Prevention of water immersion stress-induced gastric lesions through the enhancement of nitric oxide synthase activity in rats

Background: Gastric mucosal microcirculation is an important factor in the protection of gastric mucosa, and nitric oxide (NO) plays a crucial role in the regulation of regional blood flow. This study was designed to evaluate the effect of cetraxate, an anti-ulcer drug, on water immersion stress-induced gastric lesions in relation to the changes in NO synthase activity. Methods: Gastric lesions were induced in rats by water immersion stress. The effects of cetraxate on NO synthase activity with or without stress was determined enzymatically. Changes in gastric mucosal prostaglandin (PG) contents with or without stress were also determined using high-performance liquid chromatography. Gastric mucosal blood flow was measured by hydrogen gas clearance technique. Results: Water immersion stress-induced gastric lesions. Cetraxate significantly mitigated the lesions but N^G-monomethyl-l -arginine (l -NMMA), a specific inhibitor of NO synthase, exacerbated the lesions. The favourable effect of cetraxate was remarkably diminished by administration of l -NMMA. NO synthase activity decreased significantly by 6 h after stress. Cetraxate treatment increased NO synthase activity throughout the experiment in rats with or without stress treatment. Water immersion stress decreased all PGs detected, i.e. 6-keto-PGF_1α, PGF_2α PGE₂ and PGD₂. Cetraxate prevented stress-induced decreases in PG contents. l -NMMA showed no significant effect on PG contents. Cetraxate increased gastric mucosal blood flow significantly and l -NMMA cancelled out cetraxate-induced increase in blood flow. Conclusions: The pharmacological efficacy of anti-ulcer drugs such as cetraxate might be attributable to the enhancement of NO synthase activity resulting in an increase in gastric mucosal blood flow.     

Exacerbatory mechanism responsible for water immersion stress-induced gastric lesions in aged rats compared with young rats

1. The present study was designed to investigate whether or not ageing affects the development of water immersion stress-induced gastric lesions in rats. Effects of cetraxate, an anti-ulcer drug, were also examined. 2. Gastric lesions were induced by 6 h water immersion stress in rats. Gastric mucosal blood flow was determined by the hydrogen gas clearance technique and nitric oxide synthase (NOS) activity was measured enzymatically. 3. Early development of gastric lesions was observed in aged rats and exacerbation of gastric lesions was also found. Lowering of gastric mucosal blood flow and reduced NOS activity were observed in aged rats. 4. Cetraxate mitigated the development of gastric lesions in young rats and also increased gastric mucosal blood flow and NOS activity. However, these favourable effects were diminished in aged rats. 5. Decreased NOS activity may be an important exacerbatory factor to the development of gastric lesions in aged rats. 6. Effects of cetraxate differed between young rats and aged rats. 7. These results may explain the refractoriness and drug resistance in gastric ulcers encountered by elderly individuals.     

颈交感神经干离断减轻鼠急性胃黏膜损伤

目的 探讨颈交感神经干离断(TCST)对大鼠急性胃黏膜损伤的保护作用.方法 30只雄性SD大鼠,随机分为假手术(A)组、假手术后浸水(B)组和TCST后浸水(C)组,每组10只.B、c组大鼠垂卣浸水至剑突水平6h,测各组大鼠胃黏膜血流量(GMBF),评定黏膜溃疡指数(UI).采用放免法检测胃黏膜组织降钙素基因相关肽(CGRP)含量,硝酸还原酶法测定胃黏膜组织中一氧化氮合酶(NOS)含量.结果 B、C组胃黏膜见出血性溃疡,B组损伤较重.B组GMBF、CGRP降低及UI、NOS明显高于C组(P<0.05或P<0.01).结论 TCST对大鼠急性胃黏膜损伤有保护作用,其机制可能与调节胃黏膜组织CGRP及NOS含量有关.     

L-arginine protects against stress-induced gastric mucosal lesions by preserving gastric mucus

1. We have shown that exogenously administered L-arginine protects against water immersion restraint (WIR) stress-induced gastric mucosal lesions in rats through preservation of nitric oxide (NO) generation via constitutive nitric oxide synthase (cNOS), but not inducible nitric oxide synthase (iNOS), in the gastric mucosa. We have also indicated that impaired gastric mucus synthesis and secretion occur through a decrease in gastric cNOS activity in WIR-stressed rats. Therefore, in the presesnt study, we examined whether exogenously administered L-arginine exerts a protective effect against WIR stress-induced gastric mucosal lesions in rats through preservation of gastric mucus synthesis and secretion by NO generated from the administered amino acid via cNOS in the gastric mucosa. 2. Rats were subjected to WIR stress for 3 and 6 h. Either L-arginine (150-600 mg/kg) or D-arginine (600 mg/kg) was injected intraperitoneally 0.5 h prior to WIR stress. Either N(G)-monomethyl L-arginine (L-NMMA; 100 mg/kg) or N(G)-monomethyl D-arginine (D-NMMA; 100 mg/kg) was injected subcutaneously 0.5 h prior to WIR stress. Total NOS, cNOS, iNOS, nitrite and nitrate (breakdown products of NO), hexosamine (an index of gastric mucin) and adherent mucus were assayed in the gastric mucosa. 3. Pretreatment with L-arginine, but not D-arginine, protected against gastric mucosal lesions in rats subjected to WIR stress for 3 and 6 h in a dose-dependent manner. Pretreatment with L-arginine, but not D-arginine, attenuated decreases in hexosamine and adherent mucus concentrations and cNOS activity and increases in total NOS and iNOS activities and nitrite/nitrate concentration in the gastric mucosal tissue of rats subjected to WIR stress for 3 and 6 h in a dose-dependent manner. Both the protective effect of L-arginine against gastric mucosal lesions and the attenuating effect of the amino acid on the decreases in gastric mucosal hexosamine and adherent mucus concentrations and cNOS activity in rats subjected to WIR stress for 6 h were counteracted by cotreatment with L-NMMA, a nitric oxide synthase inhibitor, but not D-NMMA. 4. These results suggest that exogenously administered L-arginine exerts a protective effect against stress-induced gastric mucosal lesions in rats at least partly through preservation of gastric mucus synthesis and secretion by NO produced from the administered amino acid via cNOS in gastric mucosal tissue.     

Effect of nitric oxide on integrity, blood flow and cyclic GMP levels in the rat gastric mucosa: modulation by sialoadenectomy.

1. The effects of the nitrosothiol, S-nitroso N-acetylpenicillamine (SNAP) which liberates nitric oxide (NO), on ethanol-mediated gastric damage, blood flow and cyclic GMP levels in siaoloadenectomized (SALX) rats have been investigated. 2. Intraluminal instillation of ethanol (5-50% w/v) dose-dependently induced haemorrhagic damage and decreased NO synthase activity in the gastric mucosa. Both the extent of mucosal damage and inhibition of NO synthase activity were exacerbated in SALX rats. 3. Epidermal growth factor administration (5 and 10 micrograms kg-1, s.c.) reduced mucosal damage but did not restore NO synthase activity in ethanol-treated SALX rats. 4. SNAP infusion (0.01-1.0 micrograms kg-1 min-1, i.v.) attenuated haemorrhagic damage in ethanol-treated rats. The reduction in mucosal damage was significantly greater in SALX rats. 5. SNAP administration also caused an increase in gastric mucosal blood flow and cyclic GMP levels in control rats and both responses were augmented in SALX animals. 6. These data suggest that SALX is associated with increases in mucosal susceptibility to ethanol-mediated damage and reduces mucosal NO synthase activity. Epidermal growth factor does not appear to influence mucosal NO synthase in ethanol-treated rats. Furthermore, SALX augments the responsiveness of the gastric mucosa to NO administration. Therefore, factors from the salivary glands influence gastric NO formation and mucosal responsiveness to a NO donor.     

牛乳铁蛋白对实验性胃黏膜损伤及胃溃疡大鼠模型的影响

目的 观察牛乳铁蛋白对实验性大鼠胃黏膜损伤及胃溃疡的保护作用。方法 建立无水乙醇、幽门结扎致大鼠胃黏膜损伤模型,水浸应激、乙酸灼烧致大鼠胃溃疡模型,测定模型大鼠胃黏膜损伤程度、溃疡面积、溃疡指数,以及胃黏膜中氨基己糖、PEG₂含量和血流动力学的变化,观察牛乳铁蛋白对实验性胃黏膜损伤和胃溃疡的保护作用。此外,通过连续喂养正常大鼠牛乳铁蛋白,观察其对大鼠胃液量、胃液酸度和胃蛋白酶活性的影响。结果 牛乳铁蛋白能降低乙醇及幽门结扎致胃黏膜损伤大鼠的溃疡指数,增加乙醇致胃黏膜损伤大鼠受损胃黏膜的氨基己糖和PEG₂含量以及血流量。同时,牛乳铁蛋白还能降低水浸应激以及乙酸灼烧致胃溃疡大鼠胃部的溃疡面积。此外,连续灌胃高剂量牛乳铁蛋白能抑制正常大鼠胃液分泌,减少胃液酸度。结论 牛乳铁蛋白对实验性胃黏膜损伤及胃溃疡大鼠模型胃黏膜损伤具有保护作用。     

Possible involvement of l-arginine-nitric oxide pathway in modulating regional blood flow to brown adipose tissue of rats

To evaluate whether the l-arginine-nitric oxide (NO) pathway is involved in the regulation of regional blood flow to brown adipose tissue (BAT), the effects of two specific NO synthase inhibitors, N^G-nitro-l-arginine methyl ester (l-NAME) and N^G-monomethyl-l-arginine (l-NMMA), on the blood flow to interscapular brown adipose tissue (IBAT) were studied in urethane-anesthetized rats. Regional blood flow in MAT was measured with laser-Doppler flowmetry.An intravenous injection of l-NAME and l-NMMA, but not of either d-enantiomer, caused a transient and dose-dependent increase in IBAT blood flow. Dose-response curves for these NO synthase inhibitors showed that l-NAME was more potent than l-NMMA in increasing IBAT blood flow. We also observed a concomitant pressor effect accompanied by a slight decrease in heart rate following intravenous injection of l-NAME and l-NMMA. An elevation of IBAT blood flow and blood pressure induced by both l-NAME and l-NMMA was reversed by l-arginine in an enantiomerically specific manner. The increase in IBAT blood flow induced by NO synthase inhibitors was of shorter duration and less sensitive to l-arginine than the increase in blood pressure.Our results show that the WAY blood flow is increased by inhibition of NO synthase and that the response of IBAT vasculature to NO synthase inhibitors is different from that of the resistance vessels which regulate blood pressure. The involvement of l-arginine-NO pathways in modulating microcirculation in IBAT is suggested. Correspondence to: Y. Uchida at the above address     

Preventive effect of teprenone on stress-induced gastric mucosal lesions and its relation to gastric mucosal constitutive nitric oxide synthase activity.

Recently, we demonstrated that teprenone, an anti-ulcer agent, exerts protective and preventive actions against water immersion restraint (WIR) stress-induced gastric mucosal lesions in rats both by inhibiting neutrophil infiltration into the gastric mucosal tissue and by preserving gastric mucus synthesis and secretion. In rats with WIR stress we have also found a decrease in gastric mucosal constitutive nitric oxide synthase (cNOS) activity and a drastic increase in gastric mucosal inducible nitric oxide synthase (iNOS) activity. The decrease in gastric mucosal cNOS activity is closely related to an increase in neutrophil infiltration into the gastric mucosa and a decrease in the level of gastric mucus. In this study of WIR-stressed rats, therefore, we examined whether the inhibitory actions of teprenone on neutrophil infiltration and decreases in mucus synthesis and secretion in the gastric mucosa of rats are related to the change in gastric mucosal cNOS activity during the development of gastric mucosal lesions. Pre-administration of teprenone (200 mg kg-1) prevented the decrease in gastric mucosal cNOS activity with attenuations of neutrophil infiltration into gastric mucosal tissues and decreased levels of gastric mucosal hexosamine, an index of gastric mucin, and adherent mucus in rats with 3 or 6 h of WIR stress. These preventive effects of teprenone on the gastric mucosal neutrophil infiltration and the decrease in gastric mucus levels in rats with WIR stress were completely reversed with inhibition of gastric mucosal cNOS activity by co-administration of NG-monomethyl L-arginine (L-NMMA), a non-selective NOS inhibitor. These results suggest that the inhibitory actions of teprenone on neutrophil infiltration and decreases in mucus synthesis and secretion in the gastric mucosa of rats with WIR stress are closely related to the maintenance of cNOS activity in the gastric mucosal tissue.     

Role of central and peripheral ghrelin in the mechanism of gastric mucosal defence

Ghrelin, identified in the gastric mucosa, has been involved in the control of food intake and growth hormone (GH) release, but whether this hormone influences the gastric secretion and gastric mucosal integrity has been little elucidated. We compared the effects of intraperitoneal (i.p.) and intracerebroventricular (i.c.v.) administration of ghrelin on gastric secretion and gastric lesions induced in rats by 75% ethanol or 3.5 h of water immersion and restraint stress (WRS) with or without suppression of nitric oxide (NO)-synthase or functional ablation of afferent sensory nerves by capsaicin. The number and the area of gastric lesions was measured by planimetry, the GBF was assessed by the H₂-gas clearance method and blood was withdrawn for the determination of the plasma ghrelin and gastrin levels. In addition, the gastric mucosal expression of mRNA for CGRP, the most potent neuropeptide released from the sensory afferent nerves, was analyzed in rats exposed to WRS with or without ghrelin pre-treatment. Ghrelin (5–80 μg/kg i.p. or 0.6–5 μg/kg i.c.v.) increased gastric acid secretion and attenuated gastric lesions induced by ethanol and WRS. This protective effect was accompanied by a significant rise in the gastric mucosal blood flow (GBF), luminal NO concentration and plasma ghrelin and gastrin levels. Ghrelin-induced protection was abolished by vagotomy and significantly attenuated by L-NNA and deactivation of afferent nerves with neurotoxic dose of capsaicin. The signal for CGRP mRNA was significantly increased in gastric mucosa exposed to WRS as compared to that in the intact gastric mucosa and this was further enhanced in animals treated with ghrelin. We conclude that central and peripheral ghrelin exerts a potent protective action on the stomach of rats exposed to ethanol or WRS, and these effects depend upon vagal activity and hyperemia mediated by the NOS-NO system and CGRP released from sensory afferent nerves.     

Effect of the H2-blocker famotidine on gastric mucosal prostaglandin levels in water immersion stress in rats

A quantitative and rapid method was developed for determination of tissue prostaglandin (PG) levels using reverse phase high performance liquid chromatography. Using this method, we investigated the effects of famotidine (YM-11170), an H2-blocker, on changes in gastric mucosal PG levels induced by water immersion stress in rats. Gastric mucosal phospholipase (PLase) activity was also estimated. Four kinds of PGs, i.e., 6-keto-PGF1a, PGE2, PGF2a, and PGD2 were detected in gastric mucosa. 6 h water immersion stress induced decreases in all of them at a similar degree, the reduction being about 70% of the control value. Decreases in PLase activity were also observed in rats with 6 h stress. Pretreatment with famotidine prevented decreases in levels of PGs, which are known to have cytoprotective effect, and also maintained PLase activity. These results indicate that famotidine exerts its anti-ulcer action via maintenance of PG levels and PLase activity.     

蒙脱石散对急性胃黏膜病变的修复作用及其机制

目的:了解蒙脱石散(思密达)对急性胃黏膜病变的修复作用及其机制研究。方法:构建急性胃黏膜病变的SD大鼠模型,将其分为单纯模型组、模型+思密达组、模型+硫糖铝组,以单纯模型组作为阴性对照组,以硫糖铝作为阳性对照组,所有组别大鼠均分别在造模后0,12,24,48,72 h随机立即处死3只,并在肉眼、光镜及电镜下观察各组急性胃黏膜病变的形态学改变,同时监测各时间段各组胃内pH值了解其抗酸作用;监测胃内N-乙酰氨基己糖含量了解其对胃黏液层厚度的影响;监测胃黏膜血流(GMBF)、溃疡指数(UI)、胃黏膜厚度、表皮生长因子(EGF)、一氧化氮(NO)和前列腺素E₁(PGE₁)的表达水平了解其对胃黏膜的修复作用及机理研究。结果:(1)与阴性对照组相比,思密达组急性胃黏膜病变在肉眼、光镜及电镜下均好转。(2)思密达组胃内pH值、胃黏液层厚度、GMBF、胃内N-乙酰氨基己糖含量、NO和PGE₁的表达水平均在至少两个时间段里较阴性对照组有不同程度的升高,且有统计学差异(P<0.05)。结论:思密达对胃黏膜有保护作用。其机制可能与思密达通过升高PGE₁、EGF、NO的表达水平,增加GMBF及糖蛋白含量,从而达到抑酸及增加胃黏膜厚度,降低UI。     

Protective effect of -arginine against stress-induced gastric mucosal lesions in rats and its relation to nitric oxide-mediated inhibition of neutrophil infiltration

Pretreatment with -arginine (150–600 mg kg⁻¹, i.p.), but not -arginine (600 mg kg⁻¹, i.p.), protected against gastric mucosal lesions in rats with water immersion restraint stress over a 6-h period. This protective effect occurred in a dose-dependent manner. Increases in the activities of inducible nitric oxide synthase (iNOS) and myeloperoxidase (MPO), an index of tissue neutrophil infiltration, and the concentration of nitrite/nitrate, breakdown products of nitric oxide, and a decrease in the activity of constitutive nitric oxide synthase (cNOS) occurred in the gastric mucosal tissue with the development of gastric mucosal lesions. The -arginine pretreatment attenuated the increases in iNOS and MPO activities and nitrite/nitrate concentration and the decrease in cNOS activity in the gastric mucosal tissue in a dose-dependent manner, while the -arginine pretreatment did not. Both the protective effect of -arginine (300 mg kg⁻¹) against stress-induced gastric mucosal lesions and the attenuating effect of the amino acid on the increases in gastric mucosal iNOS and MPO activities and the decrease in gastric mucosal cNOS activity with the lesion development were counteracted by pretreatment with N^G-monomethyl- -arginine (100 mg kg⁻¹, s.c.), a nitric oxide synthase inhibitor, but not its -isomer (100 mg kg⁻¹, s.c.). These results suggest that the protective effect of exogenously administered -arginine against stress-induced gastric mucosal lesions in rats is, at least in part, due to nitric oxide-mediated inhibition of neutrophil infiltration into the gastric mucosal tissue.     

Implication of endogenous nitric oxide in gastric mucosal protective effect of T-593, a novel anti-ulcer agent, in rats

The relationship of endogenous nitric oxide (NO) to the gastric mucosal protective effect of the novel anti-ulcer agent T-593, (+/-)-(E)-1-[2-hydroxy-2-(4-hydroxyphenyl)ethyl]-3-[2-[[[5-(methylamino) methyl-2-furyl]methyl]thio]ethyl]-2-(methylsulfonyl) guanidine, was investigated in rats. T-593 (3-30 mg/kg, p.o.) dose dependently prevented the formation of gastric mucosal lesions induced by oral administration of aspirin (200 mg/kg) in 0.15 N HCl (HCl-aspirin). Pretreatment with N(G)-nitro-L-arginine methylester (L-NAME), a selective inhibitor of NO synthase (NOS), attenuated the mucosal protective effect of T-593. This effect of L-NAME was antagonized by pretreatment with L-arginine, a substrate of NOS, but not with D-arginine. Activity of total NOS composed of inducible and constitutive NOS in the gastric mucosa was decreased by HCl-aspirin, and T-593 inhibited this decrease. On the other hand, HCl-aspirin and T-593 did not affect inducible NOS activity in the gastric mucosa. Furthermore, we confirmed that T-593 inhibits the decrease in gastric mucosal blood flow (GMBF) induced by HCl-aspirin, and this effect is completely inhibited by pretreatment with L-NAME. These results suggest that the mucosal protective effect of T-593 is partly mediated by endogenous NO via improvement of GMBF and that a possible mechanism for the effect of T-593 is the maintenance of constitutive NOS activity in gastric mucosa.     

秋茄提取物抗大鼠实验性胃溃疡作用研究

目的探讨海洋红树林植物秋茄枝水提取物活性部分B部位(fraction B of stem aqueous extracts of kandelia candel,SAEKC)对实验性大鼠胃溃疡的作用及其作用机制。方法将大鼠随机分为正常对照组、模型对照组、给药组(480、240、60mg·kg-13个剂量组)和西咪替丁组。各组每天灌胃给药(赋形剂,SAEKCB和西咪替丁),连续3d。除正常对照组外,其余各组大鼠在最后一次给药后通过水应激18h建立水浸束缚应激型胃溃疡大鼠模型,测定溃疡指数(UI),计算溃疡抑制率;同时建立幽门结扎型胃溃疡大鼠模型,造模后17h测定溃疡指数,计算溃疡抑制率,检测胃液量、胃蛋白酶活性,血清和胃组织一氧化氮(NO)含量。结果SAEKCB的高、中、低3个剂量组能明显减轻应激型胃溃疡大鼠胃黏膜损伤的程度(P<0.01,P<0.01,0<0.05),溃疡抑制率分别为模型对照组的0.411、0.404、0.254;SAEKCB能明显减轻幽门结扎型胃溃疡大鼠胃黏膜损伤的程度(P均<0.01),溃疡抑制率分别为模型对照组的0.556、0.361、0.306。480、240mg·kg-1剂量组能明显降低胃蛋白酶活性和胃液量(P<0.01或P<0.05)。给药3个剂量组均能提高胃组织NO含量,其中240、60mg·kg-1剂量组能明显升高血清NO含量(P均<0.01)。结论SAEKCB有明显抗应激型和幽门结扎型大鼠胃溃疡的作用,其效应呈剂量依赖性。对于幽门结扎型大鼠其机制可能在于减少胃液分泌、降低胃蛋白酶活性、提高血清和胃组织中NO水平。     

Various stress proteins protect gastric mucosal cells against non-steroidal anti-inflammatory drugs

Gastric mucosal cell death induced by non-steroidal anti-inflammatory drugs (NSAIDs) is suggested to be involved in NSAID-induced gastric lesions. Therefore, cellular factors that suppress this cell death are important for protection of the gastric mucosa from NSAIDs. When cells are exposed to various stressors, including NSAIDs, they induce a number of proteins, so-called stress proteins, in order to protect themselves against such stressors. Stress proteins contain cytosolic molecular chaperons (such as heat shock proteins), endoplasmic reticulum molecular chaperons (such as glucose-regulated proteins) and heme oxygenase-1. We recently showed that (i) these stress proteins are up-regulated by NSAIDs both in vitro and in vivo; (ii) these up-regulation make gastric mucosal cells resistant to NSAIDs in vitro; (iii) these up-regulation protects the gastric mucosa from NSAID-induced gastric lesions in vivo. In this review, I summarize these results and propose that non-toxic inducers of these stress proteins are therapeutically beneficial as anti-ulcer drugs. Received 12 July 2006; accepted 1 September 2006     

Agonist of peroxisome proliferator-activated receptor gamma (PPAR-γ: A new compound with potent gastroprotective and ulcer healing properties

Pioglitazone, a specific ligand for peroxisome proliferator-activated receptor gamma (PPAR-γ), was recently implicated in the control of inflammatory processes and in the modulation of the expression of various cytokines such as tumor necrosis factor alpha (TNF-α), but its role in the mechanism of gastric mucosal integrity has not been studied extensively. This study was designed to determine the effect of pioglitazone on gastric mucosal lesions induced in rats by topical application of 100% ethanol and by 3.5 h of water immersion and restraint stress (WRS) with or without pretreatment with indomethacin (5 mg/kg i.p.) to inhibit cyclooxygenase-1 (COX-1) and COX-2 enzyme activities and L-NNA (20 mg/kg i.p.) to suppress nitric oxide (NO)-synthase. In addition, the effect of pioglitazone on ulcer healing in rats with chronic acetic acid ulcers (ulcer area 28 mm²) was determined. Rats were killed 1 h and 3.5 h after ethanol administration or WRS exposure or at day 9 upon ulcer induction, and the number and area of gastric lesions were measured by planimetry, the gastric blood flow (GBF) was determined by H₂-gas clearance technique and the mucosal PGE₂ generation and gene expression and plasma concentration of TNF-α and IL-1β were also evaluated. Pre-treatment with pioglitazone dose-dependently attenuated gastric lesions induced by 100% ethanol and WRS; the dose reducing these lesions by 50% (ID₅₀) being 10 mg/kg and 7 mg/kg, respectively. The protective effect of pioglitazone was accompanied by the significant rise in the GBF, an increase in PGE₂ generation and the significant fall in the plasma TNF-α and IL-1β levels. Strong signals for IL-1β-and TNF-α mRNA were recorded in gastric mucosa exposed to ethanol or WRS, and these effects were significantly decreased by pioglitazone. Indomethacin which suppressed PG generation by about 90%, while augmenting WRS damage, and L-NNA, that suppressed NO-synthase activity, significantly attenuated the protective and hyperaemic activity of this PPAR-γ ligand. In the chronic study, pioglitazone significantly reduced the area of gastric ulcers on day 9 and significantly raised the GBF at the ulcer margin. The acceleration of ulcer healing by PPAR-γ ligand was accompanied by a significant increase in the expression of PECAM-1 protein, a marker of angiogenesis. We conclude that (1) pioglitazone exerts a potent gastroprotective and hyperaemic actions on the stomach involving endogenous PG and NO and attenuation of the expression and release of proinflammatory cytokines TNF-α and IL-1β, and (2) PPAR-γ ligand accelerates ulcer healing, possibly due to the enhancement in angiogenesis at ulcer margin.     

Role of gastric mucosal ascorbic acid in gastric mucosal lesion development in rats with water immersion restraint stress

We examined the role of gastric mucosal ascorbic acid (AA) in gastric mucosal lesion development in rats with water immersion restraint stress (WIRS). When fasted rats were subjected to WIRS for 1, 3 or 6 h, gastric mucosal lesions developed at 3 and 6 h. Gastric mucosal AA concentration decreased at 3 and 6 h after the onset of WIRS, while gastric mucosal non-protein SH concentration decreased at 1, 3, and 6 h and gastric mucosal vitamin E concentration decreased at 6 h. Gastric mucosal lipid peroxide concentration and myeloperoxidase activity increased at 3 and 6 h of WIRS. Pre-administration of AA (250 mg/kg) prevented gastric mucosal development with attenuation of the decreased gastric mucosal AA, non-protein SH and vitamin E concentrations, and the increased gastric mucosal lipid peroxide concentration and myeloperoxidase activity. These results suggest that gastric mucosal AA plays an important role in WIRS-induced gastric mucosal lesion development.     

Acute normovolaemic anaemia prevents ethanol-induced gastric damage in rats through a blood flow related mechanism

The aim of the study was to assess whether changes in gastric mucosal blood flow induced by acute normovolaemic anaemia influence the susceptibility of the gastric mucosa to ethanol-induced damage, and the relationship of these changes with nitric oxide biosynthesis. Acute normovolaemic anaemia, promoted by exchanging 3 ml of blood by a plasma expander, induced a significant increase in gastric mucosal blood flow measured by hydrogen gas clearance, without changes in arterial blood pressure. After intragastric 60% ethanol administration, gastric blood flow was still significantly higher in anaemic than in control rats, and this was associated with a lower macroscopic and microscopic gastric damage. Following ethanol administration, anaemic rats pretreated with an inhibitor of nitric oxide biosynthesis (l-NMMA, 50 mg/kg, i.v.) had a lower gastric blood flow and a higher macroscopic gastric damage than anaemic rats without pretreatment. Anaemic rats pretreated with vasopressin also had after ethanol administration a lower gastric blood flow and a higher macroscopic gastric damage. It is concluded that acute normovolaemic anaemia protects the gastric mucosa against damage induced by intragastric ethanol. The inhibition of nitric oxide biosynthesis reverts in part this protective effect, and this seems to be related with the capability of nitric oxide to increase gastric mucosal blood flow, since vasoconstriction by a nitric oxide-independent mechanism causes a similar effect.     

Protective effect of coadministered superoxide dismutase and catalase against stress-induced gastric mucosal lesions

1. There are conflicting reports as to the protective effect of coadministered native superoxide dismutase (SOD) and catalase against gastric mucosal lesions in rats with water immersion restraint (WIR) stress. It is unclear how coadministered native SOD and catalase protect against WIR stress-induced gastric mucosal lesions. Therefore, in the present study, we re-examined the protective effect of coadministered native SOD and catalase against gastric mucosal lesions in rats with WIR stress. 2. Gastric mucosal lesions were induced in Wistar rats by 3 h WIR. Rats were injected subcutaneously with a mixture of purified bovine erythrocyte SOD and bovine liver catalase 1 h before the onset of WIR. Ulcer index, serum SOD, catalase and xanthine oxidase (XO), uric acid and gastric mucosal SOD, catalase, XO, myeloperoxidase (MPO; an index of tissue neutrophil infiltration), non-protein sulfhydryl (NP-SH) and thiobarbituric acid-reactive substances (TBARS; an index of lipid peroxidation) were assayed in all rats used. 3. Rats with 3 h WIR showed gastric mucosal lesions. Pre-administration of SOD plus catalase to rats with WIR prevented lesion formation. In the serum of rats with WIR alone, XO activity and uric acid concentration increased, whereas SOD and catalase activities did not change. Pre-administration of SOD plus catalase to rats with WIR did not affect increased serum XO activity and uric acid concentration, but did increase serum SOD and catalase activities. In the gastric mucosa of rats with WIR alone, increases in MPO activity and TBARS concentration and a decrease in NP-SH concentration occurred, whereas XO, SOD and catalase activities did not change. Pre-administration of SOD plus catalase to rats with WIR attenuated the changes in gastric mucosal MPO activity and TBARS and NP-SH concentrations, but did not affect gastric mucosal XO, SOD and catalase activities. Pre-administration of SOD plus catalase (in an inactivated form) to rats with WIR had no effect on gastric mucosal lesion formation and the levels of serum and gastric mucosal parameters studied. 4. These results indicate that coadministered native SOD and catalase protect against gastric mucosal lesions in rats with WIR stress and suggest that this protective effect of coadministered native SOD and catalase could be due to their activity to scavenge XO-derived active oxygen species that are increased in the blood.     

Gastric mucosal blood flow in ethanol-induced mucosal damage in the rat

Gastric mucosal blood flow in ethanol-induced mucosal damage was studied in urethane-anaesthetised rats by reference to ¹⁴C-aminopyrine clearance in the gastric mucosa. Irrigation of the stomach with 30% ethanol in acid saline (100 mM HCl plus 50 mM NaCl) for 40 min broke the gastric mucosal barrier, as indicated by an increased outflow of Na⁺ and K⁺ ions and back-diffusion of H⁺ ions. Gastric mucosal blood flow also increased about 2-fold, decreasing after cessation of ethanol irrigation along with the net ion fluxes. The increase in gastric mucosal blood flow occasioned by 10, 20 and 30% ethanol in acid saline was directly proportional to the net fluxes of H⁺, Na⁺ and K⁺ ions. When the stomach was irrigated with 30% ethanol in a less acid medium (10 mM HCl, 90 mM choline chloride plus 50 mM NaCl) there was still a significant increase in the outflow of Na⁺ and K⁺ ions, but only a slight back-diffusion of H⁺ ions. During this low rate of acid back-diffusion 30% ethanol reduced gastric mucosal blood flow by about 50%. The results suggest that ethanol-induced mucosal damage in the rat is associated with an increase in gastric mucosal blood flow only if combined with back-diffusion of H⁺ ions.