Tomonori Kunikata

Pathogenic Importance of Intestinal Hypermotility in NSAID-Induced Small Intestinal Damage in Rats

Background/Aim: Nonsteroidal anti-inflammatory drugs (NSAIDs) such as indomethacin produce damage in the small intestine as a major adverse reaction. We examined the effect of various NSAIDs on intestinal motility and investigated the pathogenic importance of motility changes in the intestinal ulcerogenic response to indomethacin in rats. Methods: Animals without fasting were given various NSAIDs (indomethacin 10 mg/kg, diclofenac 40 mg/kg, flurbiprofen 20 mg/kg, naproxen 40 mg/kg) s.c., and in the case of indomethacin, the following parameters were examined in the small intestine 24 h later; the lesion score, the number of enterobacteria and myeloperoxidase (MPO) as well as inducible nitric oxide (iNOS) activity. Intestinal motility was monitored as intraluminal pressure recordings using a balloon under anesthesia. Results: All NSAIDs tested decreased mucosal PGE2 levels and produced hemorrhagic lesions in the small intestine, accompanied by intestinal hypermotility. As representative of NSAIDs, indomethacin also increased the extent of enterobacterial invasion and MPO as well as iNOS activity before the occurrence of intestinal damage, and the hypermotility response was observed earlier than the onset of any other event caused by this agent. The intestinal lesions induced by indomethacin were prevented by either supplementation with dmPGE2, inhibition of bacterial invasion with ampicillin or inhibition of iNOS activity with aminoguanidine, while the hypermotility response was prevented by dmPGE2 only. In addition, the observed effects of dmPGE2 were all mimicked by atropine when the intestinal hypermotility was suppressed by this agent. Conclusion: These results suggest the pathogenic importance of intestinal hypermotility in the intestinal ulcerogenic response to NSAIDs in rats and show that this event is critical for the occurrence of enterobacterial invasion under PG deficiency, followed by various inflammatory changes and damage in the mucosa. This study also suggests that the antispasmodic drug is protective against NSAID-induced intestinal lesions.

16,16-Dimethyl Prostaglandin E2 Inhibits Indomethacin-Induced Small Intestinal Lesions Through EP3 and EP4 Receptors

We evaluated the effect of various PGE analogs specific to EP receptor subtypes on indomethacin-induced small intestinal lesions in rats and investigated the relationship of EP receptor subtype with the PGE action using EP receptor knockout mice. Animals were administered indomethacin subcutaneously, and they were killed 24 hr later. 16,16-dimethyl prostaglandin E2 (dmPGE2) or various EP agonists were administered intravenously 10 min before indomethacin. Indomethacin caused hemorrhagic lesions in the rat small intestine, accompanied with an increase in intestinal motility and the number of enteric bacteria as well as iNOS and MPO activities. Prior administration of dmPGE2 dose-dependently prevented intestinal lesions, together with inhibition of those functional changes. These effects of dmPGE2 were mimicked by prostanoids (ONO-NT-012 and ONO-AE1-329), only specific to EP3 or EP4 receptors, although the intestinal motility was inhibited only by ONO-AE1-329. Intestinal mucus secretion and fluid accumulation were decreased by indomethacin but enhanced by dmPGE2, ONO-NT-012, and ONO-AE1-329 at the doses that prevented intestinal lesions. Indomethacin also caused intestinal lesions in both wild-type and knockout mice lacking EP1 or EP3 receptors, yet the protective action of dmPGE2 was observed in wild-type and EP1 receptor knockout mice but not the mice lacking EP3 receptors. These results suggest that the intestinal cytoprotective action of PGE2 against indomethacin is mediated by EP3/EP4 receptors and that this effect is functionally associated with an increase of mucus secretion and enteropooling as well as inhibition of intestinal hypermotility, the former two processes mediated by both EP3 and EP4 receptors, and the latter by EP4 receptors.

Protective effect of lafutidine against indomethacin-induced intestinal ulceration in rats: relation to capsaicin-sensitive sensory neurons.

Background/Aim: We examined the prophylactic effect of lafutidine, a novel histamine H2-receptor antagonist [(±)-2-(furfurylsulfinyl)-N-[4-[4-(piperidinomethyl)-2-pyridyl]oxy-(Z)-2 butenyl]acetamide], on indomethacin-induced small intestinal ulcers in rats and investigated the relation of this action to capsaicin-sensitive sensory neurons. Methods and Results: Subcutaneously administered indomethacin (10 mg/kg) provoked ulceration in the small intestine, mainly the jejunum and ileum, accompanied by increases in myeloperoxidase (MPO) and inducible nitric oxide synthase (iNOS) activities as well as the enterobacterial numbers invading the mucosa. Intestinal ulcerogenic response to indomethacin was prevented by 16,16-dimethyl prostaglandin E2 (10 μg/kg, p.o.) and capsaicin (10 mg/kg, p.o.) as well as ampicillin (800 mg/kg, p.o.), but not omeprazole (100 mg/kg, p.o.). Likewise, lafutidine (1–10 mg/kg, p.o.), but not cimetidine (100 mg/kg, p.o.), reduced the occurrence of intestinal ulcers in response to indomethacin in a dose-dependent manner, and a significant effect was observed at 3 mg/kg or greater. The protective action of lafutidine as well as capsaicin was almost totally abolished by chemical ablation of capsaicin-sensitive sensory neurons. Both lafutidine and capsaicin significantly suppressed the increases in MPO and iNOS activities as well as enterobacterial numbers in the mucosa. These agents also significantly enhanced mucus secretion in the small intestine. Conclusion: These results suggest that lafutidine protects the small intestine against ulceration via stimulation of capsaicin-sensitive sensory neurons. This action may be attributable to inhibition of enterobacterial invasion in the intestinal mucosa, probably by increasing the mucus secretion.

Prostaglandin E prevents indomethacin-induced gastric and intestinal damage through different EP receptor subtypes

Gastrointestinal ulcerogenic effect of indomethacin is causally related with an endogenous prostaglandin (PG) deficiency, yet the detailed mechanism remains unknown. We examined the effect of various PGE analogues specific to EP receptor subtypes on these lesions in rats and mice, and investigated which EP receptor subtype is involved in the protective action of PGE(2). Fasted or non-fasted animals were given indomethacin s.c. at 35 mg/kg for induction of gastric lesions or 10-30 mg/kg for intestinal lesions, and they were killed 4 or 24 h later, respectively. Various EP agonists were given i.v. 10 min before indomethacin. Indomethacin caused hemorrhagic lesions in both the stomach and intestine. Prior administration of 16,16-dimethyl PGE(2) (dmPGE(2)) prevented the development of damage in both tissues, and the effect in the stomach was mimicked by 17-phenyl PGE2 (EP1), while that in the small intestine was reproduced by ONO-NT-012 (EP3) and ONO-AE-329 (EP4). Butaprost (EP2) did not have any effect on either gastric or intestinal lesions induced by indomethacin. Similar to the findings in rats, indomethacin caused gastric and intestinal lesions in both wild-type and knockout mice lacking EP1 or EP3 receptors. However, the protective action of dmPGE(2) in the stomach was observed in wild-type and EP3 receptor knockout mice but not in mice lacking EP1 receptors, while that in the intestine was observed in EP1 knockout as well as wild-type mice but not in the animals lacking EP3 receptors. These results suggest that indomethacin produced damage in the stomach and intestine in a PGE(2)-sensitive manner, and exogenous PGE(2) prevents gastric and intestinal ulcerogenic response to indomethacin through different EP receptor subtypes; the protection in the stomach is mediated by EP1 receptors, while that in the intestine mediated by EP3/EP4 receptors.

Changes in gastric mucosal ulcerogenic responses in rats with adjuvant arthritis: role of nitric oxide

: To examine gastric mucosal ulcerogenic responses to indomethacin and HCl/ethanol in adjuvant arthritic (AA) rats.

Inducible types of cyclooxygenase and nitric oxide synthase in adaptive cytoprotection in rat stomachs.

Roles of cyclooxygenases (COX-1 and COX-2) and nitric oxide (NO) synthases (nNOS and iNOS) in adaptive cytoprotection induced by 20 mM taurocholate dissolved in 50 mM HCl (TC) were investigated in rat stomachs. Intragastric administration of 0.6 N HCl caused haemorrhagic damage in the stomach. These lesions were prevented by pretreatment of the animals with TC p.o. 0.5 h before 0.6 N HCl, and a significant protection persisted for more than 5 h. The protection afforded by TC given 0.5 h before HCl was almost totally reversed by indomethacin and slightly mitigated by N(G)-nitro-L-arginine methyl ester (L-NAME) but not affected by NS-398 or aminoguanidine. By contrast, the mucosal protective action of TC given 5 h before HCl was significantly reversed by NS-398, L-NAME and aminoguanidine as well as indomethacin. Mucosal prostaglandin E2 (PGE2) contents were significantly increased for over 5 h after TC, while luminal NOx output tended to elevate at 0.5 h and be significantly increased at 5 h after TC. The increased PGE2 generation observed 0.5 h after TC was attenuated only by indomethacin, while that observed 5 h after TC was inhibited by NS-398 as well as indomethacin. On the other hand, the NOx output determined at 5 h after TC was significantly reduced by both L-NAME and aminoguanidine. The expression of mRNA for both COX-2 and iNOS was apparently detected in the stomach from 3 h after TC treatment. These results suggest that TC induced adaptive cytoprotection in the rat stomach against 0.6 N HCl, the effect lasting for over 5 h, and the underlying mechanism differs depending on the period after the irritation. The early phase is mediated mainly by COX-1/PGs, while the later phase is mediated by iNOS/NO, in addition to prostaglandins (PGs) produced by both COX-1 and COX-2.

Protection by constitutively formed nitric oxide of intestinal damage induced by indomethacin in rats.

In the present study, we investigated a protective role of constitutively occurred nitric oxide (NO) against indomethacin-induced intestinal lesions in rats. Indomethacin (10 mg/kg) was given s.c. to animals without fasting, and the intestinal mucosa was examined for lesions 24 h later. The NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) was given s.c. 0.5 h before or 6 hr after indomethacin, while the NO donor (+/-)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexnamine (NOR-3) was given s.c. 0.5 h before indomethacin. Indomethacin caused hemorrhagic lesions in the small intestine, accompanied with an increase in intestinal motility and bacterial translocation. These lesions were markedly prevented or worsened, respectively, by later or prior administration of L-NAME (20 mg/kg), in a L-arginine-sensitive manner. The worsening effect of L-NAME (5-20 mg/kg) on these lesions was dose-dependently observed in association with further enhancement of the bacterial translocation and intestinal hypermotility following indomethacin. By contrast, prior administration of NOR-3 (1-6 mg/kg) dose-dependently prevented the development of intestinal lesions, together with suppression of the bacterial translocation and intestinal hypermotility in response to indomethacin. On the other hand, both indomethacin and L-NAME decreased intestinal mucus and fluid (water) secretion in the small intestine, while NOR-3 increased these secretions. These results suggest that (1) NO occurred constitutively exerts a protective action against indomethacin-induced intestinal ulceration, and (2) this effect is related with prevention of bacterial translocation, the process functionally associated with increase of mucus and fluid secretions as well as inhibition of intestinal hypermotility.

The roles of nitric oxide and prostaglandins in alterations of ulcerogenic and healing responses in adjuvant-induced arthritic rat stomachs.

Aim: To examine alterations of gastric ulcerogenic and healing responses in adjuvant‐induced arthritic rats.

Regulatory mechanism of acid secretion in the damaged stomach: role of endogenous nitric oxide.

The present article overviews the regulatory mechanism of acid secretion in the stomach after damage with taurocholate (TC), one of the bile acids. Mucosal exposure of a rat stomach to 20 mmol/L TC for 30 min caused a decrease of acid secretion with a concomitant increase in nitric oxide (NO) and prostaglandin (PG) E2 (PGE2) as well as Ca2+ in the luminal contents. Prior administration of NG‐nitro‐ L‐arginine methyl ester ( L‐NAME), as well as indomethacin, significantly attenuated the reduction of acid secretion by TC and acid secretion was even increased in the presence of L‐NAME. The acid stimulatory effect of L‐NAME in the damaged stomach was not mimicked by aminoguanidine and was antagonized by co‐administration of L‐arginine but not D‐arginine. Increased NO release in the damaged stomach was suppressed by pretreatment with L‐NAME or co‐application of EGTA and the latter also inhibited the increase in luminal Ca2+. The enhanced acid secretory response in the presence of L‐NAME was also inhibited by cimetidine, FPL‐52694 (a mast cell stabilizer) or sensory deafferentation. Mucosal exposure to TC caused an increase in luminal histamine output, together with a decrease in the number of mucosal mast cells in the stomach. These changes were prevented by FPL‐52694 and sensory deafferentation and were also partly suppressed by indomethacin. In addition, the acid stimulatory action of L‐NAME in the damaged stomach was significantly mitigated when indomethacin was administered together with L‐NAME. We conclude that: (i) damage in the stomach may activate acid a stimulatory pathway in addition to a PG‐, NO‐ and Ca2+‐dependent inhibitory mechanism, but the latter effect overcomes the former, resulting in a decrease in acid secretion; (ii) acid stimulation in the damaged stomach is mediated by histamine released from the mucosal mast cell, a process interacting with capsaicin‐sensitive sensory nerves; (iii) the increase in luminal Ca2+ plays a role in increasing NO production and, hence, in regulating acid secretion; and (iv) PG may have a dual role in the regulation of acid secretion in the damaged stomach: an inhibitory effect at the parietal cell and an excitatory effect, probably through enhancing the release of mucosal histamine.

Delayed Healing of Gastric Ulcers in Adjuvant Arthritis Rats: Role of Acid Secretion and Basic Fibroblast Growth Factor

Background/Aim: We examined the healing process of chronic gastric ulcers in adjuvant-induced arthritic rats and investigated the mechanism for delayed ulcer healing in arthritic rats, in relation to acid secretion and basic fibroblast growth factor (bFGF). Methods: Arthritis was induced in male dark Agouti rats by a single injection of Freund’s complete adjuvant (FCA), while gastric ulcers were induced by thermal cauterization (70°C for 30 s) 7 days after FCA injection. Results: Injection of FCA induced severe arthritis in all animals with a marked acid hypersecretion. The healing of gastric ulcers was significantly delayed in arthritic rats as compared with normal rats. Daily administration of indomethacin delayed ulcer healing in both normal and arthritic rats, but this effect was more pronounced in the latter. In contrast, the healing of gastric ulcers was significantly promoted in both normal and arthritic rats by omeprazole at a dose that inhibited acid secretion completely. The delayed healing of gastric ulcers was not influenced by twice daily administration of NG-nitro-L-arginine methyl ester, aminoguanidine or FR167653 (IL-1/TNF-α synthesis inhibitor), but was significantly accelerated by CS-23 (recombinant human bFGF) in a dose-dependent manner, without effect on the acid secretion. The expression of bFGF was markedly increased after ulceration, but this response was decreased in arthritic rats. Conclusion: The healing of gastric ulcers was delayed in arthritic rats, and this mechanism may be partly attributable to both acid hypersecretion and less expression of bFGF.