Role of gastric mucosal blood flow in cytoprotection

Angiogenic and cell proliferating action of the natural diarylnonanoids, malabaricone B and malabaricone C during healing of indomethacin-induced gastric ulceration

PURPOSE

To evaluate the plant phenolics, malabaricone B (mal B) and malabaricone C (mal C) in healing stomach ulcer by modulating angiogenesis.

MATERIALS AND METHODS

Male Swiss albino mice, ulcerated with indomethacin (18 mg/kg, p. o., single dose) were treated up to 7 days with different doses of mal B or mal C. The healing capacities of the drugs and their effects on the angiogenic parameters were assessed.

RESULTS

Maximum ulceration, observed on the 3rd day after indomethacin administration was effectively healed by mal B and mal C (each 10 mg/kg, p. o. x 3 days), the latter showing equivalent potency (~78% p < 0.001) as that of Omez (3 mg/kg, p. o. x 3 days) and misoprostol (10 mug/kg, p. o. x 3 days). Compared to the untreated mice, those treated with mal B or mal C respectively for 3 days increased the mucosal EGF level (139 and 178%, p < 0.001), the serum VEGF level (56%, p < 0.01 and 95%, p < 0.001) and microvessels formation (37%, p < 0.05 and 62%, p < 0.01), while reducing the serum endostatin level (37%, p < 0.05 and 61%, p < 0.01). The relative healing capacities of mal B and mal C correlated well with their respective abilities to modulate the angiogenic factors. The healing by Omez and misoprostol was not due to improved angiogenesis.

CONCLUSIONS

The drugs, mal B and mal C could effectively heal indomethacin-induced stomach ulceration in mice by promoting angiogenesis.

Famotidine prevents canine gastric blood flow reduction by NSAIDs

AIM

To investigate the effect of famotidine on gastric blood flow reduction induced by diclofenac sodium, a common non-steroidal anti-inflammatory drug in Japan, using laser Doppler flowmetry in the canine stomach.

METHODS

The gastric mucosal blood flow was measured by laser Doppler flowmetry in 15 healthy male beagles before and 60 min after the administration of diclofenac suppository (1.0 mg/kg) into the rectum. The examination was done in a crossover, single-blinded fashion. All dogs underwent both famotidine (0.5 mg/kg) and placebo (saline) injection simultaneously with the administration of diclofenac. In addition, the tissue concentration of prostaglandin E2 was measured.

RESULTS

The blood flow decreased by 18.3 +/- 9.1% in the gastric body, by 26.3 +/- 8.1% in the antrum in the placebo group after the administration of diclofenac sodium, while the decreases seen were significantly smaller in the famotidine group: 3.2 +/- 12.6% in the gastric body and 7.9 +/- 16.5% in the antrum (P = 0.001 for the gastric body, P = 0.0034 for the antrum). Conversely, the percentage of mucosal prostaglandin E2 concentration decrease in each group did not show a significant difference.

CONCLUSION

Famotidine alleviates the reduction of gastric blood flow induced by diclofenac sodium. Further, not only mucosal prostaglandins but also gastric acid may play an important role in non-steroidal anti-inflammatory drugs-induced gastric microcirculatory disturbance.

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.

Gastroprotective effects of pantoprazole against experimental mucosal damage

The present study investigated the gastroprotective effects of the proton pump inhibitor pantoprazole on gastric mucosal damage induced by ethanol-HCl in rats. Omeprazole was used as reference drug. The morphometric analysis of gastric histological sections revealed that pantoprazole and omeprazole dose-dependently prevented the necrotic mucosal injury evoked by ethanol-HCl (ED50 = 14.1 and 21.6 micromol/kg, respectively). These effects were associated with a marked increment of Alcian blue recovery from gastric bound mucus (ED50 = 18.8 and 29.3 micromol/kg, respectively). In addition, both pantoprazole and omeprazole inhibited gastric acid secretion in pylorus-ligated rats (ED50 = 1.5 and 3.3 micromol/kg, respectively). Further experiments indicated that the protective effects of pantoprazole were not modified by L-365,260 (a gastrin receptor antagonist), suramin (a drug able to interfere with endogenous growth factors), N(G)-nitro-L-arginine (an inhibitor of nitric oxide synthase) or systemic ablation of capsaicin-sensitive sensory nerves, whereas they were partly blocked by indomethacin (an inhibitor of prostaglandin synthesis) and fully prevented by N-ethylmaleimide (a potent blocker of sulfhydryl compounds). The present data provide histomorphometric evidence that: 1) pantoprazole is endowed with gastroprotective properties and is more active than omeprazole in preventing the necrotic mucosal damage induced by ethanol-HCl; 2) according to the rank order of ED50 values, the protective effects of both drugs appear to depend mainly on the enhancement of the gastric mucosal barrier rather than on the inhibition of acid secretion; 3) an increased production of prostaglandins, as well as an increased availability of sulfhydryl radicals at the level of the gastric mucosa may account for the gastroprotective effects of pantoprazole.

Gastropathy and defense mechanisms in common bile duct ligated portal hypertensive rats

Portal hypertensive gastropathy is associated with a broad spectrum of gastric mucosal damage inspite of decreased gastric acid secretion, suggestive of compromised endogenous protective mechanisms. To determine the mechanisms of damage in portal hypertensive gastropathy we measured lipid peroxidation, glutathione, antioxidant and lysosomal enzymes in gastric mucosal homogenates from male Wistar rats with elevated intrasplenic pulp pressure, eighteen days after common bile duct ligation. Thiobarbituric acid-reactive substances and lysosomal enzymes (beta-glucuronidase and acid phosphatase) were increased in the common bile duct ligated group as compared to the sham-operated group. The levels of antioxidant defense enzymes, superoxide dismutase, glutathione peroxidase, catalase and glutathione were decreased as compared to the sham-operated controls. Pre-operative vitamin E administration decreased mucosal lipid peroxidation increased the levels of antioxidant defense enzymes and lowered the lysosomal enzymes. The plasma vitamin E levels in this group were lower when compared to animals receiving it post-operatively. In conclusion, free radical and lysosomal enzyme mediated damage may play a role in portal hypertensive gastropathy.

Capsaicin-sensitive afferent sensory nerves in modulating gastric mucosal defense against noxious agents

In the rat stomach, evidence has been provided that capsaicin-sensitive sensory nerves (CSSN) are involved in a local defense mechanism against gastric ulcer. In the present study capsaicin or resiniferatoxin (RTX), a more potent capsaicin analogue, was used to elucidate the role of these sensory nerves in gastric mucosal protection, mucosal permeability, gastric acid secretion and gastrointestinal blood flow in the rat. In the rat stomach and jejunum, intravenous RTX or topical capsaicin or RTX effected a pronounced and long-lasting enhancement of the microcirculation at these sites, measured by laser Doppler flowmetry technique. Introduction of capsaicin into the rat stomach in very low concentrations of ng-microg x mL(-1) range protected the gastric mucosa against damage produced by topical acidified aspirin, indomethacin, ethanol or 0.6 N HCl. Resiniferatoxin exhibited acute gastroprotective effect similar to that of capsaicin and exerted marked protective action on the exogenous HCl, or the secretagogue-induced enhancement of the indomethacin injury. The ulcer preventive effect of both agents was not prevented by atropine or cimetidine treatment. Capsaicin given into the stomach in higher desensitizing concentrations of 6.5 mM markedly enhanced the susceptibility of the gastric mucosa and invariably aggravated gastric mucosal damage evoked by later noxious challenge. Such high desensitizing concentrations of capsaicin, however, did not reduce the cytoprotective effect of prostacyclin (PGI2) or beta-carotene. Capsaicin or RTX had an additive protective effect to that of atropine or cimetidine. In rats pretreated with cysteamine to deplete tissue somatostatin, capsaicin protected against the indomethacin-induced mucosal injury. Gastric acid secretion of the pylorus-ligated rats was inhibited with capsaicin or RTX given in low non-desensitizing concentrations, with the inhibition being most marked in the first hour following pylorus-ligation. Low intragastric concentrations of RTX reduced gastric hydrogen ion back-diffusion evoked by topical acidified salicylates. It is concluded that the gastropotective effect of capsaicin-type agents involves primarily an enhancement of the microcirculation effected through local release of mediator peptides from the sensory nerve terminals. A reduction in gastric acidity may contribute to some degree in the gastric protective action of capsaicin-type agents. The vasodilator and gastroprotective effects of capsaicin-type agents do not depend on vagal efferents or sympathetic neurons, involve prostanoids, histaminergic or cholinergic pathways.

Antiulcer action of Microgramma squamulosa (Kaulf.) Sota

Microgramma squamulosa (Kaulf.) Sota (Polypodiaceae) is commonly used as an antiulcer agent in the state of São Paulo, mainly in the upper land. The present work aims to study the antiulcer action of the crude extract of the plant rhizome and its toxicity. The effective dose was determined through acute ulcer induction test by stress. Using a determined dose, we performed a test against ulcer through acute induction by ethanol and hydrochloric acid, using cimetidine and misoprostol as reference drugs in both tests. The same extract, its ethanol and ethanol + water (1:1) fractions and the reference drug cimetidine were tested through subchronic induction test with acetic acid. The subchronic toxicity test was performed using a dose of 800 mg/kg of the crude extract, orally administered for 30 days. Finally the extracts and fractions were analysed in order to determine the main chemical groups of substances.

Gastric cytoprotection is secondary to increased mucosal fluid secretion: a study of six cytoprotective agents in the rat

We tested the hypothesis that rapidly developing gastric cytoprotection produced by topical application of exogenous compounds is a result of increased gastric mucosal fluid secretion. Ex vivo gastric chambers were prepared in rats which were subsequently exposed topically to one of the prostaglandin (PG) E1 analogues misoprostol or rioprostil, PGE2, nicotine, N-ethylmaleimide (NEM), 0.25 M HCl, or to their respective vehicles. All agents were added to empty chambers to avoid complications resulting from dilution by gastric contents. Effects of these agents on intraluminal volume changes, blood flow, juxtamucosal pH, histology, and on the mucosal damage resulting from necrotizing agents were studied. All six agents were cytoprotective and each increased net secretion of fluid by the chambered mucosae. Gastric blood flow was not significantly increased by NEM, by 0.25 M HCl, or by nicotine compared to controls, and the juxtamucosal pH was not significantly increased by any of the three agents for which this was studied. Vacuole formation in surface epithelial cells and subepithelial edema were seen after exposure to some agents, but none of the agents led to formation of a thick barrier of exfoliated cells and mucus. Ablation of primary afferent nerves with capsaicin abolished both protection by 0.25 M HCl and the net increase in fluid secretion by the mucosae. Capsaicin ablation did not alter either the protection afforded by NEM or the increase in volume of secretion. We conclude that increased mucosal fluid secretion is the common factor present with all six cytoprotective agents and hence may be the predominant mechanism of cytoprotection against topically applied necrotizing agents.

Acute erosions of the gastric mucosa in burned rats: effect of sucralfate

The effect of intragastric sucralfate on development of gastric erosions in burns was studied in 20 rats anaesthetised with midazolam/fentanyl/fluanisone. Gastric blood flow was measured by radioactive microspheres immediately before, and 20, 40, and 120 minutes after the rats had been burned. Significantly fewer erosions were found in the 10 rats treated with sucralfate (less than 2% of the gastric mucosal surface was affected) compared with the controls (16% of the mucosa affected). There was no difference in the rate of gastric blood flow in any part of the stomach between the rats treated with sucralfate and the controls. We conclude that sucralfate is effective in preventing gastric erosions in burned rats, but that other mechanisms of action than increase gastric blood flow are responsible for its protective effect.

Nitric oxide in gastroprotective and ulcer healing effects of sucralfate

BACKGROUND

Sucralfate is known to protect gastric mucosa against the damaging action of strong irritants and to accelerate healing of chronic ulcers, but the mechanisms underlying these effects have not been elucidated. Similar gastroprotective and healing effects can be obtained with exogenous donors of nitric oxide (NO) and prostaglandins (PG).

METHODS

The area of gastric lesions was measured by planimetry. Gastric blood flow was determined using laser Doppler flowmetry. The role of NO in the prevention of ethanol-induced gastric damage and in the healing of gastric ulcerations by sucralfate and nocloprost, a stable PGE2 analog, was therefore assessed.

RESULTS

Pretreatment with NG-nitro-L-arginine (L-NNA), an inhibitor of NO synthase, enhanced ethanol-induced mucosal damage and reduced dose-dependently the gastroprotective and hyperemic effects of sucralfate. The doses of L-NNA attenuating significantly the protective effects of sucralfate were 25-50 mg/kg. The effects of L-NNA were reversed by the addition of L-arginine but not D-arginine. For comparison, the gastroprotective (but not hyperemic) effects of nocloprost were not affected by the pretreatment with L-NNA and/or arginine. Daily treatment with L-NNA (50 mg/kg per day) prolonged the healing of chronic gastric ulcers and significantly reduced the acceleration of healing by sucralfate.

CONCLUSIONS

We conclude that (i) the gastroprotective and hyperemic effects of sucralfate involve, at least in part, the NO-arginine pathway, (ii) the ulcer healing effects of sucralfate may also involve NO, probably through the hyperemia around the ulcer, and (iii) NO is not essential for the mucosal protection of PGE2 analog, but may account for the gastric vasodilatory effect of this PG.

Nitric oxide in gastroprotection by sucralfate, mild irritant, and nocloprost. Role of mucosal blood flow

Pretreatment with sucralfate is known to protect gastric mucosa against the damaging effect of strong irritants, and this protection is accompanied by an increase in mucosal blood flow but the mechanisms underlying these effects have not been elucidated. Similar gastroprotective and hyperemic effects can be obtained with exogenous prostaglandins (PG), mild irritants such as dilute ethanol, and by capsaicin. In this study we investigated the role of nitric oxide (NO) in the prevention of ethanol-induced gastric damage and gastric blood flow by sucralfate, mild irritant such as 20% ethanol, capsaicin, and nocloprost, a stable PGE2 analog. Pretreatment with NG-nitro-L-arginine (L-NNA), an inhibitor of NO synthase, enhanced ethanol-induced mucosal damage and reduced dose-dependently the gastroprotective and hyperemic effects of sucralfate, dilute ethanol, and capsaicin. The doses of L-NNA attenuating significantly the protective effects of sucralfate or 20% ethanol were 25-50 mg/kg, while those reducing the protection by capsaicin were 6.2-12.5 mg/kg. The attenuating effect of L-NNA on gastroprotection was reversed by L-arginine but not D-arginine. For comparison, the gastroprotective (but not hyperemic) effect of nocloprost was not affected by the pretreatment with L-NNA and/or arginine. We conclude that sucralfate, mild irritant, and capsaicin activate the NO system that may contribute to their gastroprotective effect through enhancing mucosal circulation but that NO is not essential for the mucosal protection by PGE2 analog.

Fibroblast growth factor in gastroprotection and ulcer healing: interaction with sucralfate

The study was designed to determine the gastroprotective and ulcer healing efficacy of basic transforming growth factor (bFGF) and to assess whether this peptide contributes to the action of sucralfate on the rat stomach. Application of human recombinant bFGF (1-100 micrograms/kg/hour subcutaneously) failed to affect the formation of acute gastric lesions induced by 100% ethanol and acidified aspirin but reduced the stress induced by gastric lesions. Sucralfate (100-200 mg/kg given orally) protected gastric mucosa against the ethanol, aspirin, and stress induced acute gastric lesions but the addition of bFGF (100 micrograms/kg subcutaneously or intragastrically) failed to affect sucralfate induced protection against ethanol or aspirin but increased that against stress. Administration of bFGF (3-300 micrograms/kg/day) by an intragastric or an intraperitoneal route or sucralfate (400 mg/kg/day) orally to rats with acetic acid induced gastric ulcers, enhanced the healing rate of these ulcers during seven day treatment in a dose dependent manner. This was accompanied by a pronounced increase in the number of capillaries and myofibroblasts and in DNA synthesis and DNA and RNA concentrations in the granulation tissue in the ulcer area. [125I]bFGF (1 microCi) applied subcutaneously or intragastrically accumulated in two to threefold higher amounts in the ulcer area than in the intact mucosa, particularly in rats treated with sucralfate. Concurrent treatment with indomethacin (2 mg/kg intraperitoneally) delayed ulcer healing and reduced the binding of labelled bFGF to the ulcer area, angiogenesis, and DNA synthesis by sucralfate. Addition of [125I]bFGF to sucralfate at various pHs resulted in the coprecipitation of bFGF by sucralfate in a pH dependent manner from about 10% at pH 7.0 to 90% at pH 1.5. Thus bFGF shows little protective activity and is not essential for gastroprotection afforded by sucralfate but plays an important part in healing of gastric ulcers possibly due to its growth promoting and angiogenic actions.

Nitric oxide in gastroprotection by aluminium-containing antacids

Pretreatment with aluminium-containing antacids at their original pH or after acidification is known to protect the gastric mucosa against the damaging action of strong irritants and this protection is accompanied by an increase in gastric blood flow (GBF) but the mechanisms underlying these effects have not been elucidated. We investigated the role of endogenous nitric oxide (NO) and prostaglandins (PS) in the prevention of ethanol-induced gastric damage and the alteration of GBF by Maalox and its active component Al(OH)3. Maalox and Al(OH)3 at their original and acidic pH induced dose-dependent gastroprotection accompanied by attenuation of the reduction in GBF caused by 100% ethanol; similar protective and hyperemic effects were recorded after treatment with nocloprost, a locally active PGE2 analog, and nitroglycerin, a donor of NO. Pretreatment with indomethacin that suppressed mucosal PGE2 by about 90%, failed to affect the protective influence of Maalox or Al(OH)3 at their original or acidic pH. On the contrary, pretreatment with NG-nitro-L-arginine (L-NNA), a potent selective inhibitor of NO synthase, reversed the gastroprotective and hyperemic effects of Maalox or Al(OH)3 at original and acidic pH and this reversal was significantly antagonized by L-arginine but not D-arginine. The gastroprotective and hyperemic effects of nocloprost were not influenced by the pretreatment with L-NNA. We conclude that aluminium-containing antacids activate the NO system, which may contribute to the gastroprotective activity of these drugs through an increase in mucosal microcirculation.

Role of nitric oxide and prostaglandins in sucralfate-induced gastroprotection

We investigated the role of nitric oxide (NO) and prostaglandins (PG) in the prevention by sucralfate of ethanol-induced gastric damage and the decrease of gastric blood flow and compared them with those obtained with nocloprost, a potent locally acting gastroprotective agent. Sucralfate and nocloprost given intragastrically (i.g.) protected dose dependently the gastric mucosa against the damage by absolute ethanol and prevented the decrease in blood flow induced by ethanol. Pretreatment with NG-nitro-L-arginine (L-NNA), an inhibitor of NO synthase decreased dose dependently the protection and the maintenance of blood flow provided by sucralfate but not by nocloprost. This decrease of sucralfate protection was antagonized by L-arginine but not D-arginine. Pretreatment with indomethacin also reversed, in part, the protective and hyperemic effects of sucralfate but the combination of both indomethacin and L-NNA completely abolished these effects. We conclude that sucralfate activates both the NO and PG systems that cooperate in the gastroprotective action of this drug and that NO is not involved in the protection induced by a PGE2 analog.