Acceleration of recovery of gastric epithelial integrity by 16,16-dimethyl prostaglandin E2.

The effects of pretreatment with 16,16-dimethyl prostaglandin E2 (DmPGE2) on the recovery of gastric mucosal 'barrier' parameters after ethanol-induced damage were studied using an ex vivo chamber preparation in the rat. DmPGE2 (4-40 micrograms kg-1) significantly reduced the extent of haemorrhagic damage to the gastric mucosa induced by the topical application of 50% ethanol followed by 0.05 M hydrochloric acid. The lowest dose of DmPGE2 tested (4 micrograms kg-1) had no effect on the ethanol-induced changes in transmucosal potential difference (PD) or K+ efflux. However, DmPGE2 at doses at 20 or 40 micrograms kg-1 significantly reduced the changes in these indices of epithelial integrity. The recovery of PD and K+ efflux to control levels after ethanol-injury was accelerated by DmPGE2. With the two higher doses of DmPGE2 (20 and 40 micrograms kg-1) there was a significantly (P less than 0.001) lower level of epithelial discontinuity, measured histologically, in samples taken at the end of the experiment. These results suggest that at the higher doses, DmPGE2 confers some protection to the gastric epithelium as well as accelerating the recovery of epithelial integrity after damage induced by ethanol.     

Effect of 16,16-dimethyl prostaglandin E2 on gastric surface epithelial cell damage induced by 20% ethanol in rats

Prostaglandins protect against the gross damage of gastric mucosa induced by 50-100% ethanol, but do not protect surface epithelial cells (SEC) from necrosis. Since this induced damage to SEC is so severe, we attempted to determine the effects of a prostaglandin on slightly induced SEC damage and gastric potential difference (PD) in response to low concentrations of ethanol. The necrotizing effects of graded concentrations of ethanol (10-50%) to SEC on the rat gastric mucosa were studied by scanning electron and light microscopy. Intragastric instillation of 20% ethanol (v/v, 1 ml/100 g body wt.) to pylorus-ligated rats for 10 min induced slight and reproducible SEC damage consisting mainly of the apical cell membrane erosion of SEC. Pretreatment with 16,16-dimethyl prostaglandin E2 (dmPGE2, 3 or 30 micrograms/kg, p.o. or s.c.) afforded protection of the SEC from 20% ethanol-induced damage. However, the cytoprotective effects of dmPGE2 were abolished when gastric contents were emptied prior to 20% ethanol instillation. Intragastric instillation of ethanol immediately reduced PD in a concentration-related manner. dmPGE2 (3 or 30 micrograms/kg, s.c.) had no effect on the reduction of gastric PD after 20% ethanol treatment and the recovery of reduced PD to normal levels. We conclude that dmPGE2 has no cytoprotective effect on 20% ethanol-induced SEC damage in rat gastric mucosa.     

Surface epithelial cell damage induced by restraint and water-immersion stress in rats effects of 16,16-dimethyl prostaglandin E2 on stress-induced gastric lesions

The time-course of gastric mucosal surface epithelial cell damage and macroscopically visible lesions in response to restraint and water-immersion stress (22 degrees C) in rats was examined, and the effects on it of 16,16-dimethyl prostaglandin E2 (dmPGE2) were compared with those of papaverine, timoprazole and atropine. The stress produced surface epithelial cell damage prior to visible lesion, the former increasing in severity with time and reaching a plateau 60 min later, by which time exfoliation of surface epithelial cells was observable along the mucosal folds. In contrast, macroscopically visible lesions appeared 2 hr after stress, and severity continued to increase with time. Pretreatment injections (s.c.) of dmPGE2 (3, 30 micrograms/kg), papaverine (100 mg/kg) and atropine (1 mg/kg) protected the surface cells against stress (1 hr)-induced damage, and inhibited visible lesion formation after 4 hr stress. Timoprazole (30 mg/kg, s.c.) did not protect the surface cells, but did markedly inhibit visible lesion formation. dmPGE2, papaverine and atropine, but not timoprazole, inhibited stress-induced increases in gastric contractions. dmPGE2, timoprazole and atropine, but not papaverine, inhibited acid secretion in stress-conditions. These results indicated that stress induced damage to the gastric mucosa within 1 hr due to increased gastric contractions, and the surface epithelial cell damage developed into macroscopically visible lesions in the presence of acid, and that dmPGE2 protected the surface epithelium against stress-induced damage probably by inhibiting gastric contractions.     

16,16-Dimethyl prostaglandin E2 protects gastric mucosal surface epithelial cells from indomethacin-induced damage in rats

The protective effect of 16,16-dimethyl prostaglandin E2 (dmPGE2) against early damage induced by indomethacin in the rat gastric mucosal surface epithelial cells was studied using a scanning electron microscope. Indomethacin (10 or 25 mg/kg, p.o.) induced a widespread exfoliation of the surface epithelial cells and an exposure of the lamina propria both in the corpus and antrum within 1 hr after the administration. Pretreatment with dmPGE2 (0.3, 3 or 30 micrograms/kg, p.o.) 30 min before indomethacin (25 mg/kg) dose-dependently inhibited these damages. The effects of dmPGE2, at least on the surface epithelial cells in the corpus, appear to be related to the prevention of damage formation itself and is unrelated to the enhancement of reconstitution of once damaged mucosa. Enhanced gastric motility by indomethacin was potently inhibited by pretreatment with 3 and 30 micrograms/kg of dmPGE2, but not with 0.3 micrograms/kg. dmPGE2 pretreatment (30 micrograms/kg) significantly decreased the absorption of indomethacin (25 mg/kg) when determined 10 min after giving indomethacin, but did not affect it when determined 30 and 60 min later. We conclude that dmPGE2 protects gastric mucosal surface epithelial cells from indomethacin injury at an early stage, partly by inhibiting gastric motility.     

Effects of 16,16-dimethyl prostaglandin E2 on surface epithelial cell damage in the rat stomach induced by vagal nerve stimulation

The effect of 16,16-dimethyl prostaglandin E2 (dmPGE2) on gastric surface epithelial cell (SEC) damage induced by vagal nerve stimulation (VS) in urethane-anesthetized rats was studied using scanning electron microscopy. VS (1.25-10 Hz, 0.2 mA, 2 msec, 10 min) resulted in a graded increase in the SEC damage, increased gastric contractions, increased gastric acid secretion, and a decrease in heart rate. Pretreatment with dmPGE2 (0.3-30 micrograms/kg, s.c.) significantly protected the SEC from VS-induced damage, inhibited the increase in gastric contractions and acid secretion, but had no influence on the decrease in heart rate. Atropine (1 mg/kg, s.c.) also protected the SEC from VS-induced damage and inhibited the alterations in response to VS. Timoprazole (30 mg/kg, s.c.) had no protective effects on SEC from VS-induced damage, no effect on increased gastric contractions and heart rate, but did inhibit the increase in gastric acid secretion, in response to VS. These results suggest that: VS-induced SEC damage was caused by increased gastric contractions and not by increased gastric acid secretion, and dmPGE2 protects against SEC damage by inhibiting gastric contractions.     

Protective effect of 16,16-dimethyl prostaglandin E2 on the hepatotoxicity of bromobenzene in mice

It has been suggested that 16,16-dimethyl prostaglandin E2 may have a cytoprotective effect in the liver. To assess this hypothesis, we determined the effects of this prostaglandin on the metabolism and toxicity of bromobenzene in mice. Administration of 16,16-dimethyl prostaglandin E2 (50 micrograms/kg s.c., 30 min before, and every 6 hr after, the administration of bromobenzene) did not modify the disappearance curves of unchanged bromobenzene from plasma and liver, and did not modify the amount of bromobenzene metabolites covalently bound to hepatic proteins 1-24 hr after the administration of a toxic dose of bromobenzene (0.36 ml/kg i.p.). The prostaglandin, however, markedly reduced serum alanine aminotransferase activity, the extent of liver cell necrosis, the depletion of glutathione, and the disappearance of cytochrome P-450 after administration of this toxic dose of bromobenzene (0.36 ml/kg i.p.). It also markedly reduced mortality after administration of a lethal dose of bromobenzene (0.43 ml/kg i.p.). We conclude that 16,16-dimethyl prostaglandin E2 can prevent hepatic necrosis without decreasing the covalent binding of bromobenzene metabolites to hepatic proteins. The mechanism for this dissociation between covalent binding and toxicity remains unknown.     

Gastric mucosal damage induced by local intra-arterial administration of Paf in the rat.

1. A technique for the close-arterial administration of substances to the rat stomach in vivo has been developed. 2. Intra-arterial infusion of platelet-activating factor (Paf, 10-50 ng kg-1 min-1 for 10 min) induced macroscopically assessed damage in the corpus mucosa, characterized as vasocongestion and necrosis. 3. The threshold intra-arterial doses of Paf that induced histologically assessed damage in the antrum and corpus of the stomach (10 and 5 ng kg-1 min-1, respectively) produced minimal systemic hypotension (less than 20 mmHg) suggesting a dissociation between these events. 4. Pretreatment with the Paf-antagonist, L-652,731 (2.5 mg kg-1 i.v.) prevented the gastric damage induced by local infusion of Paf. 5. Intravenous infusion of Paf (25 ng kg-1 min-1) did not significantly damage the gastric mucosa, in contrast to the same dose infused locally, yet Paf administered by either route produced a comparable degree of hypotension. Such findings suggest minimal metabolism of Paf during its passage through the gastric circulation. 6. Local intra-arterial infusion of Paf in doses as low as 0.25 ng kg-1 min-1, which had no systemic hypotensive actions, significantly induced gastric damage in the presence of intragastric 20% ethanol. 7. These observations support a local role for Paf in the pathogenesis of gastric irritation and ulceration, such as that observed during endotoxin shock or bacterial infection. The present technique is thus useful for the study of locally administered substances on gastric function and integrity.     

11-Deoxy,16,16-dimethyl prostaglandin E2 induces specific proteins in association with its ability to protect against oxidative stress

Prostaglandins (PGs) act locally to maintain cellular homeostasis and stimulate stress response signaling pathways. These cellular effects are diverse and are tissue-dependent. PGE(2), and the synthetic analogue, 11-deoxy,16,16-dimethyl PGE(2) (DDM-PGE(2)), protect renal proximal tubular epithelial (LLC-PK1) cells against cellular injury induced by the potent nephrotoxic and nephrocarcinogenic metabolite of hydroquinone, 2,3,5-tris-(glutathion-S-yl)hydroquinone. Although this cytoprotective response (in LLC-PK1 cells) is mediated through a thromboxane or thromboxane-like receptor coupled to AP-1 signaling pathways, the mechanism of cytoprotection is unknown. In this study, we utilized HPLC-electrospray ionization tandem mass spectrometric (ESI MS/MS) and matrix-assisted laser desorption ionization time-of-flight mass spectrometric (MALDI TOF) analysis of proteins isolated from DDM-PGE(2)-stimulated LLC-PK1 cells to identify candidate cytoprotective proteins. DDM-PGE(2) selectively stimulated the synthesis of several proteins in LLC-PK1 cells. Peptide sequencing by ESI-MS/MS of in-gel tryptic protein digests revealed the identity of eight proteins: endothelial actin binding protein, myosin, elongation factor 2 (EF-2), elongation factor 1alpha-1 (EF-1alpha), heat shock protein 90beta (HSP90beta), glucose-regulated protein 78 (GRP 78), membrane-organizing extension spike protein, and actin. Both ESI-MS/MS and MALDI-MS analysis resulted in the same protein identification. Western analysis confirmed the temporal induction of the majority of these proteins, including EF-2, EF-1alpha, HSP90beta, GRP78, and actin. The collective expression of these proteins suggests that DDM-PGE(2)-mediated cytoprotection may involve alterations in cytoskeletal organization and/or stimulation of an endoplasmic reticulum (ER) stress response. The present studies provide insights into potential downstream targets of PG signaling.     

Failure of the inhibition of rat gastric mucosal 5-lipoxygenase by novel acetohydroxamic acids to prevent ethanol-induced damage.

1. The role of leukotriene B4 (LTB4) and LTC4 as mediators of gastric mucosal damage following ethanol challenge in vivo has been investigated using two selective 5-lipoxygenase inhibitors, BW A4C and BW A137C. 2. Oral administration of ethanol to rats in vivo, induced macroscopic damage to the gastric mucosa and markedly increased the formation of the 5-lipoxygenase products, LTB4 and LTC4, from the mucosa ex vivo. 3. Pretreatment with the acetohydroxamic acids BW A4C and BW A137C (5-50 mg kg-1 p.o.) dose-dependently reduced ethanol-stimulated LTB4 and LTC4 formation by the gastric mucosa, with an ID50 of approximately 5 mg kg-1 p.o. 4. A single oral dose of BW A4C (20 mg kg-1) induced near-maximal inhibition of mucosal LTB4 formation within 30 min, which was well maintained for 5 h, whereas BW A137C (20 mg kg-1 p.o.) induced maximal inhibition between 30 and 60 min after administration, which then diminished over the subsequent 5 h. 5. The mucosal formation of the cyclo-oxygenase product, 6-keto-prostaglandin F1 alpha, which was unaltered following ethanol challenge, was not inhibited by the acetohydroxamic acids. Likewise, the small increase in mucosal thromboxane B2 formation following challenge was not inhibited by BW A4C. 6. Neither BW A4C nor BW A137C, at doses that almost completely inhibited the mucosal synthesis of LTB4 or LTC4, reduced the macroscopic gastric mucosal damage induced by ethanol. 7. Pretreatment with the lipoxygenase inhibitor BW 755C (5-50 mg kg-1 p.o.) did reduce mucosal damage, but there was a dissociation between the degree of protection and the inhibition of leukotriene biosynthesis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Aspirin-induced gastric mucosal damage: prevention by enteric-coating and relation to prostaglandin synthesis.

1. Gastric damage induced by low-dose aspirin and the protective effect of enteric-coating was assessed in healthy volunteers in a double-blind placebo-controlled cross-over trial using Latin square design. Each was administered placebo, plain aspirin 300 mg daily, plain aspirin 600 mg four times daily, enteric-coated aspirin 300 mg daily, or enteric-coated aspirin 600 mg four times daily for 5 days. Gastric damage was assessed endoscopically, and gastric mucosal bleeding measured. 2. Aspirin 300 mg daily and 600 mg four times daily caused significant increases in gastric injury compared with placebo. Gastric mucosal bleeding was significantly more with the high dose, with a trend towards increased gastric erosions, compared with the low dose. 3. Enteric-coating of aspirin eliminated the injury caused by low dose aspirin and substantially reduced that caused by the higher dose. 4. All dosages and formulations caused similar inhibition of gastric mucosal prostaglandin E2 synthesis. 5. Serum thromboxane levels were suppressed equally with plain and enteric-coated aspirin. 6. In this short-term study in healthy volunteers, gastric toxicity from aspirin was largely topical, independent of inhibition of prostaglandin synthesis, and could be virtually eliminated by the use of an enteric-coated preparation.     

Local opioid-sensitive afferent sensory neurones in the modulation of gastric damage induced by Paf.

1. The role of local sensory neurones in modulating the extent of gastric mucosal damage induced by close-arterial infusion of platelet-activating factor (Paf 50 ng kg-1 min-1 for 10 min) has been investigated in the anaesthetized rat. 2. Local intra-arterial infusion of the neurotoxin, tetrodotoxin (TTX), substantially augmented the mucosal damage induced by Paf, as assessed by both macroscopic and histological techniques. 3. In rats pretreated with capsaicin 2 weeks prior to study, to induce a functional ablation of primary afferent neurones, gastric damage induced by Paf was significantly augmented. 4. Administration of morphine (0.75-3 mg kg-1 i.v.) or its peripherally acting quaternary analogue, N-methyl morphine (15 mg kg-1 i.v.), also significantly enhanced the gastric damage induced by Paf. 5. The potentiation by morphine of Paf-induced gastric damage was inhibited by administration of the opioid antagonists, naloxone (1 mg kg-1 i.v.) or the peripherally acting N-methyl nalorphine (3 mg kg-1 i.v.). 6. Administration of TTX or morphine alone, or pretreatment with capsaicin did not induce any detectable mucosal damage, suggesting that interference with local sensory neuronal activity itself does not directly induce mucosal disruption. 7. These results indicate that peripheral opiate-sensitive afferent sensory neurones play a physiological defensive role in the mucosa, attenuating the extent of gastric damage induced by Paf.     

Effects of antimuscarinic agents and prostaglandin E2 on the gastric mucosal lesions induced by necrotizing agents and water-immersion stress in rats

The role of antimuscarinic action in gastric mucosal protection against necrotizing agents and the role of such mucosal protection in antiulcerogenic action were studied in rats with i.v. administered antimuscarinic agents. Pirenzepine, as well as PGE2, prevented the gastric mucosal lesions induced by all necrotizing agents (99.5% ethanol, 0.6 N HCI, 0.15 N NaOH, 0.4 N HCI-50 mM taurocholate), but atropine did not prevent the HCI-induced lesions. Cimetidine inhibited only the ethanol-induced lesions even at the antisecretory dose. Higher doses of pirenzepine (5-fold) and atropine (10-fold) were required to inhibit the gastric secretion in Shay rats than in vagally stimulated rats. There was no difference between the antisecretory doses of cimetidine in Shay rats and vagally stimulated rats. PGE2 (0.03-0.1 mg/kg) did not affect gastric secretion. The protective doses of pirenzepine and atropine against mucosal lesions induced by necrotizing agents were similar to the dose in inhibiting vagally stimulated acid secretion and water-immersion stress-induced lesions. PGE2 (100 micrograms/kg) did not prevent the water-immersion stress induced gastric lesions. These results suggested that antimuscarinic agents protect the gastric mucosa from necrotizing agents via a blocking action on the activation of the intrinsic cholinergic nerve. However, antiulcerogenic action is more deeply concerned with antisecretory action than cytoprotection.     

Effect of zaldaride maleate, an antidiarrheal compound, on 16,16-dimethyl prostaglandin E2-induced intestinal ion secretion in rats

The effect of zaldaride, a calmodulin inhibitor, on 16,16-dimethyl prostaglandin E2 (dmPGE2)-induced intestinal ion secretion was investigated in rats. Zaldaride inhibited the dmPGE2-induced increase in water content in the colon, but not that in the small intestine. In the colonic mucosa, zaldaride attenuated the dmPGE2-induced short-circuit current; however, it did not affect the forskolin or dibutyryl cAMP-induced effect. These results suggest that zaldaride inhibits dmPGE2-induced intestinal ion secretion by reducing the activity of Ca2+/calmodulin-dependent adenylate cyclase linked to a receptor, and the colon may be an important site in the action of zaldaride.     

Gastroprotective effect of 2-mercaptoethane sulfonate against acute gastric mucosal damage induced by ethanol

Gastric mucosal damage induced by ethanol is a serious medical problem. Recent evidences suggest that reactive oxygen species and inflammatory mediators play a key role in the destruction of gastric mucosa. The present study was aimed to evaluate the potential beneficial effect of MESNA (2-mercaptoethane sulfonate) against ethanol-induced gastric mucosal damage in mice. The animals were orally pretreated with vehicle or MESNA and then treated with acidified ethanol to induce gastric mucosal damage. One hour after ethanol ingestion mice were euthanized and stomach samples were collected for biochemical analysis. Macroscopic and histopathological evaluation of gastric mucosa showed that pretreatment with MESNA attenuated gastric lesions induced by ethanol. Administration of MESNA significantly increased glutathione content and superoxide dismutase and catalase activity in the gastric tissues. In addition, MESNA markedly reduced ethanol-induced lipid peroxidation, myeloperoxidase activity, tumor necrosis factor-alpha, interleukin (IL)-1β, IL-6, and monocyte chemotactic protein-1 levels. These findings suggest that the thiol-containing compound MESNA is able to decrease alcohol-induced oxidative stress and inflammation in the gastric tissue. It seems that MESNA may have a protective effect against ethanol-induced gastric mucosal damage.     

Effects of the synthesized prostaglandin E2-analogue arbaprostil on gastric mucosal lesions in rats

The effects of arbaprostil (CU-83), a newly synthesized prostaglandin (PG) E2 analogue, on gastric lesions were investigated. Experiment 1: The animals were divided into 3 groups: 1. the control group: untreated, 2. 50% ethanol group: rats were given 1 ml of 50% ethanol intragastrically, and 3. arbaprostil + 50% ethanol group: arbaprostil (10 micrograms/kg) was administered p.o. 30 min before 50% ethanol administration. 1 h after ethanol administration, stomachs were isolated, and gastric mucosal lesions were observed. Experiment 2: Rats were divided into 4 groups; 1. the control group; untreated, 2. 6 h stress group; animals were placed in a stress cage and immersed into a water bath (23 degrees C) for 6 h, 3. arbaprostil (10 micrograms/kg) + 6 h stress group, and 4. arbaprostil (100 micrograms/kg) + 6 h stress group; arbaprostil 10 micrograms/kg or 100 micrograms/kg was administered 30 min before 6 h of water immersion stress, respectively. In each experiment, stomachs were isolated and gastric mucosal lesions were observed. Immediately after the observation of lesions, the fundic mucosal layer was separated from the muscle layer, and mucosal PGs levels were measured by high performance liquid chromatography. Four kinds of PGs, i.e., 6-keto-PG F1 alpha, PGF2 alpha, PGE2, and PGD2 were detected in gastric mucosa. Administration of 50% ethanol and water immersion stress induced gastric lesions and decreased all 4 mucosal PGs levels. Arbaprostil, 10 micrograms/kg, reduced ethanol-induced gastric lesions and maintained mucosal PGs levels, concomitantly, however, the same doses of arbaprostil did not show a protective effect against water immersion stress-induced gastric lesions or decreases in PGs levels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanisms underlying gastric mucosal damage induced by indomethacin and bile-salts, and the actions of prostaglandins.

1 The mechanisms by which -he bile salt, sodium taurocholate, potentiates the formation of gastric mucosal erosions induced by indomethacin has been investigated in the rat. 2 Systemic administration of indomethacin lowered resting mucosal blood flow but had no effect on the acid back-diffusion across the mucosa. 3 Gastric perfusion of taurocholate in acid solution increased acid back-diffusion and lowered the potential differences. This was accompanied by an increase in mucosal blood flow, which may represent a protective mechanism in the mucosa. 4 Administration of indomethacin during acid-taurocholate perfusion reduced this elevated mucosal blood flow without any further change in acid back-diffusion. 5 The results suggest that although a decrease in mucosal blood flow or an increase in acid back-diffusion can lead to a low incidence of erosions, a combination of both produces extensive mucosal damage. 6 The (15S)-methyl analogue of prostaglandin E2 reduced erosion formation induced by indomethacin and acid-taurocholate administration. 7 It is suggested that this protective action of the prostaglandin analogue may be linked to changes in gastric mucosal permeability and in mucosal blood flow.     

Role of antioxidants in gastric mucosal damage induced by indomethacin in rats

Reactive oxygen species play a role in the formation of gastric lesions induced by nonsteroidal antiinflammatory drugs. The present study was undertaken to determine whether endogenous antioxidants in gastric mucosa can protect it against the damaging effects of oxygen free radicals. This study examine oxygen free radical production (superoxide anions and hydrogen peroxide), gastric mucosa antioxidant defense mechanisms (glutathione, catalase, superoxide dismutase), the lesion-inducing effects of the generated oxygen free radicals (vascular permeability, lipid peroxidation) and gastric ulceration in rats treated orally with indomethacin at 10 mg/kg at 2 and 6 h after drug administration. Two hours after administration of the antiinflammatory drug, there was a sharp increase in production of oxygen free radicals in the gastric mucosa with no alteration in other parameters examined. Six hours after indomethacin administration the production of oxygen free radicals returned to basal levels, but there was a high degree of gastric ulceration and a significant increase in lipid peroxidation and vascular permeability together with decreases of 45% in glutathione concentration and 30% in catalase relative to the control group. These results suggest that like plasma, the gastric mucosa has an antioxidant capacity and only when this capacity is exhausted are the lesive effects of the oxygen free radicals manifested.