood flow increase in response to barrier disruption, whereas morphine injection (2 mg/kg) inhibited it. The current findings show that the increase in gastric mucosal blood flow that follows disruption of the gastric mucosal barrier in the presence of acid is mediated by sensory neurons that seem to monitor acid back-diffusion and in turn signal for a protective increase in blood flow.     

一氧化氮和前列腺素在门静脉高压性胃病大鼠胃粘膜灌注中的作用

目的 探讨一氧化氮（NO）和前列腺素在门静脉高压性胃病（PHG）大鼠胃粘膜灌注中的作用。方法 部分结扎大鼠门静脉主干2周后,采用中性红清除率法测定大鼠胃粘膜血流量（GMBF）,同时观察门静脉压力（PVP）的变化。结果 PHG组大鼠GMBF和PVP显著高于假手术组（t=3.431、3．312,P＜0．01）。低剂量的NO合成酶抑制剂L－硝基－精氨酸甲酯（L－NAME）呈剂量依赖性降低PHG大鼠GMBF,而对假手术组GMBF无明显影响;高剂量的L－NAME（12mg/kg)能非常显著降低PHG和假手术组大鼠GMBF。前列腺素环氧合酶抑制剂消炎痛能明显降低PHG组大鼠GMBF,而对假手术组GMBF无明显影响;预先给消炎痛处理后在假手术组大鼠中,静脉注射低剂量L－NAME（4mg/kg)前后GMBF无明显变化,高剂量L－NAME（12mg/kg)降低大鼠的GMBF与未用消炎痛处理组比无明显变化;预先给消炎痛处理后在PHG组大鼠中,L－NAME剂量（4mg/kg、12mg/kg)依赖性降低大鼠的GMBF与未用消炎痛处理组比无明显改变。结论 NO、前列腺素在调节PHG大鼠的GMBF起重要作用,但两者无协同作用。