Relationship between gastric mucosal prostaglandin levels and healing of gastric lesions in rats

Gastric mucosal integrity: gastric mucosal blood flow and microcirculation. An overview

The stomach is in a state of continuous exposure to potentially hazardous agents. Hydrochloric acid together with pepsin constitutes a major and serious threat to the gastric mucosa. Reflux of alkaline duodenal contents containing bile and pancreatic enzymes are additional important injurious factors of endogenous origin. Alcohol, cigarette smoking, drugs and particularly aspirin and aspirin-like drugs, and steroids are among exogenous mucosal irritants that can inflict mucosal injury. The ability of the stomach to defend itself against these noxious agents has been ascribed to a number of factors constituting the gastric mucosal defense. These include mucus and bicarbonate secreted by surface epithelial cells, prostaglandins, sulfhydryl compounds and gastric mucosal blood flow. The latter is considered by several researchers to be of paramount importance in maintaining gastric mucosal integrity. The aim of this paper is to review the experimental and clinical data dealing with the role of mucosal blood flow and in particular the microcirculation in both damage and protection of the gastric mucosa.

Cyclo-oxygenase-2 inhibitors suppress epithelial cell kinetics and delay gastric wound healing in rats

BACKGROUND AND AIMS

The present study examined the effects of NS-398, a specific cyclo-oxygenase-2 inhibitor, on gastric mucosal cell kinetics and gastric wound healing following acid-induced injury.

METHODS

Male Sprague-Dawley rats were fasted for 24 h and then 0.6 mol/L hydrochloric acid (HCl; 1 mL) was administered into the stomach; NS-398 or indomethacin was administered to the animals 10 min after the acid. Levels of constitutive cyclo-oxygenase (COX-1) and mitogen-inducible cyclo-oxygenase (COX-2) in the gastric mucosa were analysed using western blotting and immunohistochemical staining. The grade of the lesion was assessed using planimetry and histological examination, including immunohistochemistry for proliferating cell nuclear antigen (PCNA).

RESULTS

Although there was strong expression of COX-1, there was minimal expression of COX-2 in the gastric mucosa. Expression of COX-2 was enhanced mainly in surface epithelial cells and neck cells following HCl administration. Gastric mucosal ulcers and erosions healed within 48 h, during which time the proliferative zone expanded in the control animals. Indomethacin and NS-398 suppressed the expansion of the proliferative zone and delayed the healing of the gastric injury.

CONCLUSION

The present study demonstrated that cyclo-oxygenase-2 inhibitors delay gastric wound healing by suppressing expansion of the mucosal proliferative zone. These results provide evidence that cyclo-oxygenase-2 has an important role in gastric mucosal regeneration.

Effects of gamma-glutamylcysteine ethyl ester in cisplatin-induced changes in prostanoid concentrations in rat gastric and colonic mucosa

We evaluated changes in gastric and colonic mucosal prostanoid contents in rats treated with cisplatin. We also determined effects of gamma-glutamylcysteine ethyl ester (GCE), a pro-drug of glutathione, on cisplatin-induced changes in prostanoid concentrations. Rats were divided into three groups--the control: 0.5 ml of physiological saline was administered intraperitoneally (i.p.); the cisplatin group: 0.5 ml of cisplatin, 10 mg/kg, was administered i.p.; the GCE + cisplatin group: GCE, 30 min before cisplatin injection. In each group, rat gastric and colonic mucosa were isolated and their prostanoid concentrations were determined using high-performance liquid chromatography. 6-Keto-PGF1 alpha, PGF2 alpha, PGE2 were detected in gastric mucosa. In addition to these prostaglandins (PGs), thromboxane (TX) B2 was also detected in the colonic mucosa. In the cisplatin group, gastric mucosal 6-keto-PGF1 alpha concentration decreased significantly 24 h after administration, while PGE2 and PGD2 concentrations were increased significantly after 12 and 24 h, respectively. In colonic mucosa, cisplatin increased PGE2 and PGD2 concentrations, while it decreased TXB2 concentration. 6-Keto-PGF1 alpha concentration was not affected by cisplatin in colonic mucosa. GCE canceled out these changes in prostanoid concentrations in both gastric and colonic mucosa. Changes in prostanoid concentrations might be implicated in the adverse gastrointestinal effects of cisplatin, and clinical application of GCE could be expected.

Prevention of water immersion stress-induced gastric lesions through the enhancement of nitric oxide synthase activity in rats

BACKGROUND

Gastric mucosal microcirculation is an important factor in the protection of gastric mucosa, and nitric oxide (NO) plays a crucial role in the regulation of regional blood flow. This study was designed to evaluate the effect of cetraxate, an anti-ulcer drug, on water immersion stress-induced gastric lesions in relation to the changes in NO synthase activity.

METHODS

Gastric lesions were induced in rats by water immersion stress. The effects of cetraxate on NO synthase activity with or without stress was determined enzymatically. Changes in gastric mucosal prostaglandin (PG) contents with or without stress were also determined using high-performance liquid chromatography. Gastric mucosal blood flow was measured by hydrogen gas clearance technique.

RESULTS

Water immersion stress-induced gastric lesions. Cetraxate significantly mitigated the lesions but N(G)-monomethyl-L-arginine (L-NMMA), a specific inhibitor of NO synthase, exacerbated the lesions. The favourable effect of cetraxate was remarkably diminished by administration of L-NMMA. NO synthase activity decreased significantly by 6 h after stress. Cetraxate treatment increased NO synthase activity throughout the experiment in rats with or without stress treatment. Water immersion stress decreased all PGs detected, i.e. 6-keto-PGF1alpha, PGF2alpha, PGE2 and PGD2. Cetraxate prevented stress-induced decreases in PG contents. L-NMMA showed no significant effect on PG contents. Cetraxate increased gastric mucosal blood flow significantly and L-NMMA cancelled out cetraxate-induced increase in blood flow.

CONCLUSIONS

The pharmacological efficacy of anti-ulcer drugs such as cetraxate might be attributable to the enhancement of NO synthase activity resulting in an increase in gastric mucosal blood flow.

Effects of FK506, an immunosuppressive agent, on genesis of water-immersion stress-induced gastric lesions in rats

We examined the effects of FK506, an immunosuppressive agent, on the genesis of water immersion stress-induced gastric lesions in rats. Using high-performance liquid chromatography, four kinds of prostaglandins, ie, 6-keto-prostaglandin F1 alpha, prostaglandin F2 alpha, prostaglandin E2, and prostaglandin D2, were detected, and no leukotrienes were detected in gastric mucosa in rats without stress. After 6 hr of stress, gastric lesions developed with decreases in all prostaglandin contents, and the emergence of peptide leukotrienes was observed. Intramuscular administration of FK506 (0.1, 0.25, 0.5, 1.0, and 2.0 mg/kg) reduced lesion index dose-dependently. Administration of FK506 at doses over 0.25 mg/kg decreased all prostaglandin contents, but did not affect the increase in leukotriene contents. Pretreatment with famotidine or omeprazole reduced lesion index, and the protective effects were equivalent to those of 1.0 mg/kg of FK506, although FK506 did not affect gastric secretion during water-immersion stress. Water-immersion stress did not change the activities of xanthine oxidase in either stomach or serum. Polyoxyethylene-modified superoxide dismutase did not prevent gastric lesions. Water-immersion stress significantly increased myeloperoxidase activity in gastric mucosa, and FK506 reduced the increase in myeloperoxidase activity induced by stress. From our results, other factors besides gastric acid secretion and tissue eicosanoid contents, such as chemoattractant factor, might also be involved in the genesis of water-immersion stress-induced gastric lesions in rats.

Mechanism and prevention of chronic colonic inflammation with trinitrobenzene sulfonic acid in rats

1. The role of prostanoids in experimental colitis with trinitrobenzene sulfonic acid (TNBS) in rats was investigated. The effects of cyclosporine A (CsA) on the development of experimental colitis were also examined. 2. Five kinds of prostanoids were detected in rat colonic tissue by high performance liquid chromatography. These were 6-keto-prostaglandin (PG) F1 alpha, PGF2 alpha, PGE2, PGD2 and thromboxane B2. 3. In TNBS-induced experimental colitis, all prostanoid concentrations except PGD2 increased, although the time courses differed from each other. 4. Medication with indomethacin markedly reduced prostanoid concentrations in TNBS-induced colitis. However, indomethacin did not show any effect on damage scores. 5. Cyclosporine A reduced damage scores 14 days after TNBS treatment, and the protective effects were observed, whereas CsA did not affect colonic tissue prostanoid concentrations. 6. Prostanoids might be produced secondarily in the genesis of TNBS-induced colitis, although they may attenuate the inflammatory response. It was also suggested that CsA was likely to have therapeutic effects on experimental colitis by inhibiting the immune reaction with TNBS, which induced the chronic inflammation.