Does omeprazole-induced hypergastrinaemia contribute to the enhanced healing of aceticacid-induced gastric ulcers in rats?

[An overview of acetic acid ulcer models and their utility for drug screening]

Since Takagi et al. reported an experimental chronic gastric ulcer model [acetic acid ulcers induced by submucosal injection of acetic acid (Type 1)], we further modified the methodology and subsequently devised three more models. The second model involves inducing ulcers by serosal application of an acetic acid solution (Type 2) and the third model achieves ulcer induction by intragastric application of an acetic acid solution (Type 3). The forth model was modification of the third model by giving the acetic acid solution and the same volume of air to make one ulcer in the stomach (Type 4). In general, animals accepted the procedures without problems and no undesirable effects were noticed. More importantly, this experimental animal model allows production of ulcers that highly resemble human ulcers in terms of both pathology and healing. Indeed, relapse is even endoscopically observed for 360 days after ulceration. The ulcers produced not only respond well to various anti-ulcer medications, such as antisecretory and mucosal protective drugs and growth factors, but also demonstrate appropriate responses to ulcerogenic agents such as NSAIDs. In addition, we have recently demonstrated that H. pylori infection resulted in delayed ulcer healing and recurrence of healed acetic acid ulcers induced in Mongolian gerbils. The present article gives a brief summary of the ulcer history before establishment of acetic acid ulcers and characteristic features of acetic acid ulcer, including both their merits and shortcomings.

Pharmacological control of gastric acid secretion for the treatment of acid-related peptic disease: past, present, and future

Pharmacological agents, such as histamine H(2) receptor antagonists and acid pump inhibitors, are now the most frequently used treatment for such acid-related diseases as gastroduodenal ulcers and reflux esophagitis. Based on increased understanding of the precise mechanisms of gastric acid secretion at the level of receptors, enzymes, and cytoplasmic signal transduction systems, further possibilities exist for the development of effective antisecretory pharmacotherapy. Gastrin CCK(2) receptor antagonists and locally active agents appear to represent promising therapies for the future. Development of gene targeting techniques has allowed production of genetically engineered transgenic and knockout mice. Such genetic technology has increased the investigative power for pharmacotherapy for not only antisecretory agents, but also treatment of mucosal diseases, such as atrophy, hyperplasia, and cancer. Elucidation of the origin of gastric parietal cells also represents an interesting investigative target that should allow a better understanding of not only acid-related diseases, but also the evolution of the stomach as an acid-secreting organ.

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.