The influence of acute or chronic nicotine treatment on ethanol-induced gastric mucosal damage in rats

Nicotine Exerts a Stronger Immunosuppressive Effect than Its Structural Analogs and Regulates Experimental Colitis in Rats

Ulcerative colitis (UC) is an intractable disease that causes persistent colonic inflammation. Numerous studies have reported that smoking can afford clinical benefits in UC. This study aimed to elucidate whether nicotine, the main component in cigarettes, can exert pharmacological effects against experimental UC. To achieve this objective, we compared the effects of nicotine with those of structural nicotine analogs in a UC rodent model (Slc: Wistar rats, male, 9-week-old, and 220–250 g/rat). Nicotine, or a respective structural analog (nornicotine, cotinine, anabasine, myosmine, and anatabine), was administered intraperitoneally daily to rats (n = 6/group) exhibiting dextran sulfate sodium-induced experimental colitis. Examining the colon tissues of model rats, we compared disease severity, cytokine secretion, and α7 nicotine acetylcholine receptor (nAChR7) expression. We observed that nicotine administration induced weight loss at 2.35% in 10 days. Notably, the reduction in histological severity (score) of UC was more pronounced in rats treated with nicotine (score = 4.83, p = 0.042) than in untreated rats (score = 8.17). Nicotine administration increased nAChR7 expression 6.88-fold (p = 0.022) in inflammatory sites of the colon, mainly by suppressing the production of interleukin (IL)-1β and IL-6. Moreover, the secretion of these cytokines was suppressed in lipopolysaccharide-stimulated rat macrophages (MΦ) treated with nicotine. In conclusion, nicotine better alleviates experimental UC than the examined structural analogs by activating nAChR7 expression and suppressing proinflammatory cytokines in MΦ.

Polyethylene glycol: its adverse gastric effects in rats

The effects of polyethylene glycol (PEG) on gastric function and on lesion formation, evoked by topical applications of absolute ethanol to an ex-vivo stomach chamber preparation have been examined. Parenteral injection (i.p. or s.c.) of PEG with different molecular weights (PEG 300, 400 or 4000), dose-dependently reduced the gastric mucosal blood flow and volume of gastric secretion; these effects were greater in rats given PEG by the i.p. route, which also lowered acid output. Topical application of 1·5 mL absolute ethanol produced severe gastric mucosal injury, which was exacerbated by PEG; this lesion-aggravating effect was higher in the i.p.-injected groups. These findings indicate that when PEG is given by injection, it can adversely affect gastric function and increase the damaging action of alcohol. It is suggested that the use of PEG as a vehicle for injection should be re-assessed.

Dysregulation of gastric H,K-ATPase by cigarette smoke extract

AIM

To test whether the expression and activity of H,K-ATPase in parietal cells would be affected by cigarette smoke extract.

METHODS

Extracts of cigarette smoke were administered into mice by gastric gavage (5 mg/kg body weight/day) for 3 d or in drinking water for 7 or 14 d. For the latter, each day a mouse consumed 5 mL water containing extracts of two cigarettes, on average. Control littermate mice received only vehicle. To compare the amount of H,K-ATPase in control and smoke-treated mice, the stomach was processed for Western blotting and immunohistochemical analysis using monoclonal antibodies specific for alpha- or beta-subunits of H,K-ATPase. The p-nitrophenylphosphatase activity assay was used as a measurement for K-dependent H,K-ATPase activity.

RESULTS

Probed transblots showed an increase in the amount of H,K-ATPase in smoke-treated mice which was confirmed by immunohistochemistry and was found to be due to increased amounts of protein per parietal cell rather than an increased parietal cell number. The increase in the amount of H,K-ATPase was associated with an enhancement of its enzymatic activity. K-dependent activity in control and smoke-treated mice was significantly different (respectively, 0.12 micromol/mg vs 0.27 micromol/mg per minute, P < 0.05).

CONCLUSION

Administration of cigarette smoke extract is associated with an increase in the amount and activity of H,K-ATPase and hence, smokers are susceptible to development of peptic ulcer.

Mechanisms of Disease: nicotine—a review of its actions in the context of gastrointestinal disease

Smoking tobacco is associated with a number of gastrointestinal disorders. In some, such as Crohn's disease and peptic ulcer disease, it increases the risk of disease and has a detrimental effect on their course. In others, such as ulcerative colitis, it decreases the risk of disease and can have a favorable effect on disease course and severity. In the eighteenth and nineteenth centuries, nicotine was used as a 'panacea' for various ailments, including abdominal symptoms--it is now under investigation to elucidate its role in gastrointestinal diseases that are associated with smoking. The actions of nicotine are complex; it is likely that its effects on the central nervous system, gastrointestinal tract and immune system interact with other risk factors, such as genetic susceptibility, to influence disease outcomes. This review focuses on the mechanisms of action of nicotine that might be relevant in gastrointestinal disease.

The pharmacological actions of nicotine on the gastrointestinal tract

Increasing use of tobacco and its related health problems are a great concern in the world. Recent epidemiological findings have demonstrated the positive association between cigarette smoking and several gastrointestinal (GI) diseases, including peptic ulcer and cancers. Interestingly, smoking also modifies the disease course of ulcerative colitis (UC). Nicotine, a major component of cigarette smoke, seems to mediate some of the actions of cigarette smoking on the pathogenesis of GI disorders. Nicotine worsens the detrimental effects of aggressive factors and attenuates the protective actions of defensive factors in the processes of development and repair of gastric ulceration. Nicotine also takes part in the initiation and promotion of carcinogenesis in the GI tract. In this regard, nicotine and its metabolites are found to be mutagenic and have the ability to modulate cell proliferation, apoptosis, and angiogenesis during tumoriogenesis through specific receptors and signalling pathways. However, to elucidate this complex pathogenic mechanism, further study at the molecular level is warranted. In contrast, findings of clinical trials give promising results on the use of nicotine as an adjuvant therapy for UC. The beneficial effect of nicotine on UC seems to be mediated through multiple mechanisms. More clinical studies are needed to establish the therapeutic value of nicotine in this disease.

Pathogenesis of nicotine treatment and its withdrawal on stress-induced gastric ulceration in rats

Previous studies showed that cigarette smoking was closely associated with gastric ulceration. People usually smoke under stress conditions, and together, these could induce more gastric damage. In the present study, we aimed to study the effects of nicotine administration and its withdrawal on stress-induced gastric ulceration in rats. Male Sprague-Dawley rats were given nicotine (25 or 50 microg/ml) for 10 days and then withdrawn for 2, 4 or 6 days. They were subjected to cold-restraint stress for 2 h after nicotine treatment or after nicotine withdrawal, and then killed. The results indicated that both nicotine treatment and its withdrawal potentiated stress-induced gastric damage. The mucosal glutathione (GSH) and mucus levels were reduced by stress and decreased further by nicotine. The prostaglandin E(2) concentration remained unchanged. To conclude, the adverse effect of nicotine on stress ulceration was prostaglandin E(2)-independent but mediated by the depression of glutathione and mucus levels in the gastric mucosa.

Beneficial intervention of experimental colitis by passive cigarette smoking through the modulation of cytokines in rats

BACKGROUND

Epidemiologic observations have indicated that cigarette smoking decreases the risk of ulcerative colitis, but the modes of action remain anonymous. The present study aimed to investigate the beneficial effects of passive cigarette smoking using an animal colitis model. We hypothesized that the underlying mechanisms may involve immunoregulation of cytokines.

METHODS

Experimental colitis was induced in rats by enema administration of 2,4-dinitrobenzene sulfonic acid (DNBS). Passive cigarette smoking by rats was performed for 1 hour once daily, from 3 days before DNBS enema until they were sacrificed on day 8. Other groups of DNBS-treated rats received therapeutic treatment of cyclosporin A or pentoxifylline, a tumor necrosis factor (TNF)-alpha inhibitor. Macroscopic and histologic damage were graded, and the colonic levels of different cytokines and the levels/activities of parameters related to neutrophil activation were also measured.

RESULTS

DNBS-induced colonic damage was improved in passive-cigarette-smoking rats. This was accompanied by attenuation of the elevated colonic myeloperoxidase and inducible nitric oxide synthase activities and leukotriene B4 level. Likewise, the augmentation in colonic levels of TNF-alpha, interleukin (IL)-1 beta, and IL-6 in colitis rats was also alleviated by passive cigarette smoking. In contrast, the deprivation of colonic IL-10 during colitis was preserved in cigarette-smoking rats. These effects were similarly accomplished by pentoxifylline and, to some degree, by cyclosporin A.

CONCLUSIONS

The results support the idea that the beneficial effects of passive cigarette smoking in experimental colitis involved immunoregulation of cytokines in colonic tissues.

Is smoking still important in the pathogenesis of peptic ulcer disease?

The pathogenesis of peptic ulcer disease is multifactorial, including the effects of Helicobacter pylori, gastric acid, pepsin, gastroduodenal motility, smoking and nicotine, and the complex interaction of an array of other so-called aggressive and protective factors. Since the discovery and acceptance of H. pylori as a major etiologic agent in peptic ulcer disease, the role of smoking has received less attention. Smokers are more likely to develop ulcers, ulcers in smokers are more difficult to heal, and ulcer relapse is more likely in smokers. These clinical observations may be explained by the adverse effects that smoking has on mucosal aggressive and protective factors. Of the aggressive factors, smoking appears to have no consistent effect on acid secretion. However, smoking impairs the therapeutic effects of histamine-2 antagonists, may stimulate pepsin secretion, promotes reflux of duodenal contents into the stomach, increases the risk for and harmful effects of H. pylori, and increases production of free radicals, vasopressin, secretion by the pituitary, secretion of endothelin by the gastric mucosa, and production of platelet activating factor. Smoking also affects the mucosal protective mechanisms. It decreases gastric mucosal blood flow and inhibits gastric mucous secretion, gastric prostaglandin generation, salivary epidermal growth factor secretion, duodenal mucosal bicarbonate secretion, and pancreatic bicarbonate secretion. These adverse effects of smoking on aggressive and protective factors quality it as an important contributor to the pathogenesis of peptic ulcer disease and indicate that smoking plays a significant facilitative role in the development and maintenance of peptic ulcer disease.

Mucosal nitric oxide is not responsible for the hemodynamic changes induced by nicotine in rat stomachs

It has been shown that chronic nicotine treatment decreases gastric mucosal blood flow (GMBF). The mechanism for this action is still not defined. In this study, nicotine treatment (5, 25 or 50 μg/ml drinking water) for 10 days dose dependently reduced the GMBF and volume of hemoglobin but increased ethanol-induced gastric damage. These effects were potentiated by N(ω)-nitro-l-arginine methyl ester (l-NAME), a nitric oxide (NO) synthase inhibitor. l-arginine but not the d-analog restored the actions of l-NAME, indicating that the selective action of l-NAME. However, the potentiating actions of l-NAME were significantly attenuated in the nicotine-pretreated rats. When the basal mucosal NO synthase (both iNOS and cNOS) activity and its second messenger cyclic GMP levels were measured, no difference was found between the nicotine and the non-nicotine groups. Furthermore, high dose of l-arginine could not reverse the action of nicotine. These findings suggest that the adverse action of chronic nicotine treatment on GMBF and lesion formation is probably mediated through a NO independent mechanism.

The anti-ulcer drug sucralfate does not affect gastric nicotine levels

OBJECTIVE

It has been claimed that sucralfate can overcome the negative effects of nicotine in patients with peptic ulcer disease, although the possible mechanism being unknown. This study was performed in order to test whether sucralfate was capable of binding intragastric nicotine, thus making it impossible for the substance to exert effect.

METHOD

Nicotine was administered via transdermal patches or as capsules yielding gastric concentrations of 40-2980 ng.ml-1. Gastric juice aspirates (n = 9) were incubated with sucralfate, which was then separated by centrifugation, and the nicotine concentration was compared in incubated and non-incubated samples.

RESULTS

A median decrease of 13% (range 0-27%) in nicotine concentration was seen after incubation with sucralfate (P = 0.01).

CONCLUSION

The binding of nicotine to the precipitating agent sucralfate is not sufficient effectively to remove nicotine from the gastric juice.

The importance of gastric emptying and mucosal folds in the adaptive cytoprotection of mild irritants in rats

This study examines the involvement of gastric emptying and mucosal folds in the adaptive cytoprotection of different mild irritants against 100% ethanol-induced gastric mucosal damage. Pre-exposure to either 20% ethanol, 5% NaCl or 0.3M HCl significantly reduced the gastric mucosal damage caused by 100% ethanol in rats. Administration of either one of the three mild irritants increased the basal gastric residual volume and decreased the area occupied by gastric mucosal folds, but only 20% ethanol reduced the gastric emptying rate. Indomethacin (5 mg/kg, s.c.) pretreatment did not affect ethanol ulceration and gastric emptying rate when given by itself, but reversed the flattening of mucosal folds produced by the three mild irritants, and abolished the protective effect of 20% ethanol. These results suggest that the gastric adaptive cytoprotection induced by the three mild irritants acts through luminal dilution of the noxious agent, possibly caused by gastric retention. The reduction of mucosal folds could also contribute to the anti-lesion action of 20% ethanol. It is therefore suggested that the protective actions of the three mild irritants act through different mechanisms.

Role of dorsal motor nucleus of vagus in gastric function and mucosal damage induced by ethanol in rats

Experimental evidence indicates that the autonomic nervous system, especially the cholinergic pathway modulates the mucosal defensive mechanism and affects mucosal damage in the stomach. The present study investigated the role of the dorsal motor nucleus of vagus (DMV) in gastric function and its influences on ethanol-induced mucosal damage in pentobarbitone-anesthetized rats. Electrolytic lesion of the DMV as compared with sham operation and lesions of other brain areas, eg, nucleus reticular gigantocellularis and cuneate nucleus, reduced the basal gastric mucosal blood flow (GMBF) and also the blood flow after ethanol administration. The same operation did not affect the acid secretion either in the basal state or during the ethanol treatment period. Lesions at the caudal half of the DMV produced a bigger depression of GMBF when compared with lesion at the rostral half. In the sham-operated rats, ethanol induced severe hemorrhagic lesions in the gastric glandular mucosa, and this was significantly potentiated by lesions at the DMV, especially in the caudal half. The present findings indicate that acute DMV damage at the caudal half markedly affects the GMBF but not the acid secretion. The action on GMBF may contribute to the aggravation of ethanol-induced gastric damage in rats. These data reinforce the idea that the central vagal pathway, especially the caudal half of the DMV, plays a significant role in the modulation of GMBF, which in turn affects the integrity of gastric mucosal barrier.

The effect of nicotine and its interaction with carbon tetrachloride in the rat liver

In order to study the effects of nicotine on liver, groups of rats were given nicotine doses that simulated those seen in chronic smoking (54 and 108 mumol/l of nicotine) for 10 days. A subgroup was also given a single subcutaneous injection of 6 g/kg of carbon tetrachloride (CCl4) shortly before the animals of the group were killed. Histology demonstrated a significant hepatotoxic effect in the group receiving 108 mumol/l of nicotine when compared with the control group in the form of fatty change, focal or confluent necrosis and dark-cell change. The effects in pregnant rats were less severe. Carbon tetrachloride alone induced significant fatty change and focal necrosis in non-pregnant rats but not in pregnant rats. Nicotine also aggravated the CCl4 induced pathological changes in livers of both non-pregnant and pregnant animals. Thus nicotine alone, when given at a concentration of 108 mumol/l, exerted hepatotoxic effects; the alkaloid also aggravated the hepatotoxicity of CCl4. Pregnant rats were more resistant to the hepatotoxic effects produced by nicotine and CCl4.

The mechanistic pathway of gastric adaptive cytoprotection: a study on different components of the autonomic nervous system

1. The involvement of different components of the autonomic nervous system in the pathogenesis of ethanol-induced damage and the adaptive cytoprotection of mild irritants were studied in the gastric mucosa of male rats. 2. Capsaicin, yohimbine, and domperidone aggravated the 100% ethanol-induced gastric mucosal damage and attenuated the cytoprotective action of 20% ethanol, but not of 5% NaCl and 0.3 M HCl. Butoxamine and prazosin blocked the adverse actions of yohimbine and domperidone respectively. 3. Atropine, pirenzepine, and lidocaine lessened the severity of 100% ethanol-induced mucosal injury and further increased the cytoprotective action of 5% NaCl and 0.3 M HCl, but not of 20% ethanol. 4. Our results demonstrated that sensory afferent neurones, alpha 2-adrenoceptors and D2-dopaminergic receptors all play a significant role in the defensive mechanism of the gastric mucosa and the adaptive cytoprotection of 20% ethanol, while the M1- and M2-muscarinic receptors and sensory chemoreceptors on the gastric mucosa contribute only to the former action. The adverse effect of yohimbine and domperidone on lesion formation is probably mediated through the release of catecholamines, which subsequently act on the beta 2- and alpha 1-adrenoceptors respectively.

Aggravation of gastric mucosal lesions in rat stomach by tobacco cigarette smoke

In the model of gastric mucosal injury induced by 2 mol/liter hypertonic saline in rats, we tested the hypothesis that tobacco cigarette smoke aggravates gastric mucosal lesions by inhibition of injury-induced gastric mucosal hyperemia. Experimental rats were treated with tobacco cigarette smoke or nicotine-free smoke from nontobacco cigarettes, and controls breathed room air. Gastric mucosal blood flow was measured by hydrogen gas clearance before and during the intragastric administration of hypertonic saline. Tobacco cigarette smoke 3 and 18 ml/min, but not nicotine-free smoke, significantly attenuated the hyperemia and aggravated the hypertonic saline-induced lesion in a dose-dependent manner. We then tested the hypothesis that 18 ml/min of tobacco cigarette smoke, and the dose of intravenous nicotine previously shown to block injury-induced hyperemia and aggravate 2 mol/liter saline-induced gastric damage, will also adversely affect gastric lesions induced by acidified aspirin or acidified ethanol. The results confirm that tobacco cigarette smoke and intravenous nicotine indeed aggravate gastric mucosal damage in these two models. Taken together, the data suggest that the inhibition of injury-induced hyperemia by nicotine and tobacco cigarette smoke is an important predictor of their ability to increase the susceptibility of the gastric mucosa to noxious damage. Although limited in their experimental nature, these data provide one plausible explanation for the adverse effect of tobacco cigarette smoke on peptic ulcer disease.

Contributions of physical and chemical properties of mild irritants to gastric cytoprotection in rats

The present study demonstrated the cytoprotective abilities of low concentrations of ethanol, NaCl and HCl, against the gastric mucosal damage caused by 100% ethanol, and the contributions of the physical and chemical properties of these mild irritants to their protective actions. The results have shown the differential protective effects of ethanol (10-40%), NaCl (2.5-12.5%) and HCl (0.15-0.45M), with the optimal cytoprotective concentrations being 20% ethanol, 5% NaCl and 0.3M HCl, respectively. Solutions of KCl and NaCl with similar osmolarity, and H2SO4 and HCl of similar acidity and osmolarity, all showed similar protective protective potentials as compared to the osmotic agent mannitol, which possessed a concentration- and tonicity-dependent protective action against 100% ethanol-induced mucosal damage. Some concentration of methanol, propan-2-ol and ethanol, having similar osmolarity with deionized water, exerted indifferent protective effects. It is therefore concluded that adaptive cytoprotection induced by low concentrations of NaCl and HCl could depend on their physical properties, while that of ethanol could act through its unique chemical property.

Topical nicotine protects rat gastric mucosa against ASA-induced damage. A role for mucosal fluid secretion in cytoprotection

Acute intragastric nicotine administration has previously been shown to protect against ethanol-induced gastric mucosal damage. The aim of this study was to examine the effects of acute nicotine exposure on ASA-induced gastric mucosal damage and to determine if nicotine's protective effect is secondary to an increase in mucosal blood flow or in mucosal fluid secretion, as reflected by changes in the juxtamucosal pH gradient and volume of intragastric fluid. Mucosal blood flow, using a laser Doppler flowmeter, juxtamucosal pH gradient (depth, magnitude, and surface pH), using antimony microelectrodes, and changes in volume of luminal bathing solutions were measured in rat ex vivo gastric chamber preparations prior to and after a 10-min exposure to topical nicotine (1 mg in 8 ml of 0.2 M mannitol in 50 mM HCl), or to mannitol-HCl solution (vehicle). This was followed by application of acidified ASA (80 mM in 160 mM HCl) to the chambered mucosae for 10 min. Lesion area, expressed as the percentage of total glandular mucosa which was damaged, was significantly (P < 0.05) reduced by nicotine pretreatment. Blood flow decreased with nicotine exposure by 18.4%, compared to 13.6% in the control group (NS). Both gradient depth and gastric fluid volume increased significantly in the nicotine group (P < 0.05) compared to controls. Yohimbine pretreatment prevented both the increase in juxtamucosal pH gradient depth and the protective effect of nicotine. These results suggest that acute intragastric nicotine exposure protects against ASA-induced gastric damage in rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Gastric cytoprotection by amoxycillin in the rat

Amoxycillin in combination with anti-ulcer agents has been shown to prolong duodenal ulcer remission. While this effect can be related to the eradication of Helicobacter pylori, it is not known if amoxycillin might possess cytoprotective properties. Protection against ethanol-induced gastric mucosal damage by intragastric instillation of amoxycillin suspension (prepared from capsule form) and solution (from injection form, 100% pure amoxycillin), and by intraperitoneal injection of amoxycillin solution was studied using an ex vivo gastric chamber in the rat. Intragastric and intraperitoneal administration of amoxycillin dose-dependently protected the rat gastric mucosa from damage by absolute ethanol. This protection was lost when the rats were pretreated with indomethacin. Gastric mucosal blood flow as measured by laser Doppler flowmetry and gastric acid output were unaffected by amoxycillin. Amoxycillin imparts gastric cytoprotection, and one possible mechanism is by the release of prostaglandins.

Effects of smoking and nicotine on the gastric mucosa: a review of clinical and experimental evidence

Epidemiological and experimental evidence have shown that nicotine has harmful effects on the gastric mucosa. The mechanisms by which cigarette smoking or nicotine adversely affect the gastric mucosa have not been fully elucidated. In this report, clinical and experimental data are reviewed. The effects of nicotine from smoking on gastric aggressive or defensive factors are discussed. Nicotine potentiates gastric aggressive factors and attenuates defensive factors; it also increases acid and pepsin secretions, gastric motility, duodenogastric reflux of bile salts, the risk of Helicobacter pylori infection, levels of free radicals, and platelet-activating factor, endothelin generation, and vasopressin secretion. Additionally, nicotine impairs the therapeutic effect of H2-receptor antagonists and decreases prostaglandin synthesis, gastric mucosal blood flow, mucus secretion, and epidermal growth factor secretion. Although many of the studies provide conflicting results, the bulk of the evidence supports the hypothesis that nicotine is harmful to the gastric mucosa.

The differential mechanisms of mild irritants on adaptive cytoprotection

The protective action of mild irritants has been established. However, the mechanisms as to how they antagonize the injurious action produced by the subsequent challenge with an ulcerogenic stimulus are still unclear. The present study examined the different protective mechanisms of an oral administration of the three mild irritants, 20% ethanol, 0.3 mol/L HCl or 5% NaCl against the gastric injurious actions of absolute ethanol in rats. In an attempt to clarify the pathways and mediators involved in the adaptive cytoprotection, [D-Pro2, D-Trp7,9]-substance P (substance P antagonist), Nw-nitro-L-arginine methyl ester (L-NAME), indomethacin, capsaicin, lidocaine, atropine or hexamethonium was given. The protective action of 20% ethanol but not the other two mild irritants, was antagonized by L-NAME, indomethacin and capsaicin, which are the inhibitors of nitric oxide (NO) and prostaglandins (PG) synthesis, and afferent sensory neuron blocker, respectively. Substance P antagonist, lidocaine or atropine given alone, prevented mucosal damage; however, only substance P antagonist enhanced the anti-lesion action of 20% ethanol, while atropine and lidocaine increased the protective effect of NaCl and HCl. The three mild irritants increased the residual gastric secretion. Only 20% ethanol and 5% NaCl but not 0.3% HCl significantly increased the basal adherent mucus and also attenuated the mucus depletion by absolute ethanol. It is concluded that the cytoprotective action of either ethanol or NaCl seems to be mediated through the increase of residual gastric secretion and adherent mucus. In the ethanol-treated group, these actions could act through the afferent sensory fibres, with NO and PG as the possible mediators.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of endogenous ulcerogenic mediators in the pathogenesis of peptic ulcer

The pathogenetic mechanisms of different types of peptic ulcer are still unclear. Extensive investigations have been focused on the identification of potential endogenous ulcerogenic mediators in animals and men. These studies are important in the development of a better therapeutic agent, either to prevent or to cure peptic ulcer in humans. Several endogenous substances have been identified and are reported to be involved in the production of gastrointestinal lesions in animals. Also these substances were increased during inflammatory responses and their actions were reported as vascular dependent and possibly free radicals related. Reports related to the types of these mediators have been extensive. The more important ones include some of the lipid metabolites, neuropeptides, biogenic amines, and also Helicobacter pylori and reactive free radicals. The present study summarizes the ulcerogenic mechanisms of these substances and the types of ulcer involved. More current information may enable us to understand better the etiology of peptic ulcer and possibly its prevention and cure in man. Any particular types of ulceration will not be specifically discussed in this article, because they have been extensively studied and reviewed.

Effect of nicotine in migration and proliferation of rabbit gastric mucosal cells in a culture cell model

The aim of this study was to assess the effects of nicotine on the gastric epithelial restoration using primary cultured rabbit gastric mucosal cell model. Confluent monolayer mucosal cell sheets consisting of mainly mucous cells were wounded using a rotating silicon tip. The process of restoration was monitored, and the size of wound was measured and analysed quantitatively. Artificial wounds recovered in 36 h in controls. The nicotine treatment (10(-5), 10(-4) and 10(-3) mol/L) did not cause any effects on the process of wound repair. Bromodeoxyuridine (BrdU) positive cells appeared around the wound 24-36 h after injury and then disappeared after the complete repair in controls and also in nicotine-treated groups. However, in the morphological observation, numerous vacuoles were detected in parietal cells of nicotine-treated groups. This effect of nicotine was reversible by removing nicotine from the medium. Present data suggest that nicotine has no direct effects on the mucosal restoration but might have an effect on the structure and function of parietal cells.

Effect of epidermal growth factor on gastric blood flow in rats: possible role in mucosal protection

BACKGROUND

The mechanism by which epidermal growth factor (EGF) protects the gastric mucosa against injury is unclear. Whether EGF has any effect on gastric blood flow has not been reported.

METHODS

Using an ex vivo gastric chamber preparation, the effect of EGF on gastric blood flow in rats was studied by laser Doppler flowmetry. Measurements of blood flow and mucosal damage were made in both intact and sialoadenectomized rats with graded doses of EGF at basal condition and after topical application of absolute ethanol.

RESULTS

Sialoadenectomy alone increased ethanol-induced gastric mucosal lesions (P < 0.05) but had no significant effect on blood flow. EGF pretreatment resulted in both a reduction in ethanol-induced gastric mucosal injury as well as a significant increase in blood flow compared with controls (both P < 0.05). Graded doses of EGF (3.12-25 micrograms) resulted in an dose-dependent increase in gastric blood flow (r = 0.68; P < 0.001), which correlated inversely with the degree of mucosal damage (r = -0.72; P < 0.001).

CONCLUSIONS

Mucosal protection by EGF is accompanied by an increase in gastric blood flow; this action may contribute to its mucosal protective effect.

The role of the vagus nerve in the protective action of acid inhibitors on ethanol-induced gastric mucosal damage in rats

The role of vagus in the actions of different acid inhibitors on ethanol-induced gastric damage and mucosal blood flow (GMBF) changes was studied in anaesthetized rats, using an ex vivo stomach chamber preparation. Subdiaphragmatic bilateral vagotomy decreased the basal gastric acid secretion and GMBF; it also intensified ethanol-evoked lesions in the glandular mucosa. Misoprostol, omeprazole and cimetidine produced a similar degree of reduction in acid output. Misoprostol given subcutaneously (s.c.) (50 micrograms/kg), or added to the incubation solution (12.5 micrograms) for 15 min, markedly prevented ethanol-induced lesion formation and reduction in GMBF. The reversing effect of s.c. injection of misoprostol on either lesion formation or on GMBF reduction was attenuated by vagotomy. Omeprazole protected against lesion formation only when present in the incubation solution (12.5 mg) of ex vivo chamber preparations of both vagus-intact and vagotomized animals, but the effect was significantly less in the latter group. The drug also prevented the depressive action of ethanol in vagus-intact animals. Cimetidine pretreatment (50 mg s.c. or 12.5 mg in incubation solution), however, did not modify the effects of ethanol on lesion formation and the GMBF. The findings indicate that the three different types of acid inhibitors exert different actions on ethanol-induced gastric mucosal damage, although they produced similar inhibition of acid output. Vagotomy lowers the GMBF and attenuates the antiulcer action of misoprostol and omeprazole, especially when the drugs are given by the parenteral route.

Effects of adenosine on gastric and cardiovascular systems, and ethanol ulceration in male and female rats

The time course of the effects of adenosine, a vasodilator, on the ulcerogenicity of ethanol was studied in male and female rats. Gastric secretory function and mucosal blood flow (GMBF), systemic blood pressure and heart rate were monitored during the 90-min experimental period. In the male rats, adenosine 7.5 mg/kg s.c. (injected at 30 min) increased the GMBF at 45 min and depressed it at 75 min. The mean blood pressure was decreased at 45 min and steadily recovered thereafter; the heart rate was unaffected throughout the experimental period. The gastric secretory volume was elevated at 60 min, with a significant drop in gastric acid output at the same time. Ethanol administration from 45 to 90 min produced haemorrhagic lesions in the glandular mucosa. The severity of gastric damage was markedly reduced by adenosine at 45 and 60 min when the GMBF and the secretory volume were increased respectively, but severity was increased at 75 min while the GMBF was significantly reduced. In the female rats, adenosine had no effect on the secretory function but still had a depressive action on GMBF at the 75th min. In these animals, adenosine exacerbated the gastric injury at 60 and 75 min. The blood pressure was also decreased at 45 min. In conclusion, adenosine produces a different pattern of effects on the ulcerogenic action of ethanol in male and in female rats. These differential effects depend on the states of GMBF and gastric secretory volume but not on the changes of systemic blood pressure and gastric acid secretion.

In vitro study of ethanol on the electrical parameters in rat stomachs

The electrophysiological effects of mucosal or submucosal ethanol (5, 10, or 20%) were assessed in isolated stomach preparation. Mucosal incubation with these concentrations of ethanol dose- and time-dependently decreased the transmucosal potential difference (PD), while the electrical current (I) and resistance (R) were unaffected. Submucosal exposure to the same concentrations of ethanol also reduced the PD, but to a lesser extent; only 20% of ethanol produced a significant effect. This same dose of ethanol not only decreased I but also increased R to a significant level. These findings indicate that transmucosal PD appears to be generated largely by the mucosal epithelial cell barrier, while the I and R are elicited by the laminea propria mucosa which is easily approached and altered by ethanol which acts from the submucosal side. The significance of the effects produced by mucosal or submucosal ethanol is discussed.

Modulatory action of adenosine on gastric function and ethanol-induced mucosal damage in rats

This study examines the gastric effects of adenosine and its antagonist, theophylline, on secretory function, mucosal blood flow, and on ethanol-induced glandular mucosal damage in rats that were fasted for 24 hr before experimentation. The animals were anesthetized with sodium pentobarbitone (50 mg/kg intraperitoneal) and their tracheae cannulated. An ex vivo stomach chamber then was prepared. The luminal bathing solution was collected every 15 min and the concentrations of H+ and Na+ were determined by a pH autotitrator and an ionmeter, respectively. The glandular mucosal blood flow was measured by a laser Doppler flowmeter and the severity of lesions was determined by measuring the hemorrhagic areas. Adenosine administration (2.5 or 7.5 mg/kg, subcutaneous) markedly lowered the H+ and Na+ output but increased the secretory volume and mucosal blood flow in a dose-dependent manner. The same doses of the nucleoside also prevented ethanol-induced mucosal damage. These effects were prevented by pretreatment with theophylline (30 or 60 mg/kg, subcutaneous). Ethanol given alone significantly depressed the H+ and Na+ secretion. Both effects were not modified by adenosine treatment. However, the depressive action of ethanol on mucosal blood flow was prevented by adenosine. These findings indicate that adenosine modulates the physiological function of the stomach. It also directly activates the defensive mechanism of the stomach, which is partially mediated by the improvement of the gastric mucosal blood flow and an increase in the nonacid component of gastric secretion.