Effects of nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester on duodenal alkaline secretory and ulcerogenic responses induced by mepirizole in rats

Involvement of nitric oxide in the gastroprotective effects of an aqueous extract of Pfaffia glomerata (Spreng) Pedersen, Amaranthaceae, in rats

The plants belonging to Pfaffia genus are used in folk medicine to treat gastric disturbances. This study examined the effects of an aqueous extract of Pfaffia glomerata (Spreng) Pedersen (AEP) on the gastrointestinal tract. Wistar rats were pretreated orally (p.o.) with the AEP (125, 250, 500 and 1000 mg.kg(-1)) before induction of ulcers by hypothermic restraint stress (HRS, 3 h restraint stress at 4 degrees C), ethanol (ET, 70%; 0.5 ml/animal; p.o.) or indomethacin (IND, 20 mg.kg(-1); s.c.). Control animals received water (C) or ranitidine (60 mg.kg(-1)) p.o. The AEP protected rats against HRS and ET-induced ulcers, but was not able to protect the gastric mucosa against IND-induced ulcers. When injected into the duodenal lumen, the AEP reduced total acidity and both basal and histamine-stimulated acid secretion in pylorus-ligated rats. In addition, gastric secretion from AEP-treated animals exhibited increased concentrations of nitrite and nitrate. Treatment of animals with L-NAME (120 mg.kg(-1), p.o.) prevented both the reduction of total acidity and the increase in NOx levels promoted by AEP treatment. In conclusion, AEP effectively protected the gastric mucosa and inhibited gastric acid secretion in rats, probably by involving the histaminergic pathway and an enhanced production of nitric oxide in the stomach.

Unique regulation of anion/HCO3- exchangers by constitutive nitric oxide in rabbit small intestine

In the rabbit small intestine, there are three functionally different brush-border membrane (BBM) anion/HCO3- exchangers: 1) Cl/HCO3- exchange on the BBM of villus cells responsible for coupled NaCl absorption; 2) Cl/HCO3- exchange on the BBM of crypt cells possibly involved in HCO3- secretion; and 3) short-chain fatty acid (SCFA)/HCO3- exchange on the BBM of villus cells, which facilitates SCFA absorption. Although constitutive nitric oxide (cNO) has been postulated to alter many gastrointestinal tract functions, how cNO may specifically alter these three transporters is unknown. Inhibition of cNO synthase with NG-nitro-L-arginine methyl ester (L-NAME) 1) did not affect villus cell BBM Cl/HCO3 change, 2) stimulated crypt cell BBM Cl/HCO3- exchange, and 3) inhibited villus cell BBM SCFA/HCO3- exchange. D-NAME, an inactive analog of L-NAME, and L-N6-(1-iminoethyl)lysine, a more selective inhibitor of inducible NO, did not affect these transport processes. Kinetic studies demonstrated that 1) the mechanism of inhibition of crypt cell BBM Cl/HCO3- exchange is secondary to a decrease in the maximal rate of uptake of Cl, without an alteration in the affinity of the transporter for Cl, and 2) the mechanism of stimulation of villus cell BBM SCFA/HCO3- exchange is secondary to an increase in the affinity of the transporter for SCFA without an alteration in the maximal rate of uptake of SCFA. These results indicate that cNO uniquely regulates the three BBM anion/HCO3- transporters in the rabbit small intestine.

The association between CagA status and the development of esophagitis after the eradication of Helicobacter pylori

BACKGROUND

Strains of Helicobacter pylori with the cytotoxine-associated gene A (cagA) are linked to severe forms of gastroduodenal disease. Although eradication of H. pylori may predispose to the development of reflux esophagitis, the effects of CagA status on risk of esophagitis after successful H. pylori treatment are not known.

METHODS

We studied 50 consecutive patients without esophagitis in whom H. pylori was eradicated successfully. CagA status was determined by immunoblotting sera from patients against H. pylori antigens. Patients underwent upper gastrointestinal endoscopy before eradication and 6, 12, 18, and 24 months after eradication or when reflux symptoms occurred. Biopsy specimens of the antrum and corpus were evaluated for gastritis before H. pylori eradication and at the end of the study. The sum of the scores for acute and chronic inflammation (both measured on a 0 [absent] to 3 [severe] scale) comprised the total gastritis severity score.

RESULTS

In a multivariate proportional hazards regression analysis, positive CagA serology (hazard ratio [HR] = 10, 95% confidence interval [CI]: 1.3 to 81) and moderate-to-severe corpus gastritis (total severity score > or =4) before eradication (HR = 2.3, 95% CI: 1.2 to 6.1) were independent risk factors for the development of esophagitis after H. pylori eradication.

CONCLUSION

Patients infected with strains of H. pylori that are cagA-positive are at increased risk of developing esophagitis after eradication of H. pylori.

Roles of endogenous prostaglandins and nitric oxide in gastroduodenal ulcerogenic responses induced in rats by hypothermic stress

We examined the roles of endogenous prostaglandins (PGs) and nitric oxide (NO) in the gastroduodenal ulcerogenic responses to hypothermic stress (28 approximately 30 degrees C) in anesthetized rats. Lowering body temperature provoked damage in the gastroduodenal mucosa, with an increase of gastric acid secretion and motility. These responses were completely abolished by bilateral vagotomy or atropine, while 16,16-dimethyl PGE2 decreased the mucosal ulcerogenic response with no effect on acid secretion. The non-selective COX inhibitors, indomethacin or aspirin, worsened these lesions with enhancement of gastric motility and no effect on acid secretion, while the selective COX-2 inhibitor NS-398 did not affect any of these responses. On the other hand, the non-selective NOS inhibitor L-NAME but not aminoguanidine (a relatively selective inhibitor of iNOS), significantly potentiated the acid secretory and mucosal ulcerogenic responses in the stomach but reduced the duodenal damage in response to hypothermia, the effects being antagonized by co-administration of L-arginine. Hypothermia itself decreased duodenal HCO3- secretion under both basal and mucosal acidification-stimulated conditions. Both indomethacin and aspirin further decreased the HCO3- response to the mucosal acidification, while L-NAME significantly increased the HCO3- secretion even under hypothermic conditions, similar to 16,16-dimethyl PGE2. These results suggest that 1) hypothermic stress caused an increase of acid secretion and motility as well as a decrease of duodenal HCO3-secretion, resulting in damage in both the stomach and duodenum, 2) the COX-1 but not COX-2 inhibition worsened these lesions by enhancing gastric motility and further decreasing duodenal HCO3- response, 3) the cNOS but not iNOS inhibition worsened gastric lesions by increasing acid secretion but decreased duodenal damage by increasing HCO3- secretion. Thus, it is assumed that the gastroduodenal ulcerogenic and functional responses to hypothermic stress are modified by cNOS/NO as well as COX-1/PGs.

Effects of pantoprazole, a novel H+/K+-ATPase inhibitor, on duodenal ulcerogenic and healing responses in rats: a comparative study with omeprazole and lansoprazole

BACKGROUND

Pantoprazole, 2-[(2-pyridylmethyl) sulphinyl] benzimidazole, is a new substituted benzimidazole that inhibits the parietal cell H+/K+-ATPase.

METHODS

In the present study, the anti-secretory and anti-ulcer activities of pantoprazole were compared with those of omeprazole and lansoprazole in rats.

RESULTS

Pantoprazole (0.3-3 mg/kg, p.o.) as well as omeprazole (1-10 mg/kg, p.o.) and lansoprazole (1-10 mg/kg, p.o.) dose-dependently decreased both basal acid secretion in pylorus-ligated rats and the stimulated acid secretion induced by mepirizole in acute fistula rats, and the effects of pantoprazole were more potent than those of omeprazole and lansoprazole, the ED50 values for the stimulated acid secretion being 0.8, 2.0 and 1.2 mg/kg, respectively. Neither of these drugs had any effect on duodenal HCO3- secretion. These pump inhibitors prevented the development of duodenal lesions in response to mepirizole in a dose-related manner, the ED50 values for pantoprazole, omeprazole and lansoprazole being 0.4, 2.0 and 1.3 mg/kg, respectively. Likewise, pantoprazole showed the healing promoting action on chronic duodenal ulcers induced by acetic acid, and this effect was also more potent when compared to omeprazole or lansoprazole.

CONCLUSIONS

We conclude that pantoprazole exhibited both anti-ulcer and healing promoting effects on duodenal ulcers in rats, and the effects may be attributable to its potent anti-secretory action. Other pump inhibitors such as omeprazole and lansoprazole were almost equally effective as pantoprazole, yet this drug was most potent on the basis of ED50 values.

Effects of S-0509, a novel CCKB/gastrin receptor antagonist, on acid secretion and experimental duodenal ulcers in rats

BACKGROUND

S-0509, 2-[(tert-butoxycarbonylmethyl) [(m-(carboxy-phenyl)-ureidomethyl-carbonyl]] aminobenzo phenone, was developed as a potent and selective CCKB/gastrin receptor antagonist that does not affect the central nervous system.

METHODS

We evaluated the effects of S-0509 on gastric acid secretion and duodenal ulcerogenic and healing responses in rats comparing it with L-365,260, another CCKB/gastrin receptor antagonist.

RESULTS

S-0509 (0.1 approximately 10 mg/kg, i.d.) was able to dose-dependently decrease basal acid secretion and inhibit the acid secretory responses induced by both pentagastrin (60 microg/kg/h, i.v.) and peptone (10%, i.g.) but not histamine (4 mg/kg/hr, i.v.) or carbachol (60 microg/kg/h, i.v.). L-365,260 (10 and 30 mg/kg, i.d.) caused only partial a suppression of the acid secretory response to pentagastrin but not to other stimuli, including peptone treatment. On the other hand, a duodenal ulcerogen, mepirizole (200 mg/kg, s.c. ) caused an increase in acid secretion and resulted in penetrating ulcers in the proximal duodenum, and these ulcers gradually healed over 3 weeks. S-0509 significantly inhibited both the acid secretory (> 1.0 mg/kg, i.d.) and ulcerogenic (> 3 mg/kg, p.o.) responses induced by mepirizole when it was given as a pre-treatment. It also promoted significantly the healing of these ulcers (> 3 x 2 mg/kg, p. o.) when it was given twice daily for 14 days. In contrast, L-365, 260 (30 mg/kg) tended to reduce the severity of mepirizole-induced duodenal ulcers, with a slight inhibition of acid secretion, but it caused no influence on the healing response of these ulcers.

CONCLUSION

These results confirmed that S-0509 is a selective CCKB/gastrin receptor antagonist with potent antisecretory action in vivo conditions, and further demonstrated that this agent not only prevents the development of duodenal ulcers but also shows healing promoting action on duodenal ulcers, probably through the blockade of CCKB/gastrin receptors.

Modulation by nitric oxide of gastric acid secretion in toads

Nitric oxide (NO) is a novel chemical messenger that mediates a variety of biological actions. This study was undertaken to investigate the effects of NO on parietal cell function. The rate of [3H]arginine conversion to [3H]citrulline, a parameter of NO synthase activity, and NO formation (as NO2-), were inhibited by the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), in a concentration-dependent manner in the non-stimulated toad gastric mucosa. This range of concentrations of L-NAME provoked stimulation of H+ secretion in a similar fashion, which was blocked by L-arginine but not by D-arginine. Pre-treatment with carbachol plus ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetra-acetic acid (EGTA) prevented the effect of L-NAME on H+ secretion and drastically reduced NO synthase activity. L-arginine had an inhibitory effect on H+ secretion in non-stimulated and carbachol-stimulated gastric mucosa, which was reversed by L-NAME. Carbachol and pentagastrin, but not histamine, significantly increased NO formation in the toad gastric mucosa. The results suggest that changes in NO synthesis in the gastric mucosa may modulate parietal cell function and that a calcium-dependent mechanism may be involved.

Effects of pituitary adenylate cyclase activating polypeptide-27 on alkaline secretory and mucosal ulcerogenic responses in rat duodenum

Effects of pituitary adenylate cyclase activating polypeptide (PACAP) on duodenal mucosal HCO3- secretion and ulcerogenic responses induced by mepirizole in anesthetized rats were examined and compared with those of vasoactive intestinal polypeptide (VIP). Animals were given mepirizole (200 mg/kg, s.c.) for induction of duodenal ulcers, and gastric acid and duodenal HCO3- secretions were measured with or without pretreatment of PACAP-27 or VIP. Mepirizole increased acid secretion and induced hemorrhagic lesions in the proximal duodenum within 6 h. Intravenous bolus injection or infusion of PACAP-27 (4 and 8 nmol/kg or 8 nmol/kg/h) increased duodenal HCO3- secretion even in the presence of mepirizole, without effect on acid secretion, and significantly reduced the severity of duodenal lesions caused by mepirizole. In contrast, VIP (8 nmol/kg, i.v.) given by bolus injection significantly decreased acid secretion induced by mepirizole, in addition to stimulation of HCO3- secretion, and prevented duodenal lesions in response to mepirizole. These results suggest that PACAP-27 increases duodenal HCO3- secretion and this action may be important in maintaining the duodenal mucosal integrity against acid, and VIP affords duodenal protection by both increasing duodenal HCO3- secretion and decreasing acid secretion. The reason for the different effects of PACAP and VIP on acid secretion is unknown.

Glutathione and nitric oxide concentrations in glutamine-infused rabbits with intestinal ischaemia/reperfusion

Intestinal ischaemia/reperfusion causes formation of reactive oxygen intermediates which lead to mucosal cell injury. Glutathione, a scavenger of reactive oxygen intermediates, protects tissues from reactive oxygen intermediate-mediated cell injury. Nitric oxide is a lipophilic gas and its synthesis is stimulated by ischaemic conditions. In this experimental study, we aimed to investigate the role of i. v. L-glutamine infusion on mucosal tissue glutathione and serum nitric oxide concentrations in intestinal ischaemia/reperfusion. External jugular vein of albino rabbits was cannulated with catheter and infused with normal saline at 4 ml/h. After 3 days, they were randomly divided into two main groups. Group 1 (n = 30) received i. v. normal saline alone, group 2 (n = 30) received normal saline + 205 mmol/l glutamine at 4 ml/h for 24 hours. Next, mucosal glutathione and serum nitric oxide concentrations were measured after 0, 30, 60 min of ischaemia/60 min of reperfusion. Basal glutathione concentrations were similar in normal saline alone and normal saline + 205 mmol/l glutamine infusion groups (p > 0.05). At 30 and 60 min of ischaemia/60 min of reperfusion, glutathione concentrations were significantly lower in normal saline-infused rabbits compared to the normal saline + 205 mmol/l glutamine-infused rabbits (p < 0.05). In addition, serum nitric oxide concentrations were found to be significantly increased in rabbits 30 and 60 min after ischaemia/reperfusion when compared to mean basal nitric oxide concentrations obtained from control animals. However, the normal saline + 205 mmol/l glutamine group had lower serum nitric oxide concentrations than did the normal saline alone group. In conclusion, this study revealed that intestinal mucosal glutathione concentrations were significantly higher in glutamine-receiving rabbits than in non-receiving ones. Additionally, it was shown that nitric oxide concentrations increased in ischaemia both in normal saline alone and normal saline + 205 mmol/l glutamine receiving groups, while this increase in nitric oxide was more prominent in the normal saline alone group (p < 0.01). These findings show that glutamine supplementation may protect the small intestine from ischaemia/reperfusion injury and may play a regulatory role in the biosynthesis of nitric oxide.

Effects of chronic nitric oxide synthase inhibition on TNB-induced colitis in rats

Nitric oxide (NO) synthesis is increased in ulcerative colitis, but the role of NO in colitis is poorly understood. The present study employed Nw-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, in rats to evaluate the effect of NO on 2,4,6-trinitrobenzenesulphonic acid (TNB)-induced colitis. L-NAME solutions were placed in subcutaneous, osmotic mini-pumps which continuously released L-NAME at 0.042, 0.208, 0.417, or 1.667 mg kg-1 h-1. L-NAME dose-dependently enhanced lesions in TNB-induced colitis. The two higher doses of L-NAME significantly increased colonic mucosal damage, although there was slight, nonsignificant reduced lesion formation with the lowest dose of L-NAME. 0.042 mg kg-1 h-1. A single dose of L-NAME at 100 mg kg-1 subcutaneously injected daily in TNB-treated rats also increased lesions, and these ulcerogenic actions of L-NAME were reversed by L-arginine but not by D-arginine (both at 500 mg kg-1, s.c.). Only the highest dose of L-NAME (mini-pump) significantly depressed myeloperoxidase (MPO) activity. Faecal occult bleeding showed a close relationship with severity of colitis. These findings suggest that there may exist a balance between NO protective and aggressive effects. In TNB-induced colitis, antagonism of endogenous NO generation was intensified, whereas slight inhibition of NO synthesis reduced lesions. Variations in responses, related to timing or dose changes in L-NAME, may reflect the differences in inducible vs constitutive NO synthase isoforms.