Studies on antiulcer agents. IV. Antiulcer effects of 2-benzylthio5,6,7,8-tetrahydro-4(3H)-quinazolinones and related compounds

With a view to finding more effective antiulcer agents, a series of 2-benzylthio-5,6,7,8-tetrahydro-4(3H)-quinazolinones and related compounds were synthesized and evaluated in a histamine-stimulated gastric secretion model. The sodium salt of the 2-(dimethylamino)benzylthio derivative (8) showed gastric mucosal protection and gastric antisecretion activities, and was also effective against experimental gastric and duodenal ulcers induced by some ulcerogenic agents. Based on a comparison of the antiulcer properties of 8 with those of the lead compounds (1 and 2) and cimetidine, it appears that, for improvement of antiulcer activity, the reduction of gastric acidity is a more important factor than the reduction of gastric volume output or gastric total acid output.

Biphasic effect of duodenal ulcerogens on gastric emptying in the rat

The effect of the duodenal ulcerogen cysteamine on gastric emptying of a liquid meal was compared to that of two newly identified duodenal ulcerogens, MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and mepirizole. Emptying rates after acute and chronic treatment with duodenal ulcerogens were obtained. Acute administration of cysteamine, MPTP, or mepirizole significantly delayed gastric emptying of the meal. Chronically treated rats, however, showed either no change or accelerated gastric emptying after cysteamine, MPTP, or mepirizole. Gastric emptying in chronically treated animals was faster in rats that developed the most severe duodenal ulcers. These results indicate that delayed gastric emptying instead of accelerated emptying is a more common abnormality during duodenal ulceration. After the ulcer develops, however, unaltered or accelerated gastric emptying is observed experimentally, thus suggesting that accelerated gastric emptying in duodenal ulcers is an acquired alteration. The implications that these experimental findings may have in the pathogenesis of duodenal ulcer, in light of the clinical data available, are discussed.

Augmentation of cysteamine and mepirizole-induced lesions in the rat duodenum and stomach by histamine or indomethacin

Repeated administration of histamine X 2HCl (40 mg/kg X 4) significantly augmented mepirizole (200 mg/kg) or cysteamine (300 mg/kg)-induced duodenal and gastric lesions in rats within 6 hr. Most of the duodenal lesions were penetrating ulcers and were located over the entire duodenum. Gastric lesions were mainly located in the antrum adjacent to the duodenum. Indomethacin pretreatment did not significantly augment the duodenal lesions induced by mepirizole or cysteamine, but did augment the gastric lesions induced by these compounds.

Decrease in alkaline secretion during duodenal ulceration induced by mepirizole in rats

The mechanisms by which the potent antiinflammatory agent, mepirizole, causes duodenal ulceration were investigated in the rat. After subcutaneous administration of 200 mg/kg of mepirizole, basal gastric acid secretion remained unchanged for 5 h but duodenal alkaline output, reliably measured, decreased significantly (p less than 0.05) within 2 h. The decrease was maximal (-45%) at 3 h and persisted for a total of 6 h. The duodenal alkaline secretion returned to near normal by 24 h. A dose-response study showed that the threshold ulcerogenic dose of mepirizole (30 mg/kg) did not significantly reduce alkaline secretion, whereas higher doses did. Plasma levels of immunoreactivity of gastrin, pancreatic polypeptide, vasoactive intestinal polypeptide, and secretin were not changed at either 6 or 24 h after oral mepirizole. Vasoactive intestinal peptide levels in the duodenal mucosa were increased by 158% at 24 h after administration. Secretin levels in the duodenal mucosa were decreased by greater than 60% at both 6 and 24 h after drug treatment. Intravenous secretin (1 CU/kg X h) had no effect on duodenal alkaline secretion in either saline- (154 mM NaCl) or mepirizole-treated animals. Exogenous 16,16-dimethyl prostaglandin E2 (10 micrograms/kg X h, i.v.) reversed the action of mepirizole on duodenal alkaline secretion. These findings suggest that mepirizole causes a reduction in duodenal alkaline secretion that can be reversed by administration of an exogenous prostaglandin.

Mepirizole-induced duodenal ulcers in rats and their pathogenesis

Duodenal ulcers were produced in rats following either an oral or parenteral administration of 200 mg/kg of mepirizole, a nonsteroidal antiinflammatory agent. Deep ulcers, including perforated ones, were induced in the proximal duodenum with an incidence of over 90%. Mortality due to perforation was less than 5%. The agent also induced several erosions in the antrum. Feeding of animals after the ingestion of mepirizole markedly suppressed the development of both duodenal ulcers and gastric erosions. Antacids, anticholinergic agents, a histamine H2-receptor antagonist and 16-DMPGE2 dose-dependently inhibited mepirizole-induced duodenal ulcers. Gastric erosions were also significantly inhibited by antacids and anticholinergic agents but not by a histamine H2-receptor antagonist and 16-DMPGE2. Intraduodenally administered mepirizole dose-dependently inhibited the gastric secretion in pylorus-ligated rats. This ulcer model should be useful for screening antiulcer agents and for the study of pathogenesis of duodenal ulcers and gastric erosions.

Interaction of indomethacin and aspirin or mepirizole in rats as shown by gastrointestinal ulcerogenic and anti-inflammatory activities

The interaction of indomethacin and aspirin or mepirizole was studied in rats. Concomitant oral administration of aspirin and indomethacin had no significant influence on the gastro-ulcerogenicity of indomethacin alone, but caused significantly less intestinal damage than an identical dose of indomethacin alone. In proportion to the inhibitory activity of intestinal lesions, aspirin also showed the activity that antagonized significantly the shortening of small intestinal length, loss of body weight and delay of charcoal transport in the intestine induced by indomethacin alone. Aspirin tended to reduce also the anti-inflammatory and analgesic effects of indomethacin in combined administration. On the other hand, mepirizole significantly reduced both gastric and intestinal ulcerogenicities by indomethacin alone in concomitant oral administration and inhibited dose-dependently the incidence and severity of those lesions. The inhibitory activity of gastrointestinal lesions by mepirizole was in proportion to the activities that antagonized the shortening of the small intestine, loss of body weight and delay of charcoal transport by indomethacin. Moreover, in contrast to aspirin, mepirizole exerted more potent anti-inflammatory and analgesic effects in combined administration than in the single administration of indomethacin. Therefore, aspirin reduced both the intestinal side effect and the anti-inflammatory effect induced by indomethacin in combination, while the combination of mepirizole reduced the gastrointestinal side effects by indomethacin alone, but seemed to be additive in the anti-inflammatory effect.

Mepirizole, a non-steroidal antiinflammatory compound, its ulcerogenicity and inhibitory action on lesions induced by acidic antiinflammatory agents in the rat stomach

Gastric lesions were produced in rats by the administration for 2 weeks of 300 mg/kg/day of mepirizole, a basic non-steroidal antiinflammatory compound. Although the single administration of 200 mg/kg of mepirizole had no effect, the addition of water-immersion stress for one hour induced lesions not only in the corpus but also in the pyloric antrum. The administration of 250 mg/kg of mefenamic acid, an acidic non-steroidal antiinflammatory compound (insufficient for producing gastric lesions at this dose alone) with the addition of one hour of water-immersion stress induced gastric lesions. The addition of 200 mg/kg of mepirizole reduced the ulcer index from 8.1 to 4.7 in the corpus and from 4 to 0.5 in the pyloric antrum. It is suggested that basic antiinflammatory compounds inhibit gastric lesions induced by combination of acidic antiinflammatory compounds and water-immersion stress.