Influence of gastric acid on gastric emptying and gastric distension-induced pain response in rats--effects of famotidine and mosapride

BACKGROUND

Gastroduodenal acidification has been reported to aggravate upper abdominal discomfort and pain that are symptoms suffered by functional dyspepsia (FD) patients. Delayed gastric emptying and hypersensitivity to gastric distension (GD) contribute importantly to the pathophysiology of FD.

METHODS

In the present study, we determined the influence of pentagastrin-stimulated endogenous gastric acid on gastric emptying and GD-induced pain responses using rat model systems. Moreover, we evaluated the effects of famotidine and mosapride on changes in gastric emptying and the GD-induced pain response to gastric acid hypersecretion. Gastric emptying was measured by excretion of glass beads that had been intragastrically administered with a liquid nutrient, and gastric pain response was evaluated by observing whether a GD-induced increase in mean blood pressure occurred.

KEY RESULTS

Pentagastrin (2 mg kg(-1), s.c.) which markedly and continuously stimulated gastric acid secretion, significantly delayed and enhanced respectively, gastric emptying and pain compared with saline-injected groups. Oral famotidine (0.1-3 mg kg(-1)) and mosapride (0.3-3 mg kg(-1)) administration in a dose-dependent manner accelerated the delay of gastric emptying. Furthermore, famotidine (0.3-3 mg kg(-1)) significantly alleviated the aggravation of the GD-induced pain response, but mosapride (10 mg kg(-1)) did not.

CONCLUSIONS & INFERENCES

We established rat models to evaluate the effect of gastric acid hypersecretion on gastric emptying and the GD-induced pain response. In these models, acid hypersecretion delayed gastric emptying and aggravated the pain response. Furthermore, we showed that famotidine ameliorated both delayed gastric emptying and gastric hypersensitivity, whereas mosapride only improved delayed gastric emptying.

Effects of serotonin 5-HT3 receptor antagonists on stress-induced colonic hyperalgesia and diarrhoea in rats: a comparative study with opioid receptor agonists, a muscarinic receptor antagonist and a synthetic polymer

In this study, we examined the effects of serotonin (5-HT)3 receptor antagonists (5-HT3RAs) including ramosetron, alosetron, and cilansetron on colonic nociceptive threshold in rats. Furthermore, we established a restraint stress-induced colonic hyperalgesia model in rats, and compared the inhibitory effects of 5-HT3RAs on restraint stress-induced colonic hyperalgesia and diarrhoea with those of loperamide, trimebutine, tiquizium and polycarbophil. The colonic nociceptive threshold was measured as the balloon pressure at the time the rat showed a nociceptive response during colonic distension by an intrarectally inserted balloon. Oral administration of ramosetron (3-30 microg kg(-1)), alosetron (30-300 microg kg(-1)), or cilansetron (30-300 microg kg(-1)) increased the colonic nociceptive threshold in a dose-dependent manner in non-stressed rats. Restraint stress for 1 h significantly decreased the colonic nociceptive threshold, but ramosetron (0.3-3 microg kg(-1)), alosetron (3-30 microg kg(-1)), cilansetron (3-30 microg kg(-1)) and trimebutine (100-1000 mg kg(-1)) significantly inhibited the decrease in the threshold. Loperamide (3-30 mg kg(-1)), tiquizium (100-1000 mg kg(-1)) and polycarbophil (1000 mg kg(-1)) did not affect the restraint stress-induced decrease in the colonic nociceptive threshold. All drugs tested in this study showed dose-dependent inhibition of restraint stress-induced diarrhoea in rats. These results indicate that, unlike existing antidiarrhoeal and spasmolytic agents, 5-HT3RAs have inhibitory effects on colonic nociception, and prevented restraint stress-induced both diarrhoea and hyperalgesia at almost the same doses in rats. This suggests that the 5-HT3RAs may be useful in ameliorating both colonic hyperalgesia and diarrhoea in patients with irritable bowel syndrome.

Pharmacological profile of ramosetron, a novel therapeutic agent for IBS

Ramosetron is a potent and selective serotonin (5-HT)(3) receptor antagonist that has been shown to affect abnormal colonic function and abdominal pain in animals. Ramosetron (0.3 to 100 microg/kg, p.o.) has been found to significantly suppress abnormal defecation induced by conditioned-fear stress (CFS), restraint stress, corticotropin releasing factor (CRF) and 5-HT in rats and mice, and these effects were more potent than those of alosetron, cilansetron or loperamide. On the other hand, ramosetron (3,000 microg/kg, p. o., once daily for 7 days) did not inhibit normal defecation in dogs while tiquizium significantly inhibited it. Ramosetron (3 to 100 microg/kg, p. o.) also significantly prevented CFS-induced acceleration of colonic transit and CRF-induced abnormal water transport in rats, respectively. Moreover, ramosetron (0.3 to 3 microg/kg, p. o.) significantly suppressed restraint stress-induced decrease in colonic pain threshold, an effect not observed with loperamide. These results indicate that ramosetron produce beneficial clinical effects on IBS symptoms.

[Pharmacological study on the pathological changes of the gastric mucosa in Helicobacter pylori-infected Mongolian gerbils]

Helicobacter pylori (H. pylori) infection has been recognized to be a causal factor of gastritis, ulcers and gastric cancer in man. Using Mongolian gerbils (M. gerbils), which are suitable for an H. pylori infection animal model, we examined 1) how H. pylori infection, indomethacin and their combination affects the healing of gastric ulcers and whether or not such factors provoke a relapse of healed acetic acid ulcers; and 2) whether or not eradication of the bacteria with drugs at specified times after infection prevents the development of mucosal changes, including gastric adenocarcinoma. 1) H. pylori infection significantly delayed ulcer healing 4 weeks following infection. Indomethacin treatment showed a tendency to delay ulcer healing. Ulcer healing in H. pylori-infected M. gerbils was significantly delayed by indomethacin. H. pylori infection resulted in a relapse of healed ulcers from 1 to 6 months after infection, with a gradual increase in size. Omeprazole markedly prevented the ulcer relapse caused by H. pylori infection. 2) Four or 8 months after H. pylori inoculation, eradication was performed by concurrent treatment with omeprazole + clarithromycin. Immediately after treatment ended in both the 5 and 9 month groups, it was verified that H. pylori were completely eradicated. Autopsy performed 18 months after H. pylori inoculation revealed gastric hyperplastic polyps with erosive lesions and ulcers that were grossly visible; and atrophic gastritis, intestinal metaplasia, carcinoids, and adenocarcinomas were histologically observed in the non-treated control group. In animals eradicated after 4 months and autopsied after 18 months, however, such mucosal changes were not observed. In contrast, intestinal metaplasia and mucosal atrophy was observed in animals eradicated after 8 months and autopsied after 18 months. It was concluded that 1) H. pylori infection delayed the healing of preexisting gastric ulcers and resulted in the relapse of healed ulcers, yet indomethacin had little or no effect on ulcer healing or relapse; and 2) early eradication of H. pylori infection with drug therapy can prevent severe gastric mucosal changes, to include adenocarcinomas, in M gerbils.

Gastric mucosal changes induced by long term infection with Helicobacter pylori in Mongolian gerbils: effects of bacteria eradication

Helicobacter pylori infection has been reported to induce various mucosal changes, including gastric adenocarcinoma, in Mongolian gerbils 62 weeks after inoculation. Using Mongolian gerbils, this study examined whether or not eradication of the bacteria with drugs at specified times after infection prevents the development of mucosal changes. After orally inoculating with H. pylori (TN2GF4, vacA- and cagA-positive), the animals were killed 18 months later. Four or 8 months after H. pylori inoculation, eradication was performed by concurrent treatment with omeprazole+clarithromycin. Immediately after treatment ended, in both the 5 and 9 month groups, it was verified that H. pylori was completely eradicated. Autopsy performed 18 months after H. pylori inoculation revealed gastric hyperplastic polyps with erosive lesions and ulcers that were grossly visible in the non-treated control group. In addition, atrophic gastritis, intestinal metaplasia, carcinoids, and adenocarcinomas were histologically observed in the animals. In animals eradicated after 4 months and autopsied after 18 months, however, such mucosal changes were not observed. In contrast, intestinal metaplasia and mucosal atrophy was observed in animals eradicated after 8 months and autopsied after 18 months. It was concluded that early eradication of H. pylori infection with drug therapy can prevent severe gastric mucosal changes, to include adenocarcinomas, in Mongolian gerbils.

Effects of dexamethasone and FK506 on Helicobacter pylori-induced gastritis and bacterial viability in Mongolian gerbils

FK506 and dexamethasone were used to investigate whether or not immunosuppression affects H. pylori colonization and gastric mucosal damage induced by Helicobacter pylori in Mongolian gerbils. Two weeks after H. pylori infection, FK506 and dexamethasone or vehicle alone were subcutaneously administered once daily for the following 2 weeks. FK506 or vehicle alone was administered subcutaneously once daily for 5 weeks (1 week before and 4 weeks after infection). In H. pylori-infected animals for 4 weeks, hemorrhagic erosions and inflammatory responses (neutrophil infiltration and lymphoid follicle formation) were induced in gastric mucosa at an incidence of 100%. Both FK506 and dexamethasone administered for 2 weeks markedly reduced such mucosal changes. In these animals, H. pylori viability in the stomach was significantly elevated. FK506 administered for 5 weeks also significantly inhibited the hemorrhagic erosions, edema and neutrophil infiltration in the stomach. H. pylori viability was slightly elevated as compared with the control. It was concluded that the host immune responses might play dual roles both by deteriorating gastritis induced by H. pylori and by protecting against H. pylori infection in its early stage.

FR167653, a p38 mitogen-activated protein kinase inhibitor, prevents Helicobacter pylori-induced gastritis in Mongolian gerbils

FR167653 was discovered as a cytokine production inhibitor, but its target molecule has remained unclear. We examined the effect of FR167653 on activities of purified protein kinases. FR167653 dose dependently inhibited p38alpha mitogen-activated protein kinase activity without affecting the activities of other kinases. FR167653 had no effect on cyclooxygenase (COX)-1 or COX-2 activities, whereas SB203580 inhibited them. FR167653 suppressed endogenous p38 kinase activity in interleukin-1-stimulated NRK-F cells. These results indicate that FR167653 is a p38 kinase-selective inhibitor without affecting COX activity. To evaluate the role of p38 kinase in Helicobacter pylori gastritis, we therefore examined the effect of FR167653 on H. pylori-induced gastritis in Mongolian gerbils. H. pylori infection activated p38 kinase in the gastric mucosa and caused neutrophil infiltration from 2 and 3 weeks of infection, respectively. At 4 weeks, severe mucosal inflammation with erosive injury was observed. When FR167653 was administered to H. pylori-infected gerbils from 2 weeks, both neutrophil infiltration and mucosal injury at 4 weeks were significantly prevented. FR167653 markedly reduced the H. pylori-induced increase in endogenous p38 kinase activity in the gastric mucosa, and also significantly inhibited neutrophil chemokine production. In contrast, the drug did not affect H. pylori colonization or acid secretion. FR167653 did not cause any pathological change in the gastric mucosa of normal animals. These results indicate that p38 kinase plays a crucial role in H. pylori-induced gastritis in Mongolian gerbils.

The inhibitory effect of KT3-671, a nonpeptide angiotensin-receptor antagonist, on rabbit and rat isolate vascular smooth muscles: a possible involvement of K(ATP) channels

The vasoinhibitory effect of KT3-671, a recently synthesized nonpeptide angiotensin II (Ang II), AT1-receptor antagonist, and the factors affecting insurmountable antagonism of Ang II were examined in rabbit and rat isolated vascular smooth muscle preparations. In rabbit and rat aortic rings, KT3-671 caused insurmountable antagonism of Ang II. In addition, KT3-671 inhibited contractile responses to angiotensin III (Ang III). In rabbit isolated smooth muscles, KT3-671 was most effective in reducing the maximal contraction induced by Ang II in the renal artery followed by the basilar artery and the aorta. In rat renal arterial rings, KT3-671 (10(-5) M) inhibited the concentration-response curves of prostaglandin F2alpha and STA2. In rabbit and rat aortic rings without endothelium, the insurmountable antagonisms of Ang II by KT3-671 and EXP 3174 were changed to surmountable antagonism by pretreatment with DuP 753 and KT3-671, respectively. In addition, KT3-671 abolished the inhibitory effect of CV- 11974 in the rat aorta but not in the rabbit aorta. Indomethacin (10(-5) M) or the removal of endothelium did not affect the inhibitory effect of Ang II by CV-11974 or EXP 3174 but enhanced the insurmountable antagonism by KT3-671. ODQ (3 x 10(-6) M), N(G)-nitro-L-arginine (3 x 10(-4) M), 4-aminopyridine (3 x 10(-3) M), tetraethylammonium (TEA; 10(-3) M), or iberiotoxin (10(-7) M) did not affect the inhibitory action of KT3-671 or CV-11974. Methylene blue (3 x 10(-6) M), KCl (10(2) M), TEA (10(-2) M), or BaC12 (10(-4) M) changed the insurmountable antagonism by KT3-671 to surmountable antagonism and abolished the inhibitory effect of CV-11974. However, glibenclamide (3 x 10(-6) M) did not affect the inhibitory action of KT3-671 but reduced the insurmountable antagonism by CV- 11974. These results indicate that KT3-671 is an insurmountable antagonist of Ang II in the rabbit and rat aorta. The results in the rat aorta also suggest that K(ATP) channels may be involved in insurmountable antagonism of Ang II by KT3-671 and CV-11974. Key Words: KT3-671-Rabbit-Rat-Vascular smooth muscle-Angiotensin II-Insurmountable antagonist-K(TP)channels.

Genistein potentiates the relaxation induced by beta1- and beta2-adrenoceptor activation in rat aortic rings

In rat aortic rings, genistein, an inhibitor of tyrosine kinase, but not daidzein, an inactive analogue of genistein, potentiated the relaxation induced by isoproterenol. Atenolol, a beta1-adrenoceptor antagonist, or ICI-118,551, a beta2-adrenoceptor antagonist, inhibited the relaxation induced by isoproterenol. The potentiating effect of genistein on the relaxation induced by isoproterenol in the presence of ICI-118,551 was apparently greater than that in the presence of atenolol. In the presence of ICI-118,551, theophylline, an inhibitor of cyclic adenosine monophosphate (cAMP)-dependent phosphodiesterase (cAMP-PDE), markedly inhibited the potentiating effect of genistein on the isoproterenol-induced relaxation, whereas in the presence of atenolol, theophylline only partly inhibited the potentiating effect of genistein. The relaxation induced by forskolin, an activator of adenylyl cyclase, was potentiated by genistein or theophylline. In the presence of theophylline, the relaxation induced by forskolin was not further affected by genistein. Genistein also inhibited the activities of cAMP-PDE. In the presence of atenolol, but not ICI-118,551, iberiotoxin, an inhibitor of Ca-activated K channels, inhibited the relaxation induced by isoproterenol and the potentiating effect of genistein. In the presence of atenolol, quinacrine, an inhibitor of phospholipase A2, and metyrapone, an inhibitor of P-450 enzymes, but not alpha-naphthoflavone, an inhibitor of P-450 enzymes, indomethacin, a cyclooxygenase inhibitor, or AA861, a 5-lipoxygenase inhibitor, inhibited the potentiating effect of genistein. These results suggest that the potentiation of the beta1-adrenoceptor-induced relaxation by activation of genistein may mostly be due to inhibition of cAMP-PDE activities. In addition, the potentiation of the relaxation induced by activation of beta2-adrenoceptors by genistein may be related to the inhibition of arachidonic acid metabolism and cAMP-PDE activities.

Healing of Helicobacter pylori-induced gastric ulcers in Mongolian gerbils: combined treatment with omeprazole and clarithromycin

Helicobacter pylori can colonize the stomachs of Mongolian gerbils and subsequently induce penetrating ulcers five months later. Using this gerbil model, the effects of both combined treatment with omeprazole and clarithromycin, as well as treatment with each drug separately, on the healing of H. pylori-induced gastric ulcers, and the effects of the cessation of the drug treatment on healed ulcers were examined. Beginning five months after H. pylori (NCTC11637) inoculation, omeprazole (four weeks), clarithromycin (two weeks), their combination, or the vehicle was orally administered once daily. These drugs, in combination or separately, markedly enhanced ulcer healing and lowered the increased myeloperoxidase (MPO) activity. While omeprazole had no effect on viable H. pylori, clarithromycin and the drug combination significantly reduced viable H. pylori. The degree of bacterial eradication was much higher in the case of the drug combination compared to clarithromycin alone. Four months after cessation of the treatment, visible ulcers, hypertrophic gastritis and increased MPO activity were found in the control animals (all H. pylori-positive). Nonetheless, only one of the eight gerbils subjected to the drug combination developed a small ulcer, although no hypertrophic gastritis was exhibited. It is concluded that: (1) the gerbil model of H. pylori infection is useful for the study of ulcer healing; (2) combined treatment with omeprazole and clarithromycin enhances the ulcer healing in infected gerbils; and (3) healed ulcers do not relapse, despite cessation of the drug treatment.

Pathological changes in the formation of Helicobacter pylori-induced gastric lesions in Mongolian gerbils

We examined pathological changes in the formation of Helicobacter pylori-induced gastric lesions in Mongorian gerbils. H. pylori (NCTC11637) was orally administered once to the animals and was detected in the gastric mucosa of all gerbils given the bacteria. The number of viable H. pylori increased during the initial two weeks and thereafter reached a plateau level. The initial pathological changes were found at one week, ie, edema/congestion and a white viscous substance only in the antrum. At two weeks, superficial damage appeared in the antrum, although inflammatory cell infiltration had not occurred. Gastritis with lymphoid follicles was observed in the antrum and fundus from three weeks. At four weeks, mucosal lesions were detected as a few hemorrhagic spots in the fundus adjacent to the antrum. In the control animals, however, no pathological changes were observed even at four weeks. In the gastric mucosa infected with H. pylori, myeloperoxidase activity was negligible at two weeks, but was extremely elevated at four weeks. Similarly, neutrophil chemotactic activity was only slightly increased at two weeks, but was markedly elevated at four weeks. These results indicate that H. pylori infection induces initial pathological changes only in the antrum, but mucosal lesions occur in the fundus adjacent to the antrum. Furthermore, it is demonstrated that the initial superficial damage is generated by factors other than chemokines and neutrophil-associated factors, although mucosal inflammation may contribute to the subsequent formation of lesions and ulcers.