Pathogenesis of experimental gastric-mucosal injury

Stress Ulcer Syndrome

Stress ulcer syndrome refers to gastroduodenal erosions or ulcers that develop acutely in relation to major physi ological stress, usually manifested clinically as upper gastrointestinal (UGI) bleeding. These lesions occur most often in the gastric fundus. Endoscopy has shown gastroduodenal mucosal lesions in 75 to 100% of inten sive care unit (ICU) patients within 72 hours of admis sion. Patients at high risk for stress ulcer include those with large body surface area burns, intracranial lesions associated with coma, fulminant hepatic failure, sepsis, and trauma and abdominal, cardiovascular, and thoracic surgery patients. Also considered high risk are ICU pa tients with superimposed complications such as shock, mechanical ventilation for more than 3 days, coagulopa thy, jaundice, and sepsis. Approximately 15% of ICU pa tients will experience UGI bleeding from stress ulcer. Patients bleeding from stress ulcer have an overall mor tality rate approaching 65% compared with 9 to 22% mortality in patients without stress ulcer. When strati fied according to occult blood loss versus clinically significant bleeding, mortality can be as high as 90% in patients overtly bleeding; 30% of deaths are directly related to bleeding. Both antacids and H2 receptor an tagonists are effective in prophylaxis for stress ulcer bleeding.

Process analytical technology to understand the disintegration behavior of alendronate sodium tablets

Various adverse events including esophagus irritations have been reported with the use of alendronate tablets, likely attributed to the rapid tablet disintegration in the mouth or esophagus. Accordingly, the disintegration of six alendronate tablet drug products was studied using a newly developed testing device equipped with in-line sensors, in addition to the official compendial procedure for measuring the disintegration time. The in-line sensors were used to monitor the particle count and solution pH change to assess the onset and duration of disintegration. A relatively large variation was observed in the disintegration time of the tested drug products using the compendial method. The data collected using the in-line sensors suggested that all tested drug products exhibited almost instantaneous onset of disintegration, under 2 s, and a sharp drop in solution pH. The drop in pH was slower for tablets with slower disintegration. The in-house prepared alendronate test tablets also showed similar trends suggesting rapid solubilization of the drug contributed to the fast tablet disintegration. This research highlights the usefulness of the newly developed in-line analytical method in combination with the compendial method in providing a better understanding of the disintegration and the accompanying drug solubilization processes for fast disintegrating tablet drug products.

[Hemodynamic effects of intravenous omeprazole in critically ill children]

INTRODUCTION

Critical patients usually have hemodynamic disturbances which may become worse by the administration of some drugs. Omeprazole is a drug used in the prophylaxis of the gastrointestinal bleeding in these patients, but its cardiovascular effects are unknown. The objective was to study the hemodynamic changes produced by intravenous omeprazole in critically ill children and to find out if there are differences between two different doses of omeprazole.

MATERIAL AND METHODS

A randomized prospective observational study was performed on 37 critically ill children aged from 1 month to 14 years of age who required prophylaxis for gastrointestinal bleeding. Of these, 19 received intravenous omeprazole 0.5mg/kg every 12 hours, and 18 received intravenous omeprazole 1mg/kg every 12 hours. Intravenous omeprazole was administered in 20 minutes by continuous infusion pump. Heart rate, systolic, diastolic and mean arterial blood pressure, central venous pressure and ECG were recorded at baseline, and at 15, 30, 60 and 120 minutes of the infusion.

RESULTS

There were no significant changes in the electrocardiogram, heart rate, blood pressure and central venous pressure. No patients required inotropic therapy modification. There were no differences between the two doses of omeprazole.

CONCLUSIONS

Intravenous omeprazole administration of 0.5mg/kg and 1mg/kg is a hemodynamically safe drug in critically ill children.

Pathophysiology and prophylaxis of stress ulcer in intensive care unit patients

Gastrointestinal complications frequently occur in patients admitted to the intensive care unit. Of these, ulceration and bleeding related to stress-related mucosal disease (SRMD) can lengthen hospitalization and increase mortality. The purpose of this review is to discuss the many risk factors and underlying illnesses that have a role in the pathophysiology of SRMD and evaluate the evidence pertaining to SRMD prophylaxis in the intensive care unit population. Suppressing acid production is fundamental to preventing stress-related mucosal ulceration and clinically important gastrointestinal bleeding. Traditional prophylactic options for SRMD in critically ill patients include antacids, sucralfate, histamine 2 -receptor antagonists (H 2 RAs), and proton pump inhibitors. Many clinicians prescribe intermittent infusions of H 2 RAs for stress ulcer prophylaxis, a practice that has not been approved for this indication and may not provide the necessary degree or duration of acid suppression required to prevent stress ulcer-related bleeding. New data suggest that proton pump inhibitors suppress acid production more completely in critically ill patients, but more studies are required to assess their clinical effectiveness and safety for this indication. The prophylactic regimen chosen to prevent stress ulcer bleeding should take into account the risk factors and underlying disease state of individual patients to provide the best therapy to those most likely to benefit.

Overview of pharmacologic agents for acid suppression in critically ill patients

PURPOSE

The physiology of acid secretion, rationale and goals for acid suppression in critically ill patients, and mechanism of action, pharmacokinetics, pharmacodynamics, and safety of histamine H2-receptor antagonists (H2RAs) and proton pump inhibitors (PPIs) are discussed.

SUMMARY

Acid-suppressant therapy may be used in critically ill patients to prevent stress-related mucosal disease or the recurrence of peptic ulcer bleeding. The intragastric pH goal is 3.5-4.5 and 6 or higher, respectively. H2RAs block only one of three pathways in acid secretion and provide less potent acid suppression than PPIs, which block the final common pathway in acid secretion. In addition, tolerance that occurs with H2RAs does not occur with PPIs. All PPIs work in a similar manner, but differences exist in the pharmacokinetic profiles and binding to the proton pump; the clinical relevance of these differences remains debated. The safety profiles of H2RAs and PPIs are similar; however, the H2RA dose, but not the PPI dose, must be adjusted for patients with renal dysfunction. The risk of drug interactions mediated by cytochrome P-450 enzymes is lower with PPIs than with cimetidine, an H2RA. Several new PPI dosage forms have been introduced, facilitating drug administration in the critical care setting.

CONCLUSION

Both H2RAs and PPIs are safe agents to use for providing acid suppression in critically ill patients, but PPIs offer several potential advantages over H2RAs.

Increase in gastric intramucosal hydrogen ion concentration following endotoxin challenge in the rat and the actions of nitric oxide synthase inhibitors

1. Cardiovascular events and outcome in septic shock may be predicted by monitoring the fall in intramural pH (pHi), as an index of splanchnic perfusion and mucosal ischaemia. In the present study, a small animal model for monitoring the changes of gastric pHi or intramucosal [H+] following challenge with the endotoxin lipopolysaccharide (LPS) was developed in the rat. The role of nitric oxide (NO) in these events in this model was evaluated using the non-selective NO synthase (NOS) inhibitors N(G)-nitro-L-arginine methyl ester (L-NAME) and N(G)-monomethyl-L-arginine (L-NMMA). 2. The pHi and intramucosal [H+] were evaluated in omeprazole-pretreated rats (30 mg/kg, i.p.) using the Henderson equation after estimating the PCO2 and the bicarbonate concentration in gastric wall. To measure gastric wall PCO2, the oesophagus was intubated and the pylorus ligated. The PCO2 was measured by a blood gas analyser in 2 mL saline instilled for 30 min in the gastric lumen to equilibrate with the gastric wall. The pHi was measured under basal conditions and 3 and 5 h after LPS (3 mg/kg) administration. Separate groups received treatment with L-NMMA (25-50 mg/kg) or L-NAME concomitantly or 2.5 h after administration of LPS. 3. Intravenous administration of Escherichia coli LPS provoked a significant fall in gastric pHi from 7.37 to 7.18 (median values; n =10-19) determined after 5 h. In groups treated concurrently with LPS and L-NAME (5 mg/kg; n = 19), there was a similar increase in intramucosal [H+] as that induced by LPS alone (n = 15) in those animals that survived. In contrast, L-NAME (5 mg/kg; n = 12), given 2.5 h after LPS challenge, at a time at which inducible NOS is known to be significantly expressed, prevented the increase in intramucosal [H+] at 3 and 5 h after LPS challenge. Similarly, L-NMMA (25-50 mg/kg; n = 23), given 2.5 h after LPS challenge, dose-dependently inhibited the increase in intramucosal [H+] at 3 and 5 h. 4. In conclusion, these findings indicate that this rat model could be useful in exploring the pathophysiology of acute endotoxin shock. Delayed administration of L-NAME and L-NMMA abolished the increase in gastric intramucosal [H+], supporting the involvement of excess NO in the tissue dysfunction associated with endotoxin shock. This suggests the potential value of this small animal model in evaluating the therapeutic activity of novel agents for use in septic shock.

Expression and function of Na+HCO3- cotransporters in the gastrointestinal tract

The stomach, duodenum, colon, and pancreas secrete HCO3- ions into the lumen. Although the importance of HCO3- secretion for the maintenance of mucosal integrity, a normal digestion, and the reabsorption of Cl- has been well established, the molecular nature of the apical and basolateral HCO3- transporting proteins has remained largely unknown. Functional studies have suggested that a Na+HCO3- cotransport system, similar but not identical to the well-characterized Na+HCO3- cotransporter in the basolateral membrane of the kidney proximal tubule, is present in duodenal and colonic enterocytes, pancreatic ducts cells, and gastric cells and involved in HCO3- uptake from the interstitium. This report describes our work towards understanding the molecular nature, cellular origin, and functional relevance of the Na+HCO3- cotransporter(s) in the stomach and intestine and reviews work by others on the function and localization of Na+HCO3- cotransport processes in the gastrointestinal tract.

Clinical utility of pH paper versus pH meter in the measurement of critical gastric pH in stress ulcer prophylaxis

OBJECTIVE

To evaluate the clinical utility of measuring gastric pH with a pH meter vs. pH paper in critical care patients.

DESIGN

Prospective comparison of gastric pH measurements, using both pH meter and pH paper.

SETTING

Surgical intensive care unit (ICU) at a rural Midwestern university medical center.

PATIENTS

Fifty-one patients who received therapy for prophylaxis of stress ulcers in the surgical ICU.

INTERVENTIONS

Therapy for stress ulcer prophylaxis was monitored.

MEASUREMENTS AND MAIN RESULTS

The pH of 985 gastric samples, taken from 51 patients, was measured with both pH meter and pH paper. The pH meter and pH paper measures demonstrated a concordance correlation coefficient of .896. The mean difference between the two measures (pH paper - pH meter) was estimated to be between -0.4 and 1.4, suggesting a positive bias for the paper. The prevalence of events representing clinically relevant differences between the pH meter and pH paper in the measurement of the same gastric sample was calculated. The frequency with which each of the events occurred consecutively (or, in one case, two nearly consecutive events on the same day) was also calculated. Bias in a clinically relevant range was estimated. A set of "probability profiles" was constructed.

CONCLUSIONS

A hand-held pH meter and pH paper are not interchangeable measures of gastric pH. The pH paper exhibits an appreciable positive bias compared with a hand-held pH meter in the clinically relevant range of 2 to 6. More research is needed to determine if that bias affects treatment outcomes. We recommend the use of a pH meter for patients who demonstrate pH readings of < or = 4, consecutive with readings of < or = 5.

Gastric mucus generation in cirrhotic patients with portal hypertension. Effects of tetraprenylacetone

We have evaluated gastric mucus generation (study 1) and the effects of tetraprenylacetone on gastric mucus generation (study 2) in cirrhotic patients with portal hypertension. Study 1: Included were 50 noncirrhotics (group A), 25 cirrhotics without portal hypertension (group B), and 25 cirrhotics with portal hypertension (group C). The antrum, corpus, and fundus mucus generation was assessed by hexosamine concentration using biopsy specimens. In groups A and B, the antrum hexosamine concentration was significantly higher compared with the corpus (P < 0.01, P < 0.01) and the fundus (P < 0.01). In contrast, the hexosamine concentration at each location was similar in group C. Furthermore, the antrum hexosamine concentration of group C was significantly lower compared with that of group A (P < 0.05). In study 2, a double-blind design, 300 mg of tetraprenylacetone was administered for four weeks in 10 cirrhotics with portal hypertension and placebo in 10. The regional hexosamine concentrations were measured before and after drug administration. Placebo administration did not change hexosamine concentration at each location. In contrast, tetraprenylacetone increased the antrum and corpus hexosamine concentration (P < 0.01, P < 0.05), although the fundus concentration did not change. These data suggest that cirrhotics with portal hypertension have reduced gastric antral mucus generation and tetraprenylacetone normalizes this.

Omeprazole administration does not impair gastrointestinal mucosal perfusion, oxygenation, and hexosamine generation

Omeprazole is a potent antisecretory drug that acts by inhibiting the gastric proton pump. In the present study, we have observed the effects of this drug on gastrointestinal mucosal perfusion, oxygenation, and hexosamine generation in humans. Sixteen healthy volunteers were included. Gastrointestinal mucosal perfusion and oxygenation (duodenum, antrum, and corpus) were assessed by laser-Doppler flowmetry and reflectance spectrophotometry. Biopsy specimens were also taken from each location to determine hexosamine content as a quantitative indicator of mucus generation. In addition, serum gastrin level was measured. After baseline data were obtained, subjects were randomly assigned to receive 20 mg of oral omeprazole once daily for 7 days (n = 8) or placebo (n = 8). All measurements were performed again after double-blinded drug administration. No effect was found after placebo administration. In contrast, omeprazole administration significantly increased serum gastrin level (p < .05), suggesting an inhibition of acid secretion. However, this drug did not alter either laser-Doppler signal or oxygen saturation at each location. In addition, no change in mucosal hexosamine content was observed at each location. We conclude that oral omeprazole, despite its well-established antisecretory effect, has no adverse effect on the mucosal defense in humans.

Effect of cardiopulmonary bypass on gastrointestinal perfusion and function

Gastric mucosal tonometry was used to determine the adequacy of gastrointestinal perfusion in 10 patients undergoing elective myocardial revascularization. Patients were prospectively randomized to receive either pulsatile or nonpulsatile flow during cardiopulmonary bypass. All patients showed a reduction in gastric mucosal perfusion during bypass, manifested by a reduction in the gastric mucosal pH, which occurred independently of variations in the arterial pH. In the group of patients receiving nonpulsatile flow, this reduction was significantly greater (p < 0.05). Cardiopulmonary bypass using nonpulsatile flow is associated with the development of a gastric mucosal acidosis, which may have implications for the development of postoperative complications.

Bolus infusion of famotidine: effects on gastric pH by repeated 12-hour doses of 20 mg in postoperative patients

This study was carried out to assess the efficacy of intravenous (IV) famotidine in suppressing gastric secretion over a 48-hour period. Twenty postoperative patients requiring a nasogastric tube received famotidine 20 mg IV every 12 hours and gastric pH was measured continuously by means of an indwelling probe. A baseline recording was performed over the first 4 hours and then the drug was infused every 12 hours (q12h) over a 15-minute period for the subsequent 48 hours. The mean pH value achieved during each time segment under active treatment was significantly higher (P < .001) than the mean basal value. Also the density distributions of minutes spent at the various pH units confirm that famotidine is highly effective (P < .001) in raising and maintaining gastric pH above 4.0 units during most of the drug-related period (44 hours). It can be concluded that repeated intravenous boli of famotidine 20 mg every 12 hours allow us to obtain an effective control of intragastric acidity. The antisecretory action is consistent over the total 48-hour period examined and therefore the use of intermittent infusion of famotidine seems to be advisable, as opposed to the recommended continuous IV administration of cimetidine and ranitidine. There is, however, a considerable intersubject variability in the antisecretory response to the drug.

Prophylaxis of gastrointestinal tract bleeding in patients admitted to a general hospital ward. Comparative study of sucralfate and cimetidine

Gastrointestinal bleeding prophylaxis is well known in patients admitted to intensive care units, but only a few reports have analyzed this problem in patients admitted to a general hospital ward. In a previous study we demonstrated that close to 20% of such seriously ill placebo-treated patients bled. We conducted a prospective, randomized trial comparing cimetidine in a single dose of 800 mg and sucralfate at a dose of 1g/6h in a group of 139 patients from a cohort of 2010 patients consecutively admitted during a 10-month period to a department of internal medicine at a teaching hospital. The severity of their illness was assessed by the simplified acute physiologic score (SAPS). Gastrointestinal bleeding was assessed at the beginning of the study and daily during the hospitalization by means of Hemoccult paper tests or when frank hematemesis or melena occurred. Two of the 71 patients assigned to cimetidine and 2 of the 68 assigned to sucralfate presented with acute gastrointestinal bleeding, which was more severe in the sucralfate group. The drugs had similar safety profiles and were well tolerated, but the easier administration of cimetidine in a single dose, together with its low cost (25% less than sucralfate) argues in favor of cimetidine to prevent gastrointestinal bleeding in seriously ill patients admitted to general hospital wards.

Effect of luminal acidification on guinea pig gastric mucosa

H+ secretion was studied in guinea pig fundic mucosa incubated in (A) bicarbonate-Ringer's gassed with 95% O2-5% CO2, or (B) HEPES gassed with 100% O2 before and after luminal pH was lowered to 2.0 for periods up to 90 min. At pH 2.0 for 60 min, H+ secretion in group A tissues fell by 35 +/- 4% (P = 0.02) from a control rate of 1.35 +/- 0.09 mu eq/cm2/hr and in group B tissues by 50 +/- 11% (P = 0.01) from a control rate of 1.59 +/- 0.08 mu eq/cm2/hr. After 90 min at pH 2.0, H+ secretion in group A fell by 53 +/- 8% (P = 0.02) from a control rate of 1.47 +/- 0.07 mu eq/cm2/hr and in group B fell by 44 +/- 6% (P = 0.01) from a control rate of 1.38 +/- 0.07 mu eq/cm2/hr. Histamine 1 x 10(-4) M stimulation following exposure to pH 2.0 for 90 min increased secretion in group A tissues from 0.80 +/- 0.14 to 1.06 +/- 0.13 mu eq/cm2/hr (P < 0.05), compared with an increase in nonacidified controls from 1.15 +/- 0.22 to 1.80 +/- 0.20 mu eq/cm2/hr (P < 0.05) and in group B tissues from 1.27 +/- 0.10 to 1.56 +/- 0.19 mu eq/cm2/hr (P < 0.05) compared with nonacidified controls from 1.43 +/- 0.22 to 2.23 +/- 0.41 mu eq/cm2/hr (P < 0.05). Secretory function and electrical characteristics were adversely affected by luminal acidification to pH 2.0 and suggested a breach in the mucosal barrier with damage to parietal cells.

Intraabdominal complications after cardiopulmonary bypass

Thirty-three intraabdominal complications occurred in 27 patients over a 16-year period in 4,629 patients who underwent cardiopulmonary bypass (0.58% incidence). The mortality was 14.8% for the intraabdominal complication group compared with 3.4% for the control group of patients (p less than 0.01). The most common complication was gastrointestinal hemorrhage (n = 20), of which esophagitis (n = 6) was the most common cause. However, patients with duodenal ulcer (n = 4) had the highest mortality; 2 patients who underwent truncal vagotomy and pyloroplasty subsequently died. Two further patients underwent operation for perforated anterior duodenal ulcers without further morbidity. Cholecystitis developed in 5 patients and acute pancreatitis in 4; all were managed nonoperatively with no mortality. Multisystem organ failure developed in 2 patients, of whom 1 died. There was a significant correlation between intraabdominal complications and prolonged bypass time. The mean bypass time was 96.7 +/- 28.6 minutes for the patients with gastrointestinal complications, compared with 81.7 +/- 48.4 minutes for the whole group (p less than 0.01). No correlation was demonstrated for type of operation undergone or the age of the patient. In the last 5 years, 2,145 patients underwent cardiopulmonary bypass, of whom 562 received pulsatile and 1,583 nonpulsatile flow. The incidence of intraabdominal complications was 0.18% (n = 1) in the pulsatile group compared with 0.63% (n = 10) for the nonpulsatile group (p = 0.14). Intraabdominal complications, although of low incidence, carry a significantly high mortality, and the clinician must be alert in the postoperative period to institute early therapy.

Prophylaxis of gastrointestinal tract bleeding with magaldrate in patients admitted to a general hospital ward

A randomized, placebo-controlled trial was performed to assess the effect of magaldrate (800 mg every 4 h) in reducing the rate of upper gastrointestinal tract bleeding among 100 consecutive patients with severe diseases admitted to a general hospital ward. Upper gastrointestinal tract bleeding occurred in 11 of 48 placebo-treated patients and in only 1 of 52 magaldrate-treated patients (p less than 0.01). Endoscopic examination of these patients showed gastric ulcer (two cases), multiple gastric mucosa ulcerations (nine), and no lesions (one). In three patients who received placebo the hemorrhage was clinically relevant and required transfusion of two or more blood units. Patients with two or more risk factors showed a higher rate of gastrointestinal hemorrhage (p less than 0.05). Respiratory failure and treatment with a high dose of corticosteroids were associated with the highest incidence of bleeding (p less than 0.05 for both). The only adverse reaction associated with magaldrate was a mild and self-limiting diarrhea in two cases. We conclude that patients seriously ill admitted to a general hospital ward should be treated with a prophylactic agent against stress-induced ulcer bleeding. Magaldrate is an effective and safe antacid to prevent gastrointestinal tract bleeding in such patients.

Control of gastric pH with ranitidine in critically ill patients. Comparison of two intravenous regimens

The effects of continuous versus bolus administration of ranitidine on gastric pH were compared in critically ill patients admitted to our intensive care unit. Patients were randomized to receive 0.2 mg/kg/hr ranitidine in continuous infusion or 50 mg in bolus every 4 hr. The pH was monitored throughout a 24-hr period, 2 hr in basal conditions and 22 hr during treatment, with a gastric probe. Basal gastric pH was 2.1 +/- 0.2 in the infused and 2.4 +/- 0.2 in the bolus group (P greater than 0.05). The hydrogen ion concentrations were 25.1 +/- 8 and 20.0 +/- 7 mmol/liter, respectively (P greater than 0.05). After ranitidine administration, mean pH was 6.3 +/- 0.6 in patients treated by infusion and 4.5 +/- 0.5 (P less than 0.001) in those who received the drug in bolus; hydrogen ion concentration was 2.5 +/- 2 and 6.9 +/- 6, respectively, (P less than 0.001). Percent of inhibition of acid secretion was 90% in the infused and 68% in the bolus group. Infusion raised pH to values constantly above 4, whereas bolus administration resulted in wide fluctuations. These data indicate that continuous infusion of ranitidine is superior to bolus administration in controlling gastric acidity in critically ill patients.

Portal hypertension predisposes the gastric mucosa to hemorrhagic shock/reperfusion injury

We have previously demonstrated that the portal hypertensive (PHT) gastric mucosa has unique functional and morphologic features which predispose it to increased damage by noxious agents such as aspirin or alcohol. In this study we examine the PHT gastric mucosa following hemorrhagic shock and reperfusion. Portal hypertension was produced in 12 rats using staged portal vein occlusion, and seven animals (controls) underwent sham procedures. All rats received 2 ml 0.1 N HCl intragastrically. Shock was then induced by withdrawing blood to reduce systemic arterial pressures to approximately 30 mm Hg for 20 min. Blood was then reinfused and stomachs were excised 20 min later for gross and microscopic quantitation of injury. We found that gross damage to gastric glandular mucosa was more than doubled in PHT rats over sham-operated controls. In PHT gastric mucosa, deep histologic necrosis involved 22.5 +/- 3.8% of mucosal section lengths compared with 6.9 +/- 2.0% in control mucosa (P less than 0.005). Histologically, mucosal injury patterns were predominantly ischemic, with deep necrosis and disintegration of glands and microvessels, all prominently more extensive in PHT mucosa. We conclude that PHT gastric mucosa has significantly increased susceptibility to damage following hemorrhagic shock/reperfusion compared with portal normotensive mucosa. Since hemorrhagic shock is a frequent complication of portal hypertension, this study suggests clinical investigations of gastric mucosal function and pathophysiology in PHT patients following hemorrhage and resuscitation.

Acute gastric mucosal lesions, haemodynamic and microcirculatory changes in the thermally injured rat

Early postburn changes in central haemodynamics, organ blood flow distribution and morphology of the gastric mucosa were studied using a standarized thermal skin injury model. Organ blood flow and cardiac output were determined using radioactive microspheres. In the control animals no marked changes in cardiac output or organ blood flow were observed, and the gastric mucosa remained essentially undamaged. After burn injury and no fluid resuscitation, cardiac output decreased by 78 per cent, and blood flow to the stomach, pancreas, spleen, muscle, skin and kidneys also decreased markedly and to about the same degree as the cardiac output, however the adrenal flow remained roughly unchanged at the baseline level. Gross and microscopic lesions developed in the stomach, especially in the corpus. In animals given fluid resuscitation after burn injury cardiac output decreased by 38 per cent during the experiment, but blood flow in the stomach, brain, kidneys and spleen remained fairly constant, while pancreatic and muscle blood flow decreased and adrenal blood flow increased markedly. The gastric mucosa showed only minor microscopic, but no macroscopic lesions at the end of the experiment. The results indicate that acute thermal skin injury induces profound changes in central haemodynamics and organ blood flow which can, however, largely be overcome by adequate fluid resuscitation. The data also suggest that, as in other examples of 'stress ulceration', impaired mucosal blood flow may underlie the stress ulceration which complicates severe burns.

Local immune defence in relation to gastritis in Billroth-II-resected stomachs

Biopsy specimens from Billroth-II-resected stomachs obtained endoscopically 28-32 years after the operation were subjected to an immunohistochemical study by two-colour immunofluorescence staining. The epithelial distribution of immunoglobulin A (IgA), secretory component (SC), lysozyme (Ly), and lactoferrin (Lf) was evaluated, and IgA-, IgM-, and IgG-producing cells were quantified in the lamina propria. Gastric body mucosa excised from resected stomachs obtained from patients with duodenal ulcer was used as control and showed considerably less extensive gastritis than the stump mucosa. Both specimen categories showed enhanced expression of epithelial IgA, SC, Ly, and Lf associated with severe gastritis, except for areas with intestinal metaplasia, which lacked Ly and Lf. The number of IgA-, IgM-, and IgG-producing cells was significantly increased with increasing degree of gastritis, particularly so for IgG cells on a relative basis. After partial gastrectomy, therefore, the stump mucosa generally responds with activation of local immune mechanisms; this response is principally similar to that seen in simple gastritis of comparable severity.

Prevention of acute gastric erosions in the rat by novel semi-synthetic amphipathic analogues of pepstatin

Pepstatin is a potent aspartyl proteinase inhibitor which is virtually insoluble in physiological media. Five semi-synthetic amphipathic analogues of pepstatin, prepared by N terminal substitution of native pepstatin with hydrophilic oligopeptides, have been assessed for their ability to protect the mucosa in two animal models of acute gastric erosions. Concentrations of approximately 90 pmol/mg were achieved in the rat gastric mucosa after oral administration of a 20 mmol solution. These levels are theoretically adequate to inhibit all pepsin like proteinase activity (including zymogens). Each pepstatin analogue was tested by intragastric administration in a controlled hypotension/luminal acid animal model of acute gastric erosions in a group of six animals. All the inhibitors tested produced marked mucosal protection, as measured by a mucosal damage index, compared with control animals (control mean 241, range 100-420; Pepstatinyl-Gly-Orn-Orn-Cys (10 mmol) mean 3, range 0-8, p less than 0.01; Pepstatinyl-Gly-Cysteic acid-Cysteic acid (10 mmol) mean 5, range 0-21, p less than 0.01; Pepstatinyl-Gly-Lys-Lys (10 mmol) mean 18, range 0-60, p less than 0.01; Pepstatinyl-Gly-Cysteic acid-Cysteic acid (1 mmol) mean 24, range 0-86, p less than 0.01; Pepstatinyl-Gly-Orn-Orn-Cys (1 mmol) mean 57, range 0-116, p less than 0.01; Pepstatinyl-Gly-Asp-Asp (1 mg/ml suspension) mean 68, range 19-126, p less than 0.01; Pepstatinyl-Arg-OMe (1 mmol) mean 93, range 4-142, p less than 0.05, Pepstatinyl-Gly-Lys-Lys (1 mmol) mean 157, range 70-286, NS). In a platelet activating factor/20% luminal ethanol model of erosions the pepstatin analogues again provided mucosal protection although this only reached statistical significance for one of three compounds tested.

Intracellular pH in isolated Necturus antral mucosa in simulated ulcerogenic conditions

Intracellular pH (pHi) was measured with proton-sensitive liquid sensor microelectrodes in isolated Necturus antral mucosa, paying special attention to arranging experimental conditions to simulate conditions frequently associated with in vivo "stress ulceration." Intracellular pH in mucosas perfused under standard conditions (Ringer's solution containing HCO3-/CO2) was 7.22 + 0.02 (n = 27). Removal of Na+ and HCO3- or addition of amiloride or 4-acetamido-4-isothiocyanostillbene-2,2-disulfonic acid (blockers of Na+/H+ and Cl-/HCO3-exchangers) had no influence on steady-state pHi, suggesting that these ion exchangers do not significantly contribute to the maintenance of pHi in the presence of normal external pH. Acidification of mucosal (luminal) perfusate to pH 3 (mimicking the presence of gastric acid) had no influence on pHi, but mucosal pH 2 (10 mM HCl) acidified pHi to 6.93 +/- 0.07. Acidification of serosal (nutrient) perfusate to pH 6 (mimicking intramucosal acidosis caused by back-diffusion of luminal H+) acidified pHi to 6.72 +/- 0.10. Removal of Na+ from and addition of amiloride to the serosal perfusate during exposure to serosal pH 6.0 induced further acidification of pHi, suggesting that in this acidotic situation (with very low ambient HCO3- concentration) a Na+/H+ exchanger does contribute to the maintenance of steady-state pHi. Increased PCO2 (10% vol/vol in the gas) in a slightly acidic milieu (mimicking mucosal ischemia) likewise acidified pHi to 6.73 +/- 0.05. A combination of mucosal acid (pH 3), high PCO2 (10% CO2), and low serosal pH (pH 6) (mimicking conditions that prevail, for example, during hemorrhagic shock) acidified pHi and ultimately resulted in cell death. These derangements of intracellular acid-base balance may have pathogenetic importance also in in vivo stress ulceration.

Dissociation of pepsinogen and acid secretion in the guinea pig

In vivo observations have suggested that acid secretion may potentiate pepsinogen release. We measured pepsinogen and acid secretion by guinea pig fundic mucosal sheets stimulated by 10(-4) M histamine, 10(-8) and 10(-9) M cholecystokinin, and 3 x 10(-7) M carbamylcholine and then investigated the effects of 10(-4) M omeprazole on basal, carbachol-stimulated, and cholecystokinin-stimulated secretion. Histamine increased basal acid secretion fivefold (p less than 0.01) without altering pepsinogen secretion. Cholecystokinin did not stimulate acid secretion but increased pepsinogen secretion by factors of 23.1 at 10(-8) M and 9.1 at 10(-9) M (both p less than 0.01). The combination of 10(-4) M histamine and 10(-9) M cholecystokinin increased acid secretion 3.5-fold and pepsinogen secretion 6.4-fold, statistically equivalent to the sum of the effects of histamine and cholecystokinin alone. Carbachol increased acid secretion and pepsinogen secretion by factors of 4.0 and 10.9, respectively (both p less than 0.01). Pretreatment with 10(-4) M omeprazole abolished basal and carbachol-stimulated acid secretion. However, pepsinogen secretion was unaffected (p greater than 0.05). Furthermore, omeprazole-treated tissues increased pepsinogen secretion by factors of 10.0 with 3 x 10(-7) M carbachol and 9.1 with 10(-9) M cholecystokinin (both p less than 0.01). Thus, basal and secretagogue-stimulated pepsinogen secretion appear independent of acid secretion in intact guinea pig mucosa.

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.

Sucralfate treatment of nonsteroidal anti-inflammatory drug-induced gastrointestinal symptoms and mucosal damage

In a randomized, double-blind trial, sucralfate therapy, 1 g four times daily, was compared with placebo in 143 symptomatic patients to assess the treatment of gastrointestinal symptoms and gastric mucosal damage associated with nonsteroidal anti-inflammatory drugs (NSAIDs). All patients followed a fixed regimen of NSAIDs, were assigned to one of two groups based on the presence or absence of gastric erosions at baseline endoscopy, and were then assigned randomly to receive sucralfate or placebo for four weeks. Patients were then followed for up to six months while receiving open-label sucralfate 1 g twice daily to up to 1 g four times daily. After four weeks of double-blind therapy, patients taking either nonsalicylate NSAIDs or long half-life NSAIDs and who were treated with sucralfate experienced a significant reduction in both peptic symptom frequency and intensity (p less than 0.03) as compared with patients receiving placebo. Sucralfate-treated patients with baseline endoscopic lesions showed a significant reduction in lesion scores (p less than 0.005) at four weeks as compared with baseline, whereas no improvement was observed in gastric mucosal lesions of patients given placebo. Long-term sucralfate therapy resulted in continued improvement in gastrointestinal symptoms and gastric lesion scores in patients receiving all types of NSAIDs. The results indicate that sucralfate used in conjunction with NSAIDs may allow patients to continue therapy by relieving gastrointestinal symptoms and mucosal damage associated with NSAID therapy.

Secretory state and acute gastric mucosal injury in sepsis

Cats were subjected to a standardized 3-h septicemia by intravenous infusion of live Escherichia coli in an LD50 dose. The effect of pentagastrin stimulation on the development of gastric mucosal injury was studied. There was no hemodynamic difference between the series during septicemia. Thus, pentagastrin did not induce increased gastric blood flow during the period of E. coli infusion. Intraluminal gastric pH was lower in the series given pentagastrin during the last 2 h of septicemia. Nevertheless, the extent of gastric mucosal injury was similar in the two groups, whereas the depth of injury was, if anything, less pronounced in the pentagastrin-stimulated group.

pH of the microclimate lining human gastric and duodenal mucosa in vivo. Studies in control subjects and in duodenal ulcer patients

Measurements of pH in the microclimate on gastric and duodenal mucosa were made during gastrointestinal endoscopy in 21 normal subjects and 9 duodenal ulcer patients. In controls luminal and juxtamucosal mean pH (+/- SEM) of 3.29 +/- 0.3 and 4.48 +/- 0.25 were recorded respectively in distal esophagus, 2.01 +/- 0.17 and 4.84 +/- 0.37 in gastric fundus, 1.82 +/- 0.12 and 5.5 +/- 0.15 in body, 3.52 +/- 0.34 and 5.42 +/- 0.29 in antrum, 6.89 +/- 0.21 and 7.16 +/- 0.13 in duodenal cap, and 6.84 +/- 0.19 and 7.03 +/- 0.19 in proximal duodenal loop. When the lumen of esophagus and duodenum were perfused with acid (pH 2) luminal and mucosal pH values were 2.18 +/- 0.11 and 4.08 +/- 0.41 in esophagus, 2.57 +/- 0.15 and 6.74 +/- 0.13 in duodenal bulb, and 2.44 +/- 0.14 and 6.39 +/- 0.2 in duodenal loop. Juxtamucosal pH in fundus, body, and duodenum remained near neutral when luminal pH was 1.5, but in distal esophagus and antrum it fell sharply at luminal pH values below 3. In duodenal ulcer patients juxtamucosal pH in the cap was significantly lower than that in normals at luminal pH values below 3. These studies support the hypothesis that a "mucus-bicarbonate" barrier inhibits mucosal acidification in humans and that duodenal mucosa in ulcer patients is less able to maintain a neutral zone adjacent to it in the face of luminal acid.

Effects of omeprazole on gastric mucosal blood flow in the conscious rat

Regional blood flow in the gastrointestinal tract (forestomach, corpus, antrum, duodenum, jejunum, and colon) was determined in the conscious rat by means of the microsphere technique. The effects on blood flow were determined after omeprazole (orally and intravenously) and cimetidine (intravenously) during both basal and pentagastrin-stimulated gastric acid secretion. Under basal conditions neither omeprazole nor cimetidine decreased the blood flow in the gastrointestinal tract in spite of pronounced inhibition of acid secretion. On the contrary, there was a tendency towards an increased blood flow in the mucosal layer of the corpus after the oral (80 mumol/kg) and the high intravenous (10 mumol/kg) dose of omeprazole. When omeprazole was given intravenously to rats during pentagastrin-stimulated acid secretion, blood flow in the gastric mucosa was unaffected in spite of complete or almost complete inhibition of acid secretion. In contrast, cimetidine decreased the mucosal blood flow, indicating that the pentagastrin-induced increase in blood flow to some extent is mediated by H2 receptors.

Prevention of gastric mucosal lesions following aortic cross-clamping

Stress ulceration is frequently encountered after cardiovascular surgery. In this study of 32 male baboons, severe gastric ischaemia was used to produce gastric stress lesions. The occurrence of these lesions was reduced by allopurinol (P = 0.03) and completely prevented by the combination of allopurinol with superoxide dismutase (P = 0.004). A shorter ischaemic period also reduced the number of lesions (P = 0.02). Concurrent with the stress lesion formation, there was a fall in mucosal glutathione and oxidized glutathione levels (P less than 0.05).

Profile of gastric stress ulceration following acute cervical cord injury: an animal model

A reproducible model of acute gastric stress ulceration has been described in the tetraplegic rat. The characteristics of the development of acute gastric ulceration and the concentrations of plasma gastrin have been examined. There was a significant increase in gastric stress ulceration within 4 h of producing the tetraplegia. The ulceration was confined to the glandular portion of the stomach and occurred equally on crests and rugal troughs. Plasma gastrin concentrations were not changed by spinal cord section. This characterized model can serve as a basis for further investigation of the aetiology and prophylaxis of acute gastric ulceration in quadriplegia.

Acute stress ulceration

Stress ulceration is usually considered a mucosal abnormality of the oesophagus, stomach or duodenum in the critically ill. It is found to a varying degree in all such patients. Only about one-quarter of lesions are associated with blood loss and less than 5% need resuscitation and treatment. However, because treatment of established bleeding is unsatisfactory, and associated with a high mortality, prophylactic measures are usually employed. These include optimising gastric mucosal blood flow and oxygen delivery, correcting coagulation abnormalities and treating underlying infection. Enteral feeding should also be employed whenever possible. Other prophylactic measures currently used involve raising gastric pH above 4, with either antacids or H2 receptor antagonists. This is best achieved by measuring the gastric pH hourly and titrating it against an appropriate dose of either type of drug or a combination of both. Newer drugs, such as omeprazole, sucralfate and prostaglandins, are proving very successful in the treatment and prevention of gastric and duodenal ulcers and may prove even more effective than currently available agents.

Focal gastric mucosal blood flow at the site of aspirin-induced ulceration

Focal gastric mucosal blood flow as measured by the hydrogen gas clearance method was compared with total gastric blood flow as determined by venous outflow in an isolated segment of canine stomach before, during, and after exposure to aspirin. Despite an increase in total gastric blood flow from 10.8 +/- 1.6 ml/min per chamber to 17.4 +/- 1.9 ml/min per chamber and mucosal blood flow at nonulcerated sites from 29.5 +/- 4.3 ml/min per 100 g to 83 +/- 14.4 ml/min per 100 g, mucosal blood flow at the site of aspirin-induced ulceration was significantly reduced from 29.5 +/- 4.3 ml/min per 100 g to 12.5 +/- 2.5 ml/min per 100 g. After the removal of aspirin, mucosal blood flow returned to control levels. Such a redistribution of mucosal blood flow in response to aspirin is consistent with the localized nature of acute aspirin-induced injury. The findings also explain the inability of previous methods measuring blood flow of the entire stomach to demonstrate mucosal ischemia during such injury.

Prophylaxis and management of stress ulcers

Stress ulcers are located in the body and fundic part of the stomach. They occur in the majority of severely ill or injured patients, but only about 10% will bleed. The most effective prophylaxis are measures against the condition giving rise to risk factors as septicaemia, shock and malnutrition. The medical prophylaxis consists of antacids and/or histamine2-blockers. Most bleedings will stop after intensive care and medication with vasopressin particularly if risk factors can be eliminated. Gastric surgery should be the last step in the treatment of bleeding stress ulcers and then we recommend non-resectional surgery as gastric devascularisation or suture ligation of bleeding vessels.

Measurement of regional gastric mucosal blood flow by hydrogen gas clearance

Gastric mucosal blood flow as measured by the hydrogen gas clearance method was compared with total gastric blood flow as determined by venous outflow in an isolated segment of canine stomach. During rest and histamine stimulation, hydrogen gas clearance correlated lineally with total gastric blood flow (p less than 0.001). Correlation analysis revealed a slope of 1.21 and a correlation coefficient of 0.97. The slope of 1.21 indicates that the ratio of mucosal to total gastric blood flow was approximately 82 percent. This fractional distribution of blood flow is in agreement with that previously reported by microsphere technique. In the intact stomach of anesthetized rats and dogs, antral mucosal blood flow was significantly higher than that of the corpus. This finding may, in part, contribute to the observation that acute stress erosion occurs predominantly in the corpus of the stomach. Histamine stimulation selectively increased the mucosal blood flow of the corpus, whereas antral mucosal blood flow remained unchanged. As a result, there was no significant difference in mucosal blood flow between the antrum and the corpus during histamine stimulation.

Rapid induction of gastric ulceration in guinea pigs by sequential exposure to a barrier breaker and indomethacin

In short term experiments under halothane anesthesia, guinea pig total gastric pouches were initially and terminally exposed to 0.1 M HCl for 30 min. During an intervening 50-min test period, the gastric mucosa was exposed at pH 7.3, either to a barrier breaker (lysolecithin or diluted bile or sodium taurocholate) or to phosphate buffered saline (PBS) for half of the period, followed by exposure to indomethacin or further PBS for the second half of the test period. Scoring of mucosal damage was assessed from coded photographs and histological slides and by measurement of the transmucosal potential difference. In comparison with controls exposed only to PBS in the test period, indomethacin did produce minor but significant mucosal damage, whereas over this short time interval, the barrier breaking agents did not. Sequential exposure of pouches to lysolecithin and indomethacin caused a highly significant increase in ulceration, compared to controls or to indomethacin or lysolecithin exposure separately.

Portal hypertension and gastric mucosal injury in rats. Effects of alcohol

The present study was performed primarily in order to determine whether gastric mucosa of rats with portal hypertension has different functional and histologic features when compared with controls, and second to quantitate and compare morphologic and functional changes after exposure to topical ethanol. Portal hypertension was produced by staged portal venous occlusion, and in these animals portal pressure was 32 +/- 2 cm saline compared with 18 +/- 2 cm in sham-operated controls (p less than 0.005). Before ethanol, portal hypertensive rats compared with controls had significantly higher luminal pH (2.9 +/- 0.3 vs. 1.9 +/- 0.1), increased H+ back-diffusion (loss of 138 +/- 10 vs. 57 +/- 16 microEq H+/h), lower potential difference (8 +/- 1 mV lower than controls), and extensive submucosal edema (submucosal thickness 325 +/- 25 vs. 138 +/- 18 micrometers). After 3 h of exposure to 2 ml intragastric absolute ethanol, the area of macroscopic hemorrhagic mucosal injury was significantly greater in portal hypertensive rats than in controls (34.0 +/- 8.7% vs. 7.6 +/- 2.1%), confirmed histologically by the greater number of deep hemorrhagic necrotic lesions and extent of mucosal length involved. Furthermore, after ethanol, portal hypertensive rats compared with controls had significantly increased gastric volume (14.4 +/- 1.5 vs. 8.3 +/- 0.6 ml), Na+ (86.6 +/- 8.0 vs. 64.6 +/- 8.0 mEq/L), pH (7.1 +/- 0.3 vs. 4.3 +/- 0.4), H+ back-diffusion (loss of 309 +/- 41 vs. 207 +/- 33 microEq H+/h), and protein and blood loss (100% increases over controls). These results indicate that gastric mucosa of portal hypertensive rats has distinctive functional and histologic abnormalities that can explain its increased susceptibility to erosive injury after ethanol. This study quantitatively confirms in an animal model the clinical observations that portal hypertension may predispose to severe gastric mucosal injury.

A morphologic and kinetic basis for the more invasive character of N-methyl-N'-nitro-N-nitrosoguanidine induced duodenal tumors following pyloroplasty

Pyloroplasty increased the invasiveness of duodenal tumors in Wistar rats receiving N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) for 12 weeks (83 mg/l in drinking water) (Arch. Surg., 117, 768-771). To assess morphologic and kinetic alterations, analyses of tritiated thymidine (3HTdR) pulse-labeled fundic, antral and duodenal mucosa were carried out. The normal appearance of MNNG-treated antral and duodenal mucosa was characterized by the appearance of elongated hyperactive columns exhibiting elevated levels of DNA synthesis. Pyloroplasty in carcinogen-treated rats induced both a 3-fold enhancement in the number of these elongated columns and an elevation in the number of proliferating cells within them (P less than 0.001). In the MNNG and pyloroplasty treated duodenal mucosa 26% of columns contained over 130 cells/column rather than an average of 100 cells in normal appearing MNNG-treated mucosa. DNA synthesis was increased by 23% within these hyperactive glands (11.3 proliferative cells/column vs. 9.4/column in normal appearing mucosa). Pyloroplasty creates both an increase of gastric bile reflux and an increase of the gastric evacuation rate, conditions which influence cell proliferation. Such alterations in antro-pyloro-duodenal physiology contribute to the increased cellular activity observed, promote malignant transformation and foster the expression of invasiveness.