Involvement of nitric oxide and prostaglandins in gastroprotection induced by bacterial lipopolysaccharide

The Role of Inducible-Nitric Oxide in Cocaine-Induced Kindling

Experimentally naive male Sprague Dawley rats (weighing 85–110 g) were used to examine the role of inducible nitric oxide synthase (iNOS) in cocaine-induced kindling. Repeated administration of cocaine (45 mg/kg, ip) to Sprague Dawley male rats for 7 consecutive days produced a progressive increase in the Convulsive responsiveness and death. Pretreatment with iNOS inhibitors, L-N6-(1-iminoethyl)lysine (NIL; 10 mg/kg, ip) and (–)-ePigalloocatechin gallate (EGCG; 10 mg/kg, ip) 30 min before cocaine (45 mg/kg, ip) administration for 7 days attenuated the development of cocaine kindling and blocked cocaine-induced death. Results of NMDA receptor binding assay in the hippocampus showed a significant increase in the affinity without changes in the density in animals treated with cocaine, but there were no changes in these parameters in the cortex. Pretreatment with NIL or EGCG prior to cocaine administration abolished the cocaine-induced effect in the NMDA receptor affinity in the hippocampus. These results suggest that iNOS induction followed by an increase of NMDA receptor affinity in the hippocampus after repeated exposure to cocaine may participate in the process of the development of cocaine kindling.

Exogenous asymmetric dimethylarginine (ADMA) in pathogenesis of ischemia-reperfusion-induced gastric lesions: interaction with protective nitric oxide (NO) and calcitonin gene-related peptide (CGRP)

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide (NO) synthesis inhibitor and pro-inflammatory factor. We investigated the role of ADMA in rat gastric mucosa compromised through 30 min of gastric ischemia (I) and 3 h of reperfusion (R). These I/R animals were pretreated with ADMA with or without the combination of l-arginine, calcitonin gene-related peptide (CGRP) or a small dose of capsaicin, all of which are known to afford protection against gastric lesions, or with a farnesoid X receptor (FXR) agonist, GW 4064, to increase the metabolism of ADMA. In the second series, ADMA was administered to capsaicin-denervated rats. The area of gastric damage was measured with planimetry, gastric blood flow (GBF) was determined by H₂-gas clearance, and plasma ADMA and CGRP levels were determined using ELISA and RIA. ADMA significantly increased I/R-induced gastric injury while significantly decreasing GBF, the luminal NO content, and the plasma level of CGRP. This effect of ADMA was significantly attenuated by pretreatment with CGRP, l-arginine, capsaicin, or a PGE₂ analogue. In GW4064 pretreated animals, the I/R injury was significantly reduced and this effect was abolished by co-treatment with ADMA. I/R damage potentiated by ADMA was exacerbated in capsaicin-denervated animals with a further reduction of CGRP. Plasma levels of IL-10 were significantly decreased while malonylodialdehyde (MDA) and plasma TNF-α contents were significantly increased by ADMA. In conclusion, ADMA aggravates I/R-induced gastric lesions due to a decrease of GBF, which is mediated by a fall in NO and CGRP release, and the enhancement of lipid peroxidation and its pro-inflammatory properties.

Anti-inflammatory action of cholecystokinin and melatonin in the rat parotid gland

OBJECTIVE

To define the influence of cholecystokinin and melatonin on the inflammatory response of the lipopolysaccharide-exposed rat parotid gland.

MATERIALS AND METHODS

Bacterial lipopolysaccharide was infused retrogradely into the parotid duct. The degree of inflammation three hours postadministration was estimated from the activity of myeloperoxidase, reflecting glandular neutrophil infiltration.

RESULTS

The myeloperoxidase activity of the lipopolysaccharide-exposed gland was 10-fold greater than that of the contralateral gland. Combined with sulphated cholecystokinin-8 (10 or 25 μg kg(-1) , given twice intraperitoneally) or melatonin (10 or 25 mg kg(-1) x 2) the lipopolysaccharide-induced response was elevated 4.6- and 3.5-folds at the most. The cholecystokinin-A receptor antagonist lorglumide reduced the inhibitory effect of cholecystokinin-8, while the melatonin 2-preferring receptor antagonist luzindole had no effect on the melatonin-induced inhibition. Unselective nitric oxide-synthase inhibition abolished the increase in myeloperoxidase activity, whereas inhibition of inducible or neuronal nitric oxide-synthase (of non-nervous origin) halved the inflammatory response.

CONCLUSION

Some hormones may contribute to anti-inflammatory action in salivary glands in physiological conditions. They are potential pharmacological tools for treating gland inflammation. The inflammation, as judged from the myeloperoxidase activity, was entirely dependent on nitric oxide-synthase activity, indicating that the hormones directly or indirectly reduced the generation of nitric oxide.

Gastroprotective effect of cyanidin 3-glucoside on ethanol-induced gastric lesions in rats

This study investigated the in vivo protective effect of cyanidin 3-glucoside (C3G) against ethanol-induced gastric lesions in rats. The experimental rats were treated with 80% ethanol after pretreatment with various doses of C3G (4 and 8 mg/kg of body weight), and the control rats received only 80% ethanol. Oral pretreatment with C3G significantly inhibited the formation of ethanol-induced gastric lesions and the elevation of the lipid peroxide level. In addition, pretreatment with C3G significantly increased the level of glutathione and the activities of radical scavenging enzymes, such as superoxide dismutase, catalase, and glutathione peroxidase, in gastric tissues. These results suggest that the gastroprotective effect of C3G removes the ethanol-induced lipid peroxides and free radicals and that it may offer a potential remedy for the treatment of gastric lesions.

Gastroprotective effect of an aqueous suspension of black cumin Nigella sativa on necrotizing agents-induced gastric injury in experimental animals

BACKGROUND/AIM

Previous studies on "Black seed" or "Black Cumin" Nigella sativa (NS) have reported a large number of pharmacological activities including its anti-ulcer potential. These studies employed either fixed oil, volatile oil components or different solvent extracts. In folkloric practices, NS seeds are taken as such, in the form of coarse dry powder or the powdered seeds are mixed with water. This study examines the effect of NS aqueous suspension on experimentally induced gastric ulcers and basal gastric secretion in rats to rationalize its use by herbal and Unani medicine practitioners.

MATERIALS AND METHODS

The study was conducted at the Medicinal, Aromatic and Poisonous Plants Research Center, College of Pharmacy, King Saud University, Riyadh, Saudi Arabia. Acute gastric ulceration was produced by various noxious chemicals (80% ethanol, 0.2 M NaOH, 25% NaCl and indomethacin) in Wistar albino rats. Anti-secretory studies were undertaken in a separate group of rats. Gastric wall mucus contents and non-protein sulfhydryl concentration were estimated, and gastric tissue was examined histopathologically.

RESULTS

An aqueous suspension of Black seed significantly prevented gastric ulcer formation induced by necrotizing agents. It also significantly ameliorated the ulcer severity and basal gastric acid secretion in pylorus-ligated Shay rats. Moreover, the suspension significantly replenished the ethanol-induced depleted gastric wall mucus content levels and gastric mucosal non-protein sulfhydryl concentration. The anti-ulcer effect was further confirmed histopathologically.

CONCLUSION

These findings validate the use of Black seed in gastropathies induced by necrotizing agents. The anti-ulcer effect of NS is possibly prostaglandin-mediated and/or through its antioxidant and anti-secretory activities.

Prevention of lipopolysaccharide-induced intussusception in mice by the COX2 inhibitor rofecoxib

Intussusception (IS), an invagination of a portion of the intestine into itself, has recently attracted considerable interest after the withdrawal of a rotavirus vaccine because of reports on increased risk of IS shortly after vaccination. The present study was designed to shed further light on the mechanism of IS formation and its prevention. Intussusception was induced in adult mice by intraperitoneal injection of lipopolysaccharide (LPS; 8 mg/kg) from salmonella typhimurium. The presence of IS was confirmed at laparotomy. The serum levels TNF-alpha were measured with ELISA. Six hours after LPS injection, 14.5% of the animals demonstrated IS. A total of 65 animals received rofecoxib (20 mg/kg), a selective COX2 inhibitor, 15-30 min before intraperitoneal injection of LPS, and only two (3%) in this group demonstrated IS 6 h later (P < 0.05 vs. control). We confirmed the well-known increase in serum TNF-alpha levels in response to LPS; however, this increase was not blocked by rofecoxib pretreatment. Notably, there was no correlation between the serum TNF-alpha levels and the development of IS. The results show that the occurrence of IS can be significantly decreased by pretreatment with a selective COX-2 inhibitor.

Quantitative measurement of nitric oxide and hydrogen peroxide in Helicobacter pylori-infected Mongolian gerbils in vivo

OBJECTIVE

Peroxynitrite formation, as reflected by nitrotyrosine expression, is low in Helicobacter pylori-infected Mongolian gerbils despite pronounced expression of radical-forming enzymes. The aim of the present study was to investigate in vivo whether H. pylori inhibits either one or both of the nitro- and oxyradical formation pathways.

MATERIAL AND METHODS

Male Mongolian gerbils were infected with two different H. pylori strains, TN2GF4 and SS1. Six months after inoculation, direct measurement of NO and H2O2 was performed in vivo using electrochemical microsensors positioned in close proximity to the gastric mucosa.

RESULTS

In the TN2GF4-infected animals the level of NO was significantly lower than that in controls. No significant difference in NO levels was detected between the SS1-infected group and the controls. H2O2 was significantly increased in the SS1 animals compared with that in controls after 6 months. The H2O2 level in the TN2GF4 group did not differ from that in controls.

CONCLUSIONS

The results indicate that H. pylori infection is associated with strain-dependent functional inhibition of both the NO and oxyradical formation pathways in the gastric mucosa.

Effect of Mouriri pusa extracts on experimentally induced gastric lesions in rodents: role of endogenous sulfhydryls compounds and nitric oxide in gastroprotection

Several plants are used in folk medicine to treat gastrointestinal disorders. Mouriri pusa Gardn. (Melastomataceae) is a medicinal plant commonly used in the central region of Brazil against gastric ulcer. Two organic extracts methanolic (MeOH) and dichloromethane (DCM) obtained by sequential extraction from the leaves of Mouriri pusa were evaluated for their ability to protect the gastric mucosa against injuries caused by necrotizing agents (0.3M HCl/60% EtOH, absolute ethanol, non-steroidal anti-inflammatory drug, stress and pylorus ligature) in mice and rats. The best results were obtained after pretreatment with MeOH extract whereas the DCM extract did not show the same significant antiulcerogenic activity. No acute toxicity was observed in animals treated with 5 g/kg, p.o. of MeOH extract. The mechanism involving the antiulcerogenic action of MeOH extract seemed to be related to NO generation and also suggested the effective participation of endogenous sulfhydryl group in the gastroprotective action. Phytochemical investigation of the MeOH extract of Mouriri pusa yielded tannins, flavonoids and (-)-epicatechin. The presence of these phenolic compounds probably would explain the antiulcerogenic effect of the polar extract of Mouriri pusa leaves.

Gastric expression of inducible nitric oxide synthase and myeloperoxidase in relation to nitrotyrosine in Helicobacter pylori-infected Mongolian gerbils

OBJECTIVE

For obscure reasons Helicobacter pylori infection of the gastric mucosa is maintained despite a pronounced host defence response. The present study elucidates possible H. pylori-related interference in the oxy- and nitro-radical formation pathways.

MATERIAL AND METHODS

Male Mongolian gerbils were infected with two different H. pylori strains, TN2GF4 and SS1. At 3, 6, 12 or 18 months after inoculation, gastric expressions of myeloperoxidase (MPO), inducible nitric oxide synthase (iNOS) and nitrotyrosine were assessed by Western blotting.

RESULTS

Expression of both iNOS and MPO was markedly up-regulated in the H. pylori-infected animals compared with non-infected controls. The TN2GF4-infected animals initially (at 3 and 6 months) demonstrated pronounced expression of both iNOS and MPO. The SSI-infected animals exhibited a slower onset with significantly increased iNOS after 12 and 18 months. Nitrotyrosine expression was slightly elevated in the infected groups at 3 and 6 months compared with that in the controls. Nitrotyrosine levels then decreased and were no longer significantly different from those of controls (TN2GF4-infected animals) or were lower (SS1-infected animals) than in the controls.

CONCLUSIONS

The results indicate that peroxynitrite formation as reflected by nitrotyrosine expression is low or even inhibited in chronic H. pylori infection despite pronounced expression of enzymes representing both the oxy- and nitro-radical formation pathways. The results support the theory that H. pylori survival is related to functional inhibition of mucosal enzymatic NO and/or oxy-radical formation.

Effects of lipopolysaccharide on gastric stasis: role of cyclooxygenase

This study was done to examine the role of cyclooxygenase (COX) in lipopolysaccharide (LPS)-induced gastroprotection and gastric stasis. In conscious rats, LPS dose and time dependently increased gastric luminal fluid accumulation. LPS decreased blood flow (laser Doppler) and prevented gastric injury from acidified ethanol at time points before significant fluid accumulation occurred. LPS increased COX-2 but not COX-1 expression. In contrast, LPS decreased gastric mucosal prostaglandin synthesis. LPS-induced gastric luminal fluid accumulation was negated by both nonselective COX inhibition with salicylate and selective COX-2 inhibition with NS-398 but not by selective COX-1 inhibition with SC-560. Neither salicylate nor NS-398 blocked LPS-induced gastroprotection. LPS-induced gastroprotection does not depend entirely on accumulation of luminal fluid and is independent of COX-1 and COX-2. However, the ability of LPS to cause gastric stasis and increase gastric luminal fluid accumulation involves COX-2.

Importance of the pineal gland, endogenous prostaglandins and sensory nerves in the gastroprotective actions of central and peripheral melatonin against stress-induced damage

Melatonin attenuates acute gastric lesions induced by topical strong irritants because of scavenging of free radicals, but its role in the pathogenesis of stress-induced gastric lesions has been sparingly investigated. In this study we compared the effects of intragastric (i.g.) or intracerebroventricular (i.c.v.) administration of melatonin and its precursor, L-tryptophan, with or without concurrent treatment with luzindole, a selective antagonist of melatonin MT2 receptors, on gastric lesions induced by water immersion and restraint stress (WRS). The involvement of pineal gland, endogenous prostaglandins (PG) and sensory nerves in gastroprotective action of melatonin and L-tryptophan against WRS was studied in intact or pinealectomized rats or those treated with indomethacin or rofecoxib to suppress cyclooxygenase (COX)-1 and COX-2, respectively, and with capsaicin to induce functional ablation of the sensory nerves. In addition, the influence of i.c.v. and i.g. melatonin on gastric secretion was tested in a separate group of rats equipped with gastric fistulas. At 3.5 hr after the end of WRS, the number of gastric lesions was counted, the gastric blood flow (GBF) was determined by H2-gas clearance technique and plasma melatonin and gastrin levels were measured by specific radioimmunoassay (RIA). Biopsy mucosal samples were taken for determination of expression of mRNA for COX-1 and COX-2 by reverse transcriptase-polymerase chain reaction (RT-PCR) and of the mucosal generation of prostaglandin E2 (PGE2) by RIA. Melatonin applied i.g. (1.25-10 mg/kg) or i.c.v. (1.25-10 microg/kg) dose-dependently inhibited gastric acid secretion and significantly attenuated the WRS-induced gastric damage. This protective effect of melatonin was accompanied by a significant rise in the GBF and plasma melatonin and gastrin levels and in mucosal generation of PGE2. Pinealectomy, which suppressed plasma melatonin levels, aggravated the gastric lesions induced by WRS and these effects were counteracted by i.g. or i.c.v. application of melatonin. Luzindole abolished completely the gastroprotective effects of melatonin and L-tryptophan and attenuated significantly the rise in GBF evoked by the indoleamine and its precursor. Indomethacin and rofecoxib, which diminished PGE2 biosynthesis by c. 90 and 75% or capsaicin denervation, attenuated significantly melatonin- and L-tryptophan-induced protection and the rise in the GBF. Both the protection and the hyperemia were restored by addition of exogenous CGRP to capsaicin-denervated animals. COX-1 mRNA was detected by RT-PCR in the intact and melatonin-treated gastric mucosa, while COX-2 mRNA, which was undetectable in the intact gastric mucosa, appeared in WRS-exposed mucosa, especially in the melatonin-treated animals and this was accompanied by increased generation of PGE2 in gastric mucosa. Pinealectomy downregulated COX-2 mRNA and this effect was reversed by supplementation of pinealectomized animals with melatonin. We conclude that, (a) exogenous melatonin and its precursor, L-tryptophan, attenuates WRS-induced gastric lesions via interaction with MT2 receptors, (b) this protective action of melatonin is because of an enhancement of gastric microcirculation, probably mediated by PGE2 derived from COX-2 overexpression and activity, the activation of brain-gut axis involving CGRP released from sensory nerves, and the release of gastrin and (c) the pineal plays an important role in the limitation of WRS-induced gastric lesions via releasing melatonin, which exerts gastroprotective and hyperemic activities against stress ulcerogenesis.

Rat gastric injury after lipopolysaccharide: Role of inducible nitric oxide synthase

BACKGROUND

Short-term treatment with lipopolysaccharide (LPS) causes morphologic, but not macroscopic, gastric injury and decreases gastric injury caused by a subsequent challenge with a luminal irritant. This effect is abrogated by inducible nitric oxide synthase (iNOS) inhibition. The effects of long-term treatment with LPS on gastric injury are unknown as is the role of iNOS. We hypothesized that LPS would cause macroscopic gastric injury at later time points through an iNOS-dependent pathway.

METHODS

Conscious rats were given saline or LPS (1 or 20 mg/kg intraperitoneal) as a single intraperitoneal injection and killed 24 to 72 hours after injection. Macroscopic gastric injury (computerized planimetry), gastric luminal fluid volume and pH, and iNOS protein levels were assessed.

RESULTS

When compared with saline, high-dose but not low-dose LPS caused macroscopic gastric injury, increased gastric luminal fluid and pH, and up-regulated iNOS at 24 and 48 hours. All assessments returned to baseline by 72 hours. Inhibition of iNOS with 1400W (1 mg/kg intraperitoneal) given 15 minutes before saline or LPS (20 mg/kg) attenuated the deleterious effects of LPS on gastric injury and pH, but not fluid accumulation.

CONCLUSIONS

These data suggest that prolonged treatment with high-dose LPS causes gastric injury through an iNOS-mediated pathway.

Preliminary studies of Mammea americana L. (Guttiferae) bark/latex extract point to an effective antiulcer effect on gastric ulcer models in mice

Plant extracts are some of the most attractive sources of new drugs and have shown promising results for the treatment of gastric ulcers. Several folk medicinal plants and herbs have been used to treat gastrointestinal disorders, including gastric ulcers. Mammea americana L. (Guttiferae) fruit is very common in the diet of the population of northern South America. Our research interest in this plant arose because of its potential medicinal value as a tonic and against stomachache, as used in folk medicine. In this paper we evaluated three different extracts (ethanolic/EtOH, methanolic/MeOH and dichloromethane/DCM) obtained from M. americana L., for their ability to protect the gastric mucosa against injuries caused by necrotizing agents (0.3 M HCl/60% EtOH), hypothermic restraint stress, nonsteroidal anti-inflammatory drugs (NSAID, indomethacin) and pylorus ligation. In the HCl/EtOH-induced gastric-ulcer model, EtOH and DCM extracts demonstrated significant inhibition of the ulcerative lesion index by 54% (12.0 +/- 2.6 mm) and 86% (3.7 +/- 1.8 mm), respectively, in relation to the control value (26.0 +/- 1.4 mm) (p<0.0001). In the NSAID/cholinomimetic-induced lesion model, both EtOH and DCM extracts showed antiulcerogenic effects with significant reduction in the damage to these gastric lesions of 36% (8.3 +/- 2.0 mm) and 42% (7.5 +/- 1.4 mm), respectively, as compared to the control group (13.0 +/- 0.9 mm) (p<0.0001). In the gastric ulcer induced by hypothermic-restraint stress, both extracts also showed significant activity, and inhibited the gastric lesion index by 58% and 75%, respectively. The EtOH and DCM extracts also changed gastric juice parameters as well as those of cimetidine, decreased gastric acid secretion significantly (p<0.0001), increased pH values and promoted reduced acid output (p<0.0001). In all gastric-ulcer-induced models, MeOH extract did not show any significant antiulcerogenic activity, nor did it change gastric-juice parameters (p>0.05). The results suggest that EtOH and DCM extracts obtained from M. americana possess excellent antisecretory and/or gastrotective effect in all gastric ulcer models. These results suggest that the antiulcerogenic compound(s) present in M. americana may be clustered in the apolar fraction, which will be investigated by our group for the probable mechanisms of action.

Gastric oxidative stress and hemorrhagic ulcer in Salmonella typhimurium-infected rats

Infection of Salmonella typhimurium (Salmonella typhi) can lead to various organ diseases. This research first proposed that Salmonella typhi-infection could result in gastric oxidative stress and hemorrhagic ulcers that were ameliorated by ofloxacin, lysozyme chloride and several antioxidants, including exogenous glutathione (GSH), allopurinol and dimethylsulfoxide (DMSO). Male Wistar rats were given intrajejunally the live culture of Salmonella typhi [1 x 10(10) colony-forming unit (CFU)/rat] and followed by deprivation of food for 36 h. Age-matched control rats received vehicle only. Rat stomachs were irrigated for 3 h with either normal saline or a simulated gastric juice containing 100 mM HCl, 17.4 mM pepsin and 54 mM NaCl. Infection of Salmonella typhi produced an aggravation of ulcerogenic factors, including enhancing gastric acid back-diffusion, mucosal lipid peroxide generation and hemorrhagic ulcer as well as an attenuation of mucosal GSH level. Intragastric irrigation of gastric juice caused further aggravation of these gastric biochemical parameters. This exacerbation of ulcerogenic factors was abolished by pretreatment of ofloxacin and lysozyme chloride. Antioxidants, such as reduced GSH, allopurinol and DMSO also produced significant (P<0.05) amelioration of gastric damage in Salmonella typhi-infected rats. In conclusion, infection of Salmonella typhi substantially caused gastric oxidative stress and disruption of gastric mucosal barriers, consequently resulted in gastric hemorrhagic ulcerations that were effectively ameliorated by ofloxacin, lysozyme chloride and various antioxidants.

Comparison of two Chinese medical herbs, Huangbai and Qianniuzi, on influence of short circuit current across the rat intestinal epithelia

Huangbai (Phellodendron spec.) and Qianniuzi (Pharbitis spec.) are two traditional Chinese medical herbs used for anti-diarrheal and laxative agents, respectively. Ethanol and water extracts of these two herbs were prepared and effects of the extracts on ion transport of the rat intestinal epithelia were studied. For measuring changes of the short circuit current across the epithelia, the rat intestinal epithelia were mounted in the Ussing chamber and attached with voltage/current clamp. The intestinal epithelia were firstly activated by serosal administration of 5 microM forskolin. As current raised and being stable, extracts of these herbs were added, respectively, and changes in the short circuit current were recorded. Ethanol extract of Huangbai attenuated the current increment; on the contrary, ethanol extract of Qianniuzi augmented the current increment additionally. Water extracts of the two herbs showed minor effects on the current in comparison to ethanol extracts. The results provide evidences to reveal the pharmacological mechanism of the two Chinese medical herbs on the intestinal tissue.

Gastric effects of the selective cyclooxygenase-2 inhibitor, celecoxib, in the rat

BACKGROUND

Recent studies have revealed that cyclooxygenase-2 is involved in the protection of the damaged gastric mucosa, mediating, in particular, the acceleration of ulcer healing and angiogenesis; therein, it has been suggested that selective cyclooxygenase-2 inhibitors, although safe in healthy stomach, may have deleterious effects on the injured gastric mucosa. Moreover, no information is available about direct effects of these drugs on gastric surface epithelium.

AIMS

To investigate the gastric effects of the selective cyclooxygenase-2 inhibitor, celecoxib, in healthy and damaged rat gastric mucosa.

METHODS

Gastric toxicity was studied in the rat by measuring gastric potential difference and mucosal lesions. Celecoxib was administered intragastrically, either in basal conditions or in combination with damaging (acetylsalicylic acid and ethanol) or protective (sodium nitroprusside and lipopolysaccharides from Escherichia coli) agents. The anti-inflammatory activity was evaluated in the carrageenan-induced paw oedema assay. The non-selective inhibitors indomethacin and acetylsalicylic acid were used for comparison.

RESULTS

In conscious rats celecoxib, indomethacin and acetylsalicylic acid significantly reduced the paw oedema induced by carrageenan. While acetylsalicylic acid and indomethacin significantly reduced basal gastric potential difference and caused gastric mucosal lesions, celecoxib was ineffective; moreover, it did not aggravate the direct damaging effect of intragastric ethanol or aspirin. Pretreatment with the non-selective nitric oxide synthase inhibitor N-nitro-L-argynine methyl ester did not significantly change the gastric effects of celecoxib. Both celecoxib and indomethacin prevented the gastroprotective effects induced by sodium nitroprusside (nitric oxide donor) or by bacterial lipopolysaccharides (inducer of nitric oxide synthesis). CONCLUSIONS. These data indicate that the selective cyclooxygenase-2 inhibitor celecoxib did not alter gastric mucosal barrier nor induced mucosal lesions in the healthy or nitric oxide-deficient rat gastric mucosa. However, cyclooxygenase-2 inhibition impaired nitric oxide-dependent gastroprotection, indicating that cyclooxygenase-2 derived prostaglandins may be involved in the gastric mucosal defence.

Involvement of Capsaicin-Sensitive Afferent Nerves and Cholecystokinin 2/Gastrin Receptors in Gastroprotection and Adaptation of Gastric Mucosa toHelicobacter pylori-Lipopolysaccharide

Lipopolysaccharide (LPS) is one of the virulence factors in the Helicobacter pylori (Hp)-infected stomach, but it remains unknown whether single and prolonged pretreatment with Hp-LPS can affect the course of gastric damage induced by aspirin (ASA). We compared the effects of Hp-LPS with those induced by LPSs isolated from intestinal Bacteroides fragilis, Yersinia enterocolitica, and Campylobacter jejuni applied for 4 days on acute ASA-induced gastric lesions in rats. The area of ASA-induced gastric lesions, gastric blood flow (GBF), expression of mRNA and protein of leptin and plasma leptin, gastrin, interleukin-1beta, and tumor necrosis factor-alpha levels were examined. Single (once) or repeated (five times) i.p. injections of Hp-LPS (1 mg/kg) or intestinal LPSs failed to produce macroscopic gastric damage and did not affect the GBF when compared with vehicle. Hp-LPS injected repeatedly suppressed the gastric acid secretion, up-regulated leptin mRNA and protein, and increased plasma leptin and gastrin levels. Hp-LPS significantly reduced the ASA-induced gastric damage and the accompanying decline in the GBF, and these effects were significantly attenuated by capsaicin denervation and selective antagonism of cholecystokinin-B (CCK2) receptors by RPR-102681 [N-(metoxy-3 phenyl) N-(N-methyl N-phenyl-carbamylmethyl) carbamoylmethyl]-3 ureido]-3 phenyl]-2 propronique] but not by loxiglumide, an antagonist of CCK1 receptors. We conclude that 1) daily application of Hp-LPS enhances gastric mucosal resistance against ASA damage due to the increase of GBF and the expression and release of leptin and gastrin exerting trophic and gastroprotective effects, and 2) this enhanced resistance to ASA damage in Hp-LPS-adapted stomach is mediated by the sensory afferents and specific CCK2/gastrin receptors.

Role of histamine and acid back-diffusion in modulation of gastric microvascular permeability and hemorrhagic ulcers in Salmonella typhimurium-infected rats

Documentation concerning the pathogenesis of gastric hemorrhagic ulcer in Salmonella typhimurium (Salmonella typhi)-infective disease is lacking. This research first proposed that alterations of mast cell histamine release, gastric acid back-diffusion and mucosal microvascular permeability are important in modulating gastric ulcer and hemorrhage in Salmonella typhi-infected rats. Additionally, effects of several histamine-related drugs on this ulcer model were evaluated. Male Wistar rats were deprived food for 36 h. Live cultures of Salmonella typhi (OU 5045, 1 x 10(10) CFU in 1.0 mL of sterilized phosphate buffer saline) were challenged, intrajejunally to rats just before withdrawal of food. Control rats received the same volume of sterilized vehicle only. Rat stomachs were irrigated for 3 h with either normal saline or simulated gastric juice. Gastric acid back-diffusion, mucosal histamine concentration, microvascular permeability as well as luminal hemoglobin content and ulcer areas were determined. Severe gastric hemorrhage and mucosal ulcerations, particularly in acidic stomachs, were observed in Salmonella typhi-infected rats. A positive correlation of histamine to gastric hemorrhage and ulcer was found in those rats with Salmonella typhi-infection. This hemorrhagic ulcer in Salmonella typhi-infected rats was effectively ameliorated by intraperitoneal ketotifen, diphenhydramine and ranitidine but was worsen by exogenous histamine or diamine oxidase. In conclusion, enhancement of acid back-diffusion, mast cell histamine release and microvascular permeability is important in modulating gastric hemorrhage and ulcer in Salmonella typhi-infected rats.

Effect of Ethanol Extracts of Three Chinese Medicinal Plants with Laxative Properties on Ion Transport of the Rat Intestinal Epithelia

The effects of ethanol extracts of three Chinese medicinal plants Dahuang (Rheum palmatum L.), Badou (Croton tiglium L.), and Huomaren (Cannabis sativa L.), on ion transport of the rat intestinal epithelia were studied. Rat intestinal epithelia mounted in an Ussing chamber attached with voltage/current clamp were used for measuring changes of the short-circuit current across the epithelia. The intestinal epithelia were activated with current raised by serosal administration of forskolin 5 microM. Ethanol extracts of the three plants all augmented the current additively when each was added after forskolin. In subsequent experiments, ouabain and bumetanide were added prior to ethanol extracts of these medicinal plants to determine their effect on Na(+) and Cl(-) movement. The results suggest that ethanol extracts of the three medicinal plants may affect the Cl(-) movement more directly than Na(+) movement in the intestinal epithelial cells. The results provide evidence for the pharmacologic mechanism of the three Chinese medicinal plants on the intestinal tract.

Effect of Ethanol Extracts of Three Chinese Medicinal Plants With Anti-diarrheal Properties on Ion Transport of the Rat Intestinal Epithelia

Effects of ethanol extracts of three Chinese medicinal plants, namely, Qinpi (Fraxini cortex), Kushen (Sophora flavescens, AITON), and Huanglian (Coptis teeta, WALLICH), on ion transport of the rat intestinal epithelia were determined in this study. Rat intestinal epithelia mounted in an Ussing chamber attached to a voltage/current clamp were used for measuring changes in the short circuit current across the epithelia. Activation of the intestinal epithelia by serosal administration of 5 microM forskolin resulted in an increase in basal short circuit current. The ethanol extracts of each of the three plants partially reduced the current stimulated by forskolin. In the following experiments, ouabain and bumetanide were added prior to adding the ethanol extract of these plants for revealing their effect on Na(+) and Cl(-) movement. The results suggest that the ethanol extract of the Qinpi would affect Cl(-) transport. On the contrary, the ethanol extract of Kushen would affect Na(+) transport rather than Cl(-) movement. This study provides evidences that reveal the pharmacological mechanism of the Chinese plants with anti-diarrheal properties.

Inducible nitric oxide synthase is involved in acid-induced gastric hyperemia in rats and mice

The role of different isoforms of nitric oxide synthase (NOS) in the gastric mucosal hyperemia, induced by 155 mM luminal hydrochloric acid (pH approximately 0.8) without a barrier breaker, was investigated. Rats were anesthetized with Inactin (120 mg/kg ip), and mice were anesthetized with Forene (2.2% in 40% oxygen gas at 150 ml/min); the gastric mucosa was exteriorized. Gastric mucosal blood flow was measured with laser-Doppler flowmetry (LDF) in rats treated with Nomega-nitro-l-arginine (l-NNA; unspecific NOS inhibitor), l-N6-(1-iminoethyl)lysine [l-NIL; inducible (i) NOS inhibitor], or S-methyl-l-thiocitrulline [SMTC; neuronal (n) NOS inhibitor], 10 mg/kg, followed by 3 mg. kg-1. h-1 iv, in iNOS-deficient (-/-) and nNOS(-/-) mice. mRNA was isolated from the gastric mucosa in iNOS(-/-) and wild-type (wt) mice, and real-time RT-PCR was performed. The effect of 155 mM acid on gastric mucosal permeability was determined by measuring the clearance of 51Cr-EDTA from blood to lumen. LDF increased by 48 +/- 13% during 155 mM HCl luminally, an increase that was abolished by l-NNA, SMTC, or l-NIL. In iNOS wt mice, LDF increased by 33 +/- 8% during luminal acid. The blood flow increase was attenuated substantially in iNOS(-/-) mice. RT-PCR revealed iNOS mRNA expression in the gastric mucosa in the iNOS wt groups. The blood flow increase in response to acid was not abolished in nNOS(-/-) mice (nNOS-sufficient mice, 39 +/- 18%; heterozygous mice, 25 +/- 19%; -/- mice, 19 +/- 7%). Mucosal permeability was transiently increased during 155 mM HCl. The results suggest that iNOS is constitutively expressed in the gastric mucosa and is involved in acid-induced hyperemia, suggesting a novel role for iNOS in gastric mucosal protection.

Low endotoxemia prevents the reduction of gastric blood flow induced by NSAIDs: role of nitric oxide

1 The role of nitric oxide (NO) in the effects of low endotoxemia on gastric damage and blood flow has been evaluated in indomethacin-treated rats. 2 Pretreatment (-1 h) with endotoxin (40 micro g kg(-1)) reduced gastric damage induced by indomethacin (20 mg kg(-1)) in conscious rats. 3 Endotoxin prevented the reduction in gastric blood flow (laser Doppler flowmetry) induced by indomethacin in pentobarbital-anaesthetised rats. 4 Pretreatment with an NO-synthase (NOS) inhibitor (L-NAME, 1 mg kg(-1)) reversed the protective effect of endotoxin on gastric blood perfusion. 5 Endotoxin did not modify the expression of mRNA for endothelial NOS or inducible NOS in the gastric corpus when evaluated 1 h postinjection. However, a 3.8-fold increase in inducible NOS mRNA and a 61% reduction in endothelial NOS mRNA were observed in the gastric corpus 4 h after endotoxin administration. 6 Evaluation of both total and Ca(2+)-dependent NOS activity by analysing the rate of conversion of L-arginine to L-citrulline in gastric corpus homogenates showed no differences between animals treated with endotoxin and those treated with saline 1 or 4 h beforehand. Ca(2+)-independent NOS activity was almost non-apparent in control as well as in endotoxin-treated rats at all the time points analysed. 7 Low endotoxemia preserves blood perfusion and protects the gastric mucosa against the deleterious effects of indomethacin through the endogenous NO release. NO synthesis in response to endotoxin does not involve the inducible NOS, but probably depends on the post-translational/biochemical regulation in vivo of a Ca(2+)-dependent NOS, most probably endothelial NOS.

Vaccine-induced reduction of Helicobacter pylori colonization in mice is interleukin-12 dependent but gamma interferon and inducible nitric oxide synthase independent

Previous studies with mice have shown that major histocompatibility complex class II (MHC-II) is required for protection from Helicobacter pylori, while MHC-I and antibodies are not. Thus, CD4(+) T cells are presumed to play an essential role in protective immunity via secretion of cytokines. To determine which cytokines are associated with a reduction of bacterial load in immunized mice, gastric cytokine expression was examined by semiquantitative reverse transcription-PCR in protected (defined as > or =2-log-unit decrease in bacterial load) and unprotected mice 4 weeks after challenge. Elevated levels of mRNA for interleukin-12p40 (IL-12p40), gamma interferon (IFN-gamma), tumor necrosis factor alpha, and inducible nitric oxide synthase (iNOS) were associated with protection in immunized-challenged (I/C) mice, but Th2 cytokine (IL-4, IL-5, IL-10, and IL-13) and chemokine (KC, MIP-2, and MCP-1) expression was not associated with protection. Despite the association of IFN-gamma and iNOS message with protection, I/C mice genetically lacking either of these products were able to reduce the bacterial load as well as the wild-type I/C controls. The I/C mice lacking IL-12p40 were not protected compared to unimmunized-challenged mice. All I/C groups developed gastritis. We conclude that neither IFN-gamma nor iNOS is essential for vaccine-induced protection from H. pylori infection. The p40 subunit of IL-12, which is a component of both IL-12 and IL-23, is necessary for protection in immunized mice. These findings suggest a novel IFN-gamma-independent function of IL-12p40 in effective mucosal immunization against H. pylori.

Pathogenesis and therapy of gastric and duodenal ulcer disease

Despite the decreasing frequency of Helicobacter pylori-induced peptic ulcers, peptic ulcer disease remains a major clinical problem partly because nonsteroidal anti-inflammatory drug ulcers have increased in frequency. The reduction in nonsteroidal anti-inflammatory drug ulcers by use of selective cyclooxygenase-2 inhibitors will not eliminate the problem because of increased use of aspirin for cardiovascular prophylaxis. This article reviews current concepts of peptic ulcer pathogenesis and therapy according to ulcer etiology; discusses potential interactions between etiologies; and considers the therapy for H pylori infection including the effects of antimicrobial resistance, and the role of bismuth quadruple therapy or furazolidone salvage therapy.

Antiulcerogenic activity of four extracts obtained from the bark wood of Quassia amara L. (Simaroubaceae)

Quassia amara L., a neotropical forest shrub of the Simaroubaceae family, is widely used in Caribbean folk medicine and in some northern states of Brazil for the treatment of gastric ulcers. This plant is a source of numerous compounds including both beta-carbonile and cantin-6 alkaloids as well as, primarily, the bitter compounds known as quassinoids. We analyzed the possible antiulcerogenic activities of four extracts of different polarities: 70% ethanol (70% EtOH), 100% EtOH, 100% dichloromethane (DCM), and 100% hexane (HEX) obtained from Quassia amara bark. All extracts, administered at doses of 5000 mg/kg orally and 1000 mg/kg intraperitoneally, caused neither toxicity or death. In the indomethacin/bethanechol-induced gastric ulcer, 70% EtOH, 100% EtOH, DCM and HEX extracts, 100 mg/kg, p.o., inhibited the gastric ulcer (22.5, 23.4, 50.5, 46.8%, respectively). 70% EtOH, 100% EtOH, DCM, and HEX extracts reduced the gastric injury induced by the hypothermic restraint-stress test in mice (70.7, 80, 60, 82.7%, respectively). In the pylorus ligature of the mouse stomach, following pre-treatment with a single intraduodenal administration of 100 mg/kg of each extract, only 70% EtOH did not change the biochemical parameters of gastric juice. 100% EtOH, DCM and HEX extracts presented decreased gastric juice content, increased pH values and decreased acid output. We also determined the antiulcerogenic activity on HCl-EtOH-induced gastric ulcers in mice at four doses (25, 50, 75, 100 mg/kg, p.o.), then evaluated the possible dose-dependent relation and calculated the ED50 values. Except for 70% EtOH at a dose of 25 mg/kg, the other extracts showed significantly activity (p<0.05). The free mucous amount in the gastric stomach content was also evaluated. All extracts showed significant increases (p<0.05) of free mucous. This effect was abolished when the animals were pre-treated with indomethacin. Prostaglandin synthesis was evaluated by the administration of HEX extracts by the oral route (100 mg/kg). Prostaglandin synthesis was significantly, increased by 52.3% (p<0.05), and this effect was abolished with prior administration of indomethacin. We concluded that Quassia amara is a probable source for a new drug to treat gastric ulcers, and the mechanism of its activity relates to cytoprotective factors, such as mucous and prostaglandins, but there is still the possibility that antisecretory activity is involved in its antiulcerogenic effect.

Gastric nitric oxide synthase expression during endotoxemia: implications in mucosal defense in rats

BACKGROUND & AIMS

This study was performed to examine expression of gastric nitric oxide synthase (NOS) isoforms during endotoxemia in rats and to assess their role(s) in gastric injury from bile and ethanol.

METHODS

Lipopolysaccharide (LPS) enhanced the expression and activity of inducible nitric oxide synthase in gastric mucosa in a dose- and time-dependent manner.

RESULTS

Endothelial nitric oxide synthase and neural nitric oxide synthase expression did not significantly change, but constitutive nitric oxide synthase activity decreased over time. LPS alone caused injury to the gastric mucosa and disrupted F-actin filaments in the same cells with enhanced immunostaining for inducible nitric oxide synthase. LPS also exacerbated gastric injury from the mild irritants 5 mmol/L acidified taurocholate and 20% ethanol as did local intra-arterial infusion of the nitric oxide donor S-nitroso-N-acetyl-penicillamine. The selective inducible nitric oxide synthase inhibitor aminoguanidine negated LPS-induced exacerbation of gastric injury from these irritants. The nonselective NOS inhibitor N(G)-nitro-L-arginine methyl ester augmented the deleterious effects of LPS, an effect reversed by L-arginine but not D-arginine. Aminoguanidine, but not N(G)-nitro-L-arginine methyl ester, negated LPS-induced accumulation of gastric luminal nitrates.

CONCLUSIONS

These data suggest that increased inducible NOS activity and decreased constitutive nitric oxide synthase activity are primarily responsible for exacerbating gastric injury from luminal irritants during endotoxemia. Moreover, septic patients may be more susceptible to gastric injury from bile during gastrointestinal ileus.

Gastroprotective effects of amtolmetin guacyl: a new non-steroidal anti-inflammatory drug that activates inducible gastric nitric oxide synthase

BACKGROUND

The novel non-steroidal anti-inflammatory drug amtolmetin guacyl has been shown to possess markedly reduced ulcerogenic effects and nitric oxide-mediated gastroprotective activity against the damage induced by ethanol in the rat.

AIMS

To investigate, in the rat, the role of nitric oxide and of inducible nitric oxide synthase isoform in the protective effect of amtolmetin guacyl against the gastric damage induced by ethanol.

METHODS

The effects of amtolmetin guacyl on gastric transmucosal potential difference and on gastric mucosal blood flow were investigated in the anaesthetised rat; myeloperoxidase activity, inducible and endothelial nitric oxide synthase protein content were determined in rat gastric mucosal homogenates. The anti-inflammatory drug tolmetin and the bacterial lipopolysaccharide from Escherichia coli were studied for comparison.

RESULTS

In the anaesthetised rat, amtolmetin guacyl, but not tolmetin, reduced by approximately 50% the fall in gastric potential difference and, to a lesser extent, the macroscopic damage induced by ethanol. The effect of amtolmetin guacyl on transmucosal potential difference was prevented by the selective inducible nitric oxide synthase inhibitor 1400W. In amtolmetin guacyl-treated rats, 1400W decreased gastric mucosal blood flow, whereas it was inactive in vehicle- and tolmetin-treated animals. In gastric mucosal homogenates, both amtolmetin guacyl and lipopolysaccharide, but not tolmetin, increased inducible, but not endothelial, nitric oxide synthase protein content, as revealed by Western immunoblotting.

CONCLUSIONS

These data confirm that amtolmetin guacyl is a non-steroidal anti-inflammatory agent devoid of gastrolesive properties, that can actually reduce the damaging effects of ethanol through the increase in nitric oxide production, via the inducible isoform of nitric oxide synthase.

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.

The role of inducible nitric oxide synthase in cocaine-induced locomotor sensitization

Experimentally naive male Sprague-Dawley rats (weighing 85-110 g) were used to examine the role of inducible nitric oxide synthase (iNOS) in cocaine-induced locomotor sensitization. Repeated administration of cocaine (15 mg/kg, ip) for 7 consecutive days produced locomotor sensitization. Pretreatment with iNOS inhibitors, L-N(6)-(1-iminoethyl) lysine (NIL) or (-)-epigallocatechin gallate (EGCG; 10 mg/kg, ip), 30 min before cocaine (15 mg/kg, ip) administration totally blocked the development of cocaine-induced locomotor sensitization. Dopamine (DA) receptor binding in the nucleus accumbens (NAC) showed a significant decrease in the density of D(2) receptor and the affinity of D(1) receptor after cocaine treatment. Pretreatment with EGCG or NIL abolished the cocaine-induced changes in these parameters. These results suggest that iNOS may participate in the process of development of locomotor sensitization through the modulation of DA receptors in the NAC.

Protective action of lipopolysaccharidesin rat caerulein-induced pancreatitis: role of nitric oxide

Lipopolysaccharides (LPS), the component of the cell wall of gram-negative bacteria, have been implicated in the pathogenesis of acute pancreatitis, but the mechanism of their action on the pancreas has not been fully explored. The aim of this study was to investigate the effects of various doses of LPS on the integrity of intact pancreas and that involved in acute caerulein-induced pancreatitis (CIP) in the rat and to compare these effects with those of nitric oxide (NO) donor, S-nitrose-acetylpenicillamine (SNAP). The expression of constitutive NO synthase (cNOS) and inducible NO synthase (iNOS) mRNA was also examined in the isolated pancreatic acini obtained from the inflamed pancreas of rats treated with LPS. CIP was produced by subcutaneous (s.c.) infusion of caerulein (5 microg/kg.h for 5 h) to conscious rats. Bolus injections of various doses of LPS (0.1, 1, 10, 20 or 40 mg/kg) or SNAP (1.5, 3 or 6 mg/kg) were made intraperitoneally (i.p.) either alone or 30 min prior to s.c. infusion of caerulein to induce CIP. Infusion of caerulein produced acute pancreatitis confirmed by histological examination and manifested by an increase of pancreatic mass (by about 200%). Blood levels of amylase and lipase were augmented by 400 and 800% respectively, whereas the pancreatic blood flow (PBF) was decreased by 50% in rats with CIP. Injection of low doses of LPS (0.1-1 mg/kg i.p.) or SNAP (1.5-3 mg/kg i.p.) 30 min prior to caerulein infusion reversed the harmful effects of pancreatic overstimulation with caerulein and reduced significantly the histological manifestations of CIP such as edema, neutrophil infiltration and vacuolization of the acinar cells. These protective effects of low doses of LPS pretreatment on the pancreas were completely antagonized by the suppression of the activity of NO synthase (NOS) with N(G)-nitro-L-arginine (L-NNA) applied (20 mg/kg i.p.) 15 min prior to the LPS injection. Combination of L-arginine (100 mg/kg i.p.), a substrate for NOS, with L-NNA given prior to low doses of LPS, restored the LPS-induced protection of the pancreas in rats with CIP. In contrast, higher doses of LPS (20-40 mg/kg i.p.) or SNAP (6 mg/kg i.p.), which produced a significant fall of the PBF, did not protect the pancreas against CIP. Administration of various doses of LPS to rats with CIP resulted in significant and dose-dependent stimulation of NO biosynthesis in the isolated acini obtained from the pancreas of these animals. LPS enhanced the expression of both cNOS and iNOS in the pancreatic acini obtained from rats subjected to CIP. The signal for cNOS mRNA was detected in all samples, reaching peak at the protective dose of LPS (1 mg/kg i. p.), while iNOS was overexpressed only at the highest doses of LPS that failed to exhibit the protective activity. We conclude that the pretreatment with low doses of LPS protects the pancreas against the damage provoked by CIP and this effect could be attributed, at least in part, to the activation of L-arginine-NO system in the pancreas.

Leptin in gastroprotection induced by cholecystokinin or by a meal. Role of vagal and sensory nerves and nitric oxide

Leptin, detected recently in the stomach, is a product of the ob gene released by cholecystokinin (CCK) and plays an important role in the control of food intake but its influence on gastroprotection against the damage caused by noxious agents has not been studied. This study was designed to compare the effects of leptin and cholecystokinin-8 (CCK-8) on gastric mucosal lesions induced by topical application of 75% ethanol or acidified aspirin. Four series of Wistar rats (A, B, C and D) were used to determine the effects of: (A) suppression of prostaglandin biosynthesis by indomethacin (5 mg/kg i.p.); (B) inhibition of nitric oxide (NO)-synthase by nitro-L-arginine methyl ester (L-NAME) (5 mg/kg i.v.); (C) blockade of sensory nerves by capsaicin (125 mg/kg s.c.) and (D) bilateral vagotomy, on the gastric lesions induced by intragastric (i.g.) application of ethanol with or without pretreatment with CCK-8, a known gastroprotective substance or leptin. CCK-8 (1-100 microg/kg i.p.) and leptin (0.1-50 microg/kg i.p.) dose dependently attenuated gastric lesions induced by 75% ethanol; the dose reducing these lesions by 50% being about 10 microg/kg and 8 microg/kg, respectively. The protective effects of CCK-8 and leptin were accompanied by a significant rise in gastric blood flow (GBF) and luminal NO concentration. Leptin was also effective to attenuate aspirin-induced damage and the accompanying fall in the GBF, whereas CCK-8 dose dependently worsened aspirin damage and failed to influence GBF. CCK (1-100 microg/kg i.p.), given in graded doses, produced a dose-dependent increase in the plasma leptin level and a rise of the expression of ob messenger RNA (mRNA) in gastric mucosa, the maximum being reached at a dose of 100 microg/kg. Pretreatment with CCK-8 (10 microg/kg i.p.) or with 8% peptone, that is known to stimulate CCK release, also produced a significant rise in plasma leptin levels and up-regulation of ob mRNA while reducing significantly the gastric lesions induced by 75% ethanol to the same extent as that induced by exogenous leptin (10 microg/kg i.p.). Indomethacin, which suppressed prostaglandin generation by approximately 90%, failed to influence leptin- or CCK-8-induced protection against ethanol, whereas L-NAME attenuated significantly CCK-8- and leptin-induced protection and hyperemia but addition to L-NAME of L-arginine, but not D-arginine, restored the protective and hyperemic effects of both hormones. The ob mRNA was detected as a weak signal in the intact gastric mucosa and in that exposed to ethanol alone but this was further enhanced after treatment with graded doses of CCK-8 or peptone meal applied prior to ethanol. We conclude that: (1) exogenous leptin or that released endogenously by CCK or meal exerts a potent gastroprotective action depending upon vagal activity, and involving hyperemia probably mediated by NO and sensory nerves but unrelated to endogenous prostaglandins; (2) leptin mimics the gastroprotective effect of CCK and probably mediates the protective and hyperemic actions of CCK in the rat stomach.