Endogenous nitric oxide and sensory neuropeptides interact in the modulation of the rat gastric microcirculation

"Azole" as privileged heterocycle for targeting the inducible cyclooxygenase enzyme

An over-expression of COX-2 isoenzyme belonging to the Cyclooxygenase Enzyme Family triggers the overproduction of pro-inflammatory prostaglandins that instigate the development of chronic inflammation and related disorders. Hence, the rationally designed drugs for mitigating over-activity of COX-2 isoenzyme play a regulatory role toward the alleviation of the progression of these disorders. However, a selective COX-2 inhibition chemotherapy prompts several side effects that necessitate the identification of novel molecular scaffolds for deliberating state-of-the-art drug designing strategies. The heterocyclic "azole" scaffold, being polar and hydrophilic, possesses remarkable physicochemical advantages for designing physiologically active molecules capable of interacting with a wide range of biological components, including enzymes, peptides, and metabolites. The substituted derivatives of azole nuclei enable a comprehensive SAR analysis for the appraisal of bioactive profile of the deliberated molecules for obtaining the rationally designed compounds with prominent activities. The comprehensive SAR analysis readily prompted the identification of Y-shaped molecules and the eminence of bulkier group for COX-2 selective inhibition. This review presents an epigrammatic collation of the pharmacophore-profile of the chemotherapeutics based on azole motif for a selective targeting of the COX-2 isoenzyme.

Endothelin and neonatal capsaicin regulate gastric resistance to injury in BDL rats

AIM: To investigate the relationship between primary afferent neurons, endothelin (ET) and the role of its receptors on ethanol-induced gastric damage in cirrhotic rats.

METHODS: Cirrhosis and portal hypertension were induced in rats by bile duct ligation (BDL) while controls had a sham operation. The association between ET and afferent neurons on the gastric mucosa was evaluated by capsaicin treatment in newborn rats, the use of ET agonists or antagonists, gastric ET-1 and -3 mRNA and synthetic capacity. Ethanol-induced damage was assessed using ex vivo gastric chamber experiments. Gastric blood flow was measured by laser-Doppler flowmetry.

RESULTS: ET-3 and an ET_B receptor antagonist significantly reduced the extent of ethanol-induced gastric damage in BDL rats. Gastric ET-1 and -3 levels were 30% higher in BDL rats compared to control rats. Capsaicin treatment restored the gastric resistance and blood flow responses to topical application of ethanol in BDL rats and ET-1 and -3 production to levels observed in controls.

CONCLUSION: Our results suggest that the reduced resistance of the gastric mucosa of cirrhotic rats to ethanol-induced injury is a phenomenon modulated by ET through the ET_B receptor and by sensory afferent neurons.

Capsaicin inhibits the spontaneous pacemaker activity in interstitial cells of cajal from the small intestine of mouse

Background/Aims

Capsaicin (8-methyl-N-vanillyl-6-ninenamide), a compound found in hot peppers, has been reported to have different physiological actions on different cell types. Not much work has been done about the effect of capsaicin on the function of interstitial cells of Cajal (ICC). In the present study, we examined the action of external application of capsaicin on pacemaker activity in the cultured ICC from the small intestine of mouse.

Methods

We investigated the effect of capsaicin on pacemaker currents in cultured ICC from the small intestine of mouse using a whole cell patch-clamp technique and Ca²⁺-imaging analysis.

Results

When capsaicin was applied externally to the pacemaker generating ICC, it completely inhibited the pacemaker potential under current-clamp mode (I = 0) and the pacemaker current under voltage-clamp mode at a -70 mV of holding potentials. The effect of capsaicin on pacemaker activity in ICC was shown dose dependently. The effect of capsaicin was not through the transient receptor potential of the vanilloid type 1 (TRPV1) channel as capsazepine did not block the effect of capsaicin. L-NAME, an inhibitor of nitric oxide synthase, also did not block the capsaicin-induced effects. When the action of capsaicin was examined in the intracellular calcium oscillation, it completely abolished the calcium oscillation.

Conclusions

These results prove that the capsaicin has the inhibitory effects on the ICC which is carried out neither through TRPV channel nor the nitric oxide production. Intracellular Ca²⁺ was also an important target for actions of capsaicin on ICC.

Gastroprotective effect of simvastatin against indomethacin-induced gastric ulcer in rats: role of nitric oxide and prostaglandins

This study investigated the possible mechanisms underlying the gastroprotective effect of simvastatin against indomethacin-induced gastric ulcer in rats. Rats were randomly assigned to vehicle-, simvastatin-, simvastatin+L-arginine- and simvastatin+N(G)-nitro-L-arginine methyl ester (L-NAME)-pretreated groups for two weeks. Pyloric ligation was performed for the collection of gastric juice, and gastric ulceration was induced by a single intraperitoneal injection of indomethacin (30 mg/kg). Gastric juice parameters (total acid output, pepsin activity and mucin concentration) were determined. The stomachs tissues were used for determination of gastric mucosal lipid peroxides, superoxide dismutase, catalase, total nitrites and prostaglandin E(2) levels. Pretreatment with simvastatin (10 mg/kg, orally, for 2 weeks) caused significant reduction in gastric mucosal lesions and lipid peroxides associated with a significant increase in gastric juice mucin concentration. Simvastatin significantly increased the gastric mucosal total nitrite and prostaglandin E(2) levels. Additionally, simvastatin attenuated the elevations in gastric mucosal superoxide dismutase observed with indomethacin. The gastroprotective effect afforded by simvastatin was significantly augmented by coadministration with L-arginine (a nitric oxide precursor) and inhibited by coadministration with L-NAME (a nitric oxide synthase inhibitor). Results confirm a gastroprotective effect for simvastatin, and indicate that the anti-ulcer effect of simvastatin is mediated by scavenging free radicals, increasing nitric oxide and prostaglandin E(2) levels, and increasing gastric juice mucin production. We conclude that simvastatin represents a more suitable antihyperlipidemic therapy for patients who are at risk of gastric ulcers that were induced by the use of nonsteroidal anti-inflammatory drugs (NSAIDs).

Gastroprotective effect of fructus evodiae water extract on ethanol-induced gastric lesions in rats

Fructus Evodiae is a widely used herbal medicine with anti-inflammatory and analgetic activities in China. The present study was designed to investigate the effect of Fructus Evodiae water extract (FE) on ethanol-induced gastric lesions in rats. Three hours before ethanol challenge, animals were intraperitoneally treated with FE (424.8 mg/kg, 141.6 mg/kg, and 47.6 mg/kg). Subsequently, we employed ex-vivo chamber technique to examine the effect of FE on gastric transmucosal potential difference (PD) changes. NO(x) (nitrate and nitrite) in gastric perfusate and gastric lesion index of whole glandular stomach were determined by intubation. The results showed that FE dose-dependently accelerated the recovery of PD reduction by ethanol, and increased NO(x) production in gastric perfusate. FE also inhibited gastric lesion formation in a dose-dependent manner. These results suggested that FE prevented ethanol-induced gastric mucosal lesions by strengthening the mucosal barrier integrity and increasing gastric mucosal nitric oxide (NO) synthesis.

Capsaicin and gastric ulcers

In recent years, infection of the stomach with the organism Helicobacter Pylori has been found to be the main cause of gastric ulcers, one of the common ailments afflicting humans. Excessive acid secretion in the stomach, reduction in gastric mucosal blood flow, constant intake of non-steroid anti-inflammatory drugs (NSAIDS), ethanol, smoking, stress etc. are also considered responsible for ulcer formation. The prevalent notion among sections of population in this country and perhaps in others is that "red pepper" popularly known as "Chilli," a common spice consumed in excessive amounts leads to "gastric ulcers" in view of its irritant and likely acid secreting nature. Persons with ulcers are advised either to limit or avoid its use. However, investigations carried out in recent years have revealed that chilli or its active principle "capsaicin" is not the cause for ulcer formation but a "benefactor." Capsaicin does not stimulate but inhibits acid secretion, stimulates alkali, mucus secretions and particularly gastric mucosal blood flow which help in prevention and healing of ulcers. Capsaicin acts by stimulating afferent neurons in the stomach and signals for protection against injury causing agents. Epidemiologic surveys in Singapore have shown that gastric ulcers are three times more common in the "Chinese" than among Malaysians and Indians who are in the habit of consuming more chillis. Ulcers are common among people who are in the habit of taking NSAIDS and are infected with the organism "Helicobacter Pylori," responsible for excessive acid secretion and erosion of the mucosal layer. Eradication of the bacteria by antibiotic treatment and avoiding the NSAIDS eliminates ulcers and restores normal acid secretion.

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.

Role of nitric oxide in the gastro-protective effect of lithium

BACKGROUND AND AIM

Lithium is widely used for the management of neuropsychiatric symptoms in bipolar disorders. A few studies have shown that lithium has a protective effect against gastric damage with an unknown mechanism. Some of the actions of lithium are mediated through nitric oxide (NO), which has an important role in the regulation of gastric wall blood flow as well as gastric mucosal integrity. The aim of this study was to test the hypothesis if the gastro-protective effect of lithium is mediated through NO.

METHODS

Male Wistar rats were pre-treated with either a non-selective NO synthase inhibitor (N(G)-nitro-l-arginine, 10mg/kg), a selective inducible NO synthase inhibitor (aminoguanidine, 100mg/kg) or saline. Lithium carbonate (10, 20, 50 and 100mg/kg) was then administered intraperitoneally 1h before the induction of gastric mucosal damage. Gastric damage was induced by either water immersion stress or ethanol gavage in rats.

RESULTS

Lithium had a significant protective effect in both stress and ethanol-induced gastric damage, but it needed in ethanol-induced gastric damage a higher dose than in the stress induced lesion. Lithium carbonate doses 20 and 50mg/kg produced plasma concentrations that were in the range of human therapeutic Li levels (0.6-1.0muM). Pre-treatment of animals with N(G)-nitro-l-arginine (20 and 40mg/kg) reduced the protective effect of lithium against ethanol-induced gastric damage, but not in stress-induced damage. Aminoguanidine administration showed no effect on the damage reduction either in control or lithium treated rats.

CONCLUSIONS

The results indicate that NO might play a role in the gastro-protective effect of lithium against ethanol-induced gastric damage in rats.

Direct effects of nitric oxide on histamine release from rat enterochromaffin-like cells

The direct effects of nitric oxide (NO) on enterochromaffin-like (ECL) cells have not yet been demonstrated. In this study we investigated the direct effects of NO donors on rat ECL cells. The NO donor, NOR3 (10 and 100 microM), decreased gastrin-induced histamine release. 100 microM NOR3 increased cGMP levels and reduced gastrin-induced calcium influx. ODQ, an inhibitor of guanylate cyclase, completely blocked NOR3-induced inhibition of histamine release. These results suggest that NO inhibits gastric acid secretion via suppression of gastrin-induced histamine release through a pathway in which NO activates guanylate cyclase, in addition to increasing cGMP levels and reducing gastrin-induced calcium influx. The use of NO as a new type of gastric acid inhibitor that decreases histamine levels in the stomach would be beneficial as increased histamine levels resulting from use of a histamine H2 receptor antagonist or proton pump inhibitor have various effects on tumors and immunological functions.

Gastrointestinal Function Regulation by Nitrergic Efferent Nerves

Gastrointestinal (GI) smooth muscle responses to stimulation of the nonadrenergic noncholinergic inhibitory nerves have been suggested to be mediated by polypeptides, ATP, or another unidentified neurotransmitter. The discovery of nitric-oxide (NO) synthase inhibitors greatly contributed to our understanding of mechanisms involved in these responses, leading to the novel hypothesis that NO, an inorganic, gaseous molecule, acts as an inhibitory neurotransmitter. The nerves whose transmitter function depends on the NO release are called "nitrergic", and such nerves are recognized to play major roles in the control of smooth muscle tone and motility and of fluid secretion in the GI tract. Endothelium-derived relaxing factor, discovered by Furchgott and Zawadzki, has been identified to be NO that is biosynthesized from l-arginine by the constitutive NO synthase in endothelial cells and neurons. NO as a mediator or transmitter activates soluble guanylyl cyclase and produces cyclic GMP in smooth muscle cells, resulting in relaxation of the vasculature. On the other hand, NO-induced GI smooth muscle relaxation is mediated, not only by cyclic GMP directly or indirectly via hyperpolarization, but also by cyclic GMP-independent mechanisms. Numerous cotransmitters and cross talk of autonomic efferent nerves make the neural control of GI functions complicated. However, the findingsrelated to the nitrergic innervation may provide us a new way of understanding GI tract physiology and pathophysiology and might result in the development of new therapies of GI diseases. This review article covers the discovery of nitrergic nerves, their functional roles, and pathological implications in the GI tract.

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.

Adaptive cytoprotection through modulation of nitric oxide in ethanol-evoked gastritis

AIM: To assess the mechanisms of protective action by different mild irritants through maintenance of gastric mucosal integrity and modulation of mucosal nitric oxide (NO) in experimental gastritis rats.

METHODS: Either 200 mL/L ethanol, 50 g/L NaCl or 0.3 mol/L HCl was pretreated to normal or 800 mL/L ethanol-induced acute gastritis Sprague-Dawley rats before a subsequent challenge with 500 mL/L ethanol. Both macroscopic lesion areas and histological damage scores were determined in the gastric mucosa of each group of animals. Besides, gastric mucosal activities of NO synthase isoforms and of superoxide dismutase, along with mucosal level of leukotriene (LT)C₄ were measured.

RESULTS: Macroscopic mucosal damages were protected by 200 mL/L ethanol and 50 g/L NaCl in gastritis rats. However, although 200 mL/L ethanol could protect the surface layers of mucosal cells in normal animals (protection attenuated by N^G-nitro-L-arginine methyl ester), no cytoprotection against deeper histological damages was found in gastritis rats. Besides, inducible NO synthase activity was increased in the mucosa of gastritis animals and unaltered by mild irritants. Nevertheless, the elevation in mucosal LTC₄ level following 500 mL/L ethanol administration and under gastritis condition was significantly reduced by pretreatment of all three mild irritants in both normal and gastritis animals.

CONCLUSION: These findings suggest that the aggravated 500 mL/L ethanol-evoked mucosal damages under gastritis condition could be due to increased inducible NO and LTC₄ production in the gastric mucosa. Only 200 mL/L ethanol is truly “cytoprotective” at the surface glandular level of non-gastritis mucosa. Furthermore, the macroscopic protection of the three mild irritants involves reduction of LTC₄ level in both normal and gastritis mucosa, implicating preservation of the vasculature.

Physiopathologie des lésions gastro-duodénales induites par les anti-inflammatoires non stéroïdiens

The pathogenesis of the gastroduodenal lesions induced by non-steroidal anti-inflammatory drugs and aspirin is primarily caused by a reduction in mucosal blood flow, which is the consequence of inhibition of cyclooxygenase-producing vasodilator prostaglandins. The subsequent phase is adherence of leukocytes to the endothelium, which may depend on cyclooxygenase-2. Endothelial lesions accentuate the fall of mucosal blood flow and promote the inflammatory process in the gastric mucosa. The inflammatory process is amplified by expression of TNFalpha in polymorphonuclears induced by non-steroidal anti-inflammatory drugs. A few days after starting treatment, epithelial proliferation and increased mucosal blood flow, partly dependent on cyclooxygenase-2 and nitric oxide expression, compensates for the damaging process. Selective inhibitors of inducible cyclooxygenase-2 have reduced gastrointestinal toxicity, which could partially be explained by the protection effect of cyclooxygenase-2 on the gastrointestinal mucosa during inflammation or epithelial repair. Selective inhibitors may worsen inflammatory bowel disease. Non-steroidal inflammatory drugs and aspirin, but perhaps not selective inhibitors, increase the mucosal lesions associated with Helicobacter pylori-induced gastritis. Co-administration of selective inhibitors and aspirin leads to gastrointestinal toxicity equivalent to that of non-specific anti-inflammatory drugs.

The pharmacology of nitric oxide in the peripheral nervous system of blood vessels

Unanticipated, novel hypothesis on nitric oxide (NO) radical, an inorganic, labile, gaseous molecule, as a neurotransmitter first appeared in late 1989 and into the early 1990s, and solid evidences supporting this idea have been accumulated during the last decade of the 20th century. The discovery of nitrergic innervation of vascular smooth muscle has led to a new understanding of the neurogenic control of vascular function. Physiological roles of the nitrergic nerve in vascular smooth muscle include the dominant vasodilator control of cerebral and ocular arteries, the reciprocal regulation with the adrenergic vasoconstrictor nerve in other arteries and veins, and in the initiation and maintenance of penile erection in association with smooth muscle relaxation of the corpus cavernosum. The discovery of autonomic efferent nerves in which NO plays key roles as a neurotransmitter in blood vessels, the physiological roles of this nerve in the control of smooth muscle tone of the artery, vein, and corpus cavernosum, and pharmacological and pathological implications of neurogenic NO have been reviewed. This nerve is a postganglionic parasympathetic nerve. Mechanical responses to stimulation of the nerve, mainly mediated by NO, clearly differ from those to cholinergic nerve stimulation. The naming "nitrergic or nitroxidergic" is therefore proposed to avoid confusion of the term "cholinergic nerve", from which acetylcholine is released as a major neurotransmitter. By establishing functional roles of nitrergic, cholinergic, adrenergic, and other autonomic efferent nerves in the regulation of vascular tone and the interactions of these nerves in vivo, especially in humans, progress in the understanding of cardiovascular dysfunctions and the development of pharmacotherapeutic strategies would be expected in the future.

Low endotoxemia prevents the reduction of gastric blood flow induced by NSAIDs: role of nitric oxide

1 The role of nitric oxide (NO) in the effects of low endotoxemia on gastric damage and blood flow has been evaluated in indomethacin-treated rats. 2 Pretreatment (-1 h) with endotoxin (40 micro g kg(-1)) reduced gastric damage induced by indomethacin (20 mg kg(-1)) in conscious rats. 3 Endotoxin prevented the reduction in gastric blood flow (laser Doppler flowmetry) induced by indomethacin in pentobarbital-anaesthetised rats. 4 Pretreatment with an NO-synthase (NOS) inhibitor (L-NAME, 1 mg kg(-1)) reversed the protective effect of endotoxin on gastric blood perfusion. 5 Endotoxin did not modify the expression of mRNA for endothelial NOS or inducible NOS in the gastric corpus when evaluated 1 h postinjection. However, a 3.8-fold increase in inducible NOS mRNA and a 61% reduction in endothelial NOS mRNA were observed in the gastric corpus 4 h after endotoxin administration. 6 Evaluation of both total and Ca(2+)-dependent NOS activity by analysing the rate of conversion of L-arginine to L-citrulline in gastric corpus homogenates showed no differences between animals treated with endotoxin and those treated with saline 1 or 4 h beforehand. Ca(2+)-independent NOS activity was almost non-apparent in control as well as in endotoxin-treated rats at all the time points analysed. 7 Low endotoxemia preserves blood perfusion and protects the gastric mucosa against the deleterious effects of indomethacin through the endogenous NO release. NO synthesis in response to endotoxin does not involve the inducible NOS, but probably depends on the post-translational/biochemical regulation in vivo of a Ca(2+)-dependent NOS, most probably endothelial NOS.

Mechanisms involved in protection afforded by L-arginine in ibuprofen-induced gastric damage: role of nitric oxide and prostaglandins

L-Arginine (L-arg) exhibits multiple biological properties and plays an important role in the regulation of different functions in pathological conditions. Many of these effects could be achieved on this amino acid serving as a substrate for the enzyme nitric oxide synthase (NOS). At the gastrointestinal level, recent reports revealed its protective activities involving a hyperemic response increasing the gastric blood flow. The aim of this study was to characterize the relationship between NOS activity/expression and prostaglandin changes (PGs) in rats gastric mucosa, with L-arg associated resistance to the nonsteroidal anti-inflammatory drug (NSAID) ibuprofen (IBP). The protective effect of oral L-arg (100 mg/kg body wt), administerred together with IBP (100 mg/kg body wt, per os), was evident enough 90 min after drug administration, although a significant protection persisted for more than 6 hr. Pretreatment with N(G)-nitro-L-arginine (L-NNA) (40 mg/kg body wt, intraperitoneally), a competitive inhibitor of constitutive NOS, partly altered the protection afforded by the amino acid. In contrast, no changes could be observed after inducible NOS inhibition [aminoguanidine (AG) 50 mg/Kg body wt, intraperitoneally). L-arg, plus IBP, produced a significant increase of the cyclic GMP (cGMP) response in tissue samples from rat stomach, 90 min and 6 h after drug administration. iNOS activity and mRNA expression were higher in IBP-treated rats, and no differences were observed in inducible responses in the L-arg plus IBP group. No variations in the cNOS activity and expression were found among the different groups of animals assayed. The measurement of mucosal PGE2 content confirmed that biosynthesis of the eicosanoid is maintained by L-arg for over 90 min after IBP, while a total inhibition was observed 6 hr later. The mechanisms of the L-arg protective effect on the damaged induced by IBP could be explained by the different period after drug administration. The early phase is mediated by cyclooxygenase/prostaglandins pathway (COX/PGs) although NO liberated by cNOS and the guanylate cyclase/cGMP pathway could be also relevant. The later phase implicates inhibition of the iNOS/NO response.

Cyclooxygenase 2-implications on maintenance of gastric mucosal integrity and ulcer healing: controversial issues and perspectives

Cyclooxygenase (COX), the key enzyme for synthesis of prostaglandins, exists in two isoforms (COX-1 and COX-2). COX-1 is constitutively expressed in the gastrointestinal tract in large quantities and has been suggested to maintain mucosal integrity through continuous generation of prostaglandins. COX-2 is induced predominantly during inflammation. On this premise selective COX-2 inhibitors not affecting COX-1 in the gastrointestinal tract mucosa have been developed as gastrointestinal sparing anti-inflammatory drugs. They appear to be well tolerated by experimental animals and humans following acute and chronic (three or more months) administration. However, there is increasing evidence that COX-2 has a greater physiological role than merely mediating pain and inflammation. Thus gastric and intestinal lesions do not develop when COX-1 is inhibited but only when the activity of both COX-1 and COX-2 is suppressed. Selective COX-2 inhibitors delay the healing of experimental gastric ulcers to the same extent as non-COX-2 specific non-steroidal anti-inflammatory drugs (NSAIDs). Moreover, when given chronically to experimental animals, they can activate experimental colitis and cause intestinal perforation. The direct involvement of COX-2 in ulcer healing has been supported by observations that expression of COX-2 mRNA and protein is upregulated at the ulcer margin in a temporal and spatial relation to enhanced epithelial cell proliferation and increased expression of growth factors. Moreover, there is increasing evidence that upregulation of COX-2 mRNA and protein occurs during exposure of the gastric mucosa to noxious agents or to ischaemia-reperfusion. These observations support the concept that COX-2 represents (in addition to COX-1) a further line of defence for the gastrointestinal mucosa necessary for maintenance of mucosal integrity and ulcer healing.

Nitric oxide: relation to integrity, injury, and healing of the gastric mucosa

Nitric oxide (NO) plays a multifaceted role in mucosal integrity. The numerous functions of NO and the double-edged role played by NO in most of them provide a great complexity to the NO action. The three enzymatic sources of NO, neuronal NO-synthase (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS), have been characterised in the gastrointestinal tract. The protective properties of the NO derived from constitutive NO-synthases (eNOS and nNOS) have already been well established. Less clear is the role assigned to iNOS. The simplistic initial view of low levels of NO synthesised by constitutive NOS being protective while exaggerated NO levels after iNOS induction leading irremediably to cytotoxicity is being questioned by new evidence. As initially reported for constitutive NOS, iNOS activity may be associated to reduced leukocyte-endothelium interaction and platelet aggregation as well as protection of mucosal microcirculation. Moreover, iNOS activity may be important to resolve inflammation by increasing apoptosis in inflammatory cells. It is entirely possible that a low level of expression of iNOS will reflect a positive host-defense response to challenge, but that exaggerated or uncontrolled expression of iNOS itself becomes detrimental. There is no doubt about the protective role of NO in physiological conditions. However, when the mucosa is threatened, the role of NO becomes multiple and the final effect will probably depend on the nature of the insult, the environment involved, and the interaction with other mediators.

Induction of nitric oxide synthesis by probiotic Lactobacillus rhamnosus GG in J774 macrophages and human T84 intestinal epithelial cells

BACKGROUNDS AND AIMS

Probiotic Lactobacillus rhamnosus GG (LGG) has proved to be beneficial in the treatment of viral- and antibiotic-associated diarrhea but the mechanisms of action remain unknown. Nitric oxide (NO) is involved in the protective mechanisms in the gastrointestinal tract and may contribute to some of the beneficial effects of probiotics. The aim of the present study was to investigate if induction of NO synthesis is involved in the cellular actions of LGG.

METHODS

NO synthesis and its regulation were measured in cultures of J774 murine macrophages and human T84 colon epithelial cells. NO production was measured as its metabolite nitrite accumulated into the culture medium. Inducible nitric oxide synthase (iNOS) protein and iNOS mRNA were detected by Western blot and RT-PCR, respectively.

RESULTS

In J774 macrophages, LGG induced a low level production of NO in the presence of gamma interferon (IFNgamma) and it was inhibited by NOS inhibitors, cycloheximide and by a NF-kappa B inhibitor pyrrolidinedithiocarbamate. Accordingly, LGG and IFNgamma-stimulation increased iNOS mRNA and protein levels. T84 cells produced NO in response to LGG when first primed with a combination of IL-1beta, TNFalpha and IFNgamma. Lipoteichoic acid (LA), an antigenic structure in gram-positive bacteria, also induced NO formation in J774 cells in the presence of IFNgamma suggesting that LA may be the active component in LGG.

CONCLUSIONS

LGG induces NO production in J774 macrophages and in human T84 colon epithelial cells through induction of iNOS by a mechanism involving activation of transcription factor NF-kappaB. Induction of iNOS and low-level synthesis of NO may be involved in the protective actions of LGG in the gastrointestinal tract.

The effect of nitric oxide inhibition on blood pressure depends on rat strain

BACKGROUND

Nitric oxide is a continuously released endothelium-derived vasodilator and plays an important role in the maintenance of blood pressure (BP). Rat strains appear to differ in their resting BP and their response to the intravenous administration of N(omega)-nitro-l-arginine methyl ester (l-NAME), a nitric oxide synthase inhibitor. The presence of diabetes and hypertension also leads to differences in BP responses to l-NAME. We postulated that the contribution of NO to resting BP varies between rat strains and certain strains may be more sensitive to the effects of NO blockade.

METHODS

Blood pressure was continuously measured using a carotid arterial catheter and the responses to l-NAME were compared in anesthetized Lewis and Sprague-Dawley rats during a 2-h control period and a 2-h experimental period. l-NAME was given by a 50 mg/kg bolus followed by a 10 mg/kg/h infusion via a mesenteric vein.

RESULTS

During the control period, the Lewis animals had lower systolic and diastolic BPs of 103 +/- 1 and 80 +/- 1 mm Hg compared with 127 +/- 1 and 105 +/- 1 mm Hg measured in Sprague-Dawley rats (P < 0.01). Although l-NAME infusion increased systolic BP in both strains compared with control values (P < 0.00005), the magnitude was significantly greater in Sprague-Dawley than Lewis animals (P = 0.0142); additionally, the BP was unstable in the Lewis animals. Furthermore, pulse pressure decreased during l-NAME in Lewis animals but increased in Sprague-Dawley animals (P < 0.00005). There were no significant changes in serum concentrations of aspartate transaminase nor of nitrite plus nitrate after l-NAME in either group.

CONCLUSION

These results indicate that the effect of l-NAME on systemic BP differs markedly in Sprague-Dawley and Lewis rats, suggesting that the role of nitric oxide in regulation of resting vascular resistance may differ significantly between these rat strains. Rat strain is an important consideration for valid comparisons between studies.

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.

Nitric oxide donating compounds inhibit HCl-induced gastric mucosal lesions mainly via prostaglandin

Prostaglandin (PG) and nitric oxide (NO) have been known to inhibit the lesion formation induced by necrotic agents. However, no clear correlation between PG and NO has been shown in the gastroprotective action against necrotic agent-induced gastric mucosal lesions in rats. Thus, the present study was performed to clarify this correlation. Gastric mucosal lesions were induced by the oral administration of 0.6 M HCl in rats. 16,16-Dimethyl PGE2 (0.3-3 microg/kg, p.o.; dim-PGE2), sodium nitrite (0.3 and 1 mg/kg, s.c.) and sodium nitroprusside (30 and 100 microg/kg, i.v.; SNP) dose-dependently inhibited the lesion formation. Orally administered sodium nitrite or SNP (3 mg/kg) also significantly inhibited the lesion formation. The gastroprotective action by dim-PGE2 was not affected by the pre-treatment with N(G)-nitro-L-arginine methylester (10 mg/kg, i.v.). The gastroprotective effect by sodium nitrite or SNP was markedly attenuated by the pre-treatment with indomethacin (10 mg/kg, s.c.). These findings suggest that NO donating compounds inhibit the HCl-induced mucosal lesions mainly through prostaglandin, but dim-PGE2 directly inhibits the lesions without involvement of NO in rats.

Gastric mucosal integrity: gastric mucosal blood flow and microcirculation. An overview

The stomach is in a state of continuous exposure to potentially hazardous agents. Hydrochloric acid together with pepsin constitutes a major and serious threat to the gastric mucosa. Reflux of alkaline duodenal contents containing bile and pancreatic enzymes are additional important injurious factors of endogenous origin. Alcohol, cigarette smoking, drugs and particularly aspirin and aspirin-like drugs, and steroids are among exogenous mucosal irritants that can inflict mucosal injury. The ability of the stomach to defend itself against these noxious agents has been ascribed to a number of factors constituting the gastric mucosal defense. These include mucus and bicarbonate secreted by surface epithelial cells, prostaglandins, sulfhydryl compounds and gastric mucosal blood flow. The latter is considered by several researchers to be of paramount importance in maintaining gastric mucosal integrity. The aim of this paper is to review the experimental and clinical data dealing with the role of mucosal blood flow and in particular the microcirculation in both damage and protection of the gastric mucosa.

Autonomic nervous function assessment using thermal reactivity of microcirculation

There are only a few reliable objective methods of diagnosing peripheral neuronal damage suitable for routine use; the most important is based on measurement of nerve conduction velocity, which only shows changes when severe disturbances are already present. However, it is precisely at this stage that the possibilities of therapy are no longer satisfactory. As small fibres are affected earlier in the course of most forms of PNP than the large ones, assessment of afferent as well as efferent C-fibre function gains importance in the management of this widespread disease. In assessment of autonomic dysfunction, variability of the heartbeat with deep breathing or the Valsalva manoeuvre is a good and generally accepted test, although not strongly associated with other PNP test abnormalities. However, axonal degeneration starts in the most distal parts of the axon due to impaired axonal transport. Therefore, the longest C-fibres, i.e. in the lower extremities, are affected first, and incipient changes are most prominent there. For this reason HLDF, a reflex response of the skin blood flow stimulated by heat, has advantages in assessment of early C-fibre dysfunction. Considering the fact that the afferent and efferent sympathetic C-fibres are involved in regulation of microcirculation, the skin blood flow regulation is investigated by means of laser Doppler flowmetry. The microcirculation is stimulated by heat and the reaction of microcirculation is assessed as a value for the function of afferent and efferent (sympathetic) C-fibres. The results of this method are in close correlation with electrophysiologic tests, which is not achieved with sudomotor function.

Nitric oxide synthase inhibition negates bombesin-induced gastroprotection

BACKGROUND

Bombesin prevents gastric injury primarily by the release of endogenous gastrin. Gastroprotection by exogenous gastrin is negated by nitric oxide synthase inhibition, which implicates a role for nitric oxide as a protective mediator. Because both endothelial and inducible isoforms of this enzyme can play a role in mucosal defense, this study was done to examine the contrasting effects of 2 nitric oxide synthase inhibitors on bombesin-induced gastroprotection.

METHODS

Rats were given subcutaneous saline or bombesin (10-100 microg/kg) 30 minutes before they received a 1-mL orogastric bolus of acidified ethanol (150 mmol/L of hydrochloric acid/50% ethanol) and rats were killed 5 minutes later for assessment of macroscopic injury (mm(2)). Gastric mucosal blood flow was measured by laser Doppler. Endothelial, neural, and inducible nitric oxide synthase were assessed by using Western immunoblot.

RESULTS

Bombesin decreased gastric mucosal damage, and dose-dependently increased blood flow when compared with saline-treated rats. Endothelial but not neural or inducible nitric oxide synthase immunoreactivity was increased by bombesin. In additional studies, intraperitoneal administration of N(G)-nitro-l-arginine methyl ester (l-NAME, 5-10 mg/kg), a nonselective nitric oxide synthase inhibitor, negated bombesin-induced gastroprotection and hyperemia, whereas the selective inducible inhibitor aminoguanidine (45 mg/kg) did not. Subcutaneous (SC) l-arginine (300 mg/kg), but not d-arginine, abolished the effects of l-NAME.

CONCLUSIONS

Taken together, these data suggest that nitric oxide produced by the endothelial isoform of nitric oxide synthase plays an important role in mediating the gastroprotective and hyperemic actions associated with bombesin.

Protective effect of Irsogladine on monochloramine induced gastric mucosal lesions in rats: a comparative study with rebamipide

AIM: To examine the effect of irsogladine, a novel antiulcer drug, on the mucosal ulcerogenic response to monochloramine ( NH₂Cl ) in rat stom ach, in comparison with rebamipide, another antiulcer drug with cytoprotective activity.

METHODS AND RESULTS: Oral administration of NH₂Cl (120 mM) produced severe hemorrhagic lesions in unanesthetized rat stomachs. Both irso gladine (1 mg/kg-10 mg/kg, po) and rebamipide (30 mg/kg-100 mg/kg, po) dose-dependently prevented the development of these lesions in response to NH₂Cl, the effect of irsogladine was significant at 3 mg/kg or greater, and that of rebamipide only at 100 mg/kg. The protective effect of irsogladine on NH₂Cl-induced gastric lesions was significantly reduced by N^G-nitro-L-arginine methyl ester (L-NAME) but not by indomethacin, while that of rebamipide was significantly mitigated by indom ethacin but not by L-NAME. Topical application of NH₂Cl (20mM) caused a marked reduction of potential difference (PD) in ex-vivo stomachs. This PD reduction was not affected by mucosal application of irsogladine, but significa ntly prevented by rebamipide. The mucosal exposure to NH₄OH (120 mM) also caused a marked PD reduction in the ischemic stomach (bleeding from the carotid artery), resulting in gastric lesions. These ulcerogenic and PD responses caused by NH₄OH plus ischemia were also significantly mitigated by rebamipide, in an indomethacin-sensitive manner, while irsogladine potently prevented such lesions without affecting the PD response, in a L-NAME-sensitive manner.

CONCLUSION: These results suggest that (1) NH₂Cl generated either exogenously or endogenously damages the gastric mucosa, (2) both irsogladine and rebamipide protect the stomach against injury caused by NH₂Cl, and (3) the mechanism underlying the protective action of irsogladine is partly mediated by endogenous nitric oxide, while that of rebamipide is in part mediated by endogenous prostaglandins.

The ulcer healing effect of protamine sulphate in rat stomach

BACKGROUND

Protamine sulphate has been reported to stimulate nitric oxide production from blood vessels, which is a pivotal factor for gastric ulcer healing. Our preliminary study also showed that protamine sulphate potentiated the ulcer healing effect of heparin.

METHODS

Male SD rats with acetic acid-induced gastric ulcers were given protamine sulphate (40-80 mg/kg, s.c.) twice daily for 4 or 7 days. L-NG-nitroarginine methyl ester (L-NAME, 5 mg/kg), an inhibitor of nitric oxide synthase (NOS), was given s.c. prior to protamine sulphate (80 mg/kg) treatment. Ulcer healing, angiogenesis, mucosal histological changes, NOS activity and growth factors were determined.

RESULTS

Protamine sulphate dose-dependently accelerated gastric ulcer healing, which was accompanied by a significant increase in angiogenesis, mucosal regeneration and constitutive NOS activity. Inhibition of gastric secretion was observed. Epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), tumour necrosis factor-alpha (TNF-alpha) or inducible NOS activity was also affected. L-NAME completely blocked the beneficial effects of protamine sulphate.

CONCLUSIONS

Protamine sulphate accelerates gastric ulcer healing through a mucosal nitric oxide-dependent and possibly also the EGF-and bFGF-associated pathways, which are followed by an increase of angiogenesis and mucosal regeneration. Acid inhibition contributes in part to the ulcer healing action of protamine sulphate.

Expression of endothelial cell-derived nitric oxide synthase (eNOS) is increased during gastric adaptation to chronic aspirin intake in humans

BACKGROUND

Gastric adaptation to aspirin is well-documented. However, the mechanisms underlying the reduction of aspirin-induced mucosal damage despite continued ingestion of the drug remain poorly understood.

METHODS

Eight healthy volunteers who received aspirin 1 g b.d. for 14 days were compared with eight placebo-dosed controls. Gastroscopy with mucosal biopsy was performed, and gastric mucosal blood flow was measured before and following 3, 7 and 14 days of aspirin treatment. At the same time points, tissue concentration and the content of prostaglandin E2 in the gastric juice were determined and expression of endothelial cell-derived nitric oxide synthase (eNOS) in mucosal biopsies was measured using Western blot analysis.

RESULTS

Aspirin-induced mucosal damage that reached a maximum on day 3, declining significantly by day 14. Concomitantly, mucosal blood flow significantly increased on day 3 and returned to initial values on day 14. Aspirin intake led to a significant decrease in prostaglandin E2 concentration in the gastric mucosa and in gastric juice during the whole period of aspirin consumption. eNOS expression started to increase on day 7 in oxyntic mucosa and on day 3 in antral mucosa, reaching its highest values at the end of the consumption of aspirin.

CONCLUSIONS

The human gastric mucosa adapts to prolonged aspirin intake, and this is accompanied by an increase in mucosal blood flow and reduced prostaglandin synthesis. Increase of mucosal eNOS expression might compensate for reduced prostaglandin synthesis and be responsible for gastric adaptation to chronic aspirin intake in humans.

Effects of cigarette smoking on gastric ulcer formation and healing: possible mechanisms of action

Epidemiologic studies have shown that cigarette smoking is closely related to peptic ulcer disease. The mechanisms by which cigarette smoking adversely affects gastric mucosa have been suggested and elucidated. This article reviews some of the mechanisms involved in cigarette smoking-related gastric ulceration and healing. Experimental findings suggest that cigarette smoking increases xanthine oxidase activity, leukotrienes, and nitric oxide production and also neutrophil infiltration in the gastric mucosa. On the other hand, it reduces blood flow, prostaglandin production, epithelial cell proliferation, and formation of blood vessels in the tissue. These actions are important for ulcer formation and healing. The evidence thus far available strengthens the hypothesis that cigarette smoke is indeed harmful to gastric mucosa through defined mechanisms.

Anti-ulcer effects of antioxidants, quercetin, alpha-tocopherol, nifedipine and tetracycline in rats

When free radical-scavenging activities of quercetin, alpha-tocopherol, nifedipine and tetracycline were measured by an electron spin resonance technique, all test compounds (10(-5) to 10(-3) M) scavenged both superoxide anions and hydroxyl radicals. The oral administration of quercetin (50 and 100 mg/kg), alpha-tocopherol (8 and 16 mg/kg), nifedipine (20 and 40 mg/kg) or tetracycline (10 and 20 mg/kg) markedly prevented the HCl plus ethanol-induced gastric mucosal injury and the increase in the content of thiobarbituric acid-reactive substances in the injured mucosa in rats. In addition, quercetin (25, 50 and 100 mg/kg), alpha-tocopherol (4, 8 and 16 mg/kg), nifedipine (10, 20 and 40 mg/kg) and tetracycline (5, 10 and 20 mg/kg), given orally, twice daily for 14 consecutive days from the day after acetic acid injection, dose-dependently promoted the ulcer healing and inhibited the increase in the content of thiobarbituric acid-reactive substances in the ulcerated mucosa. These results indicate that quercetin, alpha-tocopherol, nifedipine and tetracycline possess gastric cytoprotective and gastric ulcer healing-promoting actions. In addition, the free radical-scavenging properties of these compounds may be partly related to their anti-ulcer effects.

Central and peripheral vagal mechanisms involved in gastric protection against ethanol injury

Activation of medullary thyrotropin-releasing hormone (TRH), at a dose subthreshold to increase gastric acid secretion, protects the gastric mucosa against ethanol injury through vagal cholinergic pathways in urethane-anaesthetized rats. Peripheral mediators involve the efferent function of capsaicin-sensitive splanchnic afferents leading to calcitonin gene-related peptide (CGRP)- and nitric oxide (NO)-dependent gastric vasodilatory mechanisms. In addition, gastric prostaglandins participate in gastric protection through mechanisms independent of the stimulation of gastric mucosal blood flow and mucus secretion. Medullary TRH has physiological relevance in the vagal-dependent adaptive gastric protection induced by mild (acid or ethanol), followed by strong, irritants. Additional neuropeptides, namely peptide YY (PYY), somatostatin analogues, CGRP and adrenomedullin, also act in the brainstem to induce a vagal-dependent gastric protection against ethanol through interactions with their specific receptors in the medulla. Central PYY and adrenomedullin act through vagal cholinergic prostaglandins and NO pathways, while somatostatin analogue acts through vagal non-adrenergic, non-cholinergic vasoactive intestinal peptide and NO mechanisms. Although their biological relevance is still to be established, these peptides provide additional tools to investigate the multiple vagal-dependent mechanisms which increase the resistance of the gastric mucosa to injury.

Vagal mechanisms underlying gastric protection induced by chemical activation of raphe pallidus in rats

Peripheral mechanisms involved in kainic acid injected into the raphe pallidus (Rpa)-induced gastric protection were investigated in urethan-anesthetized rats. Gastric mucosal blood flow (GMBF), acid secretion, and gastric injury induced by intragastric ethanol (60%) were measured in response to kainic acid (25 pg) injected into the Rpa. Kainic acid reduced ethanol-induced gastric lesions by 57%. The protective effect was blocked by vagotomy, capsaicin deafferentation, and intravenous injection of the calcitonin gene-related peptide (CGRP) antagonist CGRP-(8-37) and NG-nitro-L-arginine methyl ester (L-NAME). L- but not D-arginine reversed the L-NAME action. Kainic acid injected into the Rpa, unlike outside sites, increased basal GMBF but not acid secretion. Indomethacin unmasked an acid secretory response to kainic acid. These results show that kainic acid injected into the Rpa at a dose that did not stimulate acid secretion, due to the inhibitory effect of prostaglandins, protects against ethanol-induced gastric injury through vagal-dependent activation of CGRP contained in capsaicin-sensitive afferents and nitric oxide-mediated gastric vasodilatory mechanisms.

Effects of endotoxin on gastric injury from luminal irritants in rats: potential roles of nitric oxide

The expression and function of inducible nitric oxide synthase (iNOS) in the stomach is unclear. This study assessed the effects of endotoxin on rat gastric iNOS expression and its role in gastric injury from luminal irritants. In conscious rats, a 5-h treatment with intraperitoneal lipopolysaccharide (LPS; 1-20 mg/kg) dose dependently increased gastric mucosal iNOS immunoreactivity and increased gastric luminal nitrate and nitrite accumulation (Griess reaction). LPS also increased gastric luminal fluid accumulation and reduced macroscopic gastric injury from orogastric acidified ethanol. Aminoguanidine (45 mg/kg) did not prevent LPS-induced gastroprotection or gastric fluid accumulation. NG-nitro-L-arginine methyl ester increased gastric luminal fluid and caused macroscopic gastric injury when given with LPS. Using an anesthetized preparation followed by removal of luminal fluid, LPS reduced gastric mucosal blood flow and exacerbated gastric injury from either acidified ethanol or acidified taurocholate, an effect that was negated by aminoguanidine. These data indicate that in conscious rats, the gastroprotective effect of endotoxin is dependent on constitutive NOS but not iNOS activity. However, the inducible isoform participates in the ability of endotoxin to exacerbate gastric injury from luminal irritants in the anesthetized rat.

Involvement of nitric oxide and prostaglandins in gastroprotection induced by bacterial lipopolysaccharide

BACKGROUND

Lipopolysaccharide (LPS) has been proposed to act as one of the pathogens in endotoxemia-induced gastric lesions, but its action on mucosal integrity has not been fully clarified.

METHODS

We compared the effects of LPS originating from Escherichia coli and the chemical donor of nitric oxide (NO), S-nitroso-acetylpenicillamine (SNAP), on acute gastric lesions induced by 100% ethanol, mucosal blood flow (GBF), and mucosal generation of prostaglandin E2 (PGE2) and examined the expression of constitutive NO synthase (cNOS) and inducible NO synthase (iNOS) mRNA in the gastric mucosa of rats treated with LPS, by using reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

LPS (0.01-1.0 mg/kg) or SNAP (0.37-3.0 mg/kg) given intraperitoneally, dose-dependently prevented ethanol-induced mucosal lesions, and these protective effects were accompanied by a significant increase in the GBF and excessive mucosal release of NO. Suppression of NOS activity by NG-nitro-L-arginine methyl ester (L-NAME) (20mg/kg intravenously) or L-NG-(1-iminoethyl)-lysine (L-NIL) (30mg/kg intraperitoneally) and NOS induction by treatment with dexamethasone (2 mg/kg intraperitoneally) reversed the protective and hyperemic effects of LPS, and this reversal by L-NAME was significantly antagonized by addition of the substrate for NOS, L-arginine, but not D-arginine. Both LPS and SNAP increased PGE2 generation significantly, and this effect was reduced by pretreatment with L-NAME, L-NIL, or dexamethasone. Expression of cNOS was detected by RT-PCR in the intact mucosa, but intense signals for expression of both cNOS and iNOS were detected in the mucosa of LPS-treated rats.

CONCLUSIONS

Parenteral LPS, similarly to the chemical NO donor, SNAP, protects the gastric mucosa against ethanol-induced damage via an increase in GBF mediated by NO due to the activation of arginine-NO system and possibly also enhanced generation of PGE2.

Nitric oxide enhances prostaglandin production in ethanol-induced gastric mucosal injury in rats

The interaction between endogenous nitric oxide (NO), elicited by administration of Escherichia coli lipopolysaccharide, and cyclooxygenase system, in ethanol-induced injury in rat gastric mucosa, was investigated. Administration of graded doses of lipopolysaccharide reduced the gastric mucosal injury in response to ethanol. The ex vivo production of both nitrite and prostaglandin E2 was increased in dose-related manner by lipopolysaccharide. Pretreatment with dexamethasone, L-N6-(1-Iminoethyl)lysine(dihydrochloride) and L-NG-nitro arginine methyl ester inhibited the protection associated with lipopolysaccharide treatment and the ex vivo production of both, nitrite and prostaglandin E2. The pretreatment with L-arginine counteracted the decrease of nitrite and prostaglandin E2 production in lipopolysaccharide-treated rats in which nitric oxide synthesis was blocked by L-N6-(1-Iminoethyl)lysine(dihydrochloride). Administration of sodium nitroprusside and S-nitroso-N-acetyl-D,L-penicillamine caused a dose related enhancement in the accumulation of prostaglandin E2. Indomethacin administration and N-(2-Cyclohexyloxy-4-nitrophenyl)methanesulfonamide were ineffective in suppressing lipopolysaccharide-mediated protection against ethanol-induced damage, and in suppressing ex vivo increase of nitrite whereas the ex vivo increase of prostaglandin E2 was prevented in a dose-related fashion. These results indicate that in ethanol-induced rat gastric injury, endogenous NO elicited by lipopolysaccharide or released by NO donors is able to activate the cyclooxygenase pathway, and the protective effect of lipopolysaccharide is dependent upon NO formation.

Role of nitric oxide in oxidative damage in isolated rabbit gastric cells exposed to hypoxia-reoxygenation

The present study aimed to investigate the role of nitric oxide on the oxidative damage in isolated rabbit gastric cells exposed to hypoxia-reoxygenation. Nitric oxide synthesis modulators such as L-arginine and NG-nitro-L-arginine methyl ester, a nitric oxide donor, sodium nitroprusside, and superoxide dismutase were used to treat the cells, and the synthesis and secretion of mucus, lipid peroxide production, and glutathione contents of the cells were determined. As a result, hypoxia-reoxygenation decreased nitric oxide production and the synthesis and secretion of mucus, as well as glutathione contents of gastric cells, but hypoxia-reoxygenation increased lipid peroxide production. Pretreatment with L-arginine, a substrate for nitric oxide synthase, sodium nitroprusside, and superoxide dismutase prevented the increase in lipid peroxide production and the decreases in glutathione contents, as well as the synthesis and secretion of mucus induced by hypoxia-reoxygenation. However, NG-nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor, had no effect on these alterations. In conclusion, nitric oxide has an antioxidant defensive role on gastric cells by maintaining mucus and glutathione.

Neural emergency system in the stomach

The maintenance of gastric mucosal integrity depends on the rapid alarm of protective mechanisms in the face of pending injury. Afferent neurons of extrinsic origin constitute an emergency system that is called into operation when the gastric mucosa is endangered by acid and other noxious chemicals. The function of these chemoceptive afferents can be manipulated selectively and explored with the excitotoxin capsaicin. Most of the homeostatic actions of capsaicin-sensitive afferents are brought about by peptides released from their peripheral endings in the gastric wall. When stimulated, chemoceptive afferents enhance gastric blood flow and activate hyperemia-dependent and hyperemia-independent mechanisms of protection and repair. In the rodent stomach, these local regulatory roles of sensory neurons are mediated by calcitonin gene-related peptide acting via calcitonin gene-related peptide 1 receptors and neurokinin A acting via neurokinin 2 receptors, with both peptides using nitric oxide as their common messenger. In addition, capsaicin-sensitive neurons form the afferent arc of autonomic reflexes that control secretory and motor functions of the stomach. The pathophysiological potential of the neural emergency system is best portrayed by the gastric hyperemic response to acid backdiffusion, which is signaled by afferent nerve fibers. This mechanism limits damage to the surface of the mucosa and creates favorable conditions for rapid restitution and healing of the wounded mucosa.

Role of nitric oxide in regulation of gastric acid secretion in rats: effects of NO donors and NO synthase inhibitor

1. The role of nitric oxide (NO) in the regulation of acid secretion was examined in the anaesthetized rat. 2. A rat stomach was mounted in an ex vivo chamber, instilled with 2 ml of saline every 15 min, and the recovered sample was titrated at pH 7.0 against 0.1 N NaOH by use of an automatic titrator for acid secretion. Gastric mucosal blood flow (GMBF) was measured simultaneously by laser Doppler flowmeter. 3. Intragastric application of NO donors such as FK409 (3 and 6 mg ml[-1]) and sodium nitroprusside (SNP; 6 and 12 mg ml[-1]) as well as i.p. administration of cimetidine (60 mg kg[-1]), a histamine H2-receptor antagonist, significantly inhibited the increase in acid secretion in response to pentagastrin (60 microg kg(-1) h(-1), i.v.), in doses that increased gastric mucosal blood flow (GMBF). 4. Intragastric application of FK409 (6 mg ml[-1]) increased both basal and stimulated acid secretion induced by YM-14673 (0.3 mg kg(-1), i.v.), an analogue of thyrotropin-releasing hormone (TRH), but had no effect on the acid secretory response induced by histamine (4 mg kg(-1) h(-1), i.v.). 5. Pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME; 10 mg kg(-1), i.v.) did not affect basal acid secretion, but significantly potentiated the increase in acid secretion induced by YM-14673 and slightly augmented the acid secretory response to pentagastrin. 6. Both pentagastrin and YM-14673 increased the release of nitrite plus nitrate (NOx), stable NO metabolites, into the gastric lumen, and these changes were completely inhibited by prior administration of L-NAME (10 mg kg(-1), i.v.). 7. Pentagastrin caused an increase in luminal release of histamine and this response was significantly suppressed by intragastric application of FK409 (6 mg ml[-1]). 8. These results suggest that either exogenous or endogenous NO has an inhibitory action on gastric acid secretion through suppression of histamine release from enterochromaffin-like (ECL) cells.

Nitric oxide in the rat spinal cord in Freund's adjuvant-induced hyperalgesia

To elucidate the involvement of nitric oxide in spinal nociceptive processing, the correlation of thermal withdrawal latency with nitric oxide synthase-stained neurons in the rat lumbar dorsal horn was analyzed after adjuvant-induced inflammation. From 4 hr through 5 days after subcutaneous injection of complete Freund's adjuvant into the hind paw, a marked thermal hyperalgesia was observed for heat stimulus applied to the affected region. NADPH-diaphorase- and nitric oxide synthase-positive neurons increased significantly in the superficial layers of the dorsal horn ipsilateral to the inflamed hind paw at day 3 of adjuvant-induced inflammation. No change in NADPH-diaphorase-positive neurons was observed at 1 hr and 1 day of adjuvant-induced inflammation. The intravenous administration of N omega-nitro-L-arginine methyl ester (L-NAME, 50 mg/kg), an inhibitor of nitric oxide synthase, significantly blocked the adjuvant-induced thermal hyperalgesia at day 3 of inflammation, but not at day 1; and it had no effect in non-inflamed rats. This anti-hyperalgesic effect of L-NAME at day 3 of inflammation was reversed by the prior administration of L-arginine (600 mg/kg, i.p.), a substrate of nitric oxide synthase. These data suggest that nitric oxide producing neurons in the spinal dorsal horn are involved in maintaining and facilitating the hyperalgesia associated with chronic nociception.

NADPH-diaphorase in antral gastritis of childhood

BACKGROUND

Nitric oxide has an important role in the pathophysiology of the gastric mucosa. However, to date, it is not clear if nitric oxide plays a cytoprotective or cytotoxic role in the pathogenesis of mucosal lesion.

METHODS

We have used the NADPH-diaphorase histochemistry that selectively stains cells containing nitric oxide synthase, the enzyme that catalyzes the production of nitric oxide on the antral gastric mucosa of children with antral gastritis.

RESULTS

In the lamina propria of the mucosa, the presence of the enzymatic activity was found in perivascular round cells and nerve fibers. In the epithelium, focal positivity to NADPH-diaphorase was found in superficial cells, mainly located in the extrusive zones. The epithelial cells in the pits and glands were negative, in the mucous layer, Helicobacter pylori were also stained by NADPH-diaphorase. A single H. pylori-infected child who was also examined after eradication of the H. pylori showed during the control examination absence of microorganisms and reduction of the NADPH-diaphorase-positive cells in the mucosa.

CONCLUSIONS

Our results demonstrate that, in gastric mucosa, endogenous and exogenous structures express a NADPH-diaphorase activity.

Nitric oxide, prostaglandin, and sensory neurons in gastric mucosal blood flow response during acid secretion in rats

1. The mechanism underlying the increase of gastric mucosal blood flow (GMBF) during acid secretion induced by pentagastrin was investigated in anesthetized rats, in relation to nitric oxide (NO), prostaglandin (PG), and sensory neurons. 2. An intravenous infusion of pentagastrin at 60 micrograms/kg/h (submaximal dose) produced an increase of acid secretion and GMBF as determined by laser Doppler flowmetry, and the GMBF response was totally attenuated when the acid secretion was inhibited by omeprazole or when the luminal H+ was removed by mucosal perfusion with glycine (200 mM). 3. Prior administration of NG-nitro-L-arginine methyl ester (L-NAME, 5 mg/kg, IV), a NO synthase inhibitor, significantly mitigated the GMBF response to pentagastrin, without any influence on acid secretion, and this effect was antagonized by coadministration of L-arginine (500 mg/kg IP). 4. The increase of GMBF during pentagastrin infusion also was significantly mitigated by indomethyacin (5 mg/kg, SC) or sensory deafferentation following capsaicin pretreatment, had no effect on the acid secretion, and was totally inhibited by the combined treatments with indomethacin plus L-NAME in addition to sensory deafferentation. 5. Pentagastrin infusion for 8 hr did not by itself cause any macroscopic damage in the stomach, but additional treatments with L-NAME, and indomethacin plus sensory deafferentation provoked severe lesions in the gastric mucosa. 6. These results suggest that the increase of GMBF induced by submaximal dose of pentagastrin totally depends on luminal H+. This process seems to be mediated by endogenous NO and PGs, as well as capsaicin-sensitive sensory neurons, and to play a pivotal role in maintaining mucosal integrity during acid secretion.

Cyclo-oxygenase isoenzymes. How recent findings affect thinking about nonsteroidal anti-inflammatory drugs

The discovery of at least 2 cyclo-oxygenase (COX) isoenzymes, referred to as COX-1 and COX-2, has updated our knowledge of nonsteroidal anti-inflammatory drugs (NSAIDs). This has lead investigators to reconsider what can be awaited from this class of drugs. The 2 COX isoenzymes share structural and enzymatic similarities, but are specifically regulated at the molecular level and may be distinguished apart in their functions, although some physiological overlap between them does occur. The major goal in developing selective COX inhibitors is to improve NSAID tolerability. Classic NSAIDs preferentially inhibit COX-1 in vitro, but it appears hazardous to judge their gastrointestinal (GI) safety profile from these data. New compounds with a high selectivity for COX-2, especially those that are non-acidic, may be better tolerated in the GI tract. While these compounds also might have a potential use in various diseases such as colorectal cancer and neurodegenerative diseases of the Alzheimer type, the possible appearance of adverse effects, perhaps renally-related, must be taken into consideration. Finally, well-designed large clinical trials are required to adequately estimate both the promising therapeutic advantages that may be offered by highly selective NSAIDs, and the potential drawbacks that may be inherent with prolonged COX-2 inhibition.

Nitric oxide stimulates prostaglandin synthesis in cultured rabbit gastric cells

Both prostaglandins (PGs) and nitric oxide (NO) have cytoprotective and hyperemic effects in the stomach. However, the effect of NO on PG synthesis in gastric mucosal cells is unclear. We examined whether sodium nitroprusside (SNP), a releaser of NO, stimulates PG synthesis in cultured rabbit gastric mucus-producing cells. These cells did not release NO themselves. Co-incubation with SNP (2 x 10(-4), 5 x 10(-4), 10(-3) M) increased PGE2 synthesis, and SNP (10(-3) M) increased PGI2 synthesis in these cells. Hemoglobin, a scavenger of NO, (10(-5) M) eliminated the increase in PGE2 synthesis by SNP, but methylene blue, an inhibitor of soluble guanylate cyclase, (5 x 10(-5) M) did not affect the increase in PGE2 synthesis by SNP. 8-bromo guanosine 3':5'-cyclic monophosphate (8-bromo cGMP), a cGMP analogue, (10(-6), 10(-5), 10(-4), 10(-3) M) did not affect PGE2 synthesis. These findings suggest that NO increased PGE2 and PGI2 synthesis via a cGMP-independent pathway in cultured rabbit gastric cells.

Inducible nitric oxide synthase in rat brown adipocytes: implications for blood flow to brown adipose tissue

Exposure of rat brown adipocytes differentiated in culture to norepinephrine (NE) results in the production of nitrites (NO2-), the breakdown product of nitric oxide (NO). This production, which is blocked by actinomycin D1 is directly related to the duration of exposure to and dose of NE. Cytosol from NE-treated brown fat cells, but not from untreated cultures, catalyzed the Ca(2+)-independent conversion of L-arginine to L-citrulline, which could be significantly blocked by the specific nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester. Reverse transcriptase-PCR demonstrates that the addition of NE; selective beta 1-, beta 2-, or beta 3-adrenergic receptor agonists; or agents increasing cAMP production, such as forskolin, to brown adipocytes stimulates inducible NOS (iNOS) messenger RNA, which is present within 4 h after exposure. That iNOS is synthesized in brown fat cells is confirmed by immunoblotting using an antibody to the iNOS of mouse macrophages, Finally, in both brown adipose tissue (BAT) and brown adipocyte preparations from animals exposed to low temperature, iNOS messenger RNA and protein were expressed, and NOS activity was detectable; these findings were unlikely for room temperature-acclimated rats. We conclude that brown fat cells can express an inducible form of NOS similar to the iNOS of macrophages, and that its production is directly dependent on sympathetic activity in physiological conditions. NO generated by stimulation of iNOS in brown adipocytes may represent an important mechanism to modulate different BAT functions, among which is vasodilation of the BAT microcirculation.

Nonsteroidal anti-inflammatory drug-induced gastrointestinal toxicity: new insights into an old problem

Nonsteroidal anti-inflammatory drugs are widely used for the treatment of chronic arthropathies, but their gastrointestinal damage remains a significant limitation to their use. In this review, the pathogenic mechanisms through which these drugs are believed to cause gastrointestinal damage are outlined. A better understanding of the pathogenesis of gastric and intestinal injury has resulted in novel strategies that are being employed to develop nonsteroidal anti-inflammatory drugs that do not have significant adverse effects on the gastrointestinal tract.