Adaptation of the gastric mucosa to repeated administration of aspirin in the rat

Adaptation of rat gastric tissue against indomethacin toxicity

Indomethacin is used in the treatment of inflammatory diseases. But the drug toxicity limits its usage. This study investigated whether adaptation occurred after various dosages of repeated (chronic) indomethacin in rats to the gastro-toxic effects of indomethacin. It also examined whether the adaptation was related to oxidant-antioxidant mechanisms and oxidative DNA damage in gastric tissue. To illuminate the adaptation mechanism in the gastric tissue of rats given various dosages of chronic indomethacin, the levels of oxidants and antioxidants (GSH, MDA, NO, SOD and MPO), activities of COX-1 and COX-2 enzymes and oxidative DNA damage (8-OHd Gua/10(5) Gua) were measured. Results were compared to 25-mg/kg single-dose indomethacin group, and the role of oxidant and antioxidant parameters and oxidative DNA damage in the adaptation mechanism was evaluated. The average ulcer areas of gastric tissue of the 0.5-, 1-, 2-, 3-, 4-, and 5-mg/kg dosages of chronic indomethacin given to rats were 19.5+/-3.7, 12.5+/-3.3, 10+/-5.2, 4.5+/-3.6, 8.6+/-2.4, and 9.5+/-2.1mm(2), respectively. This rate was measured as 21.3+/-2.6mm(2) in the single-dose indomethacin group. Consequently, after various dosages of repeated (chronic) indomethacin administration in rats, it was observed that a clear adaptation developed against gastric damage and that gastric damage was reduced. The best adaptation was observed in the gastric tissue of the 3-mg/kg chronic indomethacin group. In parallel with the damage reduction, the oxidant parameters (MDA and MPO) and oxidative DNA damage (8-OHd Gua/10(5) Gua) were reduced, and the antioxidant parameters (GSH, NO and SOD) were increased. There is no relation between COX enzymes and adaptation mechanism. This circumstance shows that not COX-1 and COX-2 enzymes, oxidant and antioxidant parameters may play a role in the adaptation mechanism.

Influence of prolonged exposure of a short half life non-steroidal anti-inflammatory drugs on gastrointestinal safety

AIMS

To test the influence of frequent concentration peaking, as occurs in multiple-dosing of non-steroidal anti-inflammatory drugs (NSAIDs) with short t (1/2), and duration of therapy of NSAIDs on gastrointestinal permeability.

METHODOLOGY

2.5 mg/(kg 12 h) flurbiprofen was administered as repeated oral and interperitoneal (i.p) doses or as i.p. osmotic pump (once implanted to mimic long t(1/2)) for 7 days to healthy rats. Urinary excretion of (51)Cr-EDTA (days 0, 1, 4 and 7 during all regimens) and sucrose (days 0, 1 and 7 for i.p. doses) were measured as markers of gastroduodenal and intestinal permeability, respectively.

RESULTS

Both i.p. regimens elevated (51)Cr-EDTA permeability suggestive of a systemic effect. There was no significant difference between the i.p regimens in (51)Cr-EDTA permeability. The first day (51)Cr-EDTA permeability was significantly higher for the oral than for the i.p. doses suggestive of a topcal effect. The effect became less potent with time despite continuous dosing indicating adaptation for both topical and systemic effects. None of the i.p. regimen altered sucrose permeability.

CONCLUSION

NSAID's potency to increase permeability reduces with time despite continuous dosing. Topical effect following oral dosing, and not the frequent peaking differentiates regimens from each other in elevating (51)Cr-EDTA permeability. The repeated dosing rather than the magnitude of t(1/2) may influence the gut safety profile of NSAIDs.

Efficacy of esomeprazole (20 mg once daily) for reducing the risk of gastroduodenal ulcers associated with continuous use of low-dose aspirin

OBJECTIVES

Low-dose aspirin is standard treatment for prevention of cardiovascular events in at-risk patients. However, long-term administration of low-dose aspirin is associated with a greater risk of adverse events, including gastroduodenal ulcers. This study determined the efficacy of esomeprazole for reducing the risk of gastric and/or duodenal ulcers and dyspeptic symptoms in patients receiving continuous, low-dose aspirin therapy.

METHODS

Patients aged > or =60 yr, without baseline gastroduodenal ulcer at endoscopy, who were receiving aspirin 75-325 mg once daily, were randomized to esomeprazole 20 mg once daily or placebo for 26 wk. The presence of endoscopic gastric and/or duodenal ulcers and esophageal lesions was assessed at weeks 8 and 26. Upper gastrointestinal symptoms were assessed at weeks 8, 16, and 26.

RESULTS

The intention-to-treat population comprised 991 patients (esomeprazole, N = 493; placebo, N = 498). Twenty-seven patients (5.4%) in the placebo group developed a gastric or duodenal ulcer during 26 weeks' treatment compared with eight patients (1.6%) in the esomeprazole group (life-table estimates: 6.2%vs 1.8%; P= 0.0007). At 26 wk, the cumulative proportion of patients with erosive esophagitis was significantly lower for esomeprazole versus placebo (4.4% and 18.3%, respectively; P < 0.0001). At 26 wk, esomeprazole-treated patients were more likely to experience resolution of heartburn, acid regurgitation, and epigastric pain (P < 0.05).

CONCLUSIONS

Esomeprazole 20 mg once daily reduces the risk of developing gastric and/or duodenal ulcers and symptoms associated with the continuous use of low-dose aspirin in patients aged > or =60 yr without preexisting gastroduodenal ulcers.

Incidence and predictors of upper gastrointestinal bleeding in patients receiving low-dose aspirin for secondary prevention of cardiovascular events in patients with coronary artery disease

AIM: The use of low-dose aspirin to prevent cardiovascular disease events is well established. However, the incidence and predictors of upper gastrointestinal bleeding (UGIB) with its use are unknown. We studied prospectively the incidence and outcome of peptic ulceration in low-dose aspirin users.

METHODS: A total of 991 patients with coronary artery disease (CAD) on low-dose aspirin were prospectively followed-up for two years for the occurrence and clinical features of first hospitalized episode of UGIB.

RESULTS: UGIB had a bimodal presentation with 45% occurring within four months of aspirin initiation and had an overall prevalence of 1.5% per year. There was no UGIB-related death. Hypertension (OR = 4.6, 95%CI 1.5 - 14.7, P = 0.009), history of peptic ulceration (OR = 3.1, 95%CI 1.1 - 9.0, P = 0.039), tertiary education (OR = 3.08, 95%CI 1.1 - 9.0, P = 0.039) and higher lean body mass (P = 0.016) were independent factors associated with UGIB. Use of nitrate did not reduce UGIB.

CONCLUSION: The incidence of UGIB in patients with CAD on long-term low-dose aspirin is low, but is accompanied with significant morbidity. With prolonged use of aspirin, UGIB continues to be a problem for those with risk factors and especially in patients with a history of peptic ulcers, in which UGIB tends to occur early after aspirin therapy.

Effect of fish oil on offensive and defensive factors in gastric ulceration in rats

The effect of fish oil (FO) derived from Scomberoides commersonianus containing omega-3 polyunsaturated fatty acids was studied on gastric ulcers and as well as on offensive and defensive factors in gastric mucosal damage, following experimental gastric ulceration. FO significantly reduced the severity of ulceration in gastric ulcers induced by aspirin, cold-restraint stress (CRS), alcohol, and pylorus ligation. The results also indicated the potentiality of FO in maintaining the integrity of gastric mucosa by virtue of its effect on both offensive and defensive gastric mucosal factors. It decreased the offensive acid-pepsin secretion and augmented the defensive factors like mucin secretion, cellular mucus and life span of mucosal cells following pylorus ligation. FO significantly increased activity of anti-oxidant enzymes (catalase and glutathione peroxidase) and decreased lipid peroxidation in gastric mucosa of CRS rats. The study indicates the beneficial role of FO in gastric ulceration by inhibition of offensive mucosal factors and oxidative stress, and augmentation of defensive mucosal factors.

Insights into the mechanisms of gastric adaptation to aspirin-induced injury: a role for regenerating protein but not trefoil peptides

The phenomenon of reduced gastric mucosal injury despite repeated doses of a damaging agent is termed adaptation. Adaptation to nonsteroidal anti-inflammatory drug-induced injury has been clearly demonstrated in both humans and experimental animals; however, the precise mechanisms remain unclear. We hypothesized that mediators of adaptation might be the regenerating protein (RegI) and the trefoil peptides TFF1 and TFF2, because these proteins play pivotal roles in gastric mucosal protection and repair. The gene expression and the protein levels of these proteins were measured and compared in normal, aspirin-injured, and aspirin-adapted rat stomachs. TFF gene and protein expression levels were similar in all three groups, whereas RegI gene expression and protein levels in adapted stomach were increased. A time course analysis of RegI expression during the onset and offset of adaptation showed that mucosal RegI increased during the development of adaptation, was maintained during subsequent aspirin dosing, and returned to baseline levels once dosing had ceased and adaptation was lost-indicative of a causal role in the adaptation process. Colocalization of increased RegI with gastric epithelial areas showing increased proliferation also suggests that RegI may be an important mediator of the resolution of mucosal injury that is characteristic of gastric adaptation to aspirin.

Selective cyclo-oxygenase-2 inhibitors: cardiovascular and gastrointestinal toxicity

The introduction of selective inhibitors of cyclo-oxygenase-2 to the marketplace has been much anticipated for several years. It would appear that these compounds have lived up to the expectations of having reduced gastrointestinal toxicity and, at least for some indications, of efficacy similar to that of conventional non-steroidal anti-inflammatory drugs. However, there is a growing body of evidence suggesting that cyclo-oxygenase-2 plays a very important role in gastrointestinal mucosal defence, particularly in situations in which the mucosa is damaged or inflamed. Moreover, physiological roles for cyclo-oxygenase-2 both in the renal and cardiovascular systems are becoming better recognized. Inhibition of cyclo-oxygenase-2 can lead to peripheral oedema and hypertension, and may promote thrombosis. Indeed, there is recent evidence of increased rates of myocardial infarction in arthritis patients taking a selective cyclo-oxygenase-2 inhibitor. Use of low-dose aspirin concurrently with use of a selective cyclo-oxygenase-2 inhibitor may provide some degree of protection against the potential cardiovascular toxicity of the latter but both laboratory and clinical studies suggest that the concomitant use of these two types of drugs results in gastrointestinal ulceration comparable to what is seen with conventional non-steroidal anti-inflammatory drugs. These recent results suggest that care must be exercised in the use of selective cyclo-oxygenase-2 inhibitors by individuals who are at increased risk of myocardial infarction and stroke, and the use of low-dose aspirin by these patients may place them at increased risk of gastrointestinal complications.

NSAIDs induce both necrosis and apoptosis in guinea pig gastric mucosal cells in primary culture

A major clinical problem encountered with the use of nonsteroidal anti-inflammatory drugs (NSAIDs) such as indomethacin is gastropathy. In this study, we examined, using guinea pig gastric mucosal cells in primary culture, how NSAIDs damage gastric mucosal cells. The short-term treatment of cells with high concentrations of indomethacin decreased cell viability in the absence of apoptotic DNA fragmentation, chromatin condensation, or caspase activation. Cells lost membrane integrity with this short-term indomethacin treatment, suggesting that indomethacin induced necrosis under these conditions. In contrast, the long-term treatment of cells with low concentrations of indomethacin decreased cell viability and was accompanied by apoptotic DNA fragmentation, chromatin condensation, and caspase activation. Pretreatment of cells with inhibitors of caspases or protein synthesis suppressed cell death caused by long-term indomethacin treatment, suggesting that apoptosis was induced when the inhibitors were not present. These results imply that NSAIDs cause gastric mucosal damage through both necrosis and apoptosis of gastric mucosal cells.

Resistance to apoptosis is a mechanism of adaptation of rat stomach to aspirin

Adaptation of the gastric mucosa to nonsteroidal anti-inflammatory drug-induced injury is a well-documented phenomenon, but the mechanisms are not known. We investigated whether changes in stress protein expression and apoptosis play roles in adaptation of rat stomach to aspirin. RT-PCR and Western blotting techniques were used to analyze mRNA and protein expression of HSP72 and HSP90 and cleavage of caspase 3 protein. Apoptosis was detected by the TUNEL method and quantified. HSP72 mRNA and protein expression was unchanged in adapted mucosa, whereas HSP90 mRNA and protein levels decreased. Caspase 3 protein was activated, and the number of apoptotic cells increased in mucosa after one aspirin dose. However, in adapted mucosa after aspirin, activated caspase 3 and the number of apoptotic cells had returned to basal levels. Induction of the stress response was found not to be a mechanism of mucosal adaptation against multiple doses of aspirin. Our results lead us to propose instead that resistance to aspirin-induced apoptosis plays a role in the protective phenomenon of adaptation.

Activation of genes for spasmolytic peptide, transforming growth factor alpha and for cyclooxygenase (COX)-1 and COX-2 during gastric adaptation to aspirin damage in rats

BACKGROUND

NSAIDs, such as aspirin (ASA), cause widespread mucosal damage, but repeated ASA insults appear to induce mucosal tolerance (adaptation) to this injury. The mechanism of the gastric adaptation to the damage induced by ASA has not been fully explained.

AIM

To determine the role of the mucosal gene expression for spasmolitic peptide (SP) (a member of trefoil peptides) and transforming growth factor alpha (TGF alpha) as well as for cyclooxygenase (COX)-1 and COX-2 during gastric adaptation to ASA in rats.

METHODS

Gastric lesions were produced by ASA (100 mg/kg in 1.5 mL of 0.2 M HCl) applied intragastrically (i.g.) as a single dose. every day for 5 days. Control rats were given 1.5 mL of vehicle (0.2 M HCl i.g.) as a single dose, during 5 consecutive days. Gastric blood flow (GBF) was measured by H2-gas clearance technique and gastric mucosal specimens were taken for the assessment of cell proliferation rate in gastric mucosa by bromodeoxyuridine (BrdU) uptake, mucosal generation of prostaglandin E2 measured by radioimmunoassay, and for expression of SP, TGF alpha COX-1 and COX-2 mRNA as determined by RT-PCR. To quantify the relative amounts of mRNA for SP and TGF alpha, southern blotting analysis of the PCR products was performed and the intensity of PCR products was compared with that of beta-actin used as a standard.

RESULTS

ASA applied once produced numerous gastric erosions, but with repeated ASA doses the adaptation to this NSAID developed, the area of gastric lesions being reduced by 86% after six consecutive ASA insults. This adaptation to ASA was accompanied by approximately a 90% reduction in prostaglandin E2 biosynthesis, by a significant rise in BrdU uptake by glandular cells predominantly in the neck region of gastric glands and by expression of SP (SP/beta-actin ratio; 0.96 +/- 0.08 in ASA-adapted mucosa vs. 0.38 +/- 0.05 in the control mucosa) and TGF alpha (TGF alpha/beta-actin ratio: 0.97 +/- 0.07 in ASA-adapted mucosa vs. 0.77 +/- 0.06 in the control mucosa). COX-1 expression was detected in vehicle-control gastric mucosa and after single exposure to ASA or after six consecutive ASA insults, while COX-2 mRNA was not detected in vehicle-control gastric mucosa, but appeared after single ASA insult and was sustained after subsequent ASA doses.

CONCLUSIONS

(i) Gastric adaptation to aspirin injury involves enhanced cell proliferation which appears to be mediated by increased expression of SP and TGF alpha, and (ii) rapid upregulation of COX-2 expression following single and repeated ASA insults may represent a compensatory response to suppression of prostaglandin generation by this NSAID.

Adaptation of the gastric epithelium to injury is maintained in vitro and is associated with increased TGF-alpha expression

Adaptation is the name given to the progressive decrease in gastric mucosal damage following repeated dosing with damaging agents. This study aimed to determine whether adaptation is an intrinsic property of the gastric epithelium and the role in the development of this process of TGF alpha. Rats were given either one or six daily doses of 10 mg/kg diclofenac or six daily doses of vehicle only (1% methylcellulose). On the 7th day, antral mucosa was taken for organ culture and loaded with [51Cr]. Explants were challenged with ethanol and damage quantified by [51Cr] release. In a separate experiment, rats were dosed as above and the gastric mucosa was extracted and TGF alpha quantified by RIA. The rate of [51Cr] release was significantly lower after ethanol injury in explants from rats previously adapted to diclofenac (9.2 +/- 2.5%) compared with those exposed to a single damaging dose of diclofenac (25.9 +/- 3.5%) or vehicle only (26.4 +/- 3.3%; P < 0.01; ANOVA). The concentration of TGF alpha was significantly higher in the gastric epithelium of rats adapted to diclofenac than other groups (P < 0.05; t-test). Cross adaptation of the gastric mucosa to injury has therefore been demonstrated in antral mucosal explants in organ culture while TGF alpha peptide expression is elevated in the adapted gastric mucosa. These findings suggest that adaptation is an inherent property of the gastric epithelium and it is likely that TGF alpha may play a role in its maintenance.

Gastric adaptation to aspirin and stress enhances gastric mucosal resistance against the damage by strong irritants

BACKGROUND

Gastric mucosal adaptation to injury induced by repeated application of aspirin (ASA) or stress is a well-documented phenomenon, but it is known whether such adaptation affects the mucosal tolerance to other strong irritants.

METHODS

In this study gastric adaptation was induced by repeated daily administration of acidified ASA for 4 consecutive days (Series A) or by 3.5H of water immersion and restraint stress (WRS) applied every other day for up to 8 days (series B). When the adaptation to ASA or WRS was fully developed, rats of series A and B were challenged with strong irritants such as 100% ethanol, 200 mM acidified taurocholate (TC), or 25% NaCl for 1 h or with WRS for 3.5 h.

RESULTS

ASA or WRS applied once produced numerous gastric lesions and deep histologic necrosis accompanied by a decrease in gastric blood flow. With repeated application of ASA or stress the mucosal adaptation to ASA and WRS developed; the area of gastric lesions was reduced by 86% and 56%, respectively, and this was accompanied by a marked decrease of superficial and deep necrosis, and increase in gastric blood flow (GBF) and the enhancement of mucosal regeneration. An increase in mucosal and luminal contents of epidermal growth factor (EGF) and in mucosal expression of EGF receptors was also observed in the mucosa adapted to ASA or stress. In rats adapted to ASA or stress and then challenged with 100% ethanol, 200 mm TC, 25% NaCl, stress or ASA, the areas of macroscopic gastric lesions and deep histologic necrosis were remarkable reduced as compared with those in non-adapted vehicle-treated rats. This was also accompanied by a significant decrease in (GBF), a marked increase of mucosal and luminal contents of EGF and expression of its receptors, and enhanced mucosal cell proliferation.

CONCLUSIONS

Gastric adaptation to ASA or stress enhances mucosal resistance to the injury induced by strong irritants, and this appears to be mediated by mucosal regeneration, probably resulting from increased luminal and mucosal contents of EGF and excessive expression of its receptors.

Gastric mucosal adaptation to diclofenac injury

Adaptation occurs to the gastric injury produced by nonsteroidal antiinflammatory drugs during continued dosing. The aim of this study was to identify characteristics of this phenomenon that might help in the search for underlying mechanisms. The time frame for onset and offset of adaptation of diclofenac (damage assessed planimetrically) was examined in rats. Adaptation to oral diclofenac took three to five days to develop, and persisted for up to five days after the last dose. It was also demonstrable after subcutaneous dosing or when injury was measured by a change in mucosal potential difference. Diclofenac-adapted rats were protected against injury induced by subsequent exposure to ethanol, indomethacin, aspirin, or piroxicam, indicating that adaptation is not specific to injury by the adapting agent. This cross-adaptation was dose-dependent and characterized histologically by a reduction in deep damage. In conclusion, gastric adaptation to diclofenac is mediated by mechanisms that take several days to develop and be lost. The route of administration appears to be unimportant, but the development of both adaptation and cross-adaptation is influenced by dosage size.

Gastric microbleeding following single and repeated dosing with naproxen

BACKGROUND

Adaptation to gastric damage from nonsteroidal anti-inflammatory drugs (NSAID) has been observed during ongoing dosage in rats and humans. However, this does not always occur, and our previous data suggest that NSAID half-life may be a determining factor.

AIM

To investigate whether adaptation occurs during 1 week of naproxen administration in humans.

SUBJECTS

Thirteen healthy volunteers were studied at baseline, and after one or seven daily doses of naproxen 750 mg. Gastric microbleeding was measured 4 h after naproxen in gastric washings collected during a 30-min period. Serum thromboxane B concentrations were also assayed, as a marker of cyclo-oxygenase inhibition.

RESULTS

Mean blood loss after placebo was 0.60 microL/10 min (95% CI: 0.21-0.98). This rose to 2.15 (0.73-3.57) and 1.75 (0.74-2.76) microL/10 min after one and seven daily doses of naproxen, respectively (P < 0.05 vs. baseline; day 1 vs. 7 not significant). Thromboxane B concentrations were < 10% of control at both day 1 and 7 of dosing.

CONCLUSION

In accord with our findings in rats, adaptation to this moderately long acting NSAID in humans was not apparent. We conclude that any adaptation to naproxen is unlikely to be clinically important.

Role of luminal ammonia in the development of gastropathy and hypergastrinemia in the rat

BACKGROUND/AIMS

Chronic infection with Helicobacter pylori causes persistent elevations in gastric juice ammonia levels. Thus, we studied the effects of experimentally induced increases in gastric juice ammonia levels on gastric structure and function and gastrin homeostasis.

METHODS

Rats were fed either normal chow or the diet supplemented (20 g/dL) with ammonium or sodium acetate.

RESULTS

Long-term dietary ammonium loading for 2 weeks or longer resulted in a 1.5-2-fold increase in the weight and mucosal thickness of the stomach and proximal duodenum with evidence of mild gastritis and enterochromaffinlike cell hyperplasia. The ammonium-containing diet also induced a significant 2-3-fold increase in both circulating gastrin levels of fed rats and an increase in the postprandial gastrin responses over control values. Antral gastrin levels were also markedly elevated by long-term ingestion of the test diet, which was increased 3-4-fold over control values in fasted animals and less so after meal stimulation. Consistent with these findings, gastrin-specific messenger RNA was increased 2.5-3-fold in the antrum of ammonium fed rats, whereas actin-specific messenger RNA was not affected or decreased. Animals fed a diet supplemented with 20 g/dL sodium acetate sustained modest increases in mucosal thickness and serum and antral gastrin concentration, suggesting that nonspecific gastric injury and inflammation is also a factor that influences G-cell function.

CONCLUSIONS

Long-term exposure of the antral mucosa to elevated levels of ammonia in the gastric juice in the presence of gastritis, conditions similar to that occurring in subjects infected with H. pylori, seem to be causative factors in the development of G-cell hyperfunction.

Gastric adaptation to stress: role of sensory nerves, salivary glands, and adrenal glands

BACKGROUND

Single exposure to water immersion and restraint stress (WRS) in rats produces acute gastric mucosal damage, but repetitive WRS insults lead to gastric adaptation to stress ulcerogenesis. This study was designed to assess the mechanism of this adaptation, particularly the role of sensory nerves, salivary glands, adrenal glands, and gastric acid secretion.

METHODS

WRS was applied for a standard period of 3.5 h, either once or repeated every other day for up to 8 days in intact rats and in animals with capsaicin-induced deactivation of sensory nerves, vagotomy, salivectomy, adrenalectomy, and inhibition of gastric acid secretion by H2-blocker.

RESULTS

WRS applied once produced multiple gastric erosions accompanied by a significant increase in gastric acid secretion and a decrease in gastric blood flow (GBF) and DNA synthesis. Repeated WRS insults resulted in a significant decrease in the number of gastric lesions, reaching a maximum after four consecutive exposures to WRS. This adaptation to stress ulcerogenesis was accompanied by a decrease in gastric acid secretion and an increase in GBF and mucosal generation of DNA synthesis. Salivectomy, which decreased the luminal content of epidermal growth factor (EGF) (by about 80%), markedly attenuated this adaptation, and this was reversed by the addition of exogenous EGF. Capsaicin-induced ablation of sensory nerves eliminated gastric adaptation to WRS, and this was accompanied by a significant decrease in the GBF, but pretreatment with calcitonin gene-related peptide restored gastric adaptation to stress in capsaicin-denervated rats. Selective vagotomy and adrenalectomy failed to affect gastric adaptation to WRS, whereas gastric acid inhibition by ranitidine enhanced this adaptation.

CONCLUSIONS

The stomach is able to adapt to repeated stress insults by enhancing GBF and DNA synthesis, and this adaptation is mediated, at least in part, by sensory nerves and EGF.

Mucosal adaptation to aspirin induced gastric damage in humans. Studies on blood flow, gastric mucosal growth, and neutrophil activation

The gastropathy associated with the ingestion of non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin is a common side effect of this class of drugs, but the precise mechanisms by which they cause mucosal damage have not been fully explained. During continued use of an injurious substance, such as aspirin, the extent of gastric mucosal damage decreases and this phenomenon is named gastric adaptation. To assess the extent of mucosal damage by aspirin and subsequent adaptation the effects of 14 days of continuous, oral administration of aspirin (2 g per day) to eight healthy male volunteers was studied. To estimate the rate of mucosal damage, gastroscopy was performed before (day 0) and at days 3, 7, 14 of aspirin treatment. Gastric microbleeding and gastric mucosal blood flow were measured using laser Doppler flowmeter and mucosal biopsy specimens were taken for the estimation of tissue DNA synthesis and RNA and DNA concentration. In addition, the activation of neutrophils in peripheral blood was assessed by measuring their ability to associate with platelets. Aspirin induced acute damage mainly in gastric corpus, reaching at day 3 about 3.5 on the endoscopic Lanza score but lessened to about 1.5 at day 14 pointing to the occurrence of gastric adaptation. Mucosal blood flow increased at day 3 by about 50% in the gastric corpus and by 88% in the antrum. The in vitro DNA synthesis and RNA concentration, an index of mucosal growth, were reduced at day 3 but then increased to reach about 150% of initial value at the end of aspirin treatment. It is concluded that the treatment with aspirin in humans induces gastric adaptation to this agent, which entails the increase in mucosal blood flow, the rise in neutrophil activation, and the enhancement in mucosal growth.

Role of neutrophils and mucosal blood flow in gastric adaptation to aspirin

Gastric mucosa adapts to ulcerogenic action of aspirin but the mechanism of this phenomenon is unknown. In this study, acute gastric lesions were produced by single or repeated oral administration of acidified aspirin in rats with intact or deactivated (by capsaicin) sensory nerves and with intact or suppressed synthase of nitric oxide (NO). Single oral dose of aspirin produced a dose-dependent increase in the area of gastric lesions accompanied by a significant increase in blood neutrophils, neutrophil infiltration into the mucosa, leukotriene B4 formation and almost complete suppression of prostaglandin synthesis. After repeated administration of aspirin, the mucosal damage progressively declined and this was accompanied by a significant augmentation in gastric blood flow. In addition, a reduction in blood neutrophil count, mucosal neutrophil infiltration and leukotriene B4 release was observed during this adaptation of the stomach to repeated aspirin insults. Capsaicin denervation of sensory nerves aggravated the damage induced by the first exposure of the stomach to aspirin and caused a significant reduction in gastric blood flow, but with repeated aspirin administration, gastric adaptation to this agent and a rise in gastric blood flow were observed. Pretreatment NG-nitro-L-arginine with (L-NNA), a specific inhibitor of nitric oxide synthase, eliminated the hyperemic response to repeated aspirin insults but failed to affect the adaptation to aspirin. We conclude that the rat stomach adapts readily to repeated aspirin insults despite sustained inhibition of prostaglandin biosynthesis and this adaptation appears to be mediated by a significant increase in gastric blood flow and a reduction in neutrophil activation and leukotriene B4 release.

Review article: controversies in NSAID-induced gastroduodenal damage--do they matter?

BACKGROUND

This article reviews various issues surrounding NSAID-induced gastroduodenal ulceration, about which there appear to be conflicting views and data in the literature. These issues include the size, clinical relevance and main site of the problem; when complications occur (early or late?); the relevance of non-ulcer lesions and whether adaptation is a clinically relevant phenomenon.

METHOD

A comprehensive literature search was carried out to identify relevant new data published since 1987.

RESULTS

NSAIDs are causally associated with more gastric than duodenal ulcers but their use may be associated with duodenal ulcers or complications. Erosive lesions may progress to more severe damage. The theories of early or late onset of complications during a course of NSAID therapy may not be mutually exclusive.

CONCLUSIONS

Available data indicate that NSAID ulcers are at least as dangerous as classic peptic ulcers, and result in significant morbidity and mortality which in the patient population does not appear to be significantly reduced by processes such as adaptation.

Gastric mucosal defensive factors: the therapeutic strategy

There are several interesting approaches to augmenting defence or repair mechanisms that can be used already or may find a place in therapy for ulcer disease. Factors such as epidermal growth factor and basic fibroblast growth factor show potential. Alternative strategies might be to stimulate mucosal blood flow with agents that release nitric oxide (NO), or to scavenge free radicals in the inflamed or ischaemic mucosa. If such approaches are to find a role in therapy, it is likely that it will be restricted: perhaps for the treatment of refractory ulcers, or for prophylaxis of stress ulceration. This is because most ulcers in future are likely to be healed with tolerable and high efficacy acid-inhibiting drugs then have their recurrence prevented by regimens that eradicate Helicobacter pylori. The most important current indication for concentrating on enhancing mucosal defences is for managing non-steroidal anti-inflammatory drug (NSAID)-induced ulcers. There is no clear advantage in using a defence-enhancing agent (rather than an acid suppressant) to heal an NSAID ulcer if the NSAID can be stopped. The main value of prostaglandins is for prophylaxis of NSAID ulcers in those patients who need ongoing treatment with NSAID. For cost-benefit reasons, prostaglandins should probably be used mainly for those at high risk of NSAID complications, and there has been progress in identifying these. Another interesting approach is aimed at clarifying mechanisms of gastric adaptation to NSAID, so that we might be able to design drugs and dosing regimens to maximize this phenomenon.

Adaptation of rat gastric mucosa to repeated doses of non-salicylate non-steroidal anti-inflammatory drugs

To determine whether gastric mucosal adaptation occurs to the damaging effects of repeated non-steroidal anti-inflammatory drug (NSAID) administration, we compared the extent of gastric damage in rats after single or repeated doses of four non-salicylate NSAID. With daily dosing, adaptation occurred only to repeated doses of the short-acting NSAID ibuprofen and diclofenac but not to indomethacin and naproxen, both of which have considerably longer half-lives. Adaptation to indomethacin was demonstrable if the dosage interval was lengthened and the drug was given on alternate days rather than daily. Histological examination of the gastric mucosa of diclofenac-treated rats showed a similar degree of superficial damage in the single and repeatedly dosed groups. However there was a highly significant reduction in the amount of deeper mucosal damage in the repeatedly dosed rats. Our findings show that under certain conditions of dosage, adaptation to non-salicylate NSAID is demonstrable. The pharmacokinetics of individual NSAID appear to be important in determining whether or not adaptation occurs. Histological examination showed that adaptation to one of the shorter acting NSAID, diclofenac, was characterized by a significant reduction in deeper mucosal damage.

Effects of chronic superficial injury on the rat gastric mucosa

The effects of chronic superficial injury on the stomach were studied in rats dosed with a mild irritant (2 mol/L NaCl intragastrically) every 48 hours for 1 month followed by 1-month recovery. A single exposure to this mild irritant induced gross protection against 6 mol/L NaCl for 1 but not 2 days. Leukotriene C4 (LTC4) levels increased slightly. Prostaglandin E2 (PGE2) concentration was unchanged. After 2-week dosing, protection was concomitant with markedly elevated PGE2 concentration. LTC4 values remained unchanged. Superficial epithelial cells were more resistant to damage. After 4-week dosing, protection occurred at 1 but not 2 days after the dose with an inverse correlation of PGE2. LTC4 concentration increased significantly at both times. Chronic injury for 1 month did not alter rapid epithelial restitution or PGE2 and LTC4 released 15 minutes after challenge with 6 mol/L NaCl. The recovery period showed loss of protection. PGE2 values returned to control levels but LTC4 values remained slightly elevated. It is concluded that short- or long-term (4-week) "adaptive cytoprotection" is not mediated by endogenous PGE2. Only extremely high levels of LTC4 correlated with loss of protection. The role of the more resistant superficial epithelium remains unknown.

Effects of nonsteroidal anti-inflammatory drugs and misoprostol on gastroduodenal epithelial proliferation in arthritis

In this study, quantitation of the epithelial proliferation status of gastric glands and duodenal crypts was performed using endoscopic biopsy specimens from patients with rheumatological conditions requiring long-term anti-inflammatory and analgesic therapy, testing the hypothesis that long-term administration of nonsteroidal anti-inflammatory drugs (NSAIDs) may lead to enhanced epithelial cell proliferation in the stomach and duodenum. After a 1-week washout period from NSAID administration, specimens were taken from endoscopically normal gastric antrum and duodenum, and microdissection was used to quantitate mitoses in these sites. Endoscopy and biopsy were then repeated after 2 weeks of NSAID administration, during which patients received in addition either the prostaglandin E1 analogue misoprostol (10 patients) or a placebo (10 patients). Mitotic counts in gastric glands increased similarly and significantly in the two groups from (mean +/- SEM) 4.45 +/- 0.57 to 7.69 +/- 1.08 (P less than 0.001) in the NSAID+placebo-treated group and from 4.31 +/- 0.53 to 7.68 +/- 1.08 (P = 0.006) in the NSAID+misoprostol-treated group. Similar changes took place in the duodenal crypts, from 5.44 +/- 0.68 to 8.60 +/- 1.28 (P = 0.013) in the NSAID+placebo-treated group and from 4.68 +/- 0.56 to 6.35 +/- 0.63 (P = 0.011) in the NSAIDs+misoprostol-treated group. NSAIDs increased the proportion of glands and crypts with bifid or more complex architectural forms. In a small group of patients, misoprostol alone did not alter mitotic rate in glands or crypts over 4 weeks. Thus, NSAIDs increase the rate of proliferation in endoscopically normal gastric and duodenal epithelium of patients with arthritis. This may form one of the mechanisms underlying gastric and duodenal adaptation to NSAIDs.

Gastric adaptation to nonsteroidal anti-inflammatory drugs in man

Adaptation describes the phenomenon in which visible gastric mucosal injury lessens or resolves completely despite continued administration of an injurious substance such as aspirin. Adaptation occurs in man although the mechanism remains unclear. Recent evidence suggests increased cell proliferation and correction of nonsteroidal anti-inflammatory drug induced reduction in gastric blood flow as possibly being important. Gastric erosions and ulcers in chronic nonsteroidal anti-inflammatory drug users represent failed adaptation. Gastric erosions and ulcers in chronic nonsteroidal anti-inflammatory drug users represent failed adaptation. The factors responsible for failure of adaptation are unknown but one clue is that there appears to be a dose-response effect relating anti-inflammatory dose and effectiveness of adaptation (i.e., adaptation is delayed, or less effective, when higher anti-inflammatory doses are administered). Gastric adaptation can be enhanced by co-therapy with synthetic prostaglandins but not with sucralfate or H2-receptor antagonists.

Adaptation of the gastric mucosa to stress. Role of prostaglandin and epidermal growth factor

This study was designed to determine whether repeated exposures to stress lead to the adaptation of the gastric mucosa to stress ulcerogenesis. Wistar rats with intact or resected salivary glands were exposed to a standard period (3.5 h) of water-immersion and restraint stress every other day up to 8 days. The significant reduction in the severity of gastric lesions was first noticed after the second exposure to stress and was maximal after 6-day exposures to stress. This tolerance to stress ulcerogenesis disappeared after a 6-day rest during which animals were not exposed to stress. Histologically, the hemorrhages and edema seen after a single stress were less frequent during adaptation; instead the mucosa regenerated in spite of continuation of exposure to stress. During adaptation, the mucosal blood flow (MBF) and mucosal biosynthesis of PG were markedly increased. Administration of indomethacin (5 mg/kg i.p.) completely abolished gastric adaptation to stress and this was accompanied by about 85% reduction in mucosal generation of PG and significant decrease in the MBF. Salivectomy, which significantly reduced the luminal contents of epidermal growth factor (EGF) in the stomach, delayed and reduced the adaptation. We conclude that the stomach has the ability to adapt to repeated exposures to stress and that this adaptation is mediated, at least in part, by endogenous PG and EGF.

Prostaglandins in the gut and their relationship to non-steroidal anti-inflammatory drugs

Prostaglandins are long-chain, saturated, oxygenated fatty acids. Relatively large quantities of prostaglandins have been found in gut mucosa, suggesting that these substances play an important role in gastrointestinal physiology. Non-steroidal anti-inflammatory drugs (NSAIDs) cause damage to the gastric, intestinal, and colonic mucosa in experimental animals and in humans. Prostaglandins protect the gastric mucosa against injury induced by NSAIDs, and this property has been labelled cytoprotection. The mechanisms of cytoprotection have been extensively evaluated and are probably multifactorial, including effects on the gastric mucosal barrier, gastric blood flow, mucus, bicarbonate, and fluid section, ionic transport, cyclic AMP, and surface-active phospholipids. Prostaglandins may also prevent NSAID-induced injury in the small intestine and colon. The mechanisms responsible for prostaglandin protection in the lower gut against injurious agents are unknown. Further studies of the role of prostaglandins in the gut and their relationship to the effects of NSAIDs are needed. The results of these investigations may lead to a better understanding of the importance of prostaglandins in the physiology of the gastrointestinal tract, and may provide information regarding actions of NSAIDs on the functional integrity of the gastric, intestinal, and colonic mucosa.

Lack of gastric mucosal protection by sucralfate during long-term aspirin ingestion in humans

The ability of sucralfate to prevent gastric mucosal erosions caused by long-term aspirin ingestion was studied in 19 normal human subjects. A placebo-controlled, double-blind, crossover design was used to study the capacity of 4 g sucralfate daily to lessen the noxious effect on gastric mucosa of 3.6 g aspirin daily for 14 days. Gastric mucosal injury was assessed by endoscopic scoring of erosions. There was no significant difference in mean erosion scores or the degree of partial mucosal protection between the two groups. It was concluded that sucralfate lacks a mucosal protection capacity at the dosage studied in human subjects ingesting large doses of aspirin over a two-week period.

Aspirin-induced human antral injury is reduced by vodka pretreatment

Mild irritants have been shown to protect the rat gastric mucosa against noxious agents. This study was designed to test the protective potential of low-dose ethanol against acetylsalicylic acid (ASA) -induced gastric injury. Ten healthy volunteers who were nondrinkers and had normal baseline upper gastrointestinal endoscopy participated in a randomized double-blind crossover study. Thirty minutes after either vodka (37.5 ml) in tomato juice or tomato juice alone, each subject took 975 mg ASA and then underwent endoscopy 1 hr later. The degree of mucosal injury was scored, and blood was taken for ethanol and salicylate levels. There was a washout interval of seven days between the two treatments. Endoscopic scores were analyzed using the sign test. After a single dose of ASA, mucosal injury was confined to the fundus and antrum, while the duodenum was minimally affected. A significant reduction in antral damage was seen with ethanol pretreatment (P less than 0.05). The same trend was evident in the fundus but did not achieve statistical significance. Serum salicylate levels averaged 13.2 +/- 0.8 mg/100 ml and were not different between the two treatments. Ethanol concentration ranged from 1.1 to 6.2 mmol/liter following the vodka drink and was 0 after the placebo.

Evidence that adaptive cytoprotection in rats is not mediated by prostaglandins

We investigated the proposition that adaptive cytoprotection (enhanced gastric mucosal integrity) caused by exposure to 20% ethanol in rats is mediated by endogenous prostaglandin synthesis. Experiments were performed both without and with indomethacin sufficient to inhibit ex vivo release of prostaglandin E2 by 56% +/- 9% (2.5 mg/kg) or 86% +/- 4% (10 mg/kg). Twenty percent ethanol significantly reduced both macroscopic and histologic signs of injury caused by subsequent exposure to 100% ethanol whether or not the rats were pretreated with indomethacin. Twenty percent ethanol itself caused extensive superficial disruption of the surface epithelium, so that about half of the mucosa was covered by desquamated debris, but did not stimulate prostaglandin release. We conclude that adaptive cytoprotection still occurs after doses of indomethacin sufficient to cause a profound depression of prostaglandin E2 release. The possibility that it could be due to formation of a protective covering of surface debris is worth further investigation.

Mechanism of gastrointestinal toxicity of NSAIDs

Non-steroidal anti-inflammatory drugs (NSAIDs) can damage the gastrointestinal tract, mainly the stomach, by a local effect and by systemic interactions with prostaglandin synthesis. A local damaging effect was first suggested by Davenport, who demonstrated that aspirin, at an acid pH, enters the gastric mucosa by non-ionic diffusion, leading to a disruption of the gastric barrier and subsequent back-diffusion of hydrogen ions into the mucosa. Consequently, this leads to local haemorrhage and cell necrosis. Systemic damage is thought chiefly to occur by inhibition of prostaglandin synthesis, with consequent interaction of the defensive functions of the gastric mucosa. Inhibition of cyclo-oxygenase is the specific target of NSAIDs. However, the lipoxygenase pathway is also affected indirectly since cyclo-oxygenase inhibition results in a spill-over effect of leukotrienes, as both prostaglandins and leukotrienes are produced from arachidonic acid. Indeed, leukotriene B4, an extremely potent vasoconstrictor, may be responsible for some of the NSAID damage. In addition, cyclo-oxygenase inhibition blocks the integrity and synthesis of mucus, the secretion of bicarbonate and profoundly changes the life cycle of gastric mucosal cells. Following acute NSAID medication, the overall cell migration from the proliferative zone to the surface is accelerated and cell shedding is increased. However, during prolonged NSAID treatment, adaptation to the noxious effects of NSAIDs can occur with increased cell reproduction and subsequent compensation of the initially increased cell loss.

Review: acute human models of gastric mucosal injury

The use of acute human models of gastric mucosal injury has been stimulated by a need to understand more fully the problems of non-steroidal anti-inflammatory drugs but such models have other applications. None is ideal and they all share certain drawbacks. For none of them has a precise relationship to clinical events been established and they have all tended to be employed on a population of young healthy subjects who are not those at greatest clinical risk. Of individual methods mucosal potential difference is an indirect measure which is too often affected by other influences to be acceptable as a measure of mucosal injury when used alone, although it has some value as an adjunct to other measurements. Assay of DNA in gastric washings is a suitable technique for quantifying desquamation of gastric epithelial cells occurring in response to acute injury; on present evidence its significance is much more difficult to assess in the context of continuing challenge over several days. By contrast, measurement of microbleeding is more suitable for quantifying injury over several days of NSAID ingestion; little bleeding is recorded with a single acute challenge. Endoscopy can demonstrate macroscopic lesions which result from mucosal injury--injury which is quantified more easily and sensitively by measurements of cellular exfoliation or bleeding. Paradoxically, endoscopy's strength has been to underline the scientific weakness of acute models because it shows that it is rare for ulcers, which are the lesions of clinical concern to develop in these studies.

Molecular weight of gastric mucus glycoprotein is a determinant of the degree of subsequent aspirin induced chronic gastric ulceration in the rat

Mucus was sampled from the gastric mucosal surface of anaesthetised rats. Three weeks later these rats were orally dosed each day with aspirin (375 mg/kg) for six months. Then the number and size of the aspirin induced chronic gastric ulcers were assessed. Gel filtration chromatography of the mucus samples showed that mucus glycoprotein was present in both high and low molecular weight forms. There was a natural variation between individual rats in the percentage of glycoprotein in the high molecular weight form (mean = 58.9%; SD = 9.6%; n = 23). This variation correlated strongly with the degree of subsequent aspirin induced chronic gastric ulceration (r = -0.85, p less than 0.001). This is the first time that a pre-existent variability in a mucosal defence factor has been shown to predict susceptibility of the stomach to chronic ulceration.

Ethanol-induced cell damage in cultured rat antral mucosa assessed by chromium-51 release

We have developed an in vitro method for studying ethanol-induced injury to gastric mucosa using organ culture of rat antrum. Cell damage was assessed by measurement of the release of [51Cr]sodium chromate from preloaded cells, a method adapted from a standard immunologic technique. This system provided rapid and highly reproducible quantitation of tissue injury as assessed by 51Cr release into the culture medium. The threshold concentration for ethanol-induced damage was between 10 and 15% v/v, similar to in vivo thresholds observed by others. 51Cr release could also be induced by very short exposure to ethanol (5-15 min), and then continued despite ethanol removal. Interestingly, after continuous ethanol exposure, a plateau of maximum 51Cr release was reached 60 min after exposure to ethanol over the concentration range 20-50%, suggesting tissue adaptation to ethanol damage. This organ culture system, which allows precise control of experimental conditions, may be useful for studying mechanisms of gastric mucosal injury and protection.

Effects of prolonged treatment with compound 48/80 on the gastric mucosa and mast cells in the rat

Effects of prolonged administration of compound 48/80 (48/80) on the gastric mucosa, serotonin and histamine levels in serum, and mast cells of rats were studied. Daily administration of 48/80 (0.75 mg/kg, i.p.) for 2 or 4 days produced widespread gastric lesions. Further administration of the agent for up to 12 days did not aggravate the lesions which had developed in the early period of administration of the drug. There were only a few visible lesions and numerous healed ones. Almost the same phenomenon was observed with the daily administration of serotonin plus histamine (10 mg/kg each, i.p.) for 2 to 12 days. While 48/80 given for 2 or 4 days increased serotonin and histamine levels in serum, it induced no appreciable increase of these amines after 8 or 12 days of treatment. Serotonin and histamine levels in peritoneal mast cells significantly decreased after the treatment with 48/80 over a 4 day period. The decrease in gastric lesions after prolonged treatment with 48/80 is due to both the depletion of serotonin and histamine from mast cells and an increased resistance of the gastric mucosa with healed lesions.

Gastric mucosal resistance to a repeated ethanol insult

The luminal gastric mucosa of anesthetised rats was uniformly exposed to 70% ethanol for 30-45 seconds. Ninety-six per cent of the superficial epithelium was immediately destroyed. The mucosa was allowed to heal for 60 minutes, during which time 85% of the superficial mucosa had re-epithelialised. A thick gelatinous layer of necrotic cells and mucosal exudate formed over the restituted epithelium. To determine whether the mucosa could withstand a second ethanol insult, the same stomachs were re-exposed to 70% ethanol for 30-45 seconds and fixed for quantitative light microscopy. Significant damage to the newly formed epithelium was observed only when the gelatinous layer was first removed and then followed by a second ethanol insult. This resulted in uniform superficial damage to 92% of the mucosal surface with accompanying vascular stasis.

Effects of water immersion restraint stress and chronic indomethacin ingestion on gastric antral and fundic epithelial proliferation

We studied the effects on gastric fundic and antral epithelial proliferation of acute water immersion restraint stress in rats and of chronic indomethacin ingestion in rats and humans using autoradiographic methods. Acute stress appeared to inhibit fundic epithelial proliferation but had no effect on antral proliferation in rats. We conjecture that this inhibition of fundic epithelial proliferation may help explain the development of stress-related mucosal lesions, which are more likely to occur in fundic mucosa. Chronic indomethacin ingestion stimulated fundic epithelial proliferation but had no effect on antral proliferation in both rats and humans. From these observations we conjecture that the failure of antral epithelial proliferation to respond to indomethacin may account in part for the ulcerogenic action of this drug.

Effect of aspirin on N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide-induced epithelial proliferation in the urinary bladder and forestomach of the rat

The co-administration of aspirin with N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide (FANFT) to rats resulted in a reduced incidence of FANFT-induced bladder carcinomas but a concomitant induction of forestomach tumors. An autoradiographic study was performed on male F-344 rats fed diet containing FANFT at a level of 0.2% and/or aspirin at a level of 0.5% to evaluate the effect of aspirin on the increased cell proliferation induced by FANFT in the forestomach and bladder. FANFT-induced cell proliferation in the bladder was significantly suppressed by aspirin co-administration after 4 weeks but not after 12 weeks. In the forestomach, and also in the liver, aspirin did not affect the FANFT-induced increase in labeling index. The present results are consistent with the carcinogenicity experiment suggesting that different mechanisms are involved in FANFT carcinogenesis in the bladder and forestomach, and that aspirin's effect on FANFT in the forestomach is not due to an irritant effect associated with increased cell proliferation. Also, there appears to be an adaptation by the rats to the chronic ingestion of aspirin.

Gastrointestinal effects of antipyretic analgesics

Aspirin and paracetamol (acetaminophen) are the most commonly used minor analgesics, but their effects on the gastrointestinal tract differ widely. Aspirin is significantly associated with major upper gastrointestinal hemorrhage, whereas acetaminophen is not. Short-term use of aspirin produces erythema, erosions, and occasionally ulcers; acetaminophen use does not. Chronic gastric ulcer is linked to aspirin intake in patients with rheumatic disease, and epidemiologically in all heavy aspirin users; paradoxically, in only one epidemiologic study was a significant association found between acetaminophen intake and chronic gastric ulcer. Fecal occult blood loss is increased in most regular aspirin users but not in those taking acetaminophen. Although studies in children have not apparently been made, in isolated small clinical series it has been shown that gastrointestinal bleeding and anemia do occur in the pediatric age group following the use of aspirin. Pathophysiologically, aspirin alters the gastric mucosal barrier to hydrogen ions and lowers gastric potential difference; acetaminophen has no effect on these parameters. Such changes correlate ultrastructurally with damage in surface epithelial cells and microerosions after the use of aspirin, but not after the use of acetaminophen. Aspirin causes a dramatic reduction in the ability of gastric mucosa to generate protective prostaglandins; however, acetaminophen also reduces prostaglandins. Other postulated mechanisms of aspirin damage include reduction in gastric mucosal secretion, bicarbonate output, and alteration of cell turnover. Because aspirin damage to gastric mucosa is often "silent," the clinician needs a high level of suspicion and awareness. In patients prone to gastric damage, or in those with a past history of aspirin-induced gastric damage, acetaminophen is the drug of choice when a minor, noninflammatory problem requires an analgesic.

Gastric adaptation occurs with aspirin administration in man

Endoscopy has become a standard method to evaluate drug-induced damage to the gastroduodenal mucosa; however, studies defining the time course, extent, and duration of the injury in man are unavailable. We report a systematic endoscopic evaluation of the effect of aspirin administration on the gastric mucosa in normal volunteers. Aspirin (2.6 g/ day) or placebo was administered for 1 or 7 days. Gastroscopy was performed after 1, 2, 4, and 8 days, and every other day thereafter until the lesions resolved. Submocosal hemorrhages and/or focal erosions were present within 24 hr in all subjects. With continuous aspirin administration, injury was maximal within 3 days and then lessened, ie, damage present after 7 days of aspirin was significantly less than after 1 day of therapy. The time to resolution of the damage was also longer following 1 day than after 7 days of aspirin (median 8 days for 1 day of aspirin vs median 3 days for 7 days of aspirin). Thus, gastric mucosal adaptation occurred and was associated both with less damage and with an accelerated healing process. Acute administration of aspirin produced well-defined areas of submucosal hemorrhages within 2 hr of administration; additional doses increased the area of involvement but not necessarily the severity of involvement.