Early vascular injury and increased vascular permeability in gastric mucosal injury caused by ethanol in the rat

Experimental pathogenesis: drugs and chemical lesions in the gastric mucosa

The goals of this article are to review the similarities and differences in the pathogenesis of acute gastric mucosal injury induced by alcohol, exemplified mostly by ethanol, and aspirin, as a representative of nonsteroidal anti-inflammatory drugs, and to deduce implications from pathogenetic studies for a better understanding of the concept of gastric cytoprotection. The main similarity between the hemorrhagic erosions caused by ethanol and aspirin is their localization in the acid-producing glandular stomach, the rate-limiting step in their pathogenesis being the extent of microvascular injury in the gastric mucosa. The major differences include the fast healing and low probability of transition into chronic gastritis after a single exposure to aspirin. On the other hand, perforated ulcer may develop, especially in the elderly, after chronic aspirin but not ethanol consumption. The main implications of pathogenetic investigations include the relative nature of gastroprotection: that is, initially, the superficial epithelial layer is not protected against concentrated luminal solutions, but it is rapidly replaced by migrating, adjacent, surviving cells if blood flow is maintained and the basement membrane is relatively intact. Vascular changes thus seem to be the rate-limiting step both in the pathogenesis and prevention of chemically induced acute gastric mucosal injury. The ultimate biochemical mechanisms of gastroprotection seem to include an effect on structural and enzymic proteins, and vascular mediators which influence vascular permeability and, indirectly, the extent of tissue injury.

Possible mechanism of gastric mucosal protection by epidermal growth factor in rats

The mechanism of the protection by human epidermal growth factor (hEGF) against the gastric mucosal lesions induced by acidified ethanol was studied in rats. At different times following the subcutaneous administration of hEGF (30 micrograms/kg), intragastric acidified ethanol (EtOH: 0.125 M HC1 = 50:50 v/v%) was administered to induce an experimental gastric mucosal lesion. Mean length of the lesion in the gastric mucosa was used as a lesion index. Extravasation of intravenously injected Evans blue into the gastric wall and gastric contents was used as an indicator of vascular permeability. Pretreatment with hEGF decreased both the gastric mucosal lesions and the increase of vascular permeability caused by acidified ethanol with similar time profiles relative to pretreatment with hEGF. Maximal protective actions of hEGF occurred about 10 to 30 min after the observed peak plasma concentration of hEGF. Indomethacin and N-ethylmaleimide, but not iodoacetamide, blocked the protective action of hEGF, indicating that endogenous prostaglandins and/or sulfhydryls may participate in the protective action of hEGF. The content of endogenous nonprotein sulfhydryls in the gastric mucosa decreased markedly after acidified ethanol. However, pretreated hEGF did not restore the sulfhydryl contents. Thus, it seemed that endogenous prostaglandins, but not sulfhydryls, are the probable mediators for protection against gastric mucosal injury caused by acidified ethanol.

Protective effect of human epidermal growth factor against the experimental gastric mucosal lesions in rats

The protective effect of human epidermal growth factor (hEGF) on the gastric mucosal lesions in rats was examined in relation to the immunoreactive concentration of plasma. Human EGF (30 micrograms/kg) was administered intravenously, intraperitoneally or subcutaneously. At different times following the administration of hEGF, rats received acidified ethanol solution to induce an experimental gastric mucosal lesion. Sum of lesion length in the gastric mucosa was used as a lesion index. Human EGF administered parenterally markedly decreased the gastric mucosal lesions in 10 min after administration of necrotizing solution, and 10 to 30 min delay was observed in the development of maximal protective action. Profiles of protective potency against the hEGF dose administered intraperitoneally or subcutaneously 30 min before administration of necrotizing solution revealed that the effective dose of hEGF (ED50) was about 5.2 and 2.6 micrograms/kg, for intraperitoneal and subcutaneous administrations, respectively.

Antacids: new perspectives in cytoprotection

There is increasing evidence that aluminum-containing antacids are able to protect the gastric mucosa against various ulcerogenic and necrotizing agents including 0.6 M HCl, 0.2 M NaOH, and absolute alcohol. Since gastric mucosal necrosis produced by alcohol is independent of luminal acid and cannot be reduced by H2-receptor antagonists, the protective action of antacids is accomplished by mechanism(s) other than acid-neutralizing ability. In addition, since acidified antacids can protect the gastric mucosa even better than an antacid with intact neutralizing capacity, it is clear that such action is independent of acid-neutralizing ability and therefore has all the features of cytoprotection. Whereas the cytoprotective action of antacids in experimental conditions is well established, the mechanisms of antacid-induced mucosal protection are not known. The clinical relevance of antacid-induced protection also requires further elucidation. Antacids have advantages over the H2 blockers in protecting the gastric mucosa against alcohol-induced necrosis and in preventing stress-induced ulcers in critically ill patients. Although more work is needed to clarify the mechanisms of cytoprotective action of antacids, the recent experimental findings gave a new life to and new potential clinical applications for antacids.

Protection of gastric mucosa against hypertonic sodium chloride by 16,16-dimethyl prostaglandin E2 or sodium thiosulfate in the rat: evidence for decreased mucosal penetration of damaging agent

Protection of the gastric mucosa may be the result of either increased cellular resistance to injury (cytoprotection) or, alternatively, decreased exposure of mucosal cells to the damaging agent. To determine whether decreased exposure of mucosal cells to damaging agents plays a role in mucosal protection by 16,16-dm PGE2 or sodium thiosulfate, we estimated the intramucosal concentration of 22NaCl and measured its absorption from the gastric lumen into the systemic circulation 1 and 5 min after intragastric administration of hypertonic (25% w/v) 22NaCl. In an attempt to explain the differences observed, we also measured the net transmucosal water flux in control animals and rats pretreated with the protective agents. Administration of hypertonic NaCl rapidly (within 1 min) induced extensive hemorrhagic mucosal lesions that were significantly reduced by pretreatment with 16,16-dm PGE2 or sodium thiosulfate. Ultra-low temperature autoradiography indicated that luminal hypertonic 22NaCl penetrates the upper layers of the mucosa in relatively high concentrations (12.5% w/v) within 1 min but its concentration decreases rapidly and reached low levels (3.12% w/v) by 5 min. Absorption of NaCl from the gastric lumen into the systemic circulation 1 and 5 min after hypertonic NaCl was lower in both pretreatment groups than in the control. Net gastric transmucosal water flux (from serosa to mucosa) increased (P less than 0.05) from 100 +/- 2 in controls, to 1470 +/- 8 and 715 +/- 9 microliters in rats pretreated with 16,16-dm PGE2 and sodium thiosulfate, respectively. We conclude that 16,16-dm PGE2 and sodium thiosulfate protect the gastric mucosa against hypertonic NaCl, diminish mucosal penetration of NaCl, decrease mucosal absorption of NaCl, and significantly increase serosal to mucosal transmucosal water flux.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelial cell growth regulation by PGE1 analog misoprostol and indomethacin

The role of prostaglandins on growth regulation of different cell types was investigated. We studied the effect of exogenous misoprostol in the presence or absence of indomethacin on the cell growth kinetics. Our results clearly show that misoprostol strongly inhibited the growth of several cancer cells but only slightly affected that of endothelial cells. Moreover, indomethacin alone (which decreases PG synthesis) had little effect on DNA synthesis in endothelial cells or C6 cells but inhibited colonic cancer cells. Conversely, misoprostol stimulated DNA synthesis in endothelial or C6 cells preincubated with indomethacin. This phenomenon was not observed with colonic cancer cells. The role of NSAIDs in the field of cytoprotection is discussed.

Dual effects of zinc sulphate on ethanol-induced gastric injury in rats: possibly mediated by an action on mucosal blood flow

The present study examines the protective effect of zinc sulphate against ethanol-induced gastric mucosal ulcers in rats. Absolute ethanol decreased the gastric mucosal blood flow and produced haemorrhagic lesions in the glandular mucosa. Zinc sulphate preincubation in an ex-vivo stomach chamber preparation prevented the formation of ethanol-induced lesions and attenuated the decrease of blood flow produced by ethanol. Subcutaneous injection of the same doses of the drug at 15 and 30 min before ethanol exposure, markedly reduced the blood flow and also aggravated ethanol-induced gastric injury; however, when injected at 23 and 24 h before ethanol administration, zinc sulphate protected against lesion formation but had no effect on the vascular changes induced by ethanol in the gastric glandular mucosa. These findings show that the antiulcer effect of zinc sulphate occurs only when the drug is given orally, or injected s.c. 23 and 24 h before ethanol challenge. Furthermore, this protective action is probably not entirely mediated by preservation of the gastric mucosal blood flow.

Probable role of both sulfhydryls and prostaglandins in gastric mucosal protection induced by S-adenosylmethionine

The role of both sulfhydryl groups and endogenous prostaglandins in the protective effect of S-adenosylmethionine against ethanol-induced gastric mucosal damage was studied in rats. Drugs were administered subcutaneously or intragastrically to fasted rats 30 or 60 min before 100% ethanol (1 ml/rat), and mucosal lesions were measured planimetrically 1 h later. The gastric mucosal protection given by S-adenosylmethionine or by 20% ethanol (adaptive protection) was significantly diminished by pretreatment of rats with the sulfhydryl blocker iodoacetamide or with the cyclooxygenase inhibitor indomethacin. The protective effect of S-adenosylmethionine could be totally abolished only by pretreatment with the combination of iodoacetamide and indomethacin. Our present data suggest that endogenous release of prostaglandins and sulfhydryl groups may play a role in the protective actions of both S-adenosylmethionine and 20% ethanol (adaptive protection) against ethanol-induced gastric mucosal damage.

Prostaglandin prevents aspirin injury in the canine stomach under in vivo but not in vitro conditions

This study compared the ability of topical 16,16-dimethyl prostaglandin E2 in a dose range of 0.3-3.0 micrograms/ml to prevent aspirin-induced injury in the canine stomach under both in vivo and in vitro conditions. For in vitro studies, isolated strips of oxyntic mucosa were exposed to 10 or 20 mM aspirin (ASA) at pH 1-4, with and without treatment with 16,16-dimethyl prostaglandin E2. For in vivo experiments, a portion of the oxyntic stomach was mounted between the rings of a Lucite chamber, with splenic vessels intact, such that the mucosa was divided into halves. Both sides were exposed to 20 mM ASA at pH 1 or 2, and one side also received concomitant treatment with 16,16-dimethyl prostaglandin E2. After ASA exposure, tissue samples were prepared for quantitative microscopic analysis of the degree of injury. Under both experimental conditions, the magnitude of gastric injury by ASA was pH-related, being most pronounced at pH 1; this damage was worse under in vitro conditions, and both concentrations of ASA were equally damaging in this setting. 16,16-Dimethyl prostaglandin E2 failed to prevent ASA injury in vitro at any pH and ASA concentration tested, but markedly reduced the magnitude of injury in vivo. The most effective protective dose of 16,16-dimethyl prostaglandin E2 under in vivo conditions was 1.0 micrograms/ml. The diminished tolerance to ASA damage in vitro when compared with in vivo, and the inability of 16,16-dimethyl prostaglandin E2 to prevent these damaging effects in vitro, underscores the probable crucial role for blood flow, and possibly neural innervation, in mediating the protective effects of prostaglandins.

Lipoxygenase metabolites in the rat gastric microvascular response to intragastric ethanol

The role of lipoxygenase metabolites in ethanol-induced gastric mucosal injury and submucosal microvascular change in the rat was studied by in vivo microscopy. Intragastric ethanol-instillation caused marked submucosal venular constriction, dilatation of small arterioles, and corpus mucosal gross lesion formation. The venoconstriction was greater in the lesion than in the nonlesion area. Intragastric pretreatment with either BW755C, a lipoxygenase inhibitor, or Rioprostil, a synthetic prostaglandin E1 analogue, significantly inhibited both the ethanol-induced venoconstriction and the gross lesion formation. In contrast, pretreatment by the submucosal application of either BW755C (50 micrograms/ml) or Rioprostil (50-500 ng/ml) had no effect on either the submucosal venoconstriction or the mucosal lesion formation. In conclusion, leukotrienes released from the gastric mucosa appear to be involved in the ethanol-induced submucosal venoconstriction associated with gastric mucosal injury. Prostaglandin pretreatment protects against this venoconstriction and gross lesion by a mucosal effect but not by a direct effect on submucosal venules.

Prostaglandin protection against hemorrhage-induced gastric stress ulceration in the rat

The present study investigates whether prostaglandins "cytoprotect" the gastric mucosa against hemorrhage-induced stress ulceration by assessing the influence of 16,16-dimethyl prostaglandin E2 (16,16-dm PGE2) on gross and microscopic lesion formation, intramucosal tissue pH, H+ back-diffusion, and mucosal blood flow in rat gastric mucosa exposed to luminal acid (100 mM HCl) during hemorrhagic shock (13 ml/kg for 20 min). Intramucosal tissue pH was measured using pH-sensitive antimony microelectrodes, and mucosal blood flow was measured by the radiolabeled microsphere technique. 16,16-dm PGE2 (5 micrograms/ml topically) significantly protected the gastric mucosa against gross (lesion index 2.25 +/- 0.34 vs 0.87 +/- 0.21) and microscopic (lesion index 2.12 +/- 0.20 vs 0.87 +/- 0.09) damage during the shock. This protection was associated with a significantly lesser acidification of the mucosa during the shock (intramural tissue pH 6.67 +/- 0.08 vs 6.03 +/- 0.17). In order to elucidate whether the lesser intramucosal acidification was due to diminished entry of H+ (H+ back diffusion) into or better disposal of H+ from the mucosa, the influences of 16,16-dm PGE2 on transmucosal H+ fluxes and mucosal blood flow were determined. It appeared that 16,16-dm PGE2 had no influence on the rate of H+ back-diffusion, but it significantly enhanced mucosal blood flow both in the corpus (0.23 +/- 0.04 vs 0.14 +/- 0.03 ml/min/g) and in the antrum (0.24 +/- 0.03 vs. 0.14 +/- 0.03 ml/min/g) during the shock.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathways of gastrointestinal protection and repair: mechanisms of action of sucralfate

Protection, i.e., prevention of major lesions and the mechanisms of repair/healing of major tissue loss in the gastrointestinal mucosa, are multifactorial processes. Conceptually, it is useful to categorize the components and mechanisms of gastroprotection and distinguish between: (1) Preservation of existing cells either by enhanced resistance of cells or by decreased exposure to damaging agents that can be achieved by maintenance of proper blood flow, vascular permeability, motility, mucus and bicarbonate secretion. If these mechanisms fail and tissue necrosis ensues, (2) replacement of lost tissue is achievable by either the original cells (e.g., epithelia), by cell migration (restitution) and proliferation (regeneration), and/or by connective tissue repair (e.g., fibroblasts, collagen) through cell proliferation and production of extracellular matrix. For acute gastroprotection ("cytoprotection"), maintenance of blood flow in the upper mucosa and epithelial restitution are listed as key mechanisms. For the long-term safeguarding of the mucosa, proper mucus and bicarbonate secretion, as well as ability to respond by cell proliferation, are the proposed key mechanisms of mucosal defense. The mechanisms of action of sucralfate are also multifactorial. The acute gastroprotection by sucralfate is a prostaglandin- and sulfhydryl-sensitive process: after early protection of microvasculature and maintenance of blood flow, along with direct or indirect preservation of the proliferative zone, rapid restitution repairs the initial epithelial defect. The mechanisms of accelerated healing by sucralfate of chronic ulcers include enhanced mucus and bicarbonate secretion, increased ability of mucus to maintain pH gradient, stimulated binding of epidermal growth factor and other growth factors, and maintained or enhanced blood flow resulting in increased cell proliferation leading to granulation tissue formation and re-epithelialization. The slight direct antipeptic and bile-acid binding property of sucralfate might also contribute to its ability to accelerate ulcer healing.

Mechanism of ethanol-induced jejunal microvascular and morphologic changes in the dog

To study the mechanism of morphologic and microvascular effects of intraluminal ethanol, we perfused jejunal segments of the dog with 6% (wt/vol) ethanol for 0 (control), 10, 20, 30, 60, and 90 min, and measured the time-dependent changes in (a) the prevalence of villi with epithelial damage (i.e., villi with intact blebs plus those with broken blebs) and those without epithelial damage (undamaged villi), (b) the height of the villus core and the patency of lacteals, (c) jejunal albumin loss, and (d) permeability of microvessels of the villus tip by colloidal carbon vascular labeling. We found that (a) the prevalence of villi with epithelial damage or with intact bleb increased progressively during the first 20 min of ethanol perfusion and then declined gradually; (b) the height of the villus core and the patency of lacteals in the undamaged villi and in those with intact bleb decreased during the first 20 min and then gradually increased; and (c) jejunal albumin loss and the prevalence of villi with carbon labeling increased for the first 30 min, after which the former declined gradually whereas the latter remained at a plateau. These findings suggest that contraction of the villus core and compression of the lymphatics are the primary cause of ethanol-induced epithelial damage, which is accentuated by increased microvascular permeability and consequent protein leakage. The mechanism of recovery of most parameters, in spite of continuous ethanol perfusion, remains to be investigated.

Beneficial effects of prostaglandin E2 in endotoxic shock are unrelated to effects on PAF-acether synthesis

The effects of endotoxic shock on the synthesis of PAF-acether by the stomach, duodenum and lung were examined in the rat. Furthermore, the effect of pretreatment with prostaglandin E2 on endotoxin induced PAF-acether synthesis and changes in vascular permeability were examined. Administration of endotoxin resulted in significant increases in PAF-acether synthesis in all tissues studied. Such increases were apparent within 5-15 minutes of the administration of endotoxin, corresponding to the time when significant hypotension, hemoconcentration and increases in gastrointestinal vascular permeability were first observed. Pretreatment with prostaglandin E2 resulted in a significant reduction of endotoxin-induced hypotension, hemoconcentration and changes in vascular permeability in the gastrointestinal tract. However, prostaglandin pretreatment did not significantly alter endotoxin-induced PAF-acether release from the gastrointestinal tissues studied. These results demonstrate that prostaglandin E2 can significantly attenuate several of the systemic and gastrointestinal manifestations of endotoxic shock. The mechanism responsible for these beneficial actions appears to be unrelated to effects of prostaglandin E2 on PAF-acether synthesis.

Modulating action of melatonin on serotonin-induced aggravation of ethanol ulceration and changes of mucosal blood flow in rat stomachs

Effects of melatonin and serotonin on ethanol ulceration and mucosal blood flow in the rat stomach were investigated. Melatonin and serotonin (5-HT) administration did not produce observable gastric injury in the ex vivo stomach, but the 5-HT dose dependently reduced glandular mucosal blood flow (GMBF) in this organ. Ethanol depressed GMBF and induced visible glandular mucosal injury. The latter effect was prevented by melatonin preincubation. Serotonin pretreatment aggravated the gastric mucosal injury and GMBF changes induced by ethanol; these actions were partially reversed by melatonin. The findings indicate that the GMBF and gastric injury are related; the reduction in FMBF, however, may not be the sole factor responsible for ulceration. The antagonistic effects of melatonin on 5-HT action on the stomach suggest that melatonin may act as a modulator for 5-HT action on the gastrointestinal tract.

Effects of dopamine on gastric mucosal lesions induced by ethanol in rats. Possible involvement of antigastric motor activity mediated with alpha 2-adrenoceptors

Acidified ethanol (60% ethanol in 150 mM HCl, per os) induced elongated bands of hemorrhagic lesions along the long axis of the stomach within 1 hr in rats. Pretreatment with dopamine hydrochloride (DA: 1-10 mg/kg, subcutaneously) dose-dependently reduced the severity of these lesions. In parallel study, DA had no effect on acid secretion but inhibited gastric motor activity in a dose-related manner. The inhibitory effects of DA on both acidified ethanol-induced lesions and gastric motor activity were significantly reversed by pretreatment with yohimbine, an inhibitor of alpha 2-adrenoceptors (5 mg/kg, subcutaneously), but not by prazosin, haloperidol, or indomethacin. Similar to DA, both norepinephrine (NE: 1 mg/kg, subcutaneously) and epinephrine (EPI: 1 mg/kg, subcutaneously) showed inhibition of the motor activity and gastroprotection against acidified ethanol, but these effects were also significantly attenuated by yohimbine. A highly significant relationship was found between the inhibitory effects of DA, NE, and EPI on the motor activity and the mucosal lesions (r = 0.8577, P less than 0.05). In addition, administration of gentian violet (0.5% w/v, per os) stained the mucosa deep blue as elongated wide bands in the corpus region, and such localized staining was significantly prevented by DA, suggesting a flattening of the mucosal foldings in the presence of DA. These results suggest that DA (and other catecholamines) protects the rat gastric mucosa against injury caused by acidified ethanol, probably through inhibition of gastric motor activity mediated with stimulation of alpha 2-adrenoceptors.

Microvascular abnormalities of the portal hypertensive gastric mucosa

Compared with normotensive mucosa, the portal hypertensive gastric mucosa has increased susceptibility to injury by noxious agents such as alcohol and aspirin, but the mechanism of this phenomenon is unclear. Since the microvasculature of the normal gastric mucosa is an important target of injury by these agents, we studied the histologic and ultrastructural features of gastric vasculature and mucosal microvasculature in rats with portal hypertension (produced by staged portal vein ligation) and in sham-operated rats. In portal hypertensive rats, the gastric mucosa was swollen and hyperemic and the endothelial cells of mucosal microvessels had very prominent enlarged cytoplasm obstructing capillary lumina. Quantitative analysis of transmission electron micrographs demonstrated that in portal hypertensive rats the gastric mucosal capillary endothelium had significantly increased cytoplasmic area (236%), increased pinocytic vesicular area (416%) and increased capillary basement membrane thickness (143%) compared to respective parameters in sham-operated control rats. Arterioles in the muscularis mucosae and in submucosa were thickened, and submucosal veins demonstrated features of arterialization. All these findings indicate that portal hypertension produces definite microvascular changes in the gastric mucosa resulting in compromise of the capillary lumina. These changes may be the basis for the observed morphologic and functional abnormalities of the portal hypertensive mucosa and its increased predisposition to injury.

Histamine is involved in ethanol-induced jejunal microvascular injury in rabbits

To examine for the possible involvement of histamine in the jejunal microvascular effects of ethanol, we investigated the effects of (a) intraluminal ethanol on histamine release by the jejunum and (b) simultaneous inhibition of both histamine1 and histamine2 receptors (using promethazine and cimetidine, respectively) on ethanol-induced intestinal plasma protein loss in rabbits. Ethanol increased histamine release by the jejunum both in vivo (p less than 0.01) and in vitro (p less than 0.05). To investigate the effect of antihistamines on ethanol-induced plasma protein loss, we determined the dose of blockers that would completely inhibit the histamine1 and histamine2 receptors. In the absence of antihistamines, ethanol caused a 10-fold increase in jejunal protein loss over the controls (p less than 0.001). Simultaneous inhibition of histamine1 and histamine2 receptors attenuated (p less than 0.025), but did not abolish, the ethanol-induced protein loss. These data are discussed in relation to the literature, and it is concluded that histamine may play a role in the jejunal microvascular effects of ethanol. As the ethanol-induced protein loss was not completely inhibited, other mediators or mechanisms were probably involved.

Factors in formation and prevention of bandlike gastric lesions in the rat

The etiology of the deep bandlike necrotic gastric mucosal lesions induced by the oral administration of corrosive agents in the rat is unclear. An understanding of why the lesions are so precisely localized and how they develop should increase our understanding of the mechanisms by which the prostaglandins prevent them. This study utilizes an innocuous dye to demonstrate that the initial mucosal contact by orally administered agents is restricted to the crests of mucosal folds. A sequential study of lesion development at the fold crest indicates that coagulative necrosis occurs on contact and that the vascular defects, hemorrhage and congestion, are secondary to deep corrosion injury. Exogenous prostaglandin and 0.35 N HCl were found to abolish mucosal folding and hence prevent the fold-related lesions. Inhibition of prostaglandin synthesis was found to sensitize the mucosal fold crest to injury by 0.35 N HCl, and hence the use of indomethacin as a proof that endogenous prostaglandin synthesis plays a role in preventing bandlike lesions by such agents is questioned. It is concluded that the gastric mucosal fold plays a major role in localizing mucosal injury to parallel bands and that the obliteration of these sensitive sites may explain the protective effect of an ever-expanding number of agents. As lesions genesis appears to be the result of a contact artifact, the use of this model in the study of the physiological role played by gastric prostaglandins is seriously questioned.(ABSTRACT TRUNCATED AT 250 WORDS)

Laparotomy stimulates an endogenous gastric mucosal protective mechanism in the rat. A microcirculatory and morphologic study of ethanol injury

In vivo microscopy in the anesthetized rat unexpectedly revealed that the topical application of 75% ethanol to the gastric mucosa had no effect on the mucosal microcirculation. If, however, the synthesis of endogenous prostaglandin was inhibited by indomethacin, the topical application of 75% ethanol resulted in complete superficial mucosal microcirculatory stasis in the majority of rats. In indomethacin-pretreated rats, Rioprostil, a synthetic prostaglandin E1 analogue, reversed this effect of topical ethanol. The degree of ethanol-induced histologic gastric mucosal damage was inversely correlated with time to complete stasis. Ethanol injury studies under various conditions revealed that laparotomy stimulated a gastric protective mechanism that persisted for between 1 and 2 h and that was blocked by indomethacin. In conclusion, (a) laparotomy stimulates a gastric mucosal protective mechanism that probably is mediated by prostaglandin synthesis, and (b) cessation of mucosal blood flow appears to be an important early step in ethanol-induced gastric mucosal injury, and maintenance of mucosal blood flow by endogenous or exogenous prostaglandin may play a major role in prostaglandin protection.

Failure of the inhibition of rat gastric mucosal 5-lipoxygenase by novel acetohydroxamic acids to prevent ethanol-induced damage

1. The role of leukotriene B4 (LTB4) and LTC4 as mediators of gastric mucosal damage following ethanol challenge in vivo has been investigated using two selective 5-lipoxygenase inhibitors, BW A4C and BW A137C. 2. Oral administration of ethanol to rats in vivo, induced macroscopic damage to the gastric mucosa and markedly increased the formation of the 5-lipoxygenase products, LTB4 and LTC4, from the mucosa ex vivo. 3. Pretreatment with the acetohydroxamic acids BW A4C and BW A137C (5-50 mg kg-1 p.o.) dose-dependently reduced ethanol-stimulated LTB4 and LTC4 formation by the gastric mucosa, with an ID50 of approximately 5 mg kg-1 p.o. 4. A single oral dose of BW A4C (20 mg kg-1) induced near-maximal inhibition of mucosal LTB4 formation within 30 min, which was well maintained for 5 h, whereas BW A137C (20 mg kg-1 p.o.) induced maximal inhibition between 30 and 60 min after administration, which then diminished over the subsequent 5 h. 5. The mucosal formation of the cyclo-oxygenase product, 6-keto-prostaglandin F1 alpha, which was unaltered following ethanol challenge, was not inhibited by the acetohydroxamic acids. Likewise, the small increase in mucosal thromboxane B2 formation following challenge was not inhibited by BW A4C. 6. Neither BW A4C nor BW A137C, at doses that almost completely inhibited the mucosal synthesis of LTB4 or LTC4, reduced the macroscopic gastric mucosal damage induced by ethanol. 7. Pretreatment with the lipoxygenase inhibitor BW 755C (5-50 mg kg-1 p.o.) did reduce mucosal damage, but there was a dissociation between the degree of protection and the inhibition of leukotriene biosynthesis. 8. Oral administration of high doses of either BW A4C or BW A137C (300mgkg-1) did not induce macroscopic gastric damage over a 3 h period. 9. These findings suggest that the leukotrienes, LTB4 and LTC4 are not the primary mediators of ethanol-induced acute mucosal damage, but do not exclude their role in more chronic gastric damage and inflammation.

Side-effects of non-steroidal anti-inflammatory drugs

Despite a continuing lack of good quality epidemiological studies, our knowledge of the side-effects of NSAIDs has advanced in recent years. The most important reactions are those which are related predictably to the pharmacology of the drugs and these need to be considered whenever a NSAID is prescribed, particularly for patients who can be identified as belonging to high-risk groups. The important reactions are: 1. Gastrointestinal damage, which is now known to extend to some degree from the oesophagus to the rectum, although the acid contact areas of the stomach and duodenum are the most important. Although the studies have produced heterogeneous results, NSAIDs probably double or triple the risk of an individual developing serious gastrointestinal haemorrhage or perforation. The risk increases with age and previous history of ulceration, and, in communities with particularly high use of NSAIDs, the drugs may account for up to 30% of all cases of ulcer complications. 2. Renal syndromes, of which functional renal impairment is the most important. This may precipitate cardiac failure, and hyperkalaemia is an additional hazard. Antagonism of the action of diuretics may contribute to the fluid retention, and antagonism of antihypertensive therapy is probably quite common and may result in additional unnecessary therapy. Patients at risk of functional renal impairment from NSAIDs can be identified readily and in these subjects the drugs have to be used with great care and with appropriate monitoring. 3. Respiratory effects, in particular acute bronchospasm in subjects with a history of aspirin sensitivity. NSAIDs should be used with caution in asthmatics, and patients purchasing NSAIDs without prescriptions need to be warned of these effects. Other uncommon serious reactions include hepatocellular damage, acute interstitial nephritis, agranulocytosis and aplastic anaemia, Stevens-Johnson syndrome and toxic epidermal necrolysis. These are unpredictable reactions which generally need not be considered before prescribing. However, in patients who present with any of these conditions, NSAIDs, because of their wide use, should always be considered as a possible cause.

Intragastric accumulation of Evan's blue as a method for assessing aspirin-induced acute gastric mucosal injury in humans

Aspirin administration results in gastric mucosal damage. Although the pathogenesis of these lesions remains unclear, in animals it appears that increased vascular permeability precedes development of grossly visible lesions. We examined the effect of aspirin administration on gastric vascular permeability in eight healthy subjects. We used gastric accumulation of Evan's blue dye (which is bound to albumin) as a marker of vascular integrity and assessed gastric accumulation of Evan's blue, blood, and DNA during serial 10-min washes. Both bleeding and Evan's blue in the gastric washings increased with time after administration of aspirin in an acid solution (P less than 0.01). Evan's blue increased from a median value of 8 micrograms/10 min to 24.5 micrograms/10 min period after 60 min of aspirin administration. By 20 min after aspirin administration, the accumulation of Evan's blue in the gastric wash was significantly greater than the initial aspirin period (P less than 0.05). Blood loss increased from 147 to 650 micrograms Hgb/10-min period. The increase in bleeding rate did not become significant until 40 min after the first aspirin dose. Our study showed that aspirin-induced gastric mucosal damage can be detected by assessing accumulation of Evan's blue in the gastric contents after aspirin administration. Studies in which various doses of aspirin or other agents are administered will be required to confirm whether the increased vascular permeability actually precedes bleeding in man. Measurement of Evan's blue dye in the gastric contents appears to provide a qualitative (and possibly quantitative) and sensitive early index of gastric mucosal injury.

Ethanol-induced gastric mucosal blood flow and vascular permeability changes in the rat

Ethanol-induced gastric mucosal injury is accompanied by complete cessation of blood flow in the lesion area. An in vivo microscopy technique was used in the rat to determine whether this cessation of blood flow could be due to increased microvascular permeability with marked plasma exudation and a resultant increase in blood viscosity. The topical application of 100% ethanol to the mucosa caused complete stasis of mucosal blood flow within 1 min. Fluorescent in vivo microscopy revealed that topical ethanol also caused a prompt increase in mucosal microvascular permeability to albumin. This, however, did not explain the slowing and cessation of mucosal microvascular blood flow as these preceded the permeability change.

Possible role of oxygen free radicals in ethanol-induced gastric mucosal damage in rats

The involvement of oxygen free radicals in the development of the ethanol-induced gastric mucosal damage has been investigated. We found that oral administration of superoxide dismutase reduced the incidence of ethanol-induced mucosal lesions. Reduction of superoxide dismutase activity by diethyldithiocarbamate led to a pronounced aggravation of mucosal damage. Inhibition of the chloride-bicarbonate channel by a stilbene derivative also aggravated the ethanol-induced hemorrhagic lesions. Neither glutathione peroxidase, catalase, nor ceruloplasmin were capable of inhibiting the development of mucosal damage. Compounds with scavenging properties such as thiourea, 1-phenyl-3-(2-thiazolyl)-2-thiourea, dimethyl sulfoxide, various inorganic compounds (elements of the first and second subgroups and of the sixth group of the periodic table) and sulfhydryl-containing substances protected the gastric mucosa against ethanol-induced injury in a dose-related manner. Naturally occurring antioxidants such as alpha-tocopherol, beta-carotene, and coenzyme Q10 were ineffective. The present results suggest that superoxide free radicals are involved in the development of ethanol-induced gastric mucosal lesions, probably via an interaction with cellular membranes.

Microcirculatory stasis precedes tissue necrosis in ethanol-induced gastric mucosal injury in the rat

The relation of blood flow stasis to the development of unequivocal histologic necrosis (loss of parietal cells from the column of contiguous cells) in ethanol-induced gastric mucosal injury was studied in anesthetized rats. The most rapid vascular change that occurred when the gastric mucosa was exposed to 100% ethanol was a severe segmental constriction of the large submucosal venules. At 22 sec, the average venular diameter was 52.2 +/- 6.0% of the original one. This was followed by complete superficial mucosal blood flow stasis at 49 +/- 4 sec and appearance of histologic evidence of necrosis in one of seven rats at 2.5 min, four of six rats at 10 min, and seven of seven rats at 60 min. We conclude that in ethanol-induced gastric mucosal injury, submucosal venular constriction occurs first, followed by cessation of mucosal blood flow to be followed later on with histologic evidence of necrosis.

Stress-induced vascular damage and ulcer

Factors controlling gastric mucosal blood flow are now better understood, and improved techniques have been established to study microcirculation in the gastrointestinal tract. In this paper, four areas are reviewed: gross and microscopic vessels that supply blood to the stomach; factors that control gastrointestinal blood flow; pathogenic role of disturbed mucosal blood flow circulation induced by stress; and findings in early vascular permeability and injury caused by cold restraint stress in the rat.

Histology of alcoholic hemorrhagic "gastritis": a prospective evaluation

The term "hemorrhagic gastritis" is frequently applied to the subepithelial hemorrhages seen at endoscopy in alcoholic patients without a clear understanding of the histologic nature of these lesions. We prospectively screened 125 actively drinking alcoholic patients undergoing upper endoscopy for gastrointestinal bleeding. Gastric subepithelial hemorrhages were found in 20 of these patients. Biopsy specimens of hemorrhagic lesions and nonhemorrhagic mucosa 1 and 3 cm away were taken with a "jumbo" forceps. Gastric biopsy specimens from 12 patients with Barrett's esophagus served as controls for biopsy-induced trauma. Biopsy slides from the patients and controls were coded before histologic scoring. Mean hemorrhage scores (range, 0-4) for the target lesions (2.9 +/- 0.3) were significantly greater than scores for the adjacent mucosa (1 cm, 1.0 +/- 0.2; 3 cm, 1.1 +/- 0.2) or control biopsy specimens (0.8 +/- 0.1). Hemorrhage was superficial, occurring primarily in the foveolar region. Mucosal edema (score range, 0-4) was a prominent feature in the adjacent, nonhemorrhagic mucosa (target lesion, 0.7 +/- 0.2; 1 cm, 1.9 +/- 0.4; 3 cm, 2.0 +/- 0.3; controls, 0.8 +/- 0.1). Edema extended into the deeper gland zones in 11 of 20 patients but in none of the 12 controls (p less than 0.05). Inflammatory cell infiltrates were mild and scores did not vary significantly among the three biopsy sites in alcoholic patients. We conclude that subepithelial hemorrhages seen at endoscopy in alcoholic patients represent localized hemorrhage of the foveolar region with edema in the surrounding mucosa but without prominent inflammatory cell infiltration. Rather than use the term "hemorrhagic gastritis," endoscopists should simply describe these lesions as subepithelial hemorrhages.

Protective effect of pentoxifylline on gastric mucosa

Pentoxifylline (PF) has been shown to increase tissue oxygen tension. This study was performed to determine if PF has a protective effect on the gastric mucosa against alcohol (EtOH)-induced injury. Fasted Sprague-Dawley rats were pretreated with randomized test solution (control, normal saline, or PF, 75 mg/kg) intraperitoneally (ip). At 30 min, 100% EtOH (pH 8.5) was given intragastric. At 90 min, laparotomy was performed and gastric serosal stomach surface oxygen tensions (pO2) were measured. Stomachs were excised and opened and pH was measured. Photographs were taken and sections were obtained for histologic analysis to determine mucosal injury. The PF-pretreated rats had significantly higher serosal pO2 and significantly lower intragastric pH than control animals. There was significantly less gross and histologic mucosal injury in PF-treated animals. We conclude that PF is protective against EtOH gastric mucosal injury. This effect correlates with increased gastric serosal pO2 and is likely due to improved microcirculatory blood flow following PF administration.

Vascular injury in acute gastric mucosal damage. Mediatory role of leukotrienes

Recent investigations indicate that microvascular injury, leading to increased vascular permeability and capillary stasis, precede the development of chemically induced hemorrhagic mucosal lesions in the stomach. The vascular damage is more amenable to protection by prostaglandins and sulfhydryls than the diffuse surface mucosal cell injury. The vascular and mucosal lesions may be the result of direct toxicity of damaging agents (eg, ethanol, HCl, NaOH) and the release of vasoactive amines and leukotrienes. We review here our recent studies performed in rats indicating that intraarterial infusion of LTC4 or LTD4 in the stomach caused vascular injury as revealed by monastral blue. Infusion of leukotrienes alone caused no hemorrhagic mucosal lesions but aggravated the damage caused by 25, 50, or 100% ethanol and 0.2 N HCl given intragastrically. The ethanol-induced mucosal lesions were slightly diminished by the lipoxygenase inhibitor L-651,392 and markedly decreased by eicosapentaenoic acid, which competes with arachiconic acid as a substrate for 5-lipoxygenase. These results are discussed and correlated with biochemical results from other laboratories demonstrating increased levels of leukotrienes in the gastric mucosa after administration of ethanol and decreased release following pretreatment with prostaglandins or sulfhydryl-related agents. New data thus support a mediatory role for leukotrienes in the pathogenesis of vascular injury and mucosal lesions in the stomach.

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.

Subepithelial hemorrhages and erosions of human stomach

Subepithelial hemorrhages and erosions of the stomach are being studied extensively in experimental animal models but have not been well-characterized in humans. The definitions of these hemorrhagic and erosive lesions are not uniform and are often further confused by being labeled with the blanket term "gastritis." We define these lesions from an endoscopic perspective, describe the clinical settings in which they occur, and provide endoscopic-histologic correlations, where available.

Prostaglandin protection of human isolated gastric glands against indomethacin and ethanol injury. Evidence for direct cellular action of prostaglandin

Isolated human gastric glands from surgical specimens were preincubated in an oxygenated medium with placebo or 16,16 dimethyl prostaglandin E2 (dmPGE2) and incubated at 37 degrees C in either medium alone, medium containing 4.43 mM indomethacin or medium containing 8% ethanol. We assessed the viability of gland cells with fast green exclusion, release of lactate dehydrogenase (LDH) into the medium, and ultrastructural damage by scanning and transmission electron microscopy. Both indomethacin and ethanol significantly reduced the viability of placebo-pretreated glands, increased LDH release into the medium, and produced prominent ultrastructural damage. DmPGE2 significantly reduced both indomethacin and ethanol-induced injury, increased the number of viable cells, reduced LDH release, and diminished the extent of ultrastructural damage. These studies indicate that PG protection of gastric mucosal cells has a direct cellular action that is not limited to replacement of depleted endogenous PGs. PG protection in our experiments did not depend on PG's previously described systemic actions, such as protection of the microvessels, preservation of the mucosal blood flow, or stimulation of bicarbonate and mucus secretion.

Gastric mucosal protection by new aryl sulfhydryl drugs

Alkyl sulfhydryl drugs protect against acute gastric hemorrhagic mucosal lesions. We tested the protective effect of cyclic drugs containing oxidized (KT1-32, KT1-39, KT1-94), or reduced (KT1-66, KT1-109, KT1-293, KT1-720, KT1-756) sulfhydryls. The most potent protective agents (KT1-32, KT1-109, KT1-720, KT1-756) were investigated in detail. Drugs were administered intragastrically to fasted rats 30 min before 100% ethanol (1 ml) or acidified aspirin (10 mg/100 g), and mucosal lesions were measured planimetrically 1 hr later. Control rats receiving only ethanol had lesions involving 14.5% of the glandular mucosa. KT1-32, KT1-109, KT1-720, or KT1-756 (10 mg/100 g) reduced lesions to 0.7, 2.7, 1.8, or 0.7% of glandular stomach respectively. Aspirin-induced lesions involved 1.52% of the glandular mucosa and 10 mg/100 g of KT1-32, KT1-109, or KT1-720, or 2 mg/100 g of KT1-756 diminished the damage to 0.13, 0.02, or 0.04, or 0.00%, respectively. Indomethacin interfered with protection against ethanol by KT1-109, while the sulfhydryl alkylator N-ethylmaleimide abolished protection by both KT1-32 and KT1-109. Among the drugs investigated in detail, KT1-756 increased gastric acid output, while KT1-720 and KT1-756 significantly enhanced pepsin secretion. All four compounds studied in detail (ie, KT1-32, KT1-109, KT1-720, KT1-756) decreased the extent of vascular lesions in the gastric mucosa as revealed by monastral blue 1 min after ethanol. Thus, the mechanism of gastric mucosal protection by these novel aryl sulfhydryl compounds cannot be ascribed to an antisecretory effect, but may be related to prevention of vascular injury.

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.

Acid-induced esophagitis in cats is prevented by sucralfate but not synthetic prostaglandin E

The cytoprotective effects of liquid sucralfate and a synthetic analog of prostaglandin E1 (PGE1) on acid-induced esophagitis in cats were studied. Esophagitis was induced in adult cats using a constant infusion of 0.1 N HCl at 1 ml/min for 20 min. Animals were infused for either one or three days. Mucosal lesions were evaluated by blinded investigators using both fiberoptic endoscopy and light microscopy. Histologic changes included basal cell hyperplasia, intraepithelial leukocytosis, and subepithelial leukocytosis. Liquid sucralfate given prior to acid infusion consistently prevented acid-induced lesions in both one- and three-day infusions, demonstrated by both endoscopy and quantitative histologic scoring. Indomethacin (200 micrograms/kg) given prior to sucralfate and acid did not affect sucralfate cytoprotection. Synthetic PGE1, given in doses of 5 micrograms/kg and 100 micrograms/kg, afforded no esophageal cytoprotection. These studies indicate that sucralfate is cytoprotective against acid-induced esophageal injury in cats, an effect that does not appear to be mediated by prostaglandin. In addition, synthetic PGE1 does not confer protection in this animal model.

Gastric mucosal defence mechanisms: a brief review

In the stomach several mucosal defence mechanisms protect the stomach against hydrochloric acid and noxious agents. The pre-epithelial protection is made up by the mucus-bicarbonate barrier. Mucus and bicarbonate, secreted by mucus cells, create a pH gradient maintaining the epithelial cell surface at near neutral pH. In humans, secretion of bicarbonate is an active process and is activated by vagal stimulation and fundic distension. Several mechanisms at the epithelial cell level contribute to an intact mucosal barrier. Surfactants in apical cell membranes prevent water-soluble agents in the gastric lumen from reaching and damaging the epithelium. Nonprotein sulphydryls in the epithelium are capable of binding reactive free radicals. Rapid cell turn-over and the process of restitution contribute to an intact epithelial lining. In subepithelial protection, mucosal blood flow is essential in supplying the epithelium with nutrients and oxygen and for disposal of hydrogen ions and noxious agents permeating the mucosa. Prostaglandins may maintain blood flow and prevent vascular endothelial injury caused by ethanol. Several agents have been established as protective for the gastric mucosa. Prostaglandins possess direct cytoprotective actions, whilst sucralfate, aluminium containing antacids, carbenoxolone and bismuth are mild irritants that induce liberation of endogenous prostaglandins of the mucosa.

A biochemical and pharmacological approach to the genesis of ulcer disease. I. A model study of ethanol-induced injury to gastric mucosa in rats

Present concepts of acute ulceration in the gastric mucosa include the hypothesis that mucosal ischemia is an important initiating event. The evidence for this is based upon observations on tissue metabolism and determinations of gastric mucosal blood flow. Using the model of gastric mucosal injury in the rat with ethanol, we have found that mucosal injury could be detected at a time when tissue oxygenation as determined by biochemical, and pharmacological studies of ATP metabolism were not compatible with ischemia. We also found that drugs acting at different subcellular levels were able to both inhibit gastric acid secretion in 4 hour pylorus-ligated rats and gastric mucosal injury after ethanol. Certain drugs, such as histamine and pentagastrin, stimulated acid secretion but inhibited the injury to the mucosa by ethanol indicating that increased cellular activity could occur during the development of mucosal injury.

Studies on the mechanism of ethanol-induced gastric damage in rats

Concentrated ethanol causes gastric lesions by a mechanism that is poorly understood. We have investigated this mechanism in the rat stomach via gross morphologic, videomicroscopic, histochemical, and pharmacologic approaches. Within 1 min of contact, ethanol caused diffuse mucosal hyperemia. By 5 min, hyperemia greatly intensified at some mucosal sites. Beneath sites where mucosal hyperemia developed, intramural venules strongly constricted at 3-13 s postethanol, whereas submucosal arterioles dilated more than two times in diameter by 25 s. Submucosal venular constriction began sooner than arteriolar dilation (9 vs. 16 s, p less than 0.05). One-third of the gastric mucosal mast cells degranulated by 15 s postethanol; 50% discharged by 30 s. Ethanol-induced hyperemia was markedly reduced by lipoxygenase-selective inhibitors BW755C or nordihydroguaiaretic acid, or by the H1-antihistamine pyrilamine, but not by indomethacin, cimetidine, phentolamine, or methysergide. Based on these results, a model for the pathogenesis of ethanol-induced gastric lesions is proposed.

Alternatives to the acid-oriented approach to ulcer disease: does 'cytoprotection' exist in man? A new classification of antiulcer agents

This review summarizes the historical contradictions and inconsistencies that form the labile arguments advocating neutralization or inhibition of secretion of gastric acid for the prevention or treatment of gastroduodenal ulcers. Re-evaluation of old concepts is needed in the wake of recognition that even the most potent antisecretory agents do not change the natural history of ulcer disease; that is, the recurrence is high after termination of treatment. New biochemical, functional, and structural targets are listed for pharmacologic intervention in ulcer disease. As a supplement or alternative to the antisecretory agents, we should now consider prosecretory agents (for example, for bicarbonate and mucus secretion) and antioxidants (for example, free radical scavengers). Gastroduodenal motility, smooth muscle, the vascular endothelial cell, and the basement membrane seem to represent additional pharmacologic targets toward which new gastroprotective drugs can be directed even though the biochemical mechanism of action of these new agents may not be fully understood. New results suggest that these elements have a role in the pathogenesis of ulcer disease, and their modulations seem to exert a beneficial effect without inhibiting gastric secretion in rodents. In man, the acid antisecretory and cytoprotective doses seem to overlap, but arguments are presented to shift defining gastric 'cytoprotection' by the dose of drugs to the characterization of the phenomenon (for example, events such as the ethanol-induced hemorrhagic erosions which cannot be decreased by antisecretory agents). Furthermore, non-prostaglandin and non-H2-receptor antagonist drugs are available that exert acid-independent gastroprotection both in animals and humans. The future is thus bright for the development of new antiulcer agents.

An electron microscope study of arteriolar branching sites in the normal gastric submucosa of rats and in experimental gastric ulcer

To observe the branching site of the rat gastric submucosal arteriole toward the mucosal capillary network, we used vascular corrosion casting, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), under various conditions, including the normal state, water immersion restraint stress for 24 h, ethanol-induced ulcer and administration of low and high doses of noradrenaline. In normal rats, the branching site of the submucosal arteriole toward the mucosa was slightly narrowed, as seen in the cast observations. The SEM and TEM observations revealed that this narrowing was due to the presence of the so-called "intra-arterial cushion". In the restraint stress rats, this narrowing was increased. TEM and direct SEM observation of the intraarterial cushion showed much the same findings. In the noradrenaline administered rats, similar changes were observed but not so in the rats with an ethanol-induced ulcer. Arterio-venous-anastomoses (AVA) were not observed in the submucosa, under any of the conditions used. We suggest that the submucosal intra-arterial cushions occurring at the branching sites of the submucosal arterioles may play an important role in regulating blood flow to the gastric mucosa.

16,16-Dimethyl prostaglandin E2 aggravates gastric mucosal injury induced by histamine in rats. Possible role of the increased mucosal vascular permeability

Histamine dihydrochloride (40 or 80 mg/kg, dissolved in 10% gelatin) subcutaneously administered to fasted rats induced few lesions in the gastric mucosa within 4 h. Pretreatment with subcutaneously administered 16,16-dimethyl prostaglandin E2 (dmPGE2; greater than or equal to 10 micrograms/kg) dose-dependently worsened mucosal injury induced by histamine, mostly with severe hemorrhage in the corpus mucosa along the greater curvature, although dmPGE2 alone did not induce any macroscopic damage. The mucosal vascular permeability as measured using Evans blue was slightly but significantly augmented by either dmPGE2 (30 micrograms/kg) or histamine (80 mg/kg) alone, but was markedly increased by histamine in the presence of dmPGE2. The increased vascular permeability occurred within 2 h, and preceded the appearance of hemorrhagic mucosal injury. Both the mucosal injury and the increased vascular permeability caused by histamine (80 mg/kg) in the presence of dmPGE2 (30 micrograms/kg) were significantly reduced by pretreatment with tripelennamine (30 mg/kg) and prednisolone (3 mg/kg), but not affected by atropine sulfate, cimetidine, methysergide, or indomethacin. The stimulation of acid secretion caused by histamine was significantly inhibited by dmPGE2 (30 micrograms/kg). Repeated administration of histamine (40 or 80 mg/kg) in the same area of the stomach in the presence of dmPGE2 (30 micrograms/kg), once or twice daily for 4 days to fed rats, induced more pronounced damage than single-dose treatment. These results suggest that dmPGE2 may aggravate gastric mucosal injury induced by histamine in rats probably due to potentiation of the increased vascular permeability caused by histamine through stimulation of H1-receptors.

Free radicals and lipid peroxidation in ethanol- or aspirin-induced gastric mucosal injury

In this study the role of free radicals and lipid peroxidation as mediators of chemically induced mucosal damage was investigated. Two enzymatic antioxidants, superoxide dismutase or catalase injected intravenously, reduced mucosal damage either by ethanol or aspirin. Of six nonenzymatic antioxidants, given in a wide dose range subcutaneously 30 min before intragastric administration of absolute ethanol, only propyl gallate decreased mucosal damage, while four of the antioxidants tested against aspirin were protective. These nonenzymatic antioxidants were antisecretory in the pylorus-ligated rat. The concentration of conjugated dienes and malondialdehyde measured in the gastric mucosa shortly after ethanol or aspirin administration remained unchanged or slightly decreased. These results indicate that free radicals may be involved in the pathogenesis of acute gastric mucosal injury caused by chemicals, but their mechanisms of action probably does not involve lipid peroxidation.