Histamine H2-receptor antagonist action of ebrotidine. Effects on gastric acid secretion, gastrin levels and NSAID-induced gastrotoxicity in the rat.

The antagonism of histamine H2-receptors by ebrotidine (N-[(E)-[[2-[[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl]thio]ethyl ] amino]methylene]-4-bromo-benzenesulfonamide, CAS 100981-43-9, FI-3542) was assessed on isolated guinea-pig right atrium. The dose-response curves obtained by histamine on the positive chronotropic effect in guinea-pig atrium were displaced to the right in parallel depending on the concentration of ebrotidine and ranitidine without change in the maximum response with pA2 values of 7.12 and 7.26, respectively. The slope of the regression line of log (DR-1) against log ebrotidine concentration was not significantly different from unity: 0.96 (95% confidence limits: 0.89-1.03). These results indicate that ebrotidine is a competitive H2-receptor antagonist. Following intravenous administration to rats, ebrotidine inhibited histamine- and pentagastrin-stimulated acid secretion in a dose-dependent manner, ED50 being 0.21 and 0.44 mg/kg, respectively. After oral administration to fasting rats 3 h before their sacrifice, ebrotidine decreased the total acid contents of the stomach in a dose-dependent manner, ED50 being 7.5 mg/kg. After a single dose of 100 mg/kg in fasting rats, ebrotidine increased significantly serum gastrin levels within 2 and 5 h after administration, but 8 h after administration serum gastrin levels returned to normal values. In contrast, ranitidine at a single oral dose of 100 mg/kg increased serum gastrin levels more markedly within 2 and 5 h after administration, while after 8 h, this increase still persisted although without significant differences with respect to control, and after 24 h levels returned to normal values. Both ebrotidine and ranitidine were administered orally at a dose of 100 mg/kg for 26 days showing significant increments in plasma gastrin levels 5 h after administration. Such increments were not so marked after ebrotidine and normal values were attained at 24 h after administration. The results obtained after repeated oral administration for 15 days of ebrotidine and ranitidine at the doses of 15 and 50 mg/kg demonstrated that ebrotidine did not increase significantly serum gastrin levels with respect to control 2 h after administration, and no dose-related effect was observed. In contrast, ranitidine increased serum gastrin levels significantly and in a dose-dependent manner with respect to control group. ED50 values of ebrotidine obtained in the experiments on the prevention of NSAID-induced gastrotoxicity in the rat were 12.2, 12.5, 11.5 and 9.8 mg/kg against diclofenac, ketoprofen, indometacin and naproxen, respectively. ED50 values of ranitidine were of the same order: 20.6, 13.9, > 50 and 15.1 mg/kg.

Effect of ebrotidine on ethanol-induced gastric mucosal damage in the rat. Comparative study with other H2-receptor antagonists.

Ebrotidine (N-[(E)-[[2-[[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl]thio]ethyl ] amino]methylene]-4-bromo-benzenesulfonamide, CAS 100981-43-9, FI-3542) is a novel H2-receptor antagonist with additional gastroprotective effect. The gastroprotective effect of oral doses of ebrotidine against ethanol-induced mucosal damage in female rats was compared with the effect of cimetidine, ranitidine and famotidine. Macroscopically, ebrotidine showed dose-dependent inhibition of the lesion, with significant differences from that of controls at doses of > or = 12.50 mg/kg (ED50 was 26.54 mg/kg). None of the other drugs tested showed gastroprotective effect under the same conditions. The histopathological study revealed significant reduction in the number of deep and superficial ulcers in ebrotidine-treated animals. The gastroprotective effect of ebrotidine is patent even in the presence of indometacin suggesting that prostaglandins play a rather negligible role in gastroprotective action. These results suggest that ebrotidine may be more useful than the classically known H2-antagonists in the treatment of peptic ulcers.

Study on the increment of the amount of gastric mucus in rats after repeated-dose administration of ebrotidine.

Ebrotidine (N-[(E)-[[2-[[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl]thio]ethyl ] amino]methylene]-4-bromo-benzenesulfonamide, CAS 100981-43-9, FI-3542) is a novel H2-receptor antagonist that also exhibits a potent gastroprotective action against ethanol damage. This study was designed to ascertain under physiological conditions the effect of ebrotidine on the secretion of gastric mucus, probably the main component of the mucosal barrier. Two groups of 20 rats each were given a daily oral dose of 10 or 35 mg/kg ebrotidine, respectively, for 17 days. A third group of 20 rats was used as a control. Once the administration period had concluded, the animals were killed and their stomachs were removed and processed by the periodic acid-Schiff (PAS) histochemical method, selective for mucopolysaccharides. PAS-positive areas exhibited a characteristic carmine colour, allowing morphometric study by computerized image analysis. All the histological sections studied were from the same region of the stomach. A significant increase in the PAS-positive area corresponding to glandular mucus was found in all treated groups. This action is consistent with an increased secretion of mucopolysaccharides and represents one of the main mechanisms of the cytoprotective action of ebrotidine.

Involvement of endogenous nitric oxide and sulfhydryl compounds in ebrotidine-induced gastroprotection.

The role of endogenous nitric oxide and sulfhydryl compounds in the prevention by ebrotidine (N-[(E)- [[2-[[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl]thio]ethyl]amino] methylene]-4-bromo-benzenesulfonamide, CAS 100981-43-9, FI-3542) (100 mg/kg i.g.) of ethanol-induced gastric damage in rats was demonstrated. When the animals were pretreated with N-nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthase, at the dose of 10 mg/kg i.v., the mucosal lesions were aggravated and the gastroprotective action of ebrotidine decreased from 85% to 24%. This decrease in ebrotidine protection was antagonized by L-arginine (200 mg/kg i.v.), the lesion inhibition rate being 69%. D-arginine (200 mg/kg i.v.) was ineffective and the inhibition afforded by ebrotidine was only 14%. Pretreatment with N-ethylmaleimide, a sulfhydryl blocker, at the dose of 50 mg/kg s.c., increased the mucosal lesion induced by ethanol, and the gastroprotective action of ebrotidine decreased from 75% to 9%. These results suggest that endogenous nitric oxide and sulfhydryl compounds play a crucial role in the gastroprotective activity of ebrotidine.