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Background and Aim: Lipopolysaccharide (LPS) has been proposed to act as one of numerous virulence factors in the Helicobacter pylori (HP)-infected stomach. However, little is known as to whether the gastric mucosa can withstand the repeated LPS insult, and how the possible adaptation to this endotoxin influences the damage induced by strong irritants. We determined the effect of a single or repeated parenteral administration of LPS obtained from HP on acute gastric lesions induced by intragastric application of 100% ethanol (1.5 ml) and by water immersion and restraint stress (WRS)., Methods: The area of the gastric lesions was measured by planimetry, mucosal gastric blood flow (GBF) was determined by H(2) gas clearance, and gastric luminal content was collected for the determination of luminal NO(2)(-)/NO(3)(-) levels by the Griess reaction. Biopsy samples were taken for the measurement of prostaglandin (PG) E(2) by radioimmunoassay and mucosal expression of constitutive and inducible nitric oxide synthase (cNOS and iNOS), constitutive (COX-1) and inducible cyclooxygenase (COX-2), heat shock protein 70 (HSP 70) mRNA and protein were analyzed by RT-PCR and Western blot., Results: HP LPS (1 mg/kg i.p.) injected once or 5 times produced negligible macroscopic injury and failed to influence GBF significantly compared to the injuries recorded in vehicle-controlled rats. Single and repeated (5 times) administration of HP LPS significantly reduced ethanol- and WRS-induced lesions, these protective effects were accompanied by a rise in GBF and excessive luminal release of NO. The suppression of NOS activity by L-NAME (20 mg/kg i.p.), a nonspecific NOS inhibitor, or L-NIL (30 mg/kg i.g.), a specific iNOS inhibitor, and of COX-2 activity by NS-398 reversed the protective and hyperemic effects of single or repeated LPS administrations against ethanol and WRS damage and the accompanying rise in NO and PGE(2) production. These effects of L-NAME were significantly antagonized by the addition of L-arginine, a substrate for NO synthesis. The signals for cNOS, COX-1 and HSP 70 mRNA were detected by RT-PCR in the vehicle-treated gastric mucosa, whereas gene and protein expression of iNOS, COX-2 and HSP 70 mRNA were significantly increased only in rats treated with 1 or 5 applications of HP LPS., Conclusions: Repeated injections of HP LPS enhance gastric mucosal resistance to the mucosal damage induced by ethanol and WRS via a mechanism involving mucosal overexpression of iNOS, COX-2 and HSP 70 with subsequent excessive production of NO and PGE(2)., (Copyright 2003 S. Karger AG, Basel)

Background/aim: Nitric oxide (NO) releasing nonsteroidal anti-inflammatory drugs do not cause gastric mucosal damage, despite inhibition of the cyclooxygenase activity to a similar extent as conventional nonsteroidal anti-inflammatory drugs that induce such damage. We compared the effects of native aspirin (ASA) with those of NO-releasing ASA (NO-ASA) on the development and healing of acute gastric lesions induced by water immersion and restraint stress (WRS) and the mucosal expression of heat shock protein 70 (HSP70)., Methods: Wistar rats received: (1). vehicle; (2). ASA (40 mg/kg i.g), and (3). NO-ASA (2.5-40 mg/kg i.g.), followed 0.5 h later by 3.5 h of WRS with or without glyceryl trinitrate, the donor of NO, and carboxy-PTIO, a NO scavenger. Healing of WRS lesions was assessed 0-24 h after termination of WRS. Number of gastric lesions, gastric mucosal blood flow (GBF), malondialdehyde (MDA) content, and RT-PCR expression of HSP70 mRNA were determined., Results: WRS caused typical bleeding erosions that were aggravated by aspirin and this was accompanied by a fall in the GBF and a significant rise in the mucosal MDA concentrations. In contrast, NO-ASA, which raised significantly the luminal content of NO(x), reduced number of WRS lesions and mucosal MDA levels while increasing significantly the GBF. These protective and hyperemic effects of NO-ASA against WRS lesions were mimicked by addition of glyceryl trinitrate to native ASA and significantly attenuated by carboxy-PTIO added to NO-ASA. HSP70 mRNA was significantly upregulated by WRS, and this was significantly attenuated by ASA, but not by NO-ASA. NO-ASA decreased significantly the MDA content and induced overexpression of HSP70 mRNA during healing of WRS lesions., Conclusion: NO-ASA exhibits mucosal protective and healing effects against WRS-induced gastric lesions due to the release of NO, which induces gastric hyperemia, and the attenuation of lipid peroxidation and counteracts the inhibition of HSP70 expression induced by native ASA., (Copyright 2002 S. Karger AG, Basel)

Background/aims: Ulcer healing involves expression of various growth factors such as epidermal growth factor (EGF), hepatocyte growth factor (HGF) and basic fibroblast growth factor (bFGF) at the ulcer margin, but the influence of EGF, HGF and bFGF applied locally with or without neutralizing anti-EGF, HGF and bFGF antibodies or cyclooxygenase (COX)-1 and COX-2 inhibitors on ulcer healing and the expression of COX-1 and COX-2 during ulcer healing have only been studied a little., Methods: Rats with gastric ulcers induced by serosal application of acetic acid (ulcer area 28 mm2 received a submucosal injection of either (1) vehicle (saline), (2) EGF, (3) HGF, and (4) bFGF with or without antibodies against EGF, HGF and bFGF or indomethacin (2 mg/kg/day i.p.), a nonspecific inhibitor of COX, or NS-398 (10 mg/kg/day i.g.) and Vioxx (5 mg/kg/day i.g.), both highly specific COX-2 inhibitors. A separate group of animals with chronic gastric fistulas was also used to assess gastric secretion during ulcer healing with and without growth factors. Each growth factor and specific antibody against EGF, HGF and bFGF (100 ng/100 microl each) were injected just around the ulcer immediately after ulcer induction and this local injection was repeated on day 2 following anesthesia and laparotomy. On days 13 and 21, the ulcer area was determined by planimetry, gastric blood flow (GBF) at the ulcer margin was examined by the H2-gas clearance technique, and mucosal generation of PGE2 and the gene expression of COX-1 and COX-2 in the non-ulcerated and ulcerated gastric mucosa were assessed. Gastric ulcers healed progressively within 21 days after induction and this effect was accompanied by a significant increase in GBF at the ulcer margin and in the expression of COX-2 in the ulcer area. Local treatment with EGF, HGF and bFGF produced a significant decrease in gastric acid secretion and significantly accelerated the rate of ulcer healing and raised GBF at the ulcer margin causing further significant upregulation of COX-2 but not COX-1 expression in the ulcerated mucosa. The acceleration of ulcer healing and hyperemia at the ulcer margin exhibited by locally applied EGF, HGF and bFGF were similar to those obtained with systemic administration of these growth factors. HGF applied submucosally, upregulated COX-2 expression and this was significantly attenuated by concurrent treatment with antibody against this peptide. Anti-EGF and anti-bFGF antibodies completely abolished the acceleration of the ulcer healing and hyperemia at the ulcer margin induced by these growth factors. Indomethacin and both COX-2 inhibitors significantly prolonged ulcer healing, while suppressing the generation of PGE2 in non-ulcerated and ulcerated gastric mucosa and GBF at the ulcer margin. The acceleration of ulcer healing by EGF, HGF and bFGF and the accompanying rise in GBF at the ulcer margin were significantly attenuated by the concurrent treatment with indomethacin or NS-398 and Vioxx., Conclusions: (1) Growth factors accelerate ulcer healing due to enhancement in the microcirculation around the ulcer and these effects are specific because they can be abolished by neutralization with antibodies; (2) COX-2-derived prostaglandins and suppression of gastric secretion may play an important role in the acceleration of ulcer healing by various growth factors, and (3) the local effects of EGF, HGF and bFGF on ulcer healing can be reproduced by their systemic application indicating the high efficacy of growth factors to accelerate this healing., (Copyright 2001 S. Karger AG, Basel)

Background: Acute Helicobacter pylori (Hp) infection in humans may be associated with markedly reduced gastric acid secretion, but the mechanism of this hypochlorhydria has not been fully explained., Aims: This study was designed to investigate how water extracts (WE) of Hp applied on rat gastric mucosa affect gastric secretion and mucosal histamine concentration as well as the gene expression for histamine decarboxylase (HDC), the key enzyme converting histidine to histamine and for interleukin-1beta (IL-1beta), the important proinflammatory cytokine., Materials and Methods: Wistar rats were surgically equipped with small cannulas to form gastric fistulas (GF). Four weeks after formation of GF, rats received either saline (control group) or WE obtained from type I Hp strain expressing CagA/VacA proteins and from type II Hp strain negative for CagA/VacA. Hp-WE was applied intragastrically (i.g.) in a volume of 1 ml at days 0, 2, 4 and 6 (total 4 times). At days 7 and 14, the secretory tests were performed during which basal gastric acid and pepsin secretion was examined and acid and pepsin outputs were measured. After secretory tests, the rats were sacrificed, the stomachs removed and the damage to the gastric mucosa was assessed by measuring the lesion area planimetrically and by histology, the gene expression in gastric mucosa for HDC and interleukin-1beta (IL-1beta) was analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern blot. Additionally, somatostatin concentration in gastric juice, gastric mucosal histamine content and plasma gastrin and IL-1beta levels were determined using radioimmunoassay (RIA)., Results: Administration of Hp-WE failed to induce gross mucosal damage but microscopic examination revealed partial denudation of gastric surface epithelium without causing deep necrosis. In secretory tests, Hp-WE produced marked hypochlorhydria but type I Hp-WE induced significantly stronger inhibition of acid and pepsin secretion than type II Hp-WE, both at days 7 and 14. Both, type I and type II Hp-WE suppressed significantly the gene expression for HDC mRNA and lowered significantly gastric mucosal histamine content as compared to respective values in vehicle-treated control gastric mucosa. Furthermore, Hp-WE, resulted in a significant increase in expression of IL-1beta mRNA and a significant fall in luminal somatostatin concentration as well as a insignificant elevation of plasma gastrin level, the type I Hp-WE being more effective in these alterations than type II Hp-WE., Conclusions: (1) Ability of Hp-WE to induce superficial damage, the reduction in HDC mRNA and accompanying fall in gastric histamine release, contribute, at least in part, to marked hypochlorhydria observed in the stomach exposed to repeated Hp-WE treatments, and (2) the deleterious effect of Hp-WE on the gastric mucosa involves an impairment of gastrin-somatostatin link possibly resulting from the action of Hp-derived toxins and the induction in mucosal cells of proinflammatory cytokine such as IL-1beta., (Copyright 2000 S. Karger AG, Basel.)

Background: Leptin, a product of the ob gene controlling food intake, has recently been detected in the stomach and shown to be released by cholecystokinin (CCK) and to induce gastroprotection against various noxious agents, but it is not known whether centrally applied leptin influences gastric secretion and mucosal integrity., Aims: In this study we compared the effects of leptin and CCK-8 applied intracerebroventricularly (i.c.v.) on gastric secretion and gastric mucosal lesions induced by topical application of 75% ethanol., Methods: Several major series of Wistar rats were used in this study. The effects of leptin or CCK applied i.c.v. on gastric secretion were examined using conscious rats with gastric fistulas. For the studies on gastroprotection the following series of rats were used to determine the effects of: (A) leptin and CCK applied centrally on this protection and the blockade of CCK(A) with loxiglumide (30 mg/kg i.p.) and CCK(B) receptors with RPR 102681 (30 mg/kg i.p.); (B) cutting of vagal nerves; (C) inactivation of sensory nerves by capsaicin (125 mg/kg s.c.); (D) inhibition of calcitonin gene-related peptide (CGRP) receptors with CGRP(8-37) (100 microg/kg i.p.), and (E) suppression of nitric oxide synthase (NOS) with N(G)-nitro-L-arginine methyl ester (L-NAME) (5 mg/kg i.v. ) on ethanol-induced gastric lesions in rats with or without the i.c.v. pretreatment with leptin or CCK-8. Rats were anesthetized 1 h after ethanol administration to measure the gastric blood flow (GBF) and then to determine the area of gastric lesions by planimetry. Blood was withdrawn for the measurement of plasma leptin and gastrin levels by radioimmunoassay and gastric biopsy samples were collected for the determination of cNOS and iNOS mRNA by RT-PCR., Results: Leptin and CCK-8 (0.01-5 microg/kg i.c.v.) dose dependently attenuated gastric lesions induced by 75% ethanol; the doses reducing these lesions by 50% (ED(50)) were 0.8 and 1.2 microg/kg, respectively. The protective effects of leptin and CCK-8 applied i.c. v. were accompanied by a significant rise in plasma leptin level and an increase in GBF. Blockade of CCK(A) receptors with loxiglumide abolished the protective and hyperemic effects of CCK but not those of leptin, while RPR 10268, a specific antagonist of CCK(B) receptors, counteracted leptin-induced protection and the rise in the GBF but failed to influence those afforded by CCK-8. For comparison, pretreatment with peripheral CCK-8 or leptin (10 microg/kg i.p.) causing a similar rise in the plasma leptin level also significantly reduced gastric lesions induced by 75% ethanol. The protective and hyperemic effects of centrally administered leptin were abolished by vagotomy, producing a fall in plasma leptin levels, and significantly attenuated by sensory denervation with capsaicin, by pretreatment with the CGRP antagonist, CGRP(8-37), or with L-NAME. A strong signal for iNOS mRNA was recorded in the gastric mucosa of leptin- and CCK-8-treated animals, whereas cNOS mRNA was unaffected., Conclusions: (1) Central leptin exerts a potent gastroprotective action at a dose that has no influence on gastric secretion; (2) this protection depends upon CCK(B) receptors, vagal activity and sensory nerves, and involves hyperemia probably mediated by NO, and (3) leptin mimics the gastroprotective effect of CCK and may be implicated in the protective and hyperemic actions of this peptide on the rat stomach., (Copyright 2000 S. Karger AG, Basel.)

Background: Helicobacter pylori (Hp) is considered as a major risk factor of peptic ulcer, but the pathogenic mechanism of its action has not been fully explained., Aims: This study was designed: (1) to compare the ulcer healing effects of water extract (WE) obtained from type-I cytotoxin-associated gene A (CagA) and vacuolating cytotoxin A (VacA) expressing Hp and from type-II CagA- and VacA-negative Hp strain with those of vehicle (saline), and (2) to determine the alterations in gastric secretion, gastric blood flow (GBF) and expression of Hp-related cytokines during the ulcer healing in rats treated with toxigenic (type-I) and non-toxigenic (type-II) Hp-derived WE., Methods: Gastric ulcers were produced by serosal application of acetic acid in rats with or without gastric fistula treated with vehicle (saline) or WE originating from type-I or type-II Hp administered intragastrically on days 1, 3, 5 and 7 upon ulcer induction. On days 3, 9 and 15, animals were lightly anesthetized with ether, the abdomen was opened and the GBF was measured by the H2-gas clearance technique in the ulcer area and non-ulcerated mucosa. Venous blood was withdrawn for the measurement of plasma cytokine (IL-1beta and TNFalpha) levels and plasma and gastric contents were also collected for gastrin and somatostatin determination by specific radioimmunoassay., Results: Gastric ulcers healed gradually in vehicle-treated controls and the ulcer area on days 3, 9 and 15 was reduced by 12, 43 and 92%, respectively. In rats treated with WE of type-I Hp, ulcer healing was significantly delayed, and gastritis and infiltration of ulcerated gastric mucosa with inflammatory cells were observed histologically. The prolongation of ulcer healing by WE of both Hp strains was accompanied by a marked fall in the GBF at the ulcer margin and transient hyposecretion especially in rats given WE of type-I Hp strain. On day 15 of ulcer healing, the plasma concentration of IL-1beta and TNFalpha was negligible in vehicle control rats, but it was significantly elevated particularly in rats treated with WE of type-I Hp. RT-PCR analysis revealed that mucosal expression of IL-1beta and TNFalpha mRNA was significantly upregulated in the gastric mucosa of rats treated with either toxigenic or non-toxigenic Hp WE. The plasma gastrin level was significantly higher and the luminal concentration of somatostatin was significantly lower in rats treated with Hp-WE than in vehicle-treated controls and these alterations were more pronounced in rats treated with WE type-I than type-II Hp., Conclusions: WE of toxigenic Hp strain delays ulcer healing due to the reduction in the gastric microcirculation at the ulcer margin, the overexpression of inflammatory cytokines and the impairment of the gastrin-somatostatin link.

Lipopolysaccharides (LPS) derived from gram-negative bacteria were reported to impair gastrointestinal mucosal integrity, but the results obtained are controversial. This study was undertaken to determine the effects of short-term administration of LPS on gastric secretion and gastric damage induced by 100% ethanol and to assess the role of the gene expression of two isoforms of cyclooxygenase (COX), constitutive (COX-1) and inducible (COX-2), and endogenous prostaglandins (PG) on these effects of LPS. Fasted rats received vehicle (control) or LPS (0.1-40 mg/kg i.g. or i.p.) without or with pretreatment with nonselective inhibitors of COX activity, indomethacin (5 mg/kg i.p.) and meloxicam (2 mg/kg i.g.), or the selective COX-2 inhibitor NS-398 (10 mg/kg i.g.), followed by intragastric application of 100% ethanol. The area of gastric lesions was determined by planimetry, gastric blood flow (GBF) was measured by the H2-gas clearance technique, mucosal PGE2 generation was measured by radioimmunoassay, and expression of COX-1 and COX-1 mRNA was determined by reverse transcription polymerase chain reaction (RT-PCR), quantitative RT-PCR with [32P]dCTP and immunohistochemistry. LPS applied intraperitoneally in various doses (0.1-10 mg/kg), dose dependently inhibited gastric acid and pepsin secretion and significantly reduced the area of gastric lesions induced by ethanol, and this was accompanied by an attenuation of the ethanol-induced fall in GBF and increased mucosal generation of PGE2. LPS applied in higher doses, such as 20 or 40 mg/kg, that caused systemic hypotension failed to protect the mucosa against 100% ethanol. Suppression of mucosal PGE2 generation by indomethacin or meloxicam, significantly reduced the inhibitory action of LPS on gastric secretion and abolished LPS-induced gastroprotection and elevation of GBF. NS-398 did not influence PGE2 generation, but significantly attenuated the protection and hyperemia induced by LPS suggesting that COX-2-derived products play an important role in gastroprotection. The expression of COX-1 mRNA, as determined by RT-PCR, quantitative RT-PCR and immunohistochemistry was found in intact gastric mucosa and after LPS administration. In contrast, the expression of COX-2 mRNA was undetectable in intact gastric mucosa but appeared in this mucosa 2, 4 and 8 h after LPS administration. COX-2 mRNA was not detected in rats treated with ethanol but, when LPS was applied before ethanol, the enhanced expression of COX-2 was detected without affecting COX-1 mRNA expression. We conclude that acute parenteral LPS affords gastroprotection against ethanol-damage through an increase in gastric microcirculation and overexpression of COX-2 and enhanced endogenous PG release.

The central and peripheral adrenergic systems are involved in the regulation of gastric secretion but little is known about the role of alpha- and beta-adrenoceptors in gastroprotection. In this study, acute gastric lesions were produced by an intragastric (i.g.) application of 100% ethanol and gastric blood flow (GBF) was determined by H2-gas clearance technique in rats with or without i.g. or intraperitoneal (i.p.) administration of alpha- or beta-adrenoceptor agonists or antagonists. Phenylephrine, alpha1-adrenergic agonist, and clonidine, alpha2-agonist, significantly augmented the ethanol-induced lesions while decreasing the GBF and these effects were reversed by the blockade of alpha1-adrenoceptors with prazosin and alpha2-adrenoceptors with yohimbine. In contrast, isoproterenol (ISO) (0.01-10 mg/kg i.g.), beta-adrenoceptor agonist, reduced dose-dependently ethanol-induced mucosal injury and this effect was accompanied by an elevation of the GBF similarly as after epidermal growth factor (EGF) (100 microg/kg x h s.c.) or after classic protective agent, 16,16-dimethyl-PGE2 (PGE2) (10 microg/kg i.g.). The pretreatment with beta-antagonist, propranolol, diminished the protective and hyperemic effects of ISO and EGF but failed to affect those induced by PGE2. Suppression of nitric oxide (NO) synthase activity by L-NAME or sensory denervation with capsaicin attenuated significantly the ISO- and EGF-induced gastroprotection and elevation of GBF, whereas the inhibition of PG biosynthesis by indomethacin remained without any significant effect. Adrenal medullectomy or chemical sympathectomy by 6-hydroxydopamine by itself failed to influence significantly the ethanol-induced damage but completely abolished the protective and hyperemic effects of EGF being without any influence on those induced by PGE2. ISO combined with EGF, restored the protective and hyperemic effects of this peptide in medullectomized rats. We conclude that (1) local activation of beta-adrenoceptors by ISO affords protection and elevation of GBF, both these effects being mediated by arginine-NO pathway and sensory nerves and (2) sympathetic system and adrenal medulla contribute to the protective and hyperemic activity of EGF.

Treatment with small doses of topical capsaicin protects the gastric mucosa from the damage by strong irritants but functional ablation of sensory nerves by pretreatment with larger dose of parenteral capsaicin augments the formation of gastric lesions via unknown mechanism. This study was designed to determine the role of gastric acid secretion, mucosal blood flow (GBF) and prostaglandins (PG) generation in the gastroprotection induced by small doses of topical or parenteral capsaicin in rats with intact or capsaicin-deactivated sensory nerves. Gastric lesions were produced in rats with intact sensory nerves (series A) or capsaicin-deactivated nerves (series B) using intragastric (i.g.) application of 100% ethanol, acidified aspirin (ASA) or water immersion and restraint stress (WRS). Pretreatment with i.g. capsaicin (0.12-1.0 mg/kg) in rats with intact sensory nerves (series A) reduced dose-dependently the mucosal damage caused by ethanol, ASA or WRS, the dose inhibiting the lesion area by 50% (ID50) being 0.3, 0.5 and 0.7 mg/kg, respectively. This protection was accompanied by a significant rise in gastric mucosal blood flow (GBF). Parenteral application of capsaicin (1.2-10 mg/kg s.c.) that in intact rats dose-dependently increased GBF, also dose-dependently reduced gastric damage induced by ASA or WRS (but not by ethanol), the ID50 being 5 and 3 mg/kg, respectively. The reduction by i.g. capsaicin of ethanol-or WRS-induced mucosal lesions was accompanied by a rise in GBF and this effect was reversed by indomethacin at a dose that suppressed endogenous PG biosynthesis by about 90%, indicating that PG are involved in the protective activities of topical capsaicin. Furthermore, topical and to a lesser extent parenteral capsaicin given to rats with intact or deactivated sensory nerves inhibited gastric acid and pepsin outputs, suggesting that this inhibition could contribute to the capsaicin-induced gastroprotection against acid-dependent mucosal lesions (ASA or WRS). Capsaicin deactivation of sensory nerves aggravated mucosal lesions induced by all three ulcerogens and this effects was accompanied by a marked decrease in GBF. In such capsaicin-deactivated rats, topical capsaicin also reduced ethanol-, ASA- or WRS-induced lesions, while parenteral capsaicin was effective only in the protection against the damage induced by acidified ASA and WRS but not by ethanol. The protection against WRS lesions and accompanying rise in GBF by parenteral capsaicin were also reversed by the pretreatment with indomethacin applied in a dose suppressing the generation of PG. We conclude that capsaicin is capable of protecting gastric mucosa in rats with both intact and capsaicin-deactivated rats and that this protective activity depends, at least in part, upon its hyperemic and antisecretory effects that may be mediated, at least in part, by endogenous release of PG.

Helicobacter pylori (Hp) is considered as the major pathogen in Hp-associated gastritis but the mechanism of its action has not been fully explained. We investigated both the damaging and protective effects of intragastric (i.g.) application of ammonia (NH4OH) and ammonium ion (NH4Cl), the major products of Hp-derived urease, on the rat stomach with intact and capsaicin-deactivated sensory nerves or suppressed prostaglandin (PG) and nitric oxide (NO) synthesis. NH4OH given i.g. resulted in a concentration-dependent mucosal damage starting at 30 mM and reaching maximum at 250 mM (pH 11), the extent of damage being similar to that obtained with 100% ethanol. NaOH solution (1 mM) at pH 11 given i.g. did not affect mucosal integrity. The damage caused by NH4OH was accompanied by the fall in gastric blood flow (GBF) reaching at 250 mM NH4OH about 30% of the vehicle control value. The NH4OH-induced gastric damage was augmented by capsaicin-induced deactivation of sensory nerves, the suppression of nitric oxide (NO) synthase with L-NAME or the decrease of i.g. acidity by ranitidine. The pretreatment with scavengers of reactive oxidants significantly reduced the area of NH4OH-induced gastric lesions. When the mucosa was first exposed to a low 15-mM concentration of NH4OH and then insulted with large 250 mM NH4OH or with 100% ethanol, the lesion area was markedly reduced as compared to that obtained with 250 mM NH4OH or 100% ethanol alone. This adaptive protection by 'mild' concentration of NH4OH against strong irritants (250 mM NH4OH or 100% ethanol) was reversed, in part, by pretreatment with L-NAME and indomethacin. NH4Cl (60-500 mM) given i.g. alone failed to affect the mucosal integrity but when applied before 100% ethanol it produced a concentration-dependent fall in the mucosal damage by these irritants. We conclude that; (1) ammonia at higher concentrations damages the gastric mucosa, while ammonium ion exerts the protective activity; (2) the ammonia-induced gastric damage may involve the formation of reactive oxidants; (3) ammonia at lower concentration acts like a mild irritant via the activation of sensory nerves, NO-arginine pathway and PG.

This study was designed to determine the efficacy of L-arginine in healing of gastric ulcers induced by acetic acid and to assess the role of nitric oxide (NO), prostaglandins, gastrin and polyamines in the healing process. Intragastric administration of L-arginine (32.5-300 mg/kg/day) enhanced the healing rate of these ulcers in a dose-dependent manner, while D-arginine (300 mg/kg/day) was not effective. The acceleration of healing by L-arginine was accompanied by a marked increase in gastric blood flow (GBF) at the ulcer margin, and an enhancement of serum gastrin level, mucosal DNA synthesis, and DNA and RNA contents and angiogenesis in the granulation tissue in the ulcer bed. A similar increase in ulcer healing associated with hyperemia at the ulcer margin and enhanced angiogenesis but without alteration in serum gastrin were observed after treatment with glyceryl trinitrate, an NO exogenous supplier. Treatment with NG-nitro-L-arginine (L-NNA), an inhibitor of NO synthase, delayed ulcer healing and this was accompanied by a reduction of GBF at the ulcer margin and in angiogenesis in granulation tissue and by a decrease in serum gastrin level and mucosal growth. Addition of L-arginine to L-NNA restored ulcer healing, hyperemia at the ulcer margin and angiogenesis and prevented the fall in serum gastrin and mucosal growth caused by L-NNA. Pretreatment with indomethacin also delayed ulcer healing and this was reversed by the coadministration of L-arginine. Inhibition of polyamine biosynthesis by difluoro-methyl-ornithine completely abolished the acceleration of the healing and the increase in mucosal growth induced by L-arginine. Our findings indicate that L-arginine accelerates ulcer healing due to its hyperemic, angiogenic and growth-promoting actions, possibly involving NO, gastrin and polyamines.

Capsaicin and papaverine are potent vasorelaxants with strong gastroprotective activity against damage induced by absolute ethanol. This protection was originally attributed to the increase in gastric mucosal blood flow (GBF) and the present study was designed to determine the possible role of nitric oxide (NO) and prostaglandins (PG) in the protective and hyperemic effects of capsaicin and papaverine on rat gastric mucosa. We found that the pretreatment with capsaicin (0.1-0.5 mg/kg i.g.) or papaverine (0.1-2 mg/kg i.g.) reduced dose dependently the area of ethanol-induced lesions, the ED50 being 0.3 and 1 mg/kg, respectively. This protection was accompanied by a gradual increase in the GBF. Intravenous injection of N omega-nitro-L-arginine (L-NNA; 1.2-5 mg/kg), a selective blocker of NO synthase, which by itself caused only a small increase in ethanol lesions, reversed dose dependently the protective and hyperemic effects of capsaicin and papaverine against ethanol-induced damage and attenuated the increase in GBF induced by each of these agents alone. This deleterious effect of L-NNA on the gastric mucosa and the GBF was fully antagonized by L-arginine (200 mg/kg i.v.) but not by D-arginine. L-arginine partly restored the decrease in GBF induced by L-NNA. Pretreatment with indomethacin (5 mg/kg i.p.), which suppressed the generation of PG by 85%, slightly enhanced the mucosal lesions induced by ethanol but failed to affect the fall in GBF induced by this irritant. Gastroprotective and hyperemic effects of capsaicin and papaverine were partly reversed by indomethacin suggesting that endogenous PG are also implicated in these effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Ebrotidine is a novel H2-receptor antagonist that exhibits both gastroprotective and ulcer-healing properties. Gastroprotection afforded by ebrotidine against ethanol damage was observed only after intragastric, but not parenteral administration, and it was accompanied by an increase in the mucosal blood flow. Ranitidine given at the same dose (100 mg/kg i.g. or s.c.) did not show any protective activity. When administered twice daily at various doses (1-100 mg/kg) for 10 days, ebrotidine reduced dose dependently the area of chronic gastric ulcers, and it was accompanied by significantly higher contents of epidermal growth factor (EGF) in the ulcer bed than in the intact mucosa. Administration of ranitidine resulted in a similar rate of ulcer healing and in a similar accumulation of EGF in the ulcer area to that observed after ebrotidine, but the increments in plasma gastrin levels in rats treated with ranitidine were observed at lower doses than in tests with ebrotidine. Concurrent administration of indomethacin delayed ulcer healing and reduced the accumulation of EGF in the ulcer area, but did not affect the ulcer healing by ebrotidine or ranitidine. We conclude that ebrotidine but not ranitidine shows gastroprotective activity, but it enhances the healing of chronic ulcerations in a similar manner to ranitidine.

Antacids containing aluminum have been shown to stimulate the protective processes in the gastric mucosa and to enhance the healing of chronic gastroduodenal ulcerations, but the mechanisms of these effects are still unexplained. This study was designed to compare the protective effects of unmodified and acidified (pH 2.0) Maalox 70 and Al(OH)3 on the formation of acute gastric mucosal lesions induced by absolute ethanol, taurocholate, acidified aspirin and stress, and to determine the role of gastric acid in healing of chronic gastroduodenal ulcerations by these antacids in rats. Acidified Maalox 70 and Al(OH)3 were significantly more potent than unmodified agents against all four tested types of acute mucosal lesions, and this action was probably due to their 'mild irritant' effect as evidenced by extensive exfoliation of the surface epithelial cells observed microscopically after the exposure of the mucosa to these agents. Mucosal generation of prostaglandins does not appear to be involved in the gastroprotection by acidified Maalox because the pretreatment with indomethacin did not affect this protection. In contrast to the protective effect, the ulcer-healing capacity of Maalox or Al(OH)3 does not appear to be dependent upon the presence of gastric acid because the reduction or elimination of endogenous acid by the pretreatment with ranitidine or omeprazole did not affect the healing of gastroduodenal ulcerations. We conclude that aluminum-containing antacids induce the mucosal protection that is enhanced in the presence of luminal acid but exhibit an ulcer-healing property that appears to be unrelated to gastric acid secretion or mucosal generation of prostaglandins.

This study was designed to compare the influence of omeprazole, a potent inhibitor of H+/K+-ATP-ase involved in the final step of H+ secretion and prostaglandin (PG) I2 on the formation of gastric mucosal lesions induced by absolute ethanol or acidified aspirin (ASA). Omeprazole given intragastrically in both inhibitory (20 or 200 mumol/kg) and noninhibitory doses (2 mumol/kg) prevented dose dependently ASA- and ethanol-induced gastric lesions. The protective effect of omeprazole against ASA-induced lesions occurred when mucosal generation of PGs was completely suppressed and that against ethanol lesions when PG generation was increased above normal values. Pretreatment with PGI2 given intragastrically or subcutaneously both in inhibitory and noninhibitory doses prevented almost completely the formation of gastric mucosal lesions caused by both absolute ethanol and acidified ASA. This study indicates that omeprazole is capable of protecting gastric mucosa against ASA- and ethanol-induced injury and that this protection is unrelated to gastric inhibition or the biosynthesis of mucosal PGs.

Gastric mucosa of the cat generates PGE2 activity at a significantly higher concentration in the antral 59.25 +/- 7.42 ng/g) than in the oxyntic (28.06 +/- 4.50 ng/ml) gland area. Intravenous (i.v.) infusion of histamine 80 micrograms/kg/h) or intragastric (i.g.) instillation of 0.1 N HCl (4 mEq/h) for 3 h significantly decreased the generation of PGE2 in antral and fundic mucosa, but did not result in the formation of gastric lesions. Aspirin (ASA) given i.v. or i.g. for 3 h caused a further fall in the generation of PGE2 in the mucosa and when combined with i.v. histamine or i.g. HCl, it caused almost complete disappearance of PGE2 activity and the formation of antral ulcers in all tested cats. Exogenous PGE2, given i.v. in a dose (30 micrograms/kg/h) reducing histamine-stimulated (80 micrograms/kg/h) acid secretion by about 50%, prevented almost completely the formation of gastric ulcers induced by a combination of ASA plus i.v. histamine or i.g. HCl. This study indicates that the gastric mucosa generates PGE2 which is capable of preventing gastric ulcers induced by ASA combined with histamine or mucosal acidification.

This study describes the model of chronic gastric and duodenal ulcerations induced by the application of acetic acid on a strictly defined area of the serosal surface of the stomach and duodenum for 10 and 20 s, respectively. Acetic acid applied for longer (20-60 s) or on a larger area (28-64 mm2) resulted in the formation of severe ulcerations which penetrated into the surrounding organs and had very prolonged healing time. Ulcers induced by the application of acetic acid for 10-20 s on a smaller area (7-13.8 mm2) healed spontaneously within 2-3 weeks, thus constituting a model suitable for evaluation of drugs affecting the process of ulcer healing. Our preliminary results of 7- to 14-day treatment with certain drugs indicate that sucralfate and De-Nol, at the dose which does not affect gastric acid secretion, accelerated the healing rate of both gastric and duodenal ulcers so that the observed ulcer healing effect could be attributed to their ulcer healing property. In contrast, 16, 16-dimethyl PGE2 (dmPGE2) in cytoprotective dose was completely ineffective in enhancing ulcer healing. Higher, gastric inhibitory dose of dmPGE2 accelerated the healing of duodenal but not gastric ulcerations, indicating that the inhibition of gastric secretion rather that cytoprotective activity is responsible for ulcer healing effect of this prostaglandin.

This study was designed to determine the influence of acetazolamide, a potent inhibitor of carbonic anhydrase, on the formation of gastric mucosal lesions induced by acidified aspirin (ASA) or absolute ethanol and on gastric cytoprotection induced by prostaglandin E2 (PGE2). Acetazolamide prevented dose-dependently ethanol-induced gastric lesions and this effect was accompanied by an increased biosynthesis of mucosal PGs, indicating that endogenous PGs may be involved in cytoprotection by acetazolamide. This is supported by the finding that acetazolamide failed to affect gastric ulcerations produced by acidified ASA when mucosal PG biosynthesis was almost completely suppressed. Pretreatment with acetazolamide did not influence the protective action of PGE2 on ethanol-induced mucosal lesions and only slightly inhibited the protective effect of PGE2 on ASA-induced gastric ulcerations. This study indicates that: (1) acetazolamide prevents ethanol- but not ASA-induced gastric mucosal lesions probably via stimulation of PG biosynthesis and (2) gastric alkaline secretion, mediated by carbonic anhydrase, is probably not an essential mechanism responsible for this cytoprotection induced by PGE2.

Intragastric administration of sulfhydryl-containing cysteamine or sulfhydryl-oxidizing diethylmaleate caused a dose-dependent reduction in the mean area of gastric lesions induced by absolute ethanol. The protective effects of these agents are abolished by the sulfhydryl blocker N-ethylmaleimide, while indomethacin, a potent inhibitor of cyclooxygenase, caused only about 50% reduction in this protection. This study indicates that mucosal generation of prostaglandins contributes to the gastric cytoprotection by these agents administered intragastrically, but endogenous sulfhydryls are also involved in the gastric mucosal protection by sulfhydryl-containing or sulfhydryl-oxidizing compounds.

Growth hormone-releasing factor (GRF) was reported to possess the growth-promoting action on the gastroduodenal mucosa that can be augmented by removal of endogenous somatostatin. Since mucosal proliferation was considered to contribute to healing of chronic gastroduodenal ulcerations, we designed the study to determine the interaction of GRF and somatostatin on the healing rate of acetic acid-induced chronic gastric and duodenal ulcers and on the growth of gastroduodenal mucosa in rats. GRF injected subcutaneously twice daily at 100 micrograms/kg/day for 7 days resulted in a significant enhancement of healing rate of both gastric and duodenal ulcerations and this was accompanied by a significant increase in the weight of the mucosa and the contents of RNA and DNA. GRF also significantly increased serum gastrin levels and the tissue contents of epidermal growth factor (EGF) in salivary glands, duodenum and pancreas, suggesting that both gastrin and EGF could contribute to mucosal trophic and ulcer healing effects of GRF. Somatostatin (100 micrograms/kg/day for 7 days) abolished almost completely the ulcer healing and mucosal growth-promoting effects of GRF and this was accompanied by the reduction in serum gastrin level and the tissue contents of EGF suggesting that the suppression of gastrin and EGF release could contribute to the observed effects of somatostatin. We conclude that GRF has both the ulcer healing and the mucosal trophic actions which can be antagonized by somatostatin and that gastrin and EGF may be implicated in these actions.