Role of luminal alkalinization in repair process of ethanol-induced mucosal damage in rat stomach

Importance of Ca(2+) in gastric epithelial restitution-new views revealed by real-time in vivo measurements

It has been a few decades since Ca(2+) was identified as one of the important factors that can accelerate gastric wound repair as well as contribute to epithelial homeostasis and regulation of gastric secretions. The mechanistic basis has remained largely unexplored in vivo because it was not possible to track in real time either intracellular Ca(2+) mobilization or wound repair in living tissues. Recent advances in technology, such as combining high resolution light microscopy and genetically encoded Ca(2+) reporters in mice, now allow the monitoring of Ca(2+) mobilization during gastric epithelial cell restitution. Ca(2+) is a ubiquitous second messenger that influences numerous cellular processes, including gastric acid/bicarbonate secretion, mucus secretion, and cell migration. We have demonstrated that cytosolic Ca(2+) mobilization within the restituting gastric epithelial cells is a central signal driving small wound repair. However, extracellular Ca(2+) is also mobilized in the juxtamucosal luminal space above a wound, and evidence suggests extracellular Ca(2+) is a third messenger that also promotes gastric epithelial restitution. Interplay between intracellular and extracellular Ca(2+) is necessary for efficient gastric epithelial restitution.

Stimulation of duodenal HCO₃⁻ secretion by hydrogen sulphide in rats: relation to prostaglandins, nitric oxide and sensory neurones

AIM

We examined the effect of H₂S on duodenal HCO₃⁻ secretion in rats and investigated the mechanism involved in this response.

METHODS

Animals were fasted for 18 h and anaesthetized with urethane. A duodenal loop was perfused with saline, and HCO₃⁻ secretion was measured at pH 7.0 using a pH stat-method. The loop was perfused at a rate of 0.2 mL min⁻¹ with NaHS (H₂S donor: 0.1-1 mm) for 5 min or 10 mm HCl for 10 min. Indomethacin or l-NAME [nitric oxide (NO) synthase inhibitor) was given s.c. 30 min or 3 h, respectively, before NaHS or acidification, while glibenclamide (K(ATP) channel blocker) or propargylglycine (cystathionine-g-lyase inhibitor) was given i.p. 30 min before.

RESULTS

Mucosal perfusion with NaHS dose dependently increased the HCO₃⁻ secretion, and this effect was significantly attenuated by indomethacin and l-NAME as well as by sensory deafferentation, but not by glibenclamide. Mucosal prostaglandin E₂ (PGE₂) production and luminal release of NO were both increased by NaHS perfusion. Mucosal acidification stimulated HCO₃⁻ secretion concomitant with an increase in PGE₂ and NO production, and these responses were mitigated by propargylglycine. The duodenal damage induced by acid (100 mm HCl for 4 h) was aggravated by pre-treatment with propargylglycine.

CONCLUSION

These results suggest that H₂S increases HCO₃⁻ secretion in the rat duodenum, and that this action is partly mediated by PG and NO as well as by capsaicin-sensitive afferent neurones. It is assumed that endogenous H₂S is involved in the regulatory mechanism of acid-induced HCO₃⁻ secretion and mucosal protection in the duodenum.

Physical and biological considerations for the use of nonaqueous solvents in oral bioavailability enhancement

This review addresses the use of nonaqueous solvents as components of oral formulations in discovery and preclinical studies. Pharmacology, pharmacokinetic, and safety studies are frequently conducted with solution formulations that use a solvent to solubilize poorly aqueous soluble drugs. The physical chemical basis for solubilization and the precipitation of solubilized drug following administration both contribute to the utility of nonaqueous solvent solutions as oral vehicles. While many of these solvents are considered nontoxic, they are not completely inert biologically. The effects of common nonaqueous solvents on the structural integrity of the epithelia, the inherent permeability of and flux across the GI membrane, the activity of efflux and metabolic enzymes, and the effects on GI motility and GI transit times will be described through an examination of available literature. The practical relevance of these factors to the development of early formulations will be examined critically and suggestions made for the suitability of nonaqueous solvents for a variety of purposes.

Less irritative action of wine and Japanese sake in rat stomachs: a comparative study with ethanol

The ingestion of alcohol, especially in excess, causes acute gastric lesions and gastritis in humans, yet the mucosal irritative action of alcoholic beverages remains largely unknown. We examined the mucosal irritative action of whiskey, wine and Japanese sake in the rat stomach both ex vivo and in vitro, in comparison with ethanol. Under urethane anesthesia, a rat stomach was mounted in an ex vivo chamber, then superfused with saline, and the transmucosal potential difference (PD) was measured. After the basal PD had stabilized, the mucosa was exposed for 30 min to 2 ml of 15% ethanol, whiskey (containing 15% ethanol), white wine, or Japanese sake (the ethanol concentration of the latter two is 12-15%). In the in vitro study, rat epithelial cells (RGM1) were treated with the alcoholic beverages for 5 min, and the cell viability was determined with crystal violet. Ethanol or whiskey applied to the chamber caused a decrease in PD, while wine or Japanese sake did not. Histologically, surface epithelial damage was observed after exposure to both ethanol and whiskey, yet no damage was induced by white wine and Japanese sake. Likewise, both ethanol and whiskey markedly reduced the viability of RGM1 cells after 5 min of incubation, while neither white wine nor Japanese sake had any effect. In addition, supplementation of glucose significantly prevented the reduction in both PD and cell viability caused by ethanol. These results suggest that the mucosal irritative action of Japanese sake and white wine is much less pronounced than that of ethanol or whiskey and that the less damaging action of Japanese sake and white wine may be, at least partly, accounted for by the glucose contained in these alcoholic beverages.

Irritative action of alcoholic beverages in rat stomachs: A comparative study with ethanol

The mucosal irritative action of alcoholic beverages such as white wine, Japanese sake and whisky was examined in rat stomachs in vivo and in vitro, in comparison with ethanol. The concentration of ethanol in these alcoholic beverages was 15%. Mucosal application of ethanol (15%) and whisky in the chambered stomach caused a decrease in gastric potential difference (PD), while that of Japanese sake and white wine caused a slight increase but not decrease in PD. Likewise, both ethanol and whisky markedly reduced the cell viability of RGM1 cells after 5 min incubation, whereas neither Japanese sake nor white wine had any effect. In addition, supplementation of glucose, one of the non-alcoholic ingredients of white wine and Japanese sake, antagonized a reduction in both PD and cell viability caused by ethanol. These results suggest that the mucosal irritative action of Japanese sake and white wine is much less than that of ethanol or whisky and that these properties may be, at least partly, due to the glucose contained in these alcoholic beverages.

Gastric transmucosal potential difference: effect of antisecretory and gastroprotective drugs

1. Ion transport and electrical resistance of the gastric mucosa are responsible for the generation of the transmucosal potential difference (PD), which is considered an index of mucosal integrity. 2. The aim of the present work was to study the effect of some antisecretory and gastroprotective agents on PD in stomachs damaged by ethanol. 3. Control PD values measured in anesthetized rats were 35 to 40 mV (mucosa negative). Oral administration of 96% ethanol or intragastric instillation of 20% ethanol induced an abrupt fall in PD from the basal values of 40.4+/-1.0 mV and 39.6+/-0.1 mV to 14.6+/-2.5 mV and 11.7+/-1.3 mV, respectively. 4. Oral and/or topical pretreatment with the antisecretory agents ranitidine and timoprazole, as well as with the gastroprotective agents PGE2 and pentacaine, but not with an aluminum- and magnesium-containing antacid and with sucralfate, reduced the maximal drop of PD caused by ethanol. 5. After the administration of concentrated ethanol, hemorrhagic lesions were formed in the glandular stomach. 6. With the exception of ranitidine, all the drugs tested prevented the development of lesions after ethanol administration. 7. The results indicate that the gastric barrier can be protected by various drugs that act through different mechanisms.

Relationship between gastric mucus synthesis, secretion and surface gel erosion measured in amphibian stomach in vitro

1. The layer of adherent mucus that protects the surface of the stomach reflects a dynamic balance between biosynthesis of glycoprotein, secretion of preformed mucus and erosion of the adherent gel layer. The present study is the first in which all these processes have been measured concomitantly and was undertaken to define interrelationships between the three parameters. 2. A chambered sac preparation of amphibian gastric mucosa is described. Biosynthesis was determined by specific incorporation of radiolabelled sugars into purified glycoprotein. Mucus secretion was determined by measuring the thickness of the adherent gel and erosion of the surface layer was assessed from the appearance of soluble mucin in the luminal solution. 3. 16,16-Dimethyl-prostaglandin (PG) E2 stimulated glucosamine incorporation by 10-fold, but did not alter the rate of incorporation of galactose. There was a rapid two-fold increase in the thickness of the adherent mucus layer but no change in the rate of erosion. Dibutyryl-cAMP also stimulated mucus release but, unlike PG, increased glycoprotein labelling by galactose. 4. Both distention or the application of a cholinergic agonist increased adherent mucus thickness. Stimulation of mucus release in response to carbachol was accompanied by a decrease in glycoprotein labelling by galactose. In contrast, the adrenergic agent noradrenaline decreased secretion but did not influence labelling. 5. These results indicate that biosynthesis and secretion of gastric mucus are subject to differential regulation. Moreover, the profile of incorporation of sugars in response to secretagogues also differs, indicating the need for caution when interpreting effects on glycoprotein biosynthesis.

Ethanol-induced gastrointestinal damage. Influence of endogenous antioxidant components and gender

This study compared the effects of undiluted and 8% ethanol administered orally on gastrointestinal antioxidant components of male and female rats. Eight percent ethanol increased the activities of duodenal glutathione peroxide (29% in males, 14% in females) and superoxide dismutase in female gastric (24%) and male duodenal (15%) mucosa. This dose of ethanol also increased the glutathione content of gastric mucosa (12% in males, 13% in females). Undiluted ethanol decreased glutathione levels in gastric mucosa (22% in males, 11% in females) and increased glutathione peroxide activity in gastric mucosa (14% in males, 9% in females). Undiluted alcohol also produced decreases in the activity of glutathione reductase in stomach (14% in males, 9% in females) and duodenum (16% in males, 12% in females). Undiluted ethanol caused mucosal damage in the body of the stomach in both genders, accompanied by an increase in luminal pH and fluid accumulation in the stomach; these changes were absent in rats given 8% ethanol. The increase in gastrointestinal antioxidant capacity associated with the administration of 8% ethanol may be a factor in the reported cytoprotective effect of lower doses of ethanol.

Gastric mucosal protection by YM638, a novel leukotriene D4 receptor antagonist, in rats

YM638 ([[5-[[3-(4-acetyl-3-hydroxy-2-propylphenoxy)propyl] thio]-1,3,4-thiadiazol-2-yl]thio] acetic acid) is a novel leukotriene D4 receptor antagonist. We investigated the involvement of the leukotriene D4 receptor blocking activity of YM638 in the gastric mucosal protection of this drug in rats. YM638 significantly prevented gastric lesion formation induced by water-immersion restraint stress, indomethacin, absolute ethanol, 0.7 N HCl and the combination of 0.2 N HCl and hemorrhagic shock, with ED50 values of 26.4, 4.1, 4.7, 35.4 and 8.0 mg/kg p.o., respectively. Cetraxate and sofalcone showed inhibitory effects on most of these gastric lesions, but the inhibitory effects of these compounds were much weaker than those of YM638. In contrast, YM638 had no effect on gastric acid secretion and gastric lesion formation in pylorus-ligated rats, or on duodenal lesion formation in cysteamine-administered rats. YM638 competitively antagonized leukotriene D4-induced contraction of the isolated stomach, with a pA2 value of 7.63 +/- 0.18. In anesthetized rats, intravenous YM638 inhibited leukotriene D4-induced aggravation of gastric lesions caused by HCl, and leukotriene D4 and HCl-induced reduction of the potential difference. In addition, oral YM638 significantly increased gastric mucosal blood flow and prevented ethanol-induced increase in gastric vascular permeability. Endogenous prostaglandins, sulfhydryls and nitric oxides were not involved in this inhibitory effect on absolute ethanol-induced gastric lesion. YM638 did not react with the stable free radical 1,1-diphenyl-2-picrylhydrazyl in vitro, indicating that YM638 does not have potential as free radical scavenger. These results suggest that the preventive effect of YM638 on gastric lesions is attributable not only to its leukotriene D4 receptor blocking activity but also to the activation of gastric mucosal defensive mechanisms such as mucosal blood flow and vascular permeability.

Role of bicarbonate in blood flow-mediated protection and repair of damaged gastric mucosa in the cat

BACKGROUND/AIMS

The hyperemic response after superficial gastric mucosal damage is essential for repair of the mucosa. Only indirect evidence suggests that this is caused by supply of bicarbonate. Therefore, this study tested the effect of maintaining the availability of bicarbonate after prevention of the hyperemic response after damage by 2 mol/L NaCl.

METHODS

Celiac artery flow was reduced, as monitored by Doppler ultrasonography, by gradual constriction of the vessel after mucosal damage. Saline (pH 1.0) was perfused through the stomach lumen and thereafter through a closed chamber with pH and PCO2 electrodes.

RESULTS

Exposure to 2 mol/L NaCl produced a marked increase of mucosal blood flow as measured by microspheres (P < 0.025) and a high degree of mucosal restitution 90 minutes after damage as judged by microscopy, whereas prevention of the hyperemic response caused extensive erosions and much less restitution (P < 0.001). The latter effect was completely counteracted by intravenous bicarbonate. High blood concentration of bicarbonate increased luminal release of bicarbonate, whereas high mucosal blood flow did not.

CONCLUSIONS

These data show that bicarbonate is an important factor in blood flow-mediated protection and repair of damaged gastric mucosa and suggest that concentration gradients are the major determinants for transport of bicarbonate across the damaged and restituted mucosa.

Release of bicarbonate from damaged and restituted gastric mucosa in the cat

BACKGROUND

Gastric mucosal damage leads to luminal alkalinization, but its dependence on mucosal blood flow and acid secretory state of the mucosa is not known. This study examined release of bicarbonate to the gastric lumen and mucosal blood flow in cats after mucosal damage caused by 2 mol/L NaCl and during 90 minutes of epithelial restitution.

METHODS

Bicarbonate was calculated from measurements of pH and PCO2 in the luminal perfusate. Mucosal blood flow was measured with microspheres.

RESULTS

Luminal bicarbonate increased more than twofold after damage in pharmacologically nontreated, pentagastrin-treated, and omeprazole-treated animals (P < 0.001). Luminal bicarbonate thereafter decreased completely to pre-damage level in pentagastrin-treated, partly in nontreated, but remained elevated in omeprazole-treated animals. Mucosal blood flow increased about 100% 15 minutes after damage (P < 0.001), irrespective of secretory state. Bicarbonate availability (arterial [HCO(3-)] x mucosal blood flow) was significantly related to luminal release of bicarbonate from the newly damaged (P < 0.01) but not from the restituted mucosa.

CONCLUSIONS

(1) From the newly damaged mucosa, the luminal release of bicarbonate is related to availability of blood-borne bicarbonate. (2) From acid-stimulated restituted mucosa, the bicarbonate produced by the parietal cells is not released to the lumen, but either consumed within the mucosa by back-diffusing H+ or distributed to the systemic circulation.

Oesophageal and gastric potential difference and pH in healthy volunteers following intake of coca-cola, red wine, and alcohol

Alcohol causes gastroesophageal reflux and mucosal damage in the oesophagus and the stomach. The transmucosal electrical potential difference gives information on gastric mucosal integrity and function, while the validity of oesophageal measurements have been discussed. Baseline oesophageal potential difference measurements were performed three times with an interval of at least one week. We found oesophageal potential difference measurements reliable with an acceptable reproducibility. Oesophageal and gastric potential difference and pH were measured by use of a new microelectrode principle in 10 healthy volunteers following intake of coca-cola, wine and alcohol. Oesophageal and gastric potential difference decreased after intake of 250 ml coca-cola, 250 ml 11 vol% red wine and 60 ml 43 vol% whisky. Gastric potential difference decreased after intake of 250 ml ethanol 11 vol% and 60 ml ethanol 43 vol%. Intake of red wine and whisky resulted in a significant greater gastric potential difference decrease compared to similar concentrations and volumes of ethanol. The time until the potential difference had regained baseline level was longer after intake of red wine compared to coca-cola, whisky and ethanol. Oesophageal pH decreased after intake of coca-cola and red wine, but was unchanged after whisky. Gastric pH was unchanged after intake of all the drinks. In conclusion, the gastric potential difference reduction was not correlated to alcohol concentration. Red wine seems to affect the gastric potential difference more than coca-cola, whisky and ethanol. The observed changes in oesophageal and gastric potential difference might be due to changes in Cl- secretion and/or due to a damaging effect of the additives of the beverages.

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.

Dual effects of N-ethylmaleimide on ethanol-induced gastric lesions in rats

The effects of N-ethylmaleimide (NEM), a sulfhydryl (SH) blocker, on ethanol-induced gastric lesions were investigated in rats by varying the route of administration. Oral administration of acidified ethanol (60% ethanol in 150 mM HCl, 1 ml) produced hemorrhagic bandlike lesions in the gastric mucosa. Pretreatment of the animals with orally administered NEM (0.1-10 mg/kg) dose-dependently inhibited these lesions (the inhibition was over 80% at 1 mg/kg or greater), and the effects were partially reversed by indomethacin (5 mg/kg, subcutaneous). However, when NEM (10 mg/kg) was given subcutaneously, this agent significantly worsened the lesions. Intragastrically applied NEM produced a dose-dependent reduction of the transmucosal potential difference (PD) and the mucosal nonprotein SH levels, an increase of the volume of gastric contents, and an inhibition of gastric motility, while these parameters remained unaltered after subcutaneous administration of the agent. The microvascular permeability in the mucosa was significantly increased by both oral and subcutaneous administration of NEM (10 mg/kg) but remained unchanged in response to lower doses of orally administered (less than 3 mg/kg). These results suggest that NEM given orally is cytoprotective to the stomach against ethanol, probably by acting as a mild irritant and due to dilution of an irritant and inhibition of gastric motility (muscle relaxation), but when given subcutaneously it aggravates the lesions by unknown mechanisms.

Afferent nerve-mediated protection against deep mucosal damage in the rat stomach

Intragastric capsaicin protects against ethanol-induced gross mucosal lesion formation by stimulation of afferent nerve endings in the rat stomach. The aims of the present study were to examine histologically the protective effect of capsaicin and to test whether this effect is related to changes in mucosal eicosanoid formation and mucosal blood flow. Intragastric capsaicin (160 microM) significantly reduced gross mucosal lesion formation induced by 25% ethanol. Light microscopy revealed that the depth of erosions was attenuated likewise. However, capsaicin did not prevent ethanol from causing superficial damage to the mucosa as observed by light and scanning electron microscopy. The protective action of capsaicin against ethanol remained unchanged by a dose of indomethacin that reduced the ex vivo formation of prostaglandin E2 and 6-oxo-prostaglandin F1 alpha in the gastric mucosa by about 90%. Capsaicin alone did not affect the ex vivo formation of these prostaglandins and of leukotriene C4. Intragastric capsaicin (160 microM) enhanced gastric mucosal blood flow by 89% as measured by the hydrogen gas clearance technique. This effect was also observed when capsaicin was administered together with 25% ethanol. These data indicate that afferent nerve stimulation by intragastric capsaicin protects against deep mucosal damage in response to ethanol, an effect that seems related to an increase in mucosal blood flow but not to eicosanoid formation.

Different effects of cytoprotective drugs on ethanol- and aspirin-induced gastric mucosal injury in pylorus-ligated rats

In anesthetized rats oral administration (2 ml) of both ethanol (50% in 150 mM HCl) and aspirin (80 mM in 150 mM HCl) produced bandlike lesions in the stomach, while more generalized lesions occurred in the pylorus-ligated stomach when the irritant was given intragastrically through the fistula prepared in the rumen and the mucosal folds were removed by stomach distension. The bandlike lesions induced in the intact stomach by both irritants were significantly and dose-dependently prevented by 16,16-dimethyl PGE2 (dmPGE2: 3 and 10 micrograms/kg, subcutaneously), cysteamine (30 and 100 mg/kg, subcutaneously) or timoprazole (10 and 30 mg/kg, per os) at the doses which significantly inhibited gastric motility. In the pylorus-ligated stomach, however, neither of these agents showed any protection against the generalized lesions induced by ethanol, but such lesions caused by aspirin were significantly prevented only by dmPGE2. These agents also showed similar effects against the reduction of transmucosal PD in the pylorus-ligated stomach exposed to ethanol and aspirin. These results suggest that (1) the formation of bandlike lesions caused by ethanol and aspirin depends on the presence of mucosal folds and may be prevented by the agents that inhibit gastric motility, (2) the pathogenesis of the lesions induced by aspirin and ethanol may be different in the pylorus-ligated stomach, and (3) dmPGE2 has a unique protective ability that is not shared by usual cytoprotective agents.

Effects of gastric distension and prostaglandin on acid ethanol-induced mucosal lesions in the rat

The effects of gastric distension on the morphology of acidified ethanol (AE) -induced mucosal lesions and on the protective action of 16,16-dm PGE2 were investigated in rats. AE (50% ethanol in 150 mM HCl) was given by gavage in the intact stomach or through a fistula prepared in the forestomach in the pylorus-ligated stomach. AE produced elongated bands of hemorrhagic necrosis within 1 hr in the former, while in the pylorus-ligated stomach the shape of lesions varied depending upon the volume of irritant. One milliliter produced bandlike lesions, whereas 2 ml or more induced widespread lesions; such volumes were observed to remove the mucosal folds. 16,16-dm PGE2 (0.3-10 micrograms/kg, subcutaneous) dose dependently reduced bandlike lesions in the intact stomach, but had no or little effect on non-band-like lesions in the pylorus-ligated stomach. This agent (10 micrograms/kg) had a slight effect on the reduction of PD caused by 10-min exposure of the stomach to AE (2 ml) in the intact stomach, while such effects were not apparent in the pylorus-ligated stomach. Oral gentian violet (2 ml, 0.3% w/v) produced bandlike staining of the mucosa in intact rats, but the effect was blocked by pyloric ligation. 16,16-dm PGE2 also significantly prevented the localized staining pattern seen in intact rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Subepithelial tissue pH of rat gastric mucosa exposed to luminal acid, barrier breaking agents, and hemorrhagic shock

Tissue pH in the immediate subepithelial layer of rat gastric mucosa was measured using H+-selective microelectrodes. Exposure of the mucosa to luminal acid (50-150 mM) caused a significant acidification of the subepithelial tissue. Contrary to expectation, disruption of the mucosal barrier with taurocholate (10 mM), acetylsalicylic acid (10 mM), or ethanol (20% vol/vol) during acid (100 mM HCl) perfusion promoted no further acidification of the subepithelial tissue but rather caused an alkalinization of the primarily acidified subepithelial tissue. When hemorrhagic shock was induced during acid perfusion, a profound acidification of the subepithelial tissue occurred even though a much lower luminal acidity (10 mM HCl) was used. Also, taurocholate had no alkalinizing influence on subepithelial pH during hemorrhagic shock, but caused a rapidly progressing and irreversible drop of the subepithelial tissue pH. The findings suggest that in normal stomach with intact "mucosal barrier," H+ back-diffusion occurs during exposure to acid. However, disruption of the mucosal barrier seems to lead to alkali (HCO3-) efflux from the mucosa, which neutralizes the influxing H+, thus "masking" H+ back-diffusion and protecting the mucosa. Yet, when adequate supply of HCO3- to the mucosa is blocked during exposure to a barrier-breaking agent and acid, increased H+ back-diffusion becomes again "unmasked," leading to extensive acidification and ulceration of the mucosa.

Effect of ethanol on frog gastric mucosa. Electrophysiologic and morphologic correlations

The effects of and recovery from luminal ethanol (0%-100%) were assessed in the in vitro chambered frog gastric mucosa. At concentrations of 5%-10%, the potential difference decreased during exposure, but recovered after washout. No gross or light microscopic changes were observed. During exposure to 20%-40% ethanol, potential difference and short circuit current decreased and resistance increased, with only partial recovery after removal of the alcohol. Acid secretion ceased at 20% ethanol and alkalinization of the luminal solution was observed at greater than or equal to 30% ethanol. Microscopy of this group showed discharge of mucus, separation of oxynticopeptic cells from the basal lamina, and slough of surface epithelium. At 60%-100% ethanol, potential difference and short circuit current decreased and resistance increased markedly but there was no recovery. Microscopy showed changes similar to those of the intermediate group (20%-40%), except that surface epithelial cells were fixed to the basal lamina rather than sloughing. The morphologic effects of 100% ethanol in vivo were similar to those in vitro. Pretreatment with 10(-5) M 16,16-dimethyl prostaglandin E2 did not prevent either the electrophysiologic or the histologic changes caused by 20% and 30% ethanol. We conclude that there is a gross discrepancy between the functional and morphologic findings after high concentrations of luminal ethanol.

The effects of steroids upon the gastrointestinal tract

The steroid hormones and bile acids are important to digestive tract structure and function. Glucocorticoids administered during pregnancy have been shown to induce cleft palate in the offspring in several species. Postnatally, a significant rise in corticosterone during week 3 in the rat coincides with profound morphological and biochemical changes in the small intestine toward the adult state. Exogenous glucocorticoids given suckling rats leads to precocious development of these changes. In the adult, glucocorticoids increase brush border enzyme levels, while adrenal insufficiency decreases mucosal weight, enzyme activity, and absorptive functions. Water and sodium absorption and potassium excretion are enhanced in both small and large intestine. The jejunum, through its sense of food, provides the entraining signal that governs corticosterone rhythm. In the stomach, high doses of glucocorticoids inhibit prostaglandin biosynthesis, thereby inhibiting the gastric alkaline response and producing severe gastric lesions. However, in man, peptic ulcer disease is not clearly associated with glucocorticoid therapy. Exacerbation of subclinical intestinal infections and perforative lesions have been observed in both animals and man given glucocorticoids. The female sex hormone estrogen, when given to rats, stimulates intestinal enzyme levels and facilitates absorption. Progesterone inhibits both circular and longitudinal smooth muscle contractile activity. Virtually the entire pool of bile acids is found in the enterohepatic circulation. The dihydroxy secondary bile acids, regardless of their conjugation states, are physiologically and morphologically more damaging to mucosal cell membranes than are the trihydroxy primary bile acids.

Irritative and protective activity of mild irritants in rat stomach

Exposure of the stomach for 30 min to acidified sodium taurocholate (TC) (1-20 mM) or sodium salicylate (SA) (10-80 mM) caused a reduction of transmucosal PD and an increase of luminal pH in anesthetized rats, in a concentration-related manner. Acidified aspirin (ASA) (10-80 mM) reduced PD in the same manner, without significant effect on pH. Histologically, these agents similarly produced damage to the surface cells. After a 30-min exposure to either 20 mM TC or 40 mM SA, acid secretion ceased and bicarbonate (0.5-1 mumol/10 min) appeared in the lumen, whereas acid secretion persisted in the stomach exposed to 40 mM ASA. However, under cimetidine infusion (8 mg/kg/hr) these agents produced similar degrees of luminal alkalinization (approximately 1 mumol/10 min). Pretreatment with indomethacin (5 mg/kg, subcutaneously) significantly inhibited the increase of pH seen after exposure to 20 mM TC, but had no effect on the increase of pH caused by 40 mM SA. Concurrent administration of 16,16-dmPGE2 (3 micrograms/kg, subcutaneously) significantly antagonized the effect of indomethacin in the stomach exposed to 20 mM TC and even increased the pH in the stomach exposed to 40 mM ASA. After a 3-hr exposure to these agents, there was macroscopically apparent damage only in the stomach exposed to ASA, although the PD was similarly reduced in response to either agent. The levels of PGE2 in the corpus mucosa were significantly increased in stomachs exposed to 20 mM TC and 40 mM SA, but decreased in those exposed to 40 mM ASA.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional and morphological alterations in the rat stomach following exposure to hypertonic NaCl solution

We examined the effects of 1 M NaCl as a mild irritant on gastric potential difference (PD), acid secretion, mucosal blood flow (MBF), and DNA synthetic activity in anesthetized rat stomachs and compared these effects with those of 4 M NaCl as a strong irritant. Both 1 M and 4 M NaCl produced a PD reduction (mucosal injury), but the reduced PD recovered faster in the mucosa exposed to 1 M NaCl as compared to 4 M NaCl. Acid secretion ceased after exposure to these hypertonic NaCl solutions, but histamine infusion (8 mg/kg/hr) stimulated acid secretion only in the mucosa exposed to 1 M NaCl. The MBF was significantly increased in response to 1 M NaCl, while exposure to 4 M NaCl had no effect on the MBF. These changes in acid secretion and MBF induced by 1 M NaCl were significantly antagonized by pretreatment with indomethacin (5 mg/kg, s.c.). The levels of PGE2 and 6-keto PGF1 alpha in the corpus mucosa were significantly increased in the stomach exposed to both 1 M and 4 M NaCl, and these increases disappeared in the presence of indomethacin. The rate of [3H]-thymidine incorporation was significantly reduced in the mucosa after exposure to 4 M NaCl, but remained unaltered in the stomach exposed to 1 M NaCl. These results suggest that although both 1 M and 4 M NaCl produced mucosal injury (PD reduction) and enhanced PGs formation, a variety of functional alterations mediated by PGs occurred in response to injury in the stomach exposed to 1 M NaCl. The presence or absence of these functional responses may be associated with the biphasic actions on the gastric mucosa of these hypertonic NaCl solutions as mild and strong irritants.

Variations of gastric transmucosal potential difference and lesion formation during hemorrhagic shock in the rat

We measured transmucosal potential difference (PD) of the stomach in anesthetized rats before, during, and after hemorrhagic shock, and investigated the effects of various drugs on the PD and gastric lesion during this period. After hemorrhagic shock, there was a decrease of PD and an increase of luminal pH in the saline-perfused stomach, the degree of these changes being dependent on a fall in the arterial blood pressure. The graded reduction of PD in response to hemorrhagic shock was similarly observed in the acid-perfused stomach as in the saline-perfused one. However, gastric lesions developed only in the former, and a significant correlation was found between the lesion index and the fall in blood pressure, the reduction in PD, or the concentration of HCl as the perfusate. Subcutaneously administered propantheline bromide (30 mg/kg) or cimetidine (100 mg/kg) had no effect on gastric lesion and PD reduction caused by hemorrhagic shock. These lesions were significantly inhibited by 16,16-dimethyl prostaglandin E2 (10 micrograms/kg) or sulindac (100 mg/kg), a scavenger of OH., and aggravated by indomethacin (1 mg/kg), with less effect on the PD reduction. Intravenous infusion of NaHCO3 (0.5 M) also significantly prevented the lesion with a concomitant suppression of the PD reduction in response to hemorrhagic shock, but these effects were significantly reversed by pretreatment of the animals with acetazolamide (50 mg/kg). These results indicate that during hemorrhagic shock the PD may largely reflect the impairment of mucosal blood flow and may be used as an indicator of mucosal vulnerability to acid, gastric lesions develop only in the presence of exogenous acid, and production of prostaglandins and superoxide radicals may be involved in the pathogenesis of gastric lesions.

Cytoprotective action of mast cell stabilizers against ethanol-induced gastric lesions in rats

We examined the effects of FPL-52694 and disodium cromoglycate (DSCG), mast cell stabilizers, on HCl X ethanol-induced gastric lesions in rats and investigated the factors involved in their protection. Oral (p.o.) administration of 1 ml of HCl X ethanol (60% in 150 mM HCl) induced linear hemorrhagic lesions in the gastric mucosa within 1 hr. FPL-52694 (1-30 mg/kg), given both p.o. and intraperitoneally (i.p.), prevented these lesions in a dose-related manner. DSCG (3-30 mg/kg) also dose-dependently reduced the formation of these lesions when this agent was given i.p. The protective effects of these drugs on HCl X ethanol-induced lesions were significantly attenuated by pretreatment with indomethacin (5 mg/kg, s.c.). Both gastric acid secretion and transmucosal potential difference were significantly reduced by topical application of FPL-52694 (greater than 10 mg/kg), but were not affected by i.p. administration of FPL-52694 and DSCG. On the other hand, gastric motor activity measured as intraluminal pressure recordings was significantly inhibited for 2 hr by both FPL-52694 (p.o. and i.p.) and DSCG (i.p.), and these effects were also significantly antagonized with prior administration of indomethacin. A significant relationship was found between the effects of these two drugs on the lesion index and the motility index (r: 0.9214, P less than 0.01), but not other factors. These results suggest that mast cell stabilizers such as FPL-52694 and DSCG protect the gastric mucosa against HCl X ethanol through a systemic action, probably mediated with endogenous prostaglandins. Although the mechanism of cytoprotection remains unknown, this property may be related to their inhibitory effects on gastric motor activity.

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.

Spizofurone, a new anti-ulcer agent, increases alkaline secretion in isolated bullfrog duodenal mucosa

The effect of spizofurone, a new anti-ulcer agent, on alkaline secretion was studied in an isolated sheet of bullfrog (10(-4)-10(-3) M) as well as prostaglandin E2 (PGE2, 10(-8)-10(-5) M) added to the nutrient solution increased alkaline secretion, transmucosal potential difference (PD) and short-circuit current (Isc), in a concentration-dependent manner. The maximum increases in alkaline secretion stimulated by spizofurone and PGE2 were much the same. Spizofurone also showed this effect when added to the secretory solution while PGE2 did not. Treatment with indomethacin partly but significantly inhibited the effect of spizofurone, but did not affect that of PGE2. These results indicate that the increase in alkaline secretion in bullfrog duodenal mucosa seen in the presence of spizofurone is mediated, at least in part, by stimulation of endogenous PGs synthesis.

Gastroduodenal HCO3-secretion in anesthetized rats: effects of 16,16-dimethyl PGE2, topical acid and acetazolamide

Alkaline secretion was measured in the whole stomach and in the proximal duodenum (2 cm proximal to the outlet of the common bile duct) of anesthetized rats, under basal conditions and in response to topical acid and 16,16-dimethyl PGE2 (16-dmPGE2) given by various routes. Gastric alkaline secretion was unmasked by intraduodenal administration of omeprazole (30 mg/kg). Both the stomach and duodenum consistently secreted bicarbonate in amounts of 0.2-0.4 microEq/15 min and 1.5-2 microEq/15 min as a basal secretion, respectively. 16-dmPGE2, either given subcutaneously (1-30 micrograms/kg), intravenously (3 micrograms/kg/hr) or by topical application for 30 min (0.3-10 micrograms/ml), (concentration)-dependently increased HCO3- secretion in both tissues, but this effect disappeared quickly after sacrifice with KCI (i.v.). Stimulation of HCO3- secretion was also caused by topical acid to the stomach (100 mM HCI for 10 min) or to the duodenum (10 mM HCI for 10 min), but was completely blocked by pretreatment with indomethacin (5 mg/kg, s.c.). Acetazolamide, given subcutaneously at 100 mg/kg, which gives over 80% inhibition of carbonic anhydrase activity in the gastroduodenal mucosa, had no effect on either basal or stimulated HCO3- secretion caused by 16-dmPGE2 (10 micrograms/kg, s.c.). These results indicate that both endogenous and exogenous (16-dmPGE2) prostaglandins stimulate alkaline secretion in the gastroduodenal mucosa of rats, and this mechanism is independent from the carbonic anhydrase activity of the tissue.

Vinegar is a dietary mild irritant to the rat gastric mucosa

Exposure of the rat stomach to acetic acid (0.3-3%) caused a concentration-dependent reduction of transmucosal potential difference (PD) and increase of luminal pH (gastric alkaline response). These concentrations of acetic acid, when given topically to the stomach, significantly prevented development of gastric lesions induced by subsequent exposure to absolute ethanol, the inhibition being 42.3%, 95.8% and 70.4% at concentrations of 0.3%, 1% and 3%, respectively. Gastric alkaline response and protection of ethanol-induced gastric lesions caused by 1% acetic acid were significantly attenuated by pretreatment of the animals with indomethacin (5 mg/kg, s.c.). Although other related carboxylic acids at 1% concentration such as citric acid (52 mM), maleic acid (86 mM) and formic acid (217 mM) affected both PD and luminal pH in varying degrees, these agents, except for 1% maleic acid, failed to prevent gastric lesions in response to absolute ethanol. Similar to 1% acetic acid (167 mM), gastric alkaline response and adaptive cytoprotection induced by 1% maleic acid were significantly antagonized by pretreatment with indomethacin. Formic acid also induced a significant gastric alkaline response, but this effect was not effected by indomethacin. These results suggest that dilute acetic acid such as vinegar (approximately 3% acetic acid) acts as a mild irritant to the stomach, and induces alkaline response and adaptive cytoprotection, mediated by endogenous prostaglandins. Other related carboxylic acids may have similar effects, but those depend upon the concentrations used.

Influence of prednisolone on gastric alkaline response in rat stomach. A possible explanation for steroid-induced gastric lesion

Exposure of the rat stomach for 10 min to 1 M NaCl produced an increase of luminal pH (alkaline response) with a concomitant reduction of the transmucosal potential difference (PD) and an increased generation of mucosal prostaglandins of E2 and 6-keto F1 alpha. Prednisolone (3-50 mg/kg), given subcutaneously 4 hr before exposure to 1 M NaCl, dose-dependently inhibited alkaline response without affecting the PD reduction, and at 50 mg/kg completely prevented the increased production of mucosal prostaglandins after exposure to 1 M NaCl. The inhibitory effect of prednisolone on alkaline response was significantly antagonized by pretreatment with 16,16-dimethyl prostaglandin E2 (16,16-dmPGE2) (3 micrograms/kg) or cycloheximide (1.5 mg/kg). A repeated administration of prednisolone (3-50 mg/kg), once daily for 4 days, produced gastric lesions dose-dependently. At 50 mg/kg, gastric lesions appeared after administration of this drug for more than 2 days, and the inhibition of alkaline response caused by 1 M NaCl became more potent as the days of treatment increased. Either 16,16-dmPGE2 (10-100 micrograms/kg) or cycloheximide (1 or 3 mg/kg), given daily in two divided doses for 4 days, dose-dependently inhibited formation of gastric lesions in response to prednisolone (50 mg/kg). These results indicate that prednisolone inhibits gastric alkaline response caused by 1 M NaCl by reducing generation of endogenous prostaglandins. The weakened self-defense mechanisms caused by prednisolone may be involved in the pathogenesis of steroid-induced gastric lesions.

Role of luminal Ca2+ on normal and damaged gastric mucosa in the rat

Influence of luminal Ca2+ on the integrity of normal mucosa and recovery of damaged mucosa in anesthetized rat stomachs was studied using a perfusion system. Changes in the mucosal integrity were monitored by measuring transmucosal potential difference (PD) and luminal pH. EDTA, a Ca2+ chelator, dose-dependently reduced PD and increased luminal pH. Five mM Ca2+ (CaCl2) alone produced no changes in either PD and luminal pH, but the PD which was reduced by 250 mM EDTA was significantly recovered. Ethanol or NaCl concentration-dependently reduced PD, but gradually reverted to baseline levels. While 5 mM Ca2+ or 5 mM EDTA did not influence the reduction in PD with 50% ethanol and 1 M NaCl, these agents either enhanced or delayed the recovery processes in reduced PD, respectively. Five mM Ca2+ enhanced the recovery of PD which was reduced by 50% ethanol plus 5 mM EDTA. Gastric damage induced by 50% ethanol plus 5 mM EDTA was much more severe than that induced by 50% ethanol alone or 50% ethanol plus 5 mM Ca2+. Both 50% ethanol and 1 M NaCl significantly increased Ca2+ contents in the gastric lumen. Luminal Ca2+ appears to play an important role in maintaining mucosal integrity, under normal physiological conditions, and in accelerating the recovery process of damaged mucosa in rat stomachs.

Gastric cytoprotection by pirenzepine in rats: evaluating method for cytoprotective activity by antisecretory agents

The effects of antisecretory agents, pirenzepine, atropine and cimetidine, on gastric mucosal lesions induced in rats by ethanol, HCI (0.6 N), HCI-acidified 50% ethanol and HCI-acidified 50 mM sodium taurocholate (TCA) were comparatively studied with PGE2. The involvement of gastric acid in the formation of ethanol-induced necrosis was also studied. PGE2 and pirenzepine inhibited necrosis induced by all necrotizing agents at the non-antisecretory doses, and the cytoprotective effect of pirenzepine was not abolished by indomethacin. Atropine and cimetidine did not inhibit HCI-induced necrosis even at the antisecretory dose. Atropine and cimetidine at the antisecretory dose inhibited necrosis induced by ethanol, but did not inhibit the red streaks. The ethanol-induced necrosis was also inhibited by neutralizing intragastric H+ with Tris buffer. In gastric fistula rats, alkalinization of the lumen was observed by exposure to ethanol, but necrosis was not produced. There is a close relationship between the necrosis and intragastric acid. Thus it is assumed that gastric acid is involved in the formation of ethanol-induced necrosis. It was suggested that pirenzepine possesses cytoprotective action which is not related to endogenous PGs. On the other hand, the antiulcer actions of atropine and cimetidine may be due, in a part, to antisecretory effects.

Possible role of endogenous prostaglandins in alkaline response in rat gastric mucosa damaged by hypertonic NaCl

Changes in gastric potential difference (PD) and luminal pH of gastric perfusate were studied in anesthetized rats before and after application of hypertonic NaCl to the stomach for 10 min. There was a concentration-dependent reduction of PD and an increase in luminal pH after exposure to NaCl. In the stomach exposed to NaCl over 0.75 M, a significant amount of HCO3- (0.5-1.5 mumol/10 min) was titrated in the lumen at pH 7.4 under cimetidine infusion (8 mg/kg/hr). After removal of hypertonic NaCl, the PD returned completely or partially to the basal values within 1 hr. Pretreatment of the rats with subcutaneously administered indomethacin (3 mg/kg) or aspirin (100 mg/kg) significantly inhibited the recovery of PD in the 1 M NaCl-treated stomach. Gastric alkaline response in the damaged mucosa was significantly attenuated in rats pretreated with indomethacin or aspirin. Intravenously administered cimetidine (8 mg/kg/hr) or subcutaneously administered 16,16-dimethyl prostaglandin E2 (3 micrograms/kg) abolished the inhibitory effect of indomethacin on gastric alkaline response caused by 1 M NaCl, and partially restored the PD recovery. These results indicate that endogenous prostaglandins released in the injured mucosa are probably responsible for the luminal alkalinization noted after exposure to 1 M NaCl. This process would lead to a protection against further damage and accelerate reestablishment of the mucosal integrity.