Mechanisms Of Gastroprotection Research Articles

Protective Effect of Pyrus ussuriensis Maxim. Extract against Ethanol-Induced Gastritis in Rats.

Pyrus ussuriensis Maxim (Korean pear) has been used for hundreds of years as a traditional herbal medicine for asthma, cough, and atopic dermatitis in Korea and China. Although it was originally shown to possess anti-inflammatory, antioxidant, and antiatopic properties, its gastroprotective effects have not been investigated. In the present study, we evaluated the protective effects of Pyrus ussuriensis Maxim extract (PUE) against ethanol-induced gastritis in rats. The bioactive compound profile of PUE was determined by gas chromatography mass spectroscopy (GC-MS) and high-performance liquid chromatography (HPLC). The gastroprotection of PUE at different doses (250 and 500 mg/kg body weight) prior to ethanol ingestion was evaluated using an in vivo gastritis rat model. Several endpoints were evaluated, including gastric mucosal lesions, cellular degeneration, intracellular damage, and immunohistochemical localization of leucocyte common antigen. The gastric mucosal injury and ulcer score were determined by evaluating the inflamed gastric mucosa and by histological examination. To identify the mechanisms of gastroprotection by PUE, antisecretory action and plasma prostaglandin E2 (PGE2), gastric mucosal cyclic adenosine monophosphate (cAMP), and histamine levels were measured. PUE exhibited significant antioxidant effects with IC50 values of 56.18 and 22.49 µg/mL for 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′- azino-di-(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) inhibition (%), respectively. In addition, GC/MS and HPLC analyses revealed several bioactive compounds of PUE. Pretreatment with PUE significantly (p < 0.05) decreased the ulcer index by preventing gastric mucosal lesions, erosion, and cellular degeneration. An immunohistochemical analysis revealed that PUE markedly attenuated leucocyte infiltration in a dose-dependent manner. The enhancement of PGE2 levels and attenuation of cAMP levels along with the inhibition of histamine release following PUE pretreatment was associated with the cytoprotective and healing effects of PUE. In contrast, the downregulation of the H+/K+ ATPase pathway as well as muscarinic receptor (M3R) and histamine receptor (H2R) inhibition was also involved in the gastroprotective effects of PUE; however, the expression of cholecystokinin-2 receptors (CCK2R) was unchanged. Finally, no signs of toxicity were observed following PUE treatment. Based on our results, we conclude that PUE represents an effective therapeutic option to reduce the risk of gastritis and warrants further study.

Mechanisms of curcumin-induced gastroprotection against ethanol-induced gastric mucosal lesions

BackgroundCurcumin, a pleiotropic substance used for centuries in traditional medicine, exhibits antioxidant, anti-inflammatory and antiproliferative efficacy against various tumours, but the role of curcumin in gastroprotection is little studied. We determined the effect of curcumin against gastric haemorrhagic lesions induced by 75% ethanol and alterations in gastric blood flow (GBF) in rats with cyclooxygenase-1 (COX-1) and COX-2 activity inhibited by indomethacin, SC-560 or rofecoxib, inhibited NO-synthase activity, capsaicin denervation and blockade of TRPV1 receptors by capsazepine.MethodsOne hour after ethanol administration, the gastric mucosal lesions were assessed by planimetry, the GBF was examined by H2 gas clearance, plasma gastrin was determined by radioimmunoassay, and the gastric mucosal mRNA expression of Cdx-2, HIF-1α, HO-1 and SOD 2 was analysed by RT-PCR.ResultsCurcumin, in a dose-dependent manner, reduced ethanol-induced gastric lesions and significantly increased GBF and plasma gastrin levels. Curcumin-induced protection was completely reversed by indomethacin and SC-560, and significantly attenuated by rofecoxib, L-NNA, capsaicin denervation and capsazepine. Curcumin downregulated Cdx-2 and Hif-1α mRNA expression and upregulated HO-1 and SOD 2, and these effects were reversed by L-NNA and further restored by co-treatment of L-NNA with l-arginine.ConclusionsCurcumin-induced protection against ethanol damage involves endogenous PG, NO, gastrin and CGRP released from sensory nerves due to activation of the vanilloid TRPV1 receptor. This protective effect can be attributed to the inhibition of HIF-1α and Cdx-2 expression and the activation of HO-1 and SOD 2 expression.

Gastroprotective activity of the rhizome ethanol extract of Zingiber simaoense Y. Y. Qian in rats

Ethnopharmacological relevanceZingiber simaoense Y. Y. Qian belongs to the Zingiberaceae family. Its rhizome has been used in Thai folk medicine to relieve gastric disorders; however, scientific evidence of its pharmacological activities has not yet been revealed. Aim of the studyThis study was designed to validate the gastroprotective activity and to identify possible mechanisms of gastroprotection of Z. simaoense rhizome ethanol extract (ZSE) in rats. Materials and methodsThe gastroprotective effect of ZSE was tested using models of gastric ulcers induced by acidified ethanol, indomethacin, and restraint water immersion stress. Models for determination of gastric wall mucus secretion and plasma malondialdehyde levels as well as pylorus ligation were used to explore the mechanisms of action. ResultsAfter oral administration by intragastric gavage, ZSE 7.5, 15, and 30mg/kg or cimetidine 100mg/kg significantly inhibited the formation of gastric ulcer in all gastric ulcer models. The gastric wall mucus amount was significantly higher than that of the ulcer control group, plasma malondialdehyde levels were normalized, and gastric secretion was partly inhibited by pretreatment with ZSE. ConclusionsThis study demonstrates the gastroprotective activity of ZSE in rats. The mechanisms of action of ZSE may depend on its ability to maintain the integrity of gastric wall mucus through the protection of gastric mucus, and/or by increasing the gastric mucus synthesis and secretion through prostaglandin synthesis. Moreover, the antioxidant activity of ZSE may also contribute to its mechanism of gastroprotection.

Gastroprotective activity of chloroform extract of Muntingia calabura and Melastoma malabathricum leaves

Context: Muntingia calabura L. (family Muntingiaceae) and Melastoma malabathricum L. (family Melastomaceae) are traditionally used to treat gastric ulcer.Objective: The present study determines the mechanisms of gastroprotective activity of the chloroform extract of leaves obtained from both the plants using several in vitro and in vivo assays.Materials and methods: Phytochemical screening, HPLC analysis, and antioxidant activity of the respective extract were carried out. Gastroprotective activity was determined using ethanol-induced gastric ulcer assay while the mechanisms of gastroprotection were determined using the pyloric ligation assay. The test solutions [8% Tween-80 (vehicle), 20 mg/kg omeprazole, and different doses of extracts (50, 250, or 500 mg/kg] were administered orally once daily for 7 consecutive days before the animals were subjected to ethanol induced gastric ulcers.Results: The chloroform-extracted M. calabura (CEMC) contains tannins, polyphenolics, triterpenes, and steroids while the chloroform-extracted M. malabathricum (CEMM) contains only triterpenes and steroids. CEMC, but not CEMM, exerted remarkably strong antioxidant activity in the 2,2-diphenyl-1-picrylhydrazyl (DPPH)- (86% versus 16%) and superoxide- (73% versus 36%) radical scavenging assays. Both extracts demonstrated significant (p < 0.05) gastroprotection with the EC50 value recorded at 192.3 or 297.7 mg/kg, respectively. In the pylorus ligation assay, CEMC and CEMM significantly (p < 0.05) reduced the total and free acidity and volume; while increased the pH of gastric juice as well as the gastric wall mucus content in comparison with the vehicle-treated group.Discussion and conclusion: CEMC and CEMM exert gastroprotective effects in animals with ethanol-induced gastric ulcers via antioxidant and anti-secretory effects.

Mechanisms of gastroprotection of methanol extract of Melastoma malabathricum leaves.

BackgroundMelastoma malabathricum L. (Melastomaceae) is a small shrub with various medicinal uses. The present study was carried out to determine the gastroprotective mechanisms of methanol extract of M. malabathricum leaves (MEMM) in rats.MethodsThe extract's mechanisms of gastroprotection (50, 250, 500 mg/kg) were studied using the pylorus-ligation in rat model wherein volume, pH, free and total acidity of gastric juice, and gastric wall mucus content were determined. The involvement of endogenous nitric oxide (NO) and sulfhydryl (SH) compounds in the gastroprotective effect of MEMM were also measured. MEMM was subjected to the antioxidant, anti-inflammatory and phytochemical analysis and HPLC profiling.ResultsMEMM contained various phyto-constituents with quercitrin being identified as part of them. MEMM and quercitrin: i) significantly (p < 0.05) reduced the volume and acidity of gastric juice while increasing the pH and gastric wall mucus content.; ii) significantly (p < 0.05) increased the level of SOD, GTP and GTR while significantly (p < 0.05) reduced the level of CAT, MPO and TBARS activities.; iii) exerted gastroprotective activity when assessed using the ethanol-induced gastric ulcer assay, which was reversed by NG-nitro-l-arginine methyl esters (L-NAME; an inhibitor of NO synthase) and N-ethylmaleimide (NEM; a sulfhydryl (SH) blocker). MEMM inhibited the lipoxygenase (LOX) and xanthine oxidase (XO) activities with the highest affinity for the former while quercitrin showed high affinity for XO activity.ConclusionsMEMM exhibited a gastroprotective activity due partly to the presence of quercitrin, its antioxidant and anti-inflammatory activities, and via the modulation of NO and SH groups.

Gastroprotective activity and mechanisms of action of &lt;i&gt;Bauhinia purpurea&lt;/i&gt; Linn (Leguminoseae) leaf methanol extract

Purpose: To determine the gastroprotective activity and mechanisms of protection of the methanol extract of Bauhinia purpurea leaves (MEBP) using ethanol-induced gastric ulcer model. Methods: Male Sprague Dawley rats (n = 6) were administered orally with 10 % DMSO, 100 mg/kg ranitidine or MEBP (50, 250 and 500 mg / kg) daily for 7 consecutive days prior to subjection to the ethanol-induced gastric ulcer assay. The mechanisms of gastroprotection were determined based on: i) antisecretory activity via pylorus ligation assay; ii) the role of nitric oxide (NO) and sulfhydryl group via pre-treatment of MEBP-treated rats with the respective N-nitro-L-arginine methyl ester (L-NAME) or carbenoxolone (CBX) followed by the ethanol-induced assay; and iii) antioxidant activity using superoxide anion radical scavenging assay and, oxygen radical absorbance capacity (ORAC) assay. Ranitidine (100 mg / kg) was used as the reference drug. . Results: MEBP exhibited a significant (p < 0.05) and dose-dependent gastroprotective activity against ethanol-induced gastric ulcer with ulcer formation ranging between 0 and 74 % (indicated by decrease in ulcer area from 21.3 to 5.5 mm 2 ). The macroscopic observation was in line with the microscopic findings and further supported by the histological scores suggesting the antiulcer potential of MEBP. MEBP also significantly (p < 0.05) reduced volume gastric juice, as well as its free and total acidity wh ile increasing its pH. Moreover, this activity was significantly (p < 0.05) modulated in the presence of sulfhydryl group, but not NO. The extract also exhibited significant (p < 0.05) antioxidant activity. Conclusion: MEBP exerts gastroprotective activity partly via its antisecretory and antioxidant activities, as well as by modulation of sulfhydryl group, but not NO action.

Mechanisms of Esophageal Protection, Gastroprotection and Ulcer Healing by Melatonin. Implications for the Therapeutic use of Melatonin in Gastroesophageal Reflux Disease (GERD) and Peptic Ulcer Disease

Melatonin is a potent reactive oxygen metabolite scavenger and antioxidant that has been shown to influence many physiological functions of the gastrointestinal (GI) tract including secretion, motility, digestion and absorption of nutrients. The role of melatonin in gastroduodenal defense and ulcer healing has been the subject of recent investigations. Melatonin produced in the GI mucosa plays an important role in protection against noxious agents thus contributing to the maintenance of GI integrity and to esophageal protection, gastroprotection and ulcer healing. This review was designed to summarize the involvement of melatonin, conventionally considered as a major hormone of the pineal gland, in the maintenance of gastric mucosal integrity, gastroprotection, ulcer healing and intestinal disorders. Melatonin was originally shown to attenuate gastric mucosal lesions but controversy exists in the literature as to whether melatonin derived from the pineal gland, considered as the major source of this indole, or rather gastrointestinal melatonin plays predominant role in gastroprotection. Intragastric and central administration of exogenous melatonin and L-tryptophan, this indoleamine precursor, affords protection against gastric hemorrhagic damage caused by the exposure of gastric mucosa to variety of non-topical and topical ulcerogens such as stress, ethanol and ischemia-reperfusion. The speed of ulcer healing in experimental animals and humans is accelerated by melatonin. This indoleamine could be also effective against the esophageal lesions provoked by reflux esophagitis in animal models and prevents the incidence of GERD in humans. The melatonin-induced gastroprotection is accompanied by an increase in gastric blood flow, plasma melatonin concentration, enhancement in mucosal generation of PGE2, luminal NO content and plasma gastrin levels. Melatonin scavenges reactive oxygen metabolites, exerts anti-oxidizing and anti-inflammatory actions and inhibits the formation of metalloproteinases- 3 and -9; both implicated in the pathogenesis of gastrointestinal injury and formation of gastric ulcers. Blockade of MT2 receptors by luzindole, significantly attenuated melatonin- and L-tryptophan-induced protection and increased the speed of ulcer healing and these effects were accompanied by an increase in the GBF and luminal content of NO suggesting that melatonin exhibits gastroprotection and hyperemia via activation of MT2 receptors and release of NO. The accumulated evidence indicates that the melatonin-induced gastroprotection and the enhancement in healing rate of gastric ulcers may involve the gastroprotective factors derived from the activation of PG/COX and NO/NOS systems as well as gastrin which also was shown to exhibit protective and trophic effects in the upper GItract. Interestingly, pinealectomy, which suppressed plasma melatonin levels, markedly exacerbated gastric lesions induced by topical and non-topical ulcerogens and these effects are counteracted by a concurrent supplementation with melatonin. Evidence is provided that exogenous melatonin and that converted from its precursor, L-tryptophan, attenuates acute gastric lesions and accelerates ulcer healing via interaction with MT2 receptors due to an enhancement of gastric microcirculation, probably mediated by NO and PG derived from NOS and COX-1 and COX-2 overexpression and activity. The pineal gland plays an important role in the limitation of gastric mucosal injury and the acceleration of ulcer healing via releasing endogenous melatonin, which attenuates oxidative stress and exerts anti-inflammatory action.

Essential oils from medicinal and aromatic plants: a review of the gastroprotective and ulcer‐healing activities

Gastric ulcer is an excoriated area of the gastric mucosa. It is among the predominant gastrointestinal chronic diseases. The essential oils represent an important part of the traditional pharmacopoeia in many countries and have been successfully used for gastroprotection and ulcer healing. Thus, this review presents the experimental activity of essential oils traditionally used in the gastric ulcer prevention and treatment, considering their families, part of the plant studied, bioassays, and their mechanisms of gastroprotection and ulcer healing, with the aim of stimulating novel studies in the search for a new phytomedicine to treat gastric diseases.

Investigation of the Mechanisms Underlying the Gastroprotective Effect of Cymbopogon Citratus Essential Oil

Cymbopogon citratus is a medicinal plant popularly used in Brazil for the treatment of various diseases, and the research interest in this plant is justifiable because of its potential medicinal value in stomachache and gastric ulcer. This study was aimed to test the validity of this practice by using experimental models of gastric ulcer and to clarify the mechanisms of gastroprotection by C. citratus leaves essential oil (EOCC). EOCC was evaluated for the ability to protect the gastric mucosa against injuries caused by necrotizing agents (absolute ethanol and aspirin) in rodents. The results of this study revealed that EOCC posses a dose-independent anti-ulcer effect against the different experimental models. EOCC pretreatment depicted a higher preventive index in ethanol-(88%) and aspirin-induced (76%) acute ulceration. On pretreatment of mice with indomethacin, the cyclooxygenase inhibitor slightly suppressed the gastroprotective effect of EOCC (48.5%). Furthermore, EOCC gastroprotection was not attenuated in mice pretreated with L-NAME (85.2%), glibenclamide (100%), or yohimbine (79.7%), the respective inhibitors of nitric oxide synthase, K+ATP channel activation, and α2 receptors. These results confirmed the traditional use of C. citratus for the treatment of gastric ulcer. Thus, we provide the first evidence that EOCC reduces gastric damage induced by ethanol, at least in part, by mechanisms that involve endogenous prostaglandins.

Gastroprotective activity of methanol extract and marrubiin obtained from leaves of Marrubium vulgare L. (Lamiaceae)

The purpose of this study was to assess the gastroprotective properties of the methanol extract and the diterpene marrubiin obtained from the leaves of M. vulgare. Assays were performed using different protocols in mice. Studies focusing on mechanisms of gastroprotection were also undertaken. In the model of ethanol-induced ulcers, we observed a significant reduction in all the parameters analysed; the curative ratios obtained were 49.31±0.57, 74.31±0.91 and 79.86±0.59 for the groups treated with 50 and 100mg/kg of extract of M. vulgare and omeprazole (30mg/kg), respectively. For indomethacin-induced ulcers, the percentages of ulcer inhibition were 50.32±5.60, 66.24±4.30, 82.17±04.09 and 67.52±4.38, for the groups treated with 25, 50 and 100mg/kg M. vulgare and positive control (cimetidine), respectively. In both models, the marrubiin (25mg/kg) produced a significant reduction in all the parameters when compared with the control group (P<0.01). There was also a significant increase in pH and mucus production in the groups treated with M. vulgare extract and marubiin. The results also demonstrated that the gastroprotection induced by the extract and marubiin is related to the activity of nitric oxide and endogenous sulfhydryls, which are important gastroprotective factors. The results of this study show that the extract of M. vulgare and marrubiin displays antiulcer activity and that this effect can be partly attributed to the isolated diterpene.

Gastroprotective activity of essential oil of the Syzygium aromaticum and its major component eugenol in different animal models

Syzygium aromaticum, a medicinal plant commonly known as clove, is used to treat toothache, respiratory disorders, inflammation, and gastrointestinal disorders. From the flower buds of S. aromaticum, it is possible to obtain an essential oil comprised of a mixture of aliphatic and cyclic volatile terpenes and phenylpropanoids, being eugenol as the main component. The aims of this study were: (1) to extract the essential oil of the flower buds of S. aromaticum, (2) to identify and quantify the main component of the essential oil, and (3) to evaluate its antiulcer activity using different animal models. Assays were performed using the following protocols in rats: indomethacin-induced and ethanol/HCl-induced ulcer model. Both essential oils from S. aromaticum and eugenol displayed antiulcer activities in the rat models of indomethacin- and ethanol-induced ulcer. Studies focusing on the possible mechanisms of gastroprotection were also undertaken using the following experiments: evaluation of gastric secretion by the pylorus-ligated model, determination of mucus in gastric content, participation of nitric oxide (NO) and endogenous sulfhydryl in gastric protection. The results show that there was no significant effect on the volume of gastric juice and total acidity. However, the quantification of free gastric mucus showed that the clove oil and eugenol were capable of significantly enhancing mucus production. With regard to the NO and endogenous sulfhydryls, the results demonstrated that the gastroprotection induced by clove oil and eugenol are not related to the activities of the nitric oxide and endogenous sulfhydryls. No sign of toxicity was observed in the acute toxicity study. In conclusion, the results of this study show that essential oil of S. aromaticum, as well as its main component (eugenol), possesses antiulcer activity. The data suggest that the effectiveness of the essential oil and eugenol is based on its ability to stimulate the synthesis of mucus, an important gastroprotective factor. However, further pharmacological and toxicological investigations are required to enable its use for the treatment of gastric ulcer.

Nigella sativa seeds: Folklore treatment in modern day medicine

<i>Nigella sativa</i> seeds: Folklore treatment in modern day medicine

Gastroprotective Mechanisms of Centipedic Acid, a Natural Diterpene from Egletes viscosa LESS.

This study was aimed to clarify the mechanisms of gastroprotection by centipedic acid (CPA), a natural diterpene from Egletes viscosa LESS. (Asteraceae) using ethanol-induced gastric mucosal damage in mice and gastric secretion in 4-h pylorus-ligated rats as model systems. In mice, intragastrically administered CPA (25, 50, 100 mg/kg) greatly reduced the mucosal lesions induced by 96% ethanol (0.2 ml, p.o.) by 18, 53, and 79%, respectively, whereas N-acetylcysteine (NAC, 300 mg/kg, i.p.), the reference compound produced a 50% inhibition. In 4-h pylorus-ligated rats, CPA (50 mg/kg) applied intraduodenally decreased both gastric secretory volume and total acidity. Similar to NAC, the plant diterpene effectively prevented the ethanol associated decrease in non-proteic sulfhydryls (NP-SH) and the elevated thiobarbituric acid-reactive substances (TBARS) in gastric tissue, suggesting that these compounds exert an antioxidant effect. Pretreatment of mice with indomethacin, the cyclooxygenase inhibitor but not with capsazepine, the transient receptor potential vanilloid-1 (TRPV1)-receptor antagonist greatly suppressed the gastroprotective effect of CPA. Furthermore, CPA gastroprotection was significantly attenuated in mice pretreated with L-NAME or glibenclamide the respective inhibitors of nitric oxide synthase and K(+)(ATP) channel activation. These data suggest that CPA affords gastroprotection by different and complementary mechanisms, which include a sparing effect on NP-SH reserve, and roles for endogenous prostaglandins, nitric oxide, and TRPV1-receptor and K(+)(ATP) channel activation.

GABAergic Mechanisms of Gastroprotection in the Rat: Role of Sensory Neurons, Prostaglandins, and Nitric Oxide

gamma-Aminobutyric acid (GABA) is a neurotransmitter found in both the central and the peripheral nervous systems including the gastrointestinal tract. The aims of the present studies were to examine mechanisms by which GABA exerts gastroprotective effects against ethanol- and water-restraint stress (WRS)-induced gastric mucosal injury in the rat. GABA, administered intragastrically (400 mg/kg), induced gastroprotection against ethanol and WRS by activating gastric sensory neurons to release calcitonin gene-related peptide (CGRP) and promote nitric oxide (NO) synthesis and release. Furthermore, these protective effects of GABA were associated with an increase in gastric mucosal blood flow (GMBF) that was dependent on sensory neuron and NO systems. GABA-mediated protection involved GABAA receptor activation and prostaglandin generation. In conclusion, intraluminal GABA protects the stomach against ethanol- and WRS-induced injury by mechanisms which involve sensory neuron/CGRP/NO pathways and increases in GMBF and prostaglandin generation.

Mechanisms of gastroprotection by lansoprazole pretreatment against experimentally induced injury in rats: role of mucosal oxidative damage and sulfhydryl compounds

This study investigated the mechanisms involved in the protective actions exerted by lansoprazole against experimental gastric injury. Following the intraluminal injection of ethanol–HCl, the histomorphometric analysis of rat gastric sections demonstrated a pattern of mucosal lesions associated with a significant increase in the mucosal contents of malondialdehyde and 8- iso-prostaglandin F 2α (indices of lipid peroxidation), as well as a decrease in the levels of mucosal sulfhydryl compounds, assayed as reduced glutathione (GSH). Pretreatment with lansoprazole 90 μmol/kg, given intraduodenally as single dose or once daily by intragastric route for 8 days, significantly prevented ethanol–HCl-induced gastric damage. The concomitant changes in the mucosal levels of malondialdehyde, 8- iso-prostaglandin F 2α and GSH elicited by ethanol–HCl were also counteracted by lansoprazole. In separate experiments, performed on animals undergoing 2-h pylorus ligation, lansoprazole did not enhance the concentration of prostaglandin E 2, bicyclo-prostaglandin E 2, or nitric oxide (NO) metabolites into gastric juice. Western blot analysis revealed the expression of both type 1 and 2 cyclooxygenase (COX) isoforms in the gastric mucosa of pylorus-ligated rats. These expression patterns were not significantly modified by single-dose or repeated treatment with lansoprazole. Lansoprazole also exhibited direct antioxidant properties by reducing 8- iso-prostaglandin F 2α generation in an in vitro system where human native low-density lipoproteins were subjected to oxidation upon exposure to CuSO 4. The present results suggest that the protective effects of lansoprazole can be ascribed to a reduction of gastric oxidative injury, resulting in an increased bioavailability of mucosal sulfhydryl compounds. It is also proposed that lansoprazole does not exert modulator effects on the gastric expression of COX isoforms as well as on the activity of NO pathways.

Somatostatin-induced gastric protection against ethanol: involvement of nitric oxide and effects on gastric mucosal blood flow

Background–aims: The mechanisms of somatostatin-mediated gastroprotection are not fully understood. Aims of this study were to determine in the rat the role of nitric oxide (NO) in somatostatin-induced effects on gastric mucosal protection and blood flow (GMBF) in the absence and in the presence of intraluminal ethanol. Methods: Ethanol (70% v/v)-induced gastric mucosal injury after orogastric dosing was quantitated at 30 min and GMBF determined in an ex vivo gastric chamber preparation. Results: Somatostatin (4 μg/kg; i.p.) protection against ethanol-induced ulceration was prevented by the NO inhibitor l-NNA and restored by l-arginine, but not d-arginine. Somatostatin (1–8 μg/kg; i.p.) did not effect basal GMBF. The gastroprotective dose of somatostatin (4 μg/kg; i.p.) prevented the decrease in GMBF caused by ethanol. l-NNA reversed this vascular effect of somatostatin. Conclusion: Somatostatin-induced gastroprotection and restoration of GMBF during ethanol exposure involve mechanisms which are dependent on NO generation.

Mechanisms of gastroprotection by transdermal nitroglycerin in the rat.

Nitric oxide (NO) donors prevent experimentally-induced gastric mucosal damage, but their clinical utility is limited by short duration of action or unsuitability of the pharmaceutical form employed. This study analyses the gastroprotection elicited by a clinically used mode of continuous administration of an NO donor, namely the nitroglycerin patch. Application to rats of a transdermal patch that releases doses of nitroglycerin comparable to those used in man (40, 80, 160 and 400 ng min(-1) rat(-1)) reduced gastric damage induced by indomethacin (25 mg kg(-1), p.o. or s.c.). The nitroglycerin patch (160 ng min(-1) rat(-1)) also diminished damage by oral administration (1 ml) of acidified bile salts (100 mg kg(-1) taurocholic acid in 150 mM HCl) or 50% ethanol. Transdermal nitroglycerin (160 ng min(-1) rat(-1)) did not influence basal gastric blood flow, as measured by lasser-doppler flowmetry, but prevented its reduction by indomethacin. Transdermal nitroglycerin (160 ng min(-1) rat(-1)) prevented in vivo leukocyte rolling and adherence in the rat mesentery microvessels superfused with indomethacin, as evaluated by intravital microscopy. The transdermal nitroglycerin patch protects the gastric mucosa from damage by mechanisms that involve maintenance of mucosal blood flow and reduction of leukocyte-endothelial cell interaction.

Role of cysteine proteases and protease inhibitors in gastric mucosal damage induced by ethanol or ammonia in the rat.

Since recent studies suggest an imbalance between cathepsin B and its tissue protease inhibitors (PI) in the pathogenesis of acute and chronic diseases, we tested the hypothesis that release of activated cysteine proteases (P) such as cathepsins B, H, and L might play a role in the pathogenesis of gastric hemorrhagic mucosal lesions (HML) induced by ethanol (E) or ammonia (A). Anesthetized rats received 1 ml of 50% E or 1% A solution intragastrically for 1 min during in situ gastric luminal perfusion. Rapid activation and release of cathepsins B, L, and H into the luminal perfusate preceded the formation of HML quantified by planimetry. Mucosal presence and activity of cysteine PI and cathepsin B have also been investigated in the pathogenesis of chemically induced HML. We extracted and partially isolated acid and thermostable inhibitors of cathepsin B in the gastric mucosa, and found rapid inactivation of PI and activation of cathepsin B in the early phase of E- or A-induced HML. Negative correlations were found between P and PI activities by E or A solutions. Both the activation of cathepsins B, L, and H and the development of E-induced HML were prevented by pretreatment with the sulfhydryl alkylator N-ethylmaleimide. These results suggest that cysteine P may be activated in the rat stomach after E or A exposure, and cysteine P may have a role in the pathogenesis of E- or A-induced gastric HML. Endogenous PI may also participate in the mechanisms of gastric mucosal lesions and gastroprotection.

Stimulation of mucosal glutathione and angiogenesis: new mechanisms of gastroprotection and ulcer healing by sucralfate.

Among the endogenous mediators (e.g., PG, SH) of gastroprotection, so far only PG was implicated in the mechanism of acute gastroprotection by sucralfate. Angiogenesis, which is stimulated by bFGF, is a recently recognized element in ulcer healing, and sucralfate binds bFGF in vitro and in vivo. In fasted rats the gastric mucosal concentration of GSH and protein SH was measured at 30, 60, 120, and 240 min after a single gastroprotective dose of sucralfate. In normally fed rats, angiogenesis was measured in the subcutaneous sponge assay 7 days after the implantation of sponges containing sucralfate and/or bFGF. A gastroprotective dose of sucralfate time-dependently increased GSH concentration in the gastric mucosa. Sucralfate alone accelerated angiogenesis, which was significantly enhanced by combination with an ineffective dose of bFGF in the subcutaneous sponge assay. The same dose of sucralfate combined with an angiogenic dose of bFGF also resulted in synergistic stimulation (e.g., more than fivefold) of angiogenesis. It appears that elevated mucosal GSH concentration may represent a new factor in the mechanism of acute gastroprotection by sucralfate, and stimulation of angiogenesis is one of the mechanisms of ulcer healing by sucralfate.

Role of vascular factors, including angiogenesis, in the mechanisms of action of sucralfate

This brief overview of our recent results implicates vascular factors in the mechanisms of acute and chronic actions of sucralfate. Pretreatment of rats with sucralfate and its components, such as SOS and sodium sulfate, prevented the ethanol-induced microvascular injury and maintained blood flow in the gastric mucosa. Thus, preservation of microvascular integrity seems to be one of the mechanisms of acute gastroprotection by sucralfate. Chronic experiments with subcutaneously implanted sponges containing sucralfate or SOS revealed that both compounds stimulated angiogenesis, whereas only sucralfate enhanced the area of granulation tissue. These processes may have a role in the ulcer-healing action of sucralfate.