Differential effects of selective and non-selective inhibition of nitric oxide synthase on the expression and activity of cyclooxygenase-2 during gastric ulcer healing

Nitric oxide synthases (NOS) and cyclooxygenase-2 (COX-2) are important enzymes involved in ulcer healing but interactions between them have not been clearly defined. The aim of this study was to investigate the effects of selective or non-selective inhibition of NOS on the expression and activity of COX-2 during healing of acetic acid-induced gastric ulcers in rats. N-[3-(aminomethyl)benzyl] acetamidine (1400 W), a potent selective inhibitor of inducible nitric oxide synthase (iNOS), at a dose of 0.1 mg/kg/day, was found to reduce the ulcer sizes at day 3 and 7 post-ulcer induction. On the other hand, 15 mg/kg/day of NG-nitro-L-arginine methyl ester (L-NAME), a non-selective NOS inhibitor that suppresses both iNOS and endothelial nitric oxide synthase (eNOS), enlarged the ulcer sizes over the same time periods. The expression of COX-2 and COX activity, together with NF-kappaB activation in the ulcer tissues were down-regulated by L-NAME but not 1400 W. It is concluded that iNOS may contribute to ulcer formation while COX-2 and eNOS promote ulcer healing. eNOS enhances COX-2 expression possibly through the activation of NF-kappaB.     

Molecular mechanisms of epithelial regeneration and neovascularization during healing of gastric and esophageal ulcers

In this paper we reviewed and updated current views on the cellular and molecular mechanisms of gastric and esophageal ulcer healing. Gastric ulcer healing encompasses inflammation, cell proliferation, epithelial regeneration, gland reconstruction, formation of granulation tissue, neovascularization (new blood vessel formation), interactions between various cells and the matrix and tissue remodeling, resulting in scar formation. All these events are controlled by the cytokines and growth factors, GI hormones including gastrin, CCK, and orexigenic peptides such as ghrelin, orexin-A and obestatin as well as Cox2 generated prostaglandins. These growth factors and hormones trigger cell proliferation, migration, and survival utilizing Ras, MAPK, PI-3K/AKT, PLC-γ and Rho/Rac/actin signaling pathways. Hypoxia triggers activation of some of these genes (e.g., VEGF) via hypoxia inducible factor (HIF). Growth factors: EGF, HGF, IGF-1, their receptors and Cox2 are important for epithelial cell proliferation, migration, re-epithelialization and regeneration of gastric glands during gastric ulcer healing. Serum response factor (SRF) is also essential for re-epithelialization and muscle restoration. VEGF, bFGF, angiopoietins, nitric oxide, endothelin, prostaglandins and metalloproteinases are important for angiogenesis, vascular remodeling and mucosal regeneration within gastric ulcer scar. SRF is critical limiting factor for VEGF-induced angiogenesis. Esophageal ulcer healing follows similar pattern to gastric ulcer, but KGF and its receptor are the key players in regeneration of the epithelium. In addition to local mucosal cells from viable mucosa bordering necrosis, circulating bone marrow derived stem and progenitor cells are potentially important for ulcer healing, contributing to the regeneration of epithelial and connective tissue components and neovascularization.     

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.     

Cigarette smoke and its extract delays ulcer healing and reduces nitric oxide synthase activity and angiogenesis in rat stomach

1. The purpose of the present study was to examine whether cigarette smoke and its extract could affect ulcer healing, angiogenesis and nitric oxide synthase (NOS) activity in the gastric mucosa. 2. Ulcerated rats were either exposed to cigarette smoke or given smoke extract once daily for 3 days. Rats were killed and stomachs were removed for the measurement of ulcer size, angiogenesis and NOS activity. 3. Angiogenesis and constitutive NOS activity were concomitantly and dose-dependently reduced by cigarette smoke or its extract. The same treatments also delayed ulcer healing. 4. These results indicate that cigarette smoke and its extract repress the processes of new blood vessel formation and NOS activity during tissue repair in the gastric mucosa. These could, in turn, retard the healing process in the gastric mucosa.     

Preventive and curative effects of curcumin on the development of gastric inflammatory diseases in rats

Preventive and curative effects of curcumin on experimental acute and chronic gastric ulcers were investigated to validate its clinical application on a remedy for peptic ulcer. Intraduodenal administration of curcumin, 5–20 mg/kg, inhibited gastric acid secretion in pylorus-ligated rats, and oral administration prevented ethanol-induced acute gastric mucosal lesions. Curcumin (20–80 mg/kg, p.o.) dose-dependently prevented both serotonin-induced gastric mucosal lesions and compound 48/80-induced gastric mucosal lesions in rats. Furthermore, oral administration of curcumin, 10–80 mg/kg, twice daily for 10 days, significantly accelerated the healing of acetic acid-induced chronic gastric ulcer and promoted mucosal regeneration in the ulcerated portion in a dose-related manner. Cimetidine prevented the formation of ethanol-induced gastric mucosal lesions, but not of serotonin-induced and compound 48/80-induced gastric mucosal lesions. Consecutive administration of cimetidine showed a marked acceleration in the healing of acetic acid-induced ulcer. Aminoguanidine, an inducible nitric oxide synthase (iNOS) inhibitor, showed anti-ulcerogenic effects similar to those oberved for curcumin. The present results indicate that curcumin exhibits gastric cytoprotection in the acute lesion models and ulcer healing promotion in the chronic ulcer model. The preventive and curative effects of curcumin might be due to an increase in the mucosal defensive mechanism through its antioxidant property and inhibition of NO or cytokine-mediated inflammation.     

Gastric mucosal protection: from prostaglandins to gene-therapy

The maintenance of gastric mucosal function and integrity highly depends on the status of microcirculation. Vasoactive agents--prostaglandins, nitric oxide and sensory neuropeptides (e.g. calcitonin gene-related peptide)--play a crucial role in mucosal defensive processes. Beside the local release of vasoactive mediators the central nervous system is also involved in regulation of gastric functions. Cerebral lesions, stimulation of different brain areas can result in gastric mucosal injury. Noxious challenge of gastric mucosa alters the sodium currents in gastric sensory neurons and induces cfos mRNA expression in nucleus tractus solitarii and area postrema. Vagal nerve has long been established to play a permissive role in the development of gastric lesions. However, several lines of evidences suggest its physiological relevance in the enhancement of gastric mucosal resistance. It was concluded that gastroprotection can be induced by low level of central vagal stimulation and the consequent release of prostaglandins, nitric oxide, and calcitonin gene-related peptide. Prostaglandins, nitric oxide and sensory neuropeptides play a role also in ulcer healing by stimulating the formation of growth factors, the epithelial proliferation and angiogenesis. Both systemic and local administration of growth factors accelerated the ulcer healing. Local, single injection of plasmid-DNA encoding vascular endothelial growth factor (VEGF) was shown to stimulate the ulcer healing in the rat. The transient, local expression of VEGF in ulcerated tissue might be a new therapeutic strategy in the treatment of gastric ulcer disease.     

EVIDENCES FOR INVOLVEMENT OF NITRIC OXIDE IN THE GASTROPROTECTIVE EFFECT OF BROMOCRIPTINE AND CYCLOSPORIN A ON WATER IMMERSION STRESS-INDUCED GASTRIC LESIONS

Previous studies have been shown that the adrenergic system involves in gastric secretion and pathogenesis of peptic lesion and activation of alpha(2)-adrenoceptors located on the vagus nerve inhibits gastric acid secretion. Bromocriptine, a dopamine receptor agonist, also has alpha(2) agonistic effect and prevents indomethacin-induced gastric ulcer. alpha(2)-Adrenoceptors involve in the release of nitric oxide which has cytoprotective activity in gastric mucosa. Cyclosporin A (CsA) has also been suppressed stress-induced gastric mucosal lesions, dose dependently. The object of this study was to clarify the interaction between the anti-ulcer effect of bromocriptine (2, 4, 8 mg kg(-1)) or cyclosporin A (5, 10, 20 mg kg(-1)) and nitric oxide. Intraperitoneal injections of bromocriptine and cyclosporin A prevented water immersion stress-induced gastric ulcer in rats. L-Nitro-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, increased stress-induced lesions while L-arginine, a precursor of nitric oxide, decreased these lesions. In conclusion, increasing level of nitric oxide by bromocriptine and cyclosporin A may be one of the contributory factors in their protective effects on gastric mucosa.     

Protective effects of zinc in indomethacin-induced gastric mucosal injury: evidence for a dual mechanism involving lipid peroxidation and nitric oxide

BACKGROUND: Indomethacin causes gastric mucosal injury, although the pathogenesis is not fully understood. Zinc, is known to have gastroprotective effects in both humans and experimental animals. Aim: To determine (i) the protective effects of zinc in indomethacin-induced gastric mucosal injury in rats, and (ii) whether these cytoprotective effects are mediated by changes in gastric lipid peroxidation and/or nitric oxide synthase activity. METHODS: Gastric lesions were induced in rats by the intragastric administration of indomethacin. Morphological changes, lipid peroxidation (malondialdehyde levels) and nitric oxide synthase activity were determined in animals pre-treated with zinc sulphate and in controls. RESULTS: Indomethacin significantly increased malondialdehyde levels and decreased NOS activity. These effects were attenuated by pre-treatment with zinc (P < 0.005 and 0.0001, respectively). The protective effects of zinc were readily abolished in animals pre-treated with N-nitro-L-arginine methyl ester (L-NAME). Morphologically, indomethacin induced large areas of mucosal ulcerations, which were completely prevented by zinc pre-treatment. CONCLUSIONS: Zinc provides protection against indomethacin-induced gastric mucosal injury. These protective effects result from the inhibition of lipid peroxidation and the preservation of mucosal nitric oxide synthase.     

Effect of nitric oxide modulators on pylorus-ligation-induced ulcers in the rat.

In the present investigation, the effect of nitric oxide (NO) modulators on pylorus-ligation-induced gastric ulcers in rats was studied. Sodium nitroprusside (SNP, 1 mg kg-1), a NO donor, l-arginine (l-Arg, 300 mg kg-1), the NO precursor, nitro-l-arginine methyl ester (l-NAME), a nitric oxide synthase (NOS) inhibitor and lipopolysaccharide (LPS, 3 mg kg-1), a NOS inducer have been administered prior to pylorus ligation. The effects of these interventions on the gastric mucosal nitrite content, the incidence of ulcers, the ulcer index, the volume of gastric secretions and the free and total acidity 4 h after pylorus ligation were investigated. SNP, l-Arg and LPS pretreatment increased the mucosal nitrite contents and protected the animals against pyloric-ligation-induced increase in acidity and ulcer index. However, inhibition of NOS activity by l-NAME (10 mg kg-1) decreased the nitrite content and augmented the ulcer-induced increase in the gastric acid contents. Coadministration of l-Arg with l-NAME prevented the l-NAME-induced changes. Interventions which increased the mucosal nitrite content were found to be protective against ulcers. However, the NOS inhibitor l-NAME decreased mucosal nitrite levels and was ulcerogenic. Results obtained thus indicate the protective effect of NO on the pyloric-ligation-induced ulcers in the rat.     

Role of nitric oxide in gastric injury induced by hemorrhagic shock in rats

The aim of this study was to investigate the effect of nitric oxide (NO) on the gastric injury induced by hemorrhagic shock. Hemorrhagic shock was created by withdrawing 3 ml blood/200 g body weight of the rats. Before the hemorrhage, N(G)-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg i.v. bolus), D-NAME (10 mg/kg i.v. bolus), or L-arginine (100 mg/kg i.v. bolus and 10 mg/kg/min infusion) + L-NAME were administered. At the end of the 1-hour hypovolemic shock period, histological analysis, gastric ulcer index, gastric myeloperoxidase (MPO) activity, and gastric protein oxidation (PO) levels were determined. In histological analysis a destructive effect of L-NAME (NO synthase inhibitor) was demonstrated. L-NAME treatment increased gastric MPO activity, L-arginine reversed this effect and D-NAME had no effect. Tissue PO activity was found to be increased in L-NAME-treated rats; L-arginine treatment reversed this activity. It is concluded that gastric barrier function is altered after hemorrhagic shock, and L-arginine (NO precursor) can prevent mucosal injury in the stomach. This effect of NO may be on gastric blood flow and can be mediated by tissue neutrophils.     

Ticlopidine prevents the formation but delays the healing of ethanol-induced gastric lesions in the rat.

The effects of acute or long-term oral ticlopidine administration in normal rat gastric mucosa or on gastric lesions induced by ethanol 50% (EtOH, 1 ml/rat, os) were examined and compared with those of acetylsalicylic acid (ASA). Ticlopidine does not affect gastric mucosal integrity either after acute (100 and 300 mg kg(-1)) or 1-week (100 mg kg(-1), die) oral administration. Ticlopidine (30-300 mg kg(-1), os) administered 1h before EtOH dose-dependently prevented the development of gastric haemorragic lesions. When ticlopidine was administered 1h after EtOH, it significantly (p<0.05) delays gastric lesions healing. Acute ASA (50 and 100 mg kg(-1), os) administration causes a mild irritant activity similar to that observed after 1 week of ASA (50 mg kg(-1), os/die) administration. In condition of mucosal damage, ASA does not modify either the induction or the healing of EtOH-induced gastric lesions. To assess the possible involvement of endogenous nitric oxide (NO) or prostaglandins (PG) in the gastric protective activity of ticlopidine, the rats were pretreated with an inhibitor of NO-synthesis, L-NAME (70 mg kg(-1), s.c.) or the inhibitor of PG synthesis, indomethacin (Indo, 10 mg kg(-1), s.c.). Indo, but not L-NAME, was able to significantly counteract the gastroprotective activity of ticlopidine against EtOH injury. Furthermore, ticlopidine increases (47%) gastric PGE(2) content in normal mucosa compared to the one detected in control rats, thus suggesting that endogenous PGs contribute to enhanced mucosal resistance by ticlopidine. These results indicate that ticlopidine exerts dual effects during the development and healing of gastric lesions induced by EtOH.     

Effect of nitric oxide synthase inhibition on the gastric mucosal barrier in rats.

The aim of this study was to investigate the effect of N-G-nitro-L-arginine-methyl ester (L-NAME), a nitric oxide synthase inhibitor, on the gastric mucosal barrier in rats. A group of Swiss albino rats received L-NAME (60 mg/kg/d) in their drinking water daily for 21 d. The mucin and prostaglandin E2 (PGE2) contents of the gastric mucosa were measured in gastric tissue samples. L-NAME intake did not affect gastric mucin, but it significantly reduced PGE2, a component of the gastric mucosal barrier. The results of this study imply that nitric oxide plays an important mediatory role in maintaining the gastric mucosal barrier. The inhibition of nitric oxide may be involved in the increased vulnerability of the gastric mucosa to injurious stimuli in rats.     

A 3.0-kDa low molecular weight heparin promotes gastric ulcer healing in rats

BACKGROUND: Previous studies have shown that intragastric administration of unfractionated heparin enhances gastric ulcer healing in rats. As the large molecule of heparin may be partially degraded in the upper gastrointestinal tract, it is likely that fragments of heparin, derived from the unfractionated parent compound, are involved in the anti-ulcer action in the stomach. Therefore, it is possible that low molecular weight heparin may have a similar ulcer healing effect. METHODS: Male Sprague-Dawley rats with acetic acid-induced gastric ulcers were given a 3.0-kDa low molecular weight heparin (0.6-6.0 mg/kg) intravenously or intragastrically once daily for 4 days. Ulcer healing, mucosal histological changes, angiogenesis and gastric mucus production both in vivo and in vitro were determined. The bleeding time was measured to indicate the anticoagulation activity. RESULTS: Both intravenous and intragastric low molecular weight heparin dose dependently accelerated gastric ulcer healing, which was accompanied by a significant increase in mucosal regeneration and proliferation, angiogenesis and mucus content in the stomach. The drug also stimulated the mucus production in MKN-28 cells. Drug administration by either route did not alter the bleeding time in rats. CONCLUSIONS: A 3.0-kDa low molecular weight heparin possesses an ulcer healing effect similar to that of unfractionated heparin in the stomach of the rat. This smaller molecular drug is superior to the unfractionated form, does not affect the coagulation activity and may show better absorption in the gastrointestinal tract.     

Pioglitazone,a specific ligand of peroxisome proliferator-activated receptor-gamma,accelerates gastric ulcer healing in rat

The peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a member of the nuclear hormone receptor superfamily that is involved in the control of inflammation and carcinogenesis. We determined the effect of the specific PPAR-gamma ligand, pioglitazone (5-40 mg/kg intragastrically), on the healing of acetic-acid gastric ulcers in rats. At day 8 after ulcer induction, the ulcer area, the gastric blood flow and mucosal expression of proinflammatory cytokines such as interleukin-1beta, tumour necrosis factor alpha (TNF-alpha) and cyclooxygenase-1, cyclooxygenase-2, constitutive nitric oxide synthase (cNOS), inducible nitric oxide synthase (iNOS) and heat shock protein 70 (HSP70) was determined. Pioglitazone reduced the area of gastric ulcers and raised significantly the gastric blood flow at the ulcer margin and downregulated the mRNA for interleukin-1beta, TNF-alpha, cyclooxygenase-2 and iNOS while cyclooxygenase-1 mRNA was not affected. The expression of PPAR-gamma mRNA was increased in the ulcerated gastric mucosa. We conclude that pioglitazone accelerates the healing of preexisting gastric ulcers due to the hyperemia at ulcer margin and the anti-inflammatory action including suppression of interleukin-1beta, TNF-alpha, cyclooxygenase-2 and iNOS and by an overexpression of HSP70.     

Nitric oxide synthase mediates delta opioid receptor-induced hypothermia in rats

The role of nitric oxide (NO) production in delta opioid receptor-induced hypothermia has not been reported. The present study investigated the effect of nitric oxide synthase (NOS) inhibitors on the hypothermic effect of (+)-4-[(aR)-a-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC-80), a nonpeptide delta opioid agonist. SNC-80 (35 mg/kg, i.p.) administered to rats caused a significant hypothermia. N-nitro-L-arginine methyl ester (L-NAME) (10, 25 and 50 mg/kg, i.p.), a NOS inhibitor, and 7-nitroindazole (7-NI) (5 and 10 mg/kg, i.p.), a neuronal NOS inhibitor, were ineffective. For combined administration, L-NAME (50 mg/kg, i.p.) or 7-NI (10 mg/kg, i.p.) attenuated SNC-80-evoked hypothermia. To determine the involvement of central NOS, L-NAME (0.25, 0.5 and 1 mg/rat) was administered i.c.v. 30 min prior to SNC-80 (35 mg/kg, i.p.). Experiments revealed that L-NAME (1 mg/rat, i.c.v.) attenuated SNC-80-induced hypothermia. The present data demonstrate that central NO production is necessary for delta opioid receptor-induced hypothermia.     

Dexamethasone delays ulcer healing by inhibition of angiogenesis in rat stomachs

Using the non-ulcerogenic doses of dexamethasone, we explored the action of glucocorticoids on ulcer healing and its relationship with angiogenic factors in the gastric mucosa. We applied dexamethasone (0.1 or 0.2 mg/kg/day) intragastrically in rats with acetic acid-induced gastric ulcer. The mucosal prostaglandin E(2) level and protein expressions of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) at the ulcer margin were determined. Ulcer induction significantly increased protein expressions of bFGF, VEGF, and prostaglandin E(2) level at the ulcer margin together with angiogenesis at the ulcer margin and base. The non-ulcerogenic doses of dexamethasone inhibited angiogenesis at the ulcer margin and ulcer base and delayed ulcer healing. These were associated with a significant decrease of prostaglandin E(2) level and VEGF expression, but not the bFGF expression. Supplementation with prostaglandin E(2) attenuated the inhibitory action of dexamethasone on VEGF expression and reversed the adverse effects of dexamethasone on angiogenesis and ulcer healing, without influencing bFGF expression. We concluded that dexamethasone given at non-ulcerogenic doses could decrease angiogenesis and delay acetic acid-induced ulcer healing; these actions were at least, in part, due to depletion of prostaglandin E(2) level followed by down-regulation of VEGF at the ulcer margin of the stomach.     

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.     

Inhibitory effects of Centella asiatica water extract and asiaticoside on inducible nitric oxide synthase during gastric ulcer healing in rats

In this study, the effects of Centella asiatica water extract (CE) and its active constituent, asiaticoside (AC), on the expression and activity of inducible nitric oxide synthase (iNOS) during gastric ulcer healing in rats were investigated. CE was prepared from Centella asiatica dry plant and the concentration of AC in CE was quantitatively determined with the use of high performance liquid chromatography analysis. Different concentrations of CE (0.10 g/kg and 0.25 g/kg) and AC (5 mg/kg and 10 mg/kg) were orally administered to rats with acetic acid-induced gastric ulcers. They were found to reduce the size of the ulcers at days 1, 3 and 7 after ulcer induction in a dose-dependent manner, with a concomitant attenuation of iNOS activity and protein expression at the ulcer tissues. The levels of nitrite and nitrate (NO(X)-), the stable end-products of nitric oxide (NO), in the gastric ulcer tissues were also decreased. N-[3-(aminomethyl)benzyl]acetamidine (1400W), a highly selective inhibitor of iNOS, was found to produce similar but more potent inhibition on iNOS activity at a dose of 0.1 mg/kg. These findings indicate that CE and AC have an anti-inflammatory property that is brought about by inhibition of NO synthesis and thus facilitates ulcer healing.     

Protective role of nitric oxide in indomethacin-induced gastric ulceration by a mechanism independent of gastric acid secretion.

Gastric ulceration was induced in rats by i.p. injection of the non-steroidal anti-inflammatory drug (NSAID), indomethacin (IND) (30 mg kg(-1)). Pyloric ligation was carried out in each animal before injection to enable collection of the gastric juice. Three hours later, the animals were killed and their stomachs were removed. In the gastric juice, the amounts of mucin, pepsin and HCl were assessed. Gastric mucosa were scrapped for the determination of nitric oxide (NO) (as nitrite) after evaluation of the gastric ulcer index. The influence of arginine (ARG) (300 mg kg(-1)), a NO precursor, N(G)-nitro- l -arginine methyl ester (l -NAME) (50 mg kg(-1)), a non-selective constitutive nitric oxide synthase/inducible nitric oxide synthase (cNOS/iNOS) inhibitor, and the selective iNOS inhibitor aminoguanidine (AMG) (50 mg kg(-1)) were studied. Each NO modulator was injected i.p. 30 min before IND administration. Results indicated that IND elevated gastric acidity by 80% of the normal group, decreased non-significantly mucosal nitrite by 22% and exhibited a remarkably high ulcer index (chi = 17). Neither mucin nor pepsin levels were significantly altered. In comparison with the IND group, pretreatment with l -NAME caused a significant decrease in gastric HCl, further decrease in mucosal nitrite (50% of normal) and a two-fold increase in the ulcer index score (chi = 34), despite the decrease in HCl. AMG did not alter gastric acidity, decreased mucosal nitrite by 38% of the normal value and failed to alter significantly the ulcer index of IND. On the other hand, pretreatment with ARG did not alter the gastric acidity and raised mucosal nitrite by 10% above normal. Surprisingly, ARG improved the gastric ulcer score (chi = 1) almost similar to the normal score (chi = zero). Therefore, this study creates a new pathway for the potential treatment of NSAID gastric ulceration through modulation of NO synthesis, regardless of the effect on gastric acidity.