Gastric nitric oxide synthase expression during endotoxemia: implications in mucosal defense in rats

The Gastroprotective Effect of Naringenin against Ethanol-Induced Gastric Ulcers in Mice through Inhibiting Oxidative and Inflammatory Responses

Naringenin is a major flavanone found in grapes, tangelos, blood oranges, lemons, pummelo, and tangerines. It is known to have anti-inflammatory, antioxidant, anticancer, antimutagenic, antifibrogenic, and antiatherogenic pharmacological properties. This study aims to investigate the anti-inflammatory effects of naringenin in ethanol-induced gastric damage in vivo and ethanol-stimulated KATO III cells in vitro. Our results showed that pretreatment with naringenin significantly protected mice from ethanol-induced hemorrhagic damage, epithelial cell loss, and edema with leucocytes. It reduced gastric ulcers (GU) by suppressing ethanol-induced nuclear factor-κB (NF-κB) activity and decreasing the levels of nitric oxide (NO), malondialdehyde (MDA), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-8 (IL-8), and myeloperoxidase (MPO). In addition, pretreatment with naringenin might inhibit the secretion of TNF-α, IL-6, and IL-8, as well as the proteins cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) via the suppression of NF-κB and mitogen-activated protein kinase (MAPK) signaling in ethanol-stimulated stomach epithelial KATO III cells. Together, the results of this study highlight the gastroprotective effect of naringenin in GU of mice by inhibiting gastric secretion and acidity, reducing inflammation and oxidative stress, suppressing NF-κB activity, and restoring the histological architecture. These findings suggested that naringenin has therapeutic potential in the alleviation of ethanol-induced GU.

The Effects of Dexmedetomidine and Ketamine on Oxidative Injuries and Histological Changes Following Blunt Chest Trauma

BACKGROUND

The objective of this research was to evaluate the oxidative and histopathological effects of dexmedetomidine and ketamine on the pulmonary contusion model resulting from blunt chest trauma.

METHODS

Rats were randomly assigned to 5 equal groups (n=6): control group (Group C), pulmonary contusion group (Group PC), PC-dexmedetomidine group (Group PC-D), PC-ketamine group (Group PC-K), and PC-dexmedetomidine + ketamine (Group PC-D+K). The PC was performed by dropping a weight of 500 g (2.45 Joules) from a height of 50 cm. In Group PC-D, after chest trauma, dexmedetomidine (100 µg/kg) was administered intraperitoneally. In Group PC-K, after chest trauma, ketamine (100 mg/kg) was administered intraperitoneally. In Group PC-D+K, dexmedetomidine and ketamine were administered together. At the end of the 6th hour, rats were sacrificed. Malondialdehyde (MDA) level, superoxide dismutase (SOD) enzyme activities, neutrophil infiltration/aggregation, and thickness of the alveolar wall were evaluated.

RESULTS

MDA levels were significantly higher in Group PC than Groups C, PC-D, and PC-D+K. SOD enzyme activity was significantly higher in Group PC than Groups C, PC-D, and PC-D+K. In addition, neutrophil infiltration/aggregation and total pulmonary injury scores were significantly higher in Group PC than in other groups, and the thickness of the alveolar wall was significantly higher in Group PC compared to Groups C, PC-D, and PC-D+K. MDA level, SOD enzyme activities, neutrophil infiltration/aggregation, and thickness of alveolar wall were similar in PC-D and PC-D+K groups.

CONCLUSION

Dexmedetomidine and dexmedetomidine+ketamine have protective effects on blunt chest trauma but no protective effect was observed when ketamine was administered alone. We concluded that the administration of dexmedetomidine and ketamine after contusion is beneficial against pulmonary injury in rats.

The Gastroprotective Effect of Small Molecule Oligopeptides Isolated from Walnut (Juglans regia L.) against Ethanol-Induced Gastric Mucosal Injury in Rats

The study investigated the protective effect of walnut oligopeptides (WOPs) against ethanol-induced gastric injury using Sprague-Dawley (SD) rats. Rats were randomly divided into seven groups based on body weight (10/group), normal group, ethanol group, whey protein group (220 mg/kg body weight), omeprazole group (20 mg/kg body weight), and three WOPs groups (220, 440, 880 mg/kg body weight). After 30 days of treatment with WOPs, rats were given 5 mL/kg absolute ethanol by gavage to induce gastric mucosal injury. Gastric ulcer index (GUI) were determined and the following measured; gastric content pH, gastric mucin, endogenous pepsinogens (PG), prostaglandin E2 (PGE2), inflammatory cytokines, oxidative stress indicators, and the expression of apoptosis-related proteins were measured to evaluate the gastroprotective effect of WOPs. The results showed that the administration with WOPs markedly mitigated the hemorrhagic gastric lesions caused by ethanol in rats, and decreased the GUI, the gastric content pH, PG1, PG2, and NO levels, enhanced mucin and PGE2. Also, WOPs repressed gastric inflammation through the reduction of TNF-α, IL-6, IL-1β and increase IL-10 levels, and revealed antioxidant properties with the enhancement of superoxide dismutase, glutathione, and catalase activity, while reduction of malondialdehyde. Moreover, WOPs treatment significantly down-regulated Bax, caspase-3 and nuclear factor-κB p65 (NF-κB p65) expression, while up-regulating the expression of Bcl-2 and inhibitor kappa Bα (IκBα) protein. These results indicated that WOPs have protective effects against ethanol-induced gastric mucosal injury in rats through anti-inflammatory, anti-oxidation, and anti-apoptosis mechanisms.

Arginine infusion in patients with septic shock increases nitric oxide production without haemodynamic instability

Arginine deficiency in sepsis may impair nitric oxide (NO) production for local perfusion and add to the catabolic state. In contrast, excessive NO production has been related to global haemodynamic instability. Therefore, the aim of the present study was to investigate the dose-response effect of intravenous arginine supplementation in post-absorptive patients with septic shock on arginine-NO and protein metabolism and on global and regional haemodynamics. Eight critically ill patients with a diagnosis of septic shock participated in this short-term (8 h) dose-response study. L-Arginine-HCl was continuously infused [intravenously (IV)] in three stepwise-increasing doses (33, 66 and 99 μmol·kg-1·h-1). Whole-body arginine-NO and protein metabolism were measured using stable isotope techniques, and baseline values were compared with healthy controls. Global and regional haemodynamic parameters were continuously recorded during the study. Upon infusion, plasma arginine increased from 48±7 to 189±23 μmol·l-1 (means±S.D.; P<0.0001). This coincided with increased de novo arginine (P<0.0001) and increased NO production (P<0.05). Sepsis patients demonstrated elevated protein breakdown at baseline (P<0.001 compared with healthy controls), whereas protein breakdown and synthesis both decreased during arginine infusion (P<0.0001). Mean arterial and pulmonary pressure and gastric mucosal-arterial partial pressure of carbon dioxide difference (Pr-aCO2) gap did not alter during arginine infusion (P>0.05), whereas stroke volume (SV) increased (P<0.05) and arterial lactate decreased (P<0.05). In conclusion, a 4-fold increase in plasma arginine with intravenous arginine infusion in sepsis stimulates de novo arginine and NO production and reduces whole-body protein breakdown. These potential beneficial metabolic effects occurred without negative alterations in haemodynamic parameters, although improvement in regional perfusion could not be demonstrated in the eight patients with septic shock who were studied.

Laparotomy attenuates lipopolysaccharide-induced gastric bleeding in the rat

Lipopolysaccharide (LPS) increases systemic inflammation and causes duodenogastric reflux of bile and gastric bleeding. Laparotomy prevents gastric injury from the luminal irritant bile, but its effects on LPS-induced gastric injury are unknown. We hypothesized that laparotomy would diminish inflammation and attenuate gastric bleeding caused by LPS. In the rat, laparotomy, done either before or after administration of LPS, attenuated LPS-induced bile reflux, gastric bleeding, and cyclooxygenase-2, but not inducible nitric oxide synthase, expression when compared to controls given LPS. Laparotomy also blunted LPS-induced changes in serum cytokine production. These data suggest that laparotomy has gastroprotective effects by preventing LPS-induced bile reflux and gastric bleeding and by a mechanism mediated, at least in part by cyclooxygenase-2.

Ketamine suppresses LPS-induced bile reflux and gastric bleeding in the rat

BACKGROUND

Although ketamine has many beneficial effects in a rat model of noninfectious inflammation with lipopolysaccharide (LPS), its effects on gut ileus are unknown. We hypothesized that ketamine would improve LPS-induced ileus and therefore examined its effects on gastric emptying and intestinal transit as well as duodenogastric bile reflux and associated gastric bleeding.

METHODS

Male rats received saline or ketamine (7 mg/kg ip) 1 hour before saline or LPS (20 mg/kg ip) for 5 hours. Thirty minutes before killing, rats received orogastric rhodamine B isothiocyanate-labeled dextran and 5 minutes later fluorescein isothiocyanate-labeled dextran via a duodenal catheter. GI contents were collected for dye, bile acid, and hemoglobin (index of bleeding) determinations.

RESULTS

LPS significantly impaired intestinal transit and increased duodenogastric bile reflux and gastric luminal hemoglobin content. Ketamine improved intestinal transit, prevented LPS-induced bile reflux, and diminished gastric bleeding. In mechanistic studies, ketamine also attenuated LPS-induced upregulation of the proinflammatory genes inducible nitric oxide synthase and cyclo-oxygenase-2 in the stomach but preserved expression of the anti-inflammatory gene heme-oxygenase-1 (Western blot).

CONCLUSIONS

These data suggest that ketamine may prevent LPS-induced gastric bleeding by decreasing bile reflux through improved intestinal transit or by local changes in nitric oxide, prostaglandin, and carbon monoxide metabolism.

Ketamine-induced hepatoprotection: the role of heme oxygenase-1

Lipopolysaccharide (LPS) causes hepatic injury that is mediated, in part, by upregulation of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Ketamine has been shown to prevent these effects. Because upregulation of heme oxygenase-1 (HO-1) has hepatoprotective effects, as does carbon monoxide (CO), an end product of the HO-1 catalytic reaction, we examined the effects of HO-1 inhibition on ketamine-induced hepatoprotection and assessed whether CO could attenuate LPS-induced hepatic injury. One group of rats received ketamine (70 mg/kg ip) or saline concurrently with either the HO-1 inhibitor tin protoporphyrin IX (50 micromol/kg ip) or saline. Another group of rats received inhalational CO (250 ppm over 1 h) or room air. All rats were given LPS (20 mg/kg ip) or saline 1 h later and euthanized 5 h after LPS or saline. Liver was collected for iNOS, COX-2, and HO-1 (Western blot), NF-kappaB and PPAR-gamma analysis (EMSA), and iNOS and COX-2 mRNA analysis (RT-PCR). Serum was collected to measure alanine aminotransferase as an index of hepatocellular injury. HO-1 inhibition attenuated ketamine-induced hepatoprotection and downregulation of iNOS and COX-2 protein. CO prevented LPS-induced hepatic injury and upregulation of iNOS and COX-2 proteins. Although CO abolished the ability of LPS to diminish PPAR-gamma activity, it enhanced NF-kappaB activity. These data suggest that the hepatoprotective effects of ketamine are mediated primarily by HO-1 and its end product CO.

Effect of iNOS inhibitor on portal hypertensive gastropathy in cirrhotic rats

AIM: To investigate the effect and mechanism of aminoguanidine (AG) on the portal hypertensive gastropathy in cirrhotic rats.

METHODS: Thirty male SD rats were randomly divided into three groups: control group (n = 10), model group (n = 10) and AG treatment group (n = 10) (AG group). The model group was induced through subcutaneous injection of CCl₄ for 12 weeks, AG group was given subcutaneous injection of CCl₄ together with oral administration of AG. The morphological and histological changes in gastric mucosa were evaluated. The expression of iNOS in gastric mucosa was detected by SABC immunohistochemical methods. And the ulcer-index (UI) of gastric mucosa, and portal pressure were measured in each group.

RESULTS: Histological changes of gastric mucosa was milder and ulcer index of gastric mucosa was significantly lower in AG group than in model group (3.00 ± 2.31 vs 10.60 ± 3.47, P < 0.01). The expression of iNOS (optical density and area density) in gastric mucosa was significantly higher in model group than in control group (0.64 ± 0.04 vs 0.25 ± 0.03; 0.344 ± 0.068 vs 0.017 ± 0.008, both P < 0.01). Optical density and area density were significantly lower in AG group than in model group (0.46 ± 0.09 vs 0.64 ± 0.04; 0.159 ± 0.021 vs 0.344 ± 0.068, both P < 0.01), and the portal pressure were lower in AG group than in model group.

CONCLUSION: Aminoguanidine may ameliorate the development of portal hypertensive gastropathy through significantly inhibiting the expression of iNOS in gastric mucosa.

Effects of anesthesia on lipopolysaccharide-induced changes in serum cytokines

BACKGROUND

The pathophysiology of sepsis is incompletely understood, however alterations in systemic inflammation and serum cytokines are thought to play a central role. In the rat, ketamine, but not isoflurane, prevents hepatic injury from lipopolysaccharide (LPS). The effect of these anesthetics on the systemic inflammatory response and other organs remains to be fully elucidated. We hypothesized that ketamine, but not isoflurane, would blunt the cytokine response to LPS administration.

METHODS

Male rats received no anesthesia, intraperitoneal ketamine (70 mg/kg), or inhalational isoflurane. One hour later, LPS (20 mg/kg, intraperitoneal) or saline was given for 5 hours and rats were killed. Gastric fluid volumes were determined as an index of gastric emptying. Serum was collected and cytokines measured via a multiplexed suspension immunoassay.

RESULTS

In nonanesthetized rats, LPS increased gastric luminal fluid accumulation and serum levels of proinflammatory cytokines when compared with saline controls. Anesthesia with either ketamine or isoflurane caused a significant reduction in LPS-induced changes in serum cytokines, although ketamine had a more dramatic reduction in tumor necrosis factor alpha levels than did isoflurane. Both anesthetics reduced the interleukin IL-6/IL-10 ratio in response to LPS when compared with LPS alone. Ketamine, but not isoflurane, prevented LPS-induced gastric luminal fluid accumulation.

CONCLUSIONS

These data indicate that both ketamine and isoflurane diminish the systemic inflammatory response to LPS in the rat as measured by serum cytokines and a reduced IL-6/IL-10 ratio. However, only ketamine improves LPS-induced gastric dysfunction, perhaps secondary to its ability to reduce serum tumor necrosis factor alpha levels more effectively.

iNOS expression in oral and gastrointestinal tract mucosa

It is known that the overproduction of nitric oxide (NO) by nitric oxide synthase (NOS) occurs during the progression of various inflammatory diseases in intestinal tract. NOS inhibitors or inducible nitric oxide synthase (iNOS) gene expression inhibitors should be considered as potential anti-inflammatory agents, as NO synthesized by iNOS is related to various pathophysiological processes including inflammation. In order to understand the relationship between iNOS and pathological reactions such as the inflammatory process and malign transformation clearly, the existence and amount of constitutive expression should be determined. It is crucial to comprehend the harmful and protective amounts of iNOS expressions in order to clarify the relationship between iNOS and pathological processes. Evidently, only after this inspection is it possible to utilize iNOS as a marker and treatment instrument during the diagnosis and treatment of malign transformation and the inflammatory process.

Gastric alkalinization after major trauma

BACKGROUND

Gastric function in trauma patients is poorly understood. In animals, shock causes gastric luminal alkalinization and bile reflux. In trauma patients, studies of stress gastritis prophylaxis demonstrated with continuous gastric pH monitoring that the stomach became alkaline even without antisecretory therapy. Therefore, we hypothesized that trauma patients have an alkaline gastric environment that may be because of bile reflux.

METHODS

A prospective observational study at an urban Level I trauma center was performed. All major torso trauma patients (severe head injuries excluded) who met the criteria for standardized shock resuscitation were eligible for inclusion. A 12.5 Fr silastic pH probe (Sandhill Scientific) was placed in the stomach and the gastric pH continuously monitored for 7 days. Patients received no stress gastritis prophylaxis. Gastric samples were obtained each day and assayed for total bile acids and pH.

RESULTS

Twelve patients were entered into the study. Mean age was 31 years +/- 4 years, 67% men, 75% blunt mechanism of injury, and mean Injury Severity Score 28 +/- 3. Three patients (25%) developed multiple organ failure and four acquired ventilator-associated pneumonia. During the first day of continuous pH monitoring, 9 of 12 patients had a gastric pH >4 for the majority of the day with 7 patients having essentially no acid production. During subsequent days, gastric pH began to drop and by the 4th day the majority of each day was spent at a pH <4. Additionally, gastric pH of patients with ventilator-associated pneumonia or multiple organ failure tended to be more alkaline. Bile acid was present in the gastric fluid of all patients in varying amounts. However, there was no significant correlation between gastric pH and bile acid concentration.

CONCLUSIONS

Traumatic injury causes gastric luminal alkalinization that may be related, only in part, to bile acid reflux. Other alkalinizing factors remain to be elucidated.

Pros and cons of L-arginine supplementation in disease

The amino acid arginine and one of its metabolites NO have gathered broad attention in the last decade. Although arginine is regarded as a conditionally essential amino acid in disease, L-arginine supplementation in severe illness has not found its way into clinical practice. This might be due to the invalid interpretation of results from studies with immune-enhancing diets containing L-arginine amongst other pharmaconutrients. However, not much attention is given to research using L-arginine as a monotherapy and the possibility of the alternative hypothesis: that L-arginine supplementation is beneficial in disease. The present review will discuss data from studies in healthy and diseased animals and patients with monotherapy of L-arginine to come to an objective overview of positive and negative aspects of L-arginine supplementation in disease with special emphasis on sepsis, cancer, liver failure and wound healing.

The gut in systemic inflammatory response syndrome and sepsis. Enzyme systems fighting multiple organ failure

The prognosis and care of critically ill ICU patients has improved over recent years, but the development of multiple organ failure (MOF) continues to cause significant morbidity and mortality. Shock, with resultant organ ischemia, appears to play a critical role in the development of MOF. It is our global hypothesis that MOF is a gut-derived phenomenon and that novel interventions can improve outcome in shock-induced gut inflammation and dysfunction in critically ill patients. We have found that the anesthetic agent ketamine has a profound impact on the response to endotoxic shock. This review summarizes our findings on the mechanisms of action by which ketamine is able to modulate the nitric oxide, cyclo-oxygenase and heme-oxygenase enzyme systems to attenuate endotoxin-induced organ dysfunction.

The effect of nitric oxide, growth factors, and estrogen on gastric cell migration

BACKGROUND

To study gastric epithelial cell migration during nitric oxide (NO) and growth factor treatment, simulating inflammation and infection. Also, the effects of estrogen on migration of different malignant and nonmalignant gastric epithelial cell lines were explored.

MATERIAL AND METHODS

Isolated primary cultured rabbit gastric epithelial cells, rat gastric mucosal cells, human gastric adenocarcinoma cells, and human colon adenocarcinoma cells (WiDr) were cultured to confluency in appropriate media (5% CO2, 37 degrees C). The cells were treated by hepatocyte growth factor (HGF), transforming growth factor-alpha (TGF-alpha) and keratinocyte growth factor (KGF), with and without sodium nitroprusside (SNP, NO donor) or 17beta-estradiol. Caspase-3 activity and cell viability and migration speed after wounding were measured.

RESULTS

HGF was the most potent growth factor to stimulate migration. SNP dose-dependently decreased the speed of migration. HGF and TGF-alpha were able to overcome the SNP-induced inhibition of migration, whereas KGF was not. SNP also induced caspase-3 activity, which was inhibited by HGF and TGF-alpha. 17beta-estradiol decreased migration in all epithelial cells, but the decrease was more profound in malignant cell lines. HGF could overcome the estrogen retarded migration.

CONCLUSIONS

Growth factors can overcome NO-induced retardation of cell migration and inhibit NO-induced caspase-3 activity, which altogether might also have physiological significance in in vivo inflammation and in gastric cancer. The more profound decrease in migration speed of gastric adenocarcinoma cell line may suggest that estrogen might be one of the protective factor against female gastric adenocarcinoma before menopausal age.

The alpha2-adrenergic receptor antagonist yohimbine improves endotoxin-induced inhibition of gastrointestinal motility in mice

BACKGROUND

Sepsis inhibits gastrointestinal motility. Although the exact mechanism of this is unclear, lipopolysaccharide is known to activate macrophages in the gastrointestinal wall, which upregulate their expression of inducible nitric oxide synthase (iNOS). This leads to an increased production of nitric oxide, which relaxes the gastrointestinal muscles. We studied endotoxaemic mice to determine whether yohimbine improved delayed gastric emptying and gastrointestinal transit.

METHODS

Male Balb/c mice (n = 49) were randomly allocated to two groups, and either yohimbine 25 microg or saline was injected s.c. Four hours later, mice in each group were further randomly allocated to two groups, and either lipopolysaccharide 100 microg or saline was injected intraperitoneally. Eight hours later, liquid containing fluorescent microbeads was infused into the stomach, and 30 min later, gastric emptying and gastrointestinal transit were measured using flow cytometry. We also studied whether yohimbine given after injection of lipopolysaccharide was effective (n = 22). In another group of mice (n = 32), iNOS in the gastrointestinal tract was measured using western blotting.

RESULTS

Lipopolysaccharide significantly inhibited gastric emptying and gastrointestinal transit. Yohimbine, given before or after lipopolysaccharide, significantly attenuated the inhibitory effects of lipopolysaccharide. Lipopolysaccharide increased the expression of iNOS in the small intestine and yohimbine suppressed the effects of lipopolysaccharide.

CONCLUSIONS

In endotoxaemic mice, yohimbine improved delayed gastric emptying and gastrointestinal transit, possibly by downregulating lipopolysaccharide-induced increased expression of iNOS.

Ketamine Attenuates Early Lipopolysaccharide-Induced Gastric Dysfunction: Role of Stress-Inducible Phosphoproteins

BACKGROUND

Ketamine exerts anti-inflammatory actions and attenuates lipopolysaccharide (LPS)-induced gastric dysfunction by an unknown mechanism. Because stress-inducible phosphoproteins mediate many inflammatory responses, we hypothesized that ketamine would disrupt the early signaling events of LPS-induced inflammation by altering phosphorylation of stress-inducible phosphoproteins JNK, p38, and IkB.

METHODS

Adult rats received saline or ketamine (70 mg/kg, intraperitoneal) 1 hour before LPS (20 mg/kg, intraperitoneal) or saline. Animals were killed at 15, 30, 45, and 60 minutes after LPS, gastric mucosa was harvested, and gastric volume and pH were recorded. Gastric mucosal phosphorylation of JNK, p38, and IkB-alpha were analyzed with a multiplexed suspension immunoassay.

RESULTS

Ketamine-attenuated LPS induced increases in gastric luminal fluid and pH. Control animals receiving saline or ketamine and no LPS had gastric volumes of 0.1 mL and luminal pH of 2 at all time points. LPS upregulated phosphorylation of JNK, p38, and IkB-alpha as early as 15 minutes after LPS. Ketamine did not effect the early phosphorylation of these proteins.

CONCLUSION

Endotoxin causes gastric dysfunction and upregulates stress-inducible phosphoproteins within minutes after LPS. Although ketamine attenuates gastric dysfunction, its salutary effects do not seem to be related to alterations in phosphorylation of JNK, p38, or IkB-alpha.

[The effect of bacterial lipopolysaccharide on the gastric emptying of rats: a pretreatment evaluation using Nw-nitro-L-arginine methyl ester (L-NAME)]

BACKGROUND

There is evidence that nitric oxide plays a role in the decrease in gastric emptying induced by bacterial lipopolysaccharide.

AIM

To evaluate the effect of pretreatment with Nw-nitro-L-arginine methyl to ester, one competitive inhibitor of the nitric oxide synthases, on the gastric emptying delay induced by lipopolysaccharide.

MATERIAL AND METHODS

Male Wistar rats, SPF, were used after 24 h fast and 1 h-water withdrawn. The pretreatment was done intravenously with vehicle (saline) or N(w)-nitro-L-arginine methyl to ester in the doses of 0.5, 1, 2.5 e 5 mg/kg. After 10 min, the animals were treated iv with lipopolysaccharide (50 microg/kg) or received vehicle (saline). The gastric emptying was evaluated 1 h after the lipopolysaccharide administration. A saline solution containing phenol red was used as the test meal. The gastric emptying was indirectly assessed by the determination of percent gastric retention of the test meal 10 min after orogastric administration.

RESULTS

The animals pretreated with vehicle and treatment with lipopolysaccharide have significant rise of the gastric retention (average = 57%) in comparison with the controls receiving only vehicle (38.1%). The pretreatment with the different doses of N(w)-nitro-L-arginine methyl to ester did not modify per se the gastric retention in comparison with the animals pretreated with vehicle. Pretreatment with N(w)-nitro-L-arginine methyl to ester with the dose of 1 mg/kg determined a discrete but significant reduction in the gastric retention (52%) of animals treated with lipopolysaccharide in comparison with vehicle-pretreated rats. Paradoxically, animals pretreated with 2.5 or 5 mg of N(w)-nitro-L-arginine methyl to ester/kg followed by treatment with lipopolysaccharide displayed a significantly higher gastric retention (74.7% and 80.5%, respectively) as compared to their controls, pretreated with the same doses of the inhibitor and treated with vehicle (40.5% and 38.7%, respectively) and to those pretreated with vehicle and treated with the same toxin.

CONCLUSION

The pretreatment with N(w)-nitro-L-arginine methyl to ester at low dose (1 mg/kg) resulted in a discrete inhibition of the gastric emptying delay induced by lipopolysaccharide. Nevertheless, N(w)-nitro-L-arginine methyl to ester at higher doses (2.5 and 5 mg/kg) induced an enhancement of the lipopolysaccharide effect on gastric emptying, despite not interfering with the gastric emptying per se.

Ketamine-induced gastroprotection during endotoxemia: role of heme-oxygenase-1

Inducible nitric oxide synthase contributes to lipopolysacharide-induced gastric injury. In contrast, heme-oxygenase-1 has anti-inflammatory effects and is protective against oxidative tissue injury. Ketamine attenuates injury from lipopolysacharide and is associated with changes in oxidative stress proteins, but its effects on the stomach remain to be fully elucidated. We hypothesized that ketamine would diminish gastric injury from lipopolysacharide via down-regulation of nuclear factor-kappass, activator protein-1, and inducible nitric oxide synthase, as well as up-regulation of heme-oxygenase-1. Ketamine up-regulated heme-oxygenase-1 and attenuated lipopolysacharide-induced changes in gastric nuclear factor-kappass, activator protein-1, and inducible nitric oxide synthase. Ketamine negated LPS-induced gastric injury from acidified ethanol, an effect reversed by tin protoporphorin IX. Ketamine diminishes the susceptibility of gastric mucosa to damage from luminal irritants during endotoxemia, which is mediated in part by down-regulation of iNOS and up-regulation of HO-1.

Integrative roles of transforming growth factor-alpha in the cytoprotection mechanisms of gastric mucosal injury

Background

Transforming growth factor α (TGFα) protects against gastric mucosal injury and facilitates wound healing. However, its overexpression is known to induce hypertrophic gastropathy resembling Menetrier's disease in transgenic (TG) mice on an FVB background, as one of the authors reported previously. We studied another TGFα-expressing mouse line on a CD1 background, whose gastric mucosa appears normal. Since this TG mouse had a strong resistance to ethanol-induced gastric injury, we considered the long-term effect of TGFα on several gastric protection mechanisms.

Methods

TGFα-expressing transgenic (TG) mouse lines bearing human TGFα cDNA under the control of the mouse metallothionein gene I promoter were generated on a CD1 mouse background, and analyzed their ethanol injury-resistant phenotypes produced by TGFα.

Results

In the TG mucosa, blood flow was well maintained after ethanol injury. Further, neural and inducible types of NO synthases were consistently and widely expressed in the TG mucosa, compared with the limited distribution of neural type NO synthase in the luminal pit region of the wild-type (WT) mucosa. COX-2 and its upstream transcription factor NfkB were constitutively elevated in the TG mucosa even before ethanol administration, whereas they were induced in the same region of the WT mucosa only after ethanol injury. Two anti-apoptotic proteins, HSP70 and Bcl-2, were upregulated in the TG mucosa even before ethanol administration, while they were not expressed in the WT mucosa before the injury. Furthermore, pro-caspase 3 activation was inhibited in the TG mucosa, while it was converted to the active form in the WT mucosa following ethanol administration.

Conclusion

We conclude that TGFα maintains the gastric mucosal defense against gastric injury by integrating other cytoprotective mechanisms.

Salicylate enhances rat gastric gelatinase activity

BACKGROUND

Increased matrix metalloproteinase (MMP) activity is associated with tissue injury in some organs. Their role in gut injury remains to be fully elucidated. We recently demonstrated that increased MMP-2 activity participated in lipopolysaccharide (LPS)-induced gastric injury. Thus we hypothesized that MMPs may play a role in other models of gastric injury.

MATERIALS AND METHODS

The effect of L-NAME (10 mg/kg IP) or salicylate (100 mg/kg IP) on gastric injury from 20% ethanol was evaluated in an anesthetized model of gastric injury. In a separate experiment, gastric metalloproteinase activity was assessed after salicylate or L-NAME administration. Rats were given either L-NAME (10 mg/kg), salicylate (100 mg/kg), or saline IP and sacrificed after 6 hours. Gastric mucosa was harvested and portions of the glandular stomach snap frozen for gelatin and in situ zymography as indices of MMP activity. Subsequently the effect of MMP inhibition on macroscopic gastric injury from salicylate and a dilute luminal irritant was determined.

RESULTS

Both L-NAME and salicylate significantly increased gastric injury from 20% ethanol versus saline controls. Salicylate treatment significantly increased gelatinase activity as determined by in situ zymography and gelatin zymography while L-NAME did not. MMP inhibition ameliorated macroscopic gastric injury secondary to salicylate and a dilute luminal irritant.

CONCLUSIONS

This is the first study to report that MMP activity increases in the stomach following salicylate treatment. These data suggest that MMPs may play a role in the ability of salicylate to exacerbate gastric injury from irritants, but likely do not play a role in mediating the deleterious effects of L-NAME.

EFFECT OF NOS INHIBITION ON RAT GASTRIC MATRIX METALLOPROTEINASE PRODUCTION DURING ENDOTOXEMIA

Matrix metalloproteinases (MMPs) degrade the extracellular matrix and contribute to LPS-induced gastric injury. MMPs are closely modulated by their activators, membrane type-MMP (MT-MMPs) and their endogenous inhibitors, the tissue inhibitors of metalloproteinases (TIMPs). As LPS-induced gastric injury is mediated in part by iNOS, and NO modulates MMP production in vitro, we hypothesized that NOS inhibition would similarly modulate LPS-induced gastric MMP production. Therefore, the purpose of these studies was to compare the effects of selective and nonselective NOS inhibition on LPS-induced gastric MMP production.

METHODS

Sprague-Dawley rats were given either the nonselective NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 5 mg/kg, s.c.), a selective iNOS inhibitor, aminoguanidine (45 mg/kg, i.p.) or L-N-iminoethyl-lysine (L-NIL; 10 mg/kg, i.p.), or vehicle 15 min before saline or LPS (20 mg/kg, i.p.) and killed 24 h after LPS administration. Stomachs were assessed for macroscopic injury (computed planimetry), and gastric mucosal MMP production was assessed by gelatin zymography, in situ zymography, and Western analysis for MMP-2, MT1-MMP, and TIMP-2. (n > or = 4/group; ANOVA).

RESULTS

Aminoguanidine treatment decreased LPS-induced macroscopic gastric injury as well as MMP-2 and MT1-MMP protein production while having no effect on TIMP-2 protein levels. L-NIL similarly attenuated the induction of MMP-2 and MT1-MMP by LPS. L-NAME failed to attenuate LPS induced gastric injury or MT1-MMP protein induction and increased MMP-2 levels. L-NAME similarly had no effect on gastric TIMP-2 production.

CONCLUSIONS

Selective iNOS inhibition decreases gastric MMP-2 activity after LPS administration, whereas nonselective inhibition increases MMP-2 levels. The ability of selective iNOS inhibition to ameliorate LPS-induced gastric injury may be due in part to its inhibition of active MMP-2 production, whereas nonselective NOS inhibitors increase MMP-2 levels and maintain gastric injury after LPS administration.

Effects of lipopolysaccharide on gastric stasis: role of cyclooxygenase

This study was done to examine the role of cyclooxygenase (COX) in lipopolysaccharide (LPS)-induced gastroprotection and gastric stasis. In conscious rats, LPS dose and time dependently increased gastric luminal fluid accumulation. LPS decreased blood flow (laser Doppler) and prevented gastric injury from acidified ethanol at time points before significant fluid accumulation occurred. LPS increased COX-2 but not COX-1 expression. In contrast, LPS decreased gastric mucosal prostaglandin synthesis. LPS-induced gastric luminal fluid accumulation was negated by both nonselective COX inhibition with salicylate and selective COX-2 inhibition with NS-398 but not by selective COX-1 inhibition with SC-560. Neither salicylate nor NS-398 blocked LPS-induced gastroprotection. LPS-induced gastroprotection does not depend entirely on accumulation of luminal fluid and is independent of COX-1 and COX-2. However, the ability of LPS to cause gastric stasis and increase gastric luminal fluid accumulation involves COX-2.

Rat gastric gelatinase induction during endotoxemia

Despite continued investigation, the pathogenesis of tissue injury secondary to sepsis remains elusive. Further evaluation of the mechanisms by which endotoxemia and sepsis induce tissue injury is necessary to formulate rational and effective treatment strategies. The purpose of these studies was to evaluate the role of the matrix metalloproteinases MMP-2 and MMP-9 in gastric injury during lipopolysaccharide induced endotoxemia. Lipopolysaccharide increased gastric gelatinase activity as determined by in situ and gelatin zymography. Specifically, lipopolysaccharide induced MMP-2, MMP-9, and tissue inhibitor of metalloproteinase-1 (TIMP-1) transcription, with subsequent increases in MMP-2 and TIMP-1 protein expression. Furthermore, selective metalloproteinase inhibition ameliorated gastric injury in this model. These data suggest that lipopolysaccharide-induced gastric injury is mediated, at least in part, by increased MMP-2 production.

Time-Dependent Aggravation or Attenuation of Lipopolysaccharide-Induced Gastric Injury by Nitric Oxide Synthase Inhibition1

BACKGROUND

This study was conducted to test the hypothesis that nonselective nitric oxide synthase (NOS) inhibitors have different effects on lipopolysaccharide (LPS)-induced gastric injury depending upon whether they are given concurrently with LPS or after LPS at a time point that inducible NOS is up-regulated.

MATERIALS AND METHODS

Female Sprague-Dawley rats received intraperitoneal (IP) LPS (20 mg/kg) for 3 h. Western immunoblot was used to determine iNOS, eNOS, and nNOS immunoreactivity after 3 h. In an additional set of experiments, we assessed the time dependent effects of nitric oxide synthase inhibition by giving rats LPS (20 mg/kg, IP) concurrently with Nitro-l-arginine methyl ester (l-NAME; 2-5 mg/kg, SC) or l-N(G)-(1-iminoethyl) lysine (l-NIL; 10 mg/kg, IP) for 5 h or LPS and delayed administration of l-NAME or l-NIL 3 h following LPS injection in identical doses. For these NOS inhibition experiments microscopic and macroscopic injury was assessed by a blinded observer using previously published scoring systems. Injury studies were conducted by exposing the stomach to 3 ml of 5 mM acidified taurocholate for 5 minutes in an anesthetized prep.

RESULTS

A 3-h treatment with LPS (20 mg/kg IP) significantly increased iNOS protein immunoreactivity (Western immunoblot) but not eNOS or nNOS. N(G)-l-NAME (2-5 mg/kg SC) dose dependently aggravated macroscopic (computerized planimetry) and morphological gastric injury caused by the intraluminal bile irritant 5 mm acidified taurocholate for 10 min when given concurrently with LPS, an effect reversed by l- but not D-arginine (300 mg/kg). In contrast, delayed administration of l-NAME (3 h after LPS) dose dependently attenuated the ability of LPS to exacerbate gastric injury from bile. Both concurrent and delayed administration of the selective iNOS inhibitor, l-NIL (10 mg/kg IP) attenuated the effects of LPS.

CONCLUSIONS

These data indicate that during endotoxemia, the stomach is rendered more susceptible to damage from luminal irritants such as bile, a frequent occurrence in septic patients with a gastrointestinal ileus. In this setting, iNOS has a pathologic role while the constitutive NOS isoforms play gastroprotective roles.

Ketamine attenuates liver injury attributed to endotoxemia: role of cyclooxygenase-2

BACKGROUND

Endotoxic shock can cause end-organ dysfunction and liver injury. Critically ill patients frequently require surgical intervention under general anesthesia for source control. However, the effects of anesthetics on organ function during sepsis and their influence on inflammatory mediators such as cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) remain to be fully elucidated. Because ketamine anesthesia has anti-inflammatory effects in some tissues, we hypothesized that it would attenuate lipopolysaccharide (LPS)-induced liver injury.

METHODS

Adult rats were given no anesthesia (saline), continuous isoflurane inhalation, or intraperitoneal (i.p.) injection of ketamine 70 mg/kg. One hour later, the rats received saline or LPS (20 mg/kg i.p.) for 5 hours. The rats were killed, and serum hepatocellular enzymes, liver COX-2, iNOS protein (Western immunoblot), and nuclear factor kappa B (NF-kappaB)-binding activity (electrophoretic mobility shift assay) determined. In a separate study, the role of COX-2 in LPS-induced liver injury was examined by pretreating rats with the selective COX-2 inhibitor NS-398 (3 mg/kg, i.p.) and the role of iNOS examined with the use of the selective inhibitor aminoguanidine (45 mg/kg, i.p.) 1 hour before LPS.

RESULTS

LPS increased serum aspartate aminotransferase and alanine aminotransferase levels, hepatic iNOS and COX-2 protein, and nuclear factor NF-kappaB. Ketamine, but not isoflurane, attenuated these effects caused by LPS. COX-2 inhibition with NS-398 as well as iNOS inhibition with aminoguanidine diminished LPS-induced changes in aspartate aminotransferase and alanine aminotransferase levels.

CONCLUSIONS

These data indicate that anesthetics differ in their effects on liver injury caused by LPS. Ketamine has hepatoprotective effects, while isoflurane does not. Moreover, the protective effects of ketamine are mediated, at least in part, through a reduction in COX-2 and iNOS protein that could be regulated via changes in NF-kappaB-binding activity.

Ketamine inhibits lipopolysacharide (LPS) induced gastric luminal fluid accumulation

INTRODUCTION

Lipopolysacharide (LPS) causes gastrointestinal ileus and gastric luminal fluid accumulation. Ketamine, an anti-inflammatory anesthetic agent attenuates accumulation of luminal fluid. However, its effects on gastrointestinal transit induced by endotoxemia are unknown. The purpose of this study was to determine if the anti-inflammatory properties of ketamine improve impaired gastric emptying and gastrointestinal transit because of LPS.

MATERIALS AND METHODS

Rats were given ketamine (70 mg/kg i.p.) or saline 1 h before LPS (20 mg/kg, i.p.) or saline injection. Five hours after LPS injection, rats were gavaged with 1 cc consisting of 0.1 ml of 5 mm FITC Dextran added to 0.9 ml of saline. After 30 min, rats were sacrificed, and gastric emptying, gastrointestinal transit, and gastric fluid accumulation determined. Gastric and ileal mucosa were harvested for analysis of inducible nitric oxide synthase (iNOS) (Western immunoblot). Results are reported as mean +/- SE (n > or = 5 per group; ANOVA).

RESULTS

Ketamine did not prevent LPS induced gastrointestinal ileus, nor did it improve gastric emptying. More importantly, it did not worsen gastrointestinal function or gastric emptying when compared to saline controls. However, it did decrease LPS induced gastric luminal fluid accumulation and blunted iNOS expression in both the stomach and ileum.

CONCLUSION

These data indicate that the ability of ketamine to attenuate gastric fluid accumulation is not because of improved gastric emptying or improved gastrointestinal transit. Moreover, while iNOS may play a role in LPS induced gastric luminal fluid accumulation, it does not appear to be a major mediator of the gastrointestinal ileus caused by LPS.

Rat gastric injury after lipopolysaccharide: Role of inducible nitric oxide synthase

BACKGROUND

Short-term treatment with lipopolysaccharide (LPS) causes morphologic, but not macroscopic, gastric injury and decreases gastric injury caused by a subsequent challenge with a luminal irritant. This effect is abrogated by inducible nitric oxide synthase (iNOS) inhibition. The effects of long-term treatment with LPS on gastric injury are unknown as is the role of iNOS. We hypothesized that LPS would cause macroscopic gastric injury at later time points through an iNOS-dependent pathway.

METHODS

Conscious rats were given saline or LPS (1 or 20 mg/kg intraperitoneal) as a single intraperitoneal injection and killed 24 to 72 hours after injection. Macroscopic gastric injury (computerized planimetry), gastric luminal fluid volume and pH, and iNOS protein levels were assessed.

RESULTS

When compared with saline, high-dose but not low-dose LPS caused macroscopic gastric injury, increased gastric luminal fluid and pH, and up-regulated iNOS at 24 and 48 hours. All assessments returned to baseline by 72 hours. Inhibition of iNOS with 1400W (1 mg/kg intraperitoneal) given 15 minutes before saline or LPS (20 mg/kg) attenuated the deleterious effects of LPS on gastric injury and pH, but not fluid accumulation.

CONCLUSIONS

These data suggest that prolonged treatment with high-dose LPS causes gastric injury through an iNOS-mediated pathway.

Bombesin-induced gastroprotection

Bombesin is an endogenous gut peptide that is prominent in the stomach. In addition to its effects on modulating acid and gut peptide secretion, recent evidence indicates that bombesin is a potent gastroprotective agent. This review article examines the ability of bombesin to prevent gastric injury. Its protective actions appear to be mediated primarily via the release of endogenous gastrin, as gastroprotection is negated by blockade of gastrin receptors. Bombesin-induced gastroprotection and gastrin release are modified by somatostatin. Immunoneutralization of endogenous somatostatin increases the ability of bombesin to prevent gastric injury by increasing gastrin release. In mechanistic studies, ablation of capsaicin-sensitive afferent neurons abolishes bombesin-induced gastroprotection while cyclo-oxygenase inhibition partially reverses this effect. Nitric oxide synthase inhibition also negates bombesin-induced gastroprotection as well as the ability of bombesin to increase gastric mucosal blood flow. Taken together, the available evidence indicates that bombesin causes release of endogenous gastrin that activates sensory neurons located in the gastric mucosa. Activation of sensory neurons causes increased production of nitric oxide through activation of constitutive nitric oxide synthase, which leads to a resultant increase in gastric mucosal blood flow and renders the stomach less susceptible to damage from luminal irritants.

Sepsis: an arginine deficiency state?

OBJECTIVE

Sepsis is a major health problem considering its significant morbidity and mortality rate. The amino acid L-arginine has recently received substantial attention in relation to human sepsis. However, knowledge of arginine metabolism during sepsis is limited. Therefore, we reviewed the current knowledge about arginine metabolism in sepsis.

DATA SOURCE

This review summarizes the literature on arginine metabolism both in general and in relation to sepsis. Moreover, arginine-related therapies are reviewed and discussed, which includes therapies of both nitric oxide (NO) and arginine administration and therapies directed toward inhibition of NO.

DATA

In sepsis, protein breakdown is increased, which is a key process to maintain arginine delivery, because both endogenous de novo production from citrulline and food intake are reduced. Arginine catabolism, on the other hand, is markedly increased by enhanced use of arginine in the arginase and NO pathways. As a result, lowered plasma arginine levels are usually found. Clinical symptoms of sepsis that are related to changes in arginine metabolism are mainly related to hemodynamic alterations and diminished microcirculation. NO administration and arginine supplementation as a monotherapy demonstrated beneficial effects, whereas nonselective NO synthase inhibition seemed not to be beneficial, and selective NO synthase 2 inhibition was not beneficial overall.

CONCLUSIONS

Because sepsis has all the characteristics of an arginine-deficiency state, we hypothesise that arginine supplementation is a logical option in the treatment of sepsis. This is supported by substantial experimental and clinical data on NO donors and NO inhibitors. However, further evidence is required to prove our hypothesis.

Rapid Up-Regulation of Endothelial Nitric-Oxide Synthase in a Mouse Model ofEscherichia coliLipopolysaccharide-Induced Bladder Inflammation

Increases in the signaling molecule nitric oxide (NO) during inflammation may be linked not only to inducible nitric-oxide synthase (iNOS) but also to endothelial (e)NOS. Escherichia coli lipopolysaccharide (LPS) induces an inflammatory response in the bladder and rapidly increases phosphorylation of Akt/protein kinase B (Akt), a key enzyme regulating proliferation, apoptosis, and inflammation. Activated Akt phosphorylates human eNOS at serine 1177 and subsequently increases NOS activity. Because Akt and eNOS are both localized in the bladder urothelium, phosphorylation of eNOS by Akt provides an attractive mechanism for rapid increases in urinary NO production. Female mice were intraperitoneally injected with LPS (25 mg/kg) or pyrogen-free water (control). Four hours before LPS injection, some mice were injected with wortmannin, which inhibits Akt phosphorylation. Levels of urinary cyclic GMP, a downstream product of NO, increase 75% within 1 h after intraperitoneal injection of LPS, and this increase is blocked by wortmannin. Bladder eNOS and phosphorylated eNOS protein increase 94 and 151%, respectively, 1 h after LPS treatment, whereas iNOS was not detected. Wortmannin decreases eNOS phosphorylation by 60%. Furthermore, bladder Ca(2+)-dependent NOS activity (eNOS, neuronal NOS) is increased 79 +/- 20% 1 h after LPS treatment, whereas there is no increase in Ca(2+)-independent (iNOS) activity (n = 4). Increases in urinary cyclic GMP, NOS activity, and eNOS protein and phosphorylation 1 h after induction of inflammation with LPS, indicate that eNOS plays a role in the early response to bladder inflammation.

Synthesis of nitric oxide in post‐ganglionic myenteric neurons during endotoxemia: implications for gastric motor function

We have investigated the mechanisms underlying acute changes in gastric motor function triggered by endotoxemia. In fundal strips from rats pre-treated with endotoxin (40 microg/kg, i.p. 30 min), mechanical activity was analyzed and the source of nitric oxide (NO) was visualized by confocal microscopy of tissue loaded with the fluorescent dye DAF-FM. NOS expression was determined by quantitative RT-PCR and Western blot, and enzyme activity by the citrulline assay. Strips from endotoxin-treated rats were hypo-contractile. This was prevented by pre-incubation with the neurotoxin tetrodotoxin, the gangliar blocker hexamethonium, or non-selective and neuronal-specific NOS inhibitors (L-NOARG and TRIM, respectively). The soluble guanylyl cyclase (sGC) inhibitor ODQ and the inhibitor of small conductance Ca2+-activated K+ channels apamin prevented relaxation induced by endotoxin, nicotine, exogenous NO (DETA-NONOate), and the NO-independent sGC activator BAY 41-2272. NO synthesis was observed in neuronal soma, axons, and nerve endings of the myenteric plexus in the fundus of endotoxin-treated rats and was prevented by L-NAME, tetrodotoxin, and hexamethonium. nNOS and iNOS mRNA and protein contents were unchanged. Our findings demonstrate synthesis of NO in post-ganglionic myenteric neurons during early endotoxemia that mediates gastric hypo-contractility. The effect of NO is mediated via sGC and small conductance Ca2+-activated K+channels.

Microcirculatory changes in the canine oesophageal mucosa during experimental reflux oesophagitis: comparison of the effects of acid and bile

BACKGROUND

The response of the oesophageal microcirculation to luminal damaging agents may play an important role in reflux-induced mucosal injury. We characterized the microcirculatory consequences of exposure to bile with or without hydrochloric acid, and determined the changes in the constitutive nitric oxide synthase and inducible nitric oxide synthase activities in a canine model of acute reflux oesophagitis.

METHODS

Group 1 served as a saline-treated control, while groups 2-4 were exposed for 3 h to bile alone, to hydrochloric acid, or to bile + hydrochloric acid, respectively. The mucosal microcirculation was observed continuously by means of intravital videomicroscopy with an orthogonal polarization spectral imaging technique. Myeloperoxidase, constitutive and inducible nitric oxide synthase activities were measured via tissue biopsies, while the degree of mucosal damage was evaluated histologically.

RESULTS

Bile evoked deep tissue damage and leucocyte accumulation in the mucosa and muscle layer. The capillary red blood cell velocity and the relative vessel area increased significantly (P < 0.05). The constitutive NO synthase activity was decreased, and the inducible NO synthase activity was increased significantly. In the hydrochloric acid-treated group the functional capillary density decreased, the mucosal damage was less severe, the constitutive NO synthase activity did not change, whereas the inducible NO synthase activity was increased significantly. The constitutive NO synthase activity did not change after the bile + hydrochloric acid treatment either.

CONCLUSION

Reflux components induce characteristic microcirculatory alterations. The structural damage and leucocyte invasion are accompanied by bile-induced constitutive NO synthase inhibition when hydrochloric acid production is suppressed.

Ketamine/xylazine attenuates LPS-induced iNOS expression in various rat tissues

Ketamine and xylazine (K/X) are commonly used in combination as an anesthetic agent in experimental animal models. We previously noted that K/X attenuated lipopolysaccharide (LPS)-induced liver injury, gastric stasis, and reduced symptoms of endotoxemia. Because ketamine attenuates expression of several proinflammatory genes, we examined the effects of K/X on inducible nitric oxide synthase (iNOS), which has been implicated in endotoxin-induced tissue injury. We hypothesized that K/X would attenuate LPS-induced expression of iNOS in various organs in the rat. Rats were given either intraperitoneal saline or ketamine (70 mg/kg) and xylazine (6 mg/kg) 1 h before saline or LPS (20 mg/kg). Rats were sacrificed 5 h later and stomach, duodenum, jejunum, ileum, colon, liver, lung, kidney, and spleen were collected for determination of iNOS protein immunoreactivity by Western immunoblot. Data reported in densitometric units (DU) as mean +/- SEM (n >/= 5; ANOVA). LPS significantly increased iNOS protein immunoreactivity in all tissues examined versus saline controls (P </= 0.05, all groups). K/X significantly attenuated LPS-induced iNOS protein immunoreactivity in all of the aforementioned organs (P </= 0.05, all groups). Furthermore, K/X almost completely blunted LPS-induced expression of iNOS in stomach, duodenum, jejunum, and colon. These data indicate that K/X attenuates LPS-induced upregulation of iNOS in a variety of tissues. Furthermore, in rat models studying the in vivo effects of endotoxin, especially those evaluating the gastrointestinal system, careful consideration needs to be given if the anesthetic combination of K/X is used, as it alters LPS-induced expression of iNOS, an important pathophysiologic mediator in endotoxemia.

Cholecystokinin secretagogue-induced gastroprotection: role of nitric oxide and blood flow

This study was done to examine the role of CCK in gastric mucosal defense and to assess the gastroprotective roles of nitric oxide and blood flow. In rats, the CCK secretagogues oleate and soybean trypsin inhibitor augmented gastric mucosal blood flow and prevented gastric injury from luminal irritants. Type A CCK receptor blockade negated CCK secretagogue-induced gastroprotection and exacerbated gastric injury from bile and ethanol but did not block adaptive cytoprotection. CCK secretagogue-induced gastroprotection and hyperemia were negated by nonselective nitric oxide synthase (NOS) inhibition (N(G)-nitro-L-arginine methyl ester) but not by selective inducible NOS inhibition (aminoguanidine). Gastric mucosal calcium-dependent NOS activity, but not calcium-independent NOS activity, was increased following CCK and CCK secretagogues. The release of endogenous CCK plays a role in the intrinsic gastric mucosal defense system against injury from luminal irritants. The protective mechanism appears to involve increased production of nitric oxide from primarily the constitutive isoforms of NOS and a resultant increase in blood flow.

Downregulation of nNOS and synthesis of PGs associated with endotoxin-induced delay in gastric emptying

A single intraperitoneal injection of endotoxin (40 microg/kg) significantly delayed gastric emptying of a solid nutrient meal. Blockade of nitric oxide synthase (NOS) with 30 mg/kg ip N(G)-nitro-L-arginine methyl ester or 20 mg/kg ip 7-nitroindazole [neuronal NOS (nNOS) inhibitor] significantly delayed gastric emptying in control animals but failed to modify gastric emptying in endotoxin-treated rats. Administration of 2.5, 5, and 10 mg/kg ip N(6)-iminoethyl-L-lysine [inducible NOS (iNOS) inhibitor] had no effect in either experimental group. Indomethacin (5 mg/kg sc), NS-398 (cyclooxygenase-2 inhibitor; 10 mg/kg ip), and dexamethasone (10 mg/kg sc) but not quinacrine (20 mg/kg ip) significantly prevented delay in gastric emptying induced by endotoxin but failed to modify gastric emptying in vehicle-treated animals. Ca(2+)-dependent NOS activity in the antrum pylorus of the stomach was diminished by endotoxin, whereas Ca(2+)-independent NOS activity was not changed. In addition, decreased nNOS mRNA and protein were observed in the antrum pylorus of endotoxin-treated rats. Our results suggest that downregulation of nNOS in the antrum pylorus of the stomach and synthesis of prostaglandins mediate the delay in gastric emptying of a solid nutrient meal induced by endotoxin.

Induction of NF-kappaB, IkappaB-alpha, and iNOS in rat gastric mucosa during endotoxemia

Upregulation of inducible nitric oxide synthase (iNOS) contributes to the development of gastric injury during endotoxemia. The molecular mechanisms related to its induction are unknown. Because the transcription factor nuclear factor-kappa B (NF-kappaB) regulates inflammatory genes in response to endotoxemia, we hypothesized that its activity in gastric mucosa would increase while its inhibitor IkappaB-alpha would decrease commensurate with changes in iNOS expression. Rats were given intraperitoneal saline or lipopolysaccharide (LPS; 20 mg/kg) for 5, 15, or 30 min, or for 1, 3, or 5 h, and killed, and the gastric mucosa was prepared for determination of iNOS and IkappaB-alpha by Western immunoblotting, iNOS mRNA by quantitative real-time RT-PCR, and NF-kappaB by electrophoretic mobility-shift assay. LPS caused a significant increase in iNOS mRNA and protein immunoreactivity at 1, 3, and 5 h compared to controls. NF-kappaB-binding activity increased in the nuclear fraction of gastric mucosa at 1 h and steadily increased over time after LPS administration. The activated NF-kappaB consisted mainly of p50 with a lesser amount of p65 subunits as demonstrated by a supershift assay. IkappaB-alpha decreased in gastric cytosolic fractions over time, consistent with its degradation. These data suggest that during endotoxemia expression of the inflammatory mediator iNOS in the gastric mucosa may be upregulated by degradation of IkappaB-alpha and subsequent translocation of NF-kappaB into the nucleus and increased NF-kappaB activity.