Acid secretory and duodenal ulcerogenic responses induced by mepirizole in anesthetized rats. Relation to body temperature

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.

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.

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

The inhibition of nitric oxide (NO) production by NO synthase inhibitors stimulates HCO3- secretion in the rat duodenal mucosa. Therefore, we examined the effects of NG-nitro-L-arginine methyl ester (L-NAME, the NO synthase inhibitor) and nitroprusside (the exogenous NO donor) on the duodenal HCO3- and ulcerogenic responses in anesthetized rats. Animals were administered mepirizole (200 mg/kg, subcutaneously) for induction of duodenal ulcers, and gastric acid and duodenal HCO3- secretions were measured with or without pretreatment with L-NAME (5 mg/kg, intravenously) or nitroprusside (4 mg/kg, intravenously). Mepirizole increased acid secretion, decreased the acid-induced duodenal HCO3- secretion, and induced hemorrhagic lesions in the proximal duodenum. The inhibition of NO production by L-NAME potentiated the acid secretory response, increased the duodenal HCO3- secretion, and prevented the duodenal lesions, and these changes were all antagonized by simultaneous administration of L-arginine (200 mg/kg, intravenously) but not D-arginine. On the other hand, nitroprusside slightly reduced the acid response but further decreased the HCO3- output, resulting in aggravation of duodenal lesions induced by mepirizole. These data suggest that the inhibition of endogenous NO production by the NO synthase inhibitor L-NAME increases duodenal HCO3- secretion and protects the duodenal mucosa against acid injury.