The Gastrin/cholecystokinin-B Receptor Antagonist L-365,260 Reduces Basal Acid Secretion and Prevents Gastrointestinal Damage Induced by Aspirin, Ethanol and Cysteamine in the Rat

L-365,260, a nonpeptide antagonist of gastrin/CCK-B receptors, was evaluated in receptor binding, antisecretory and gastrointestinal damage assays. L-365,260 binds potently and stereo-selectively to gastrin and CCK-B sites in guinea pig tissue. In contrast, L-365,260 binds to the isolated canine parietal cell gastrin receptor weakly, and without stereoselectivity. In the pylorus-ligated rat, low doses of L-365,260, given i.v., attenuated pentagastrin-stimulated acid secretion, whereas higher doses were required to inhibit both histamine-stimulated and basal acid secretion. In an aspirin-induced gastric damage model, L-365,260 was 2.4-fold less potent than the standard histamine H2 antagonist cimetidine in preventing gastric damage when given i.v., and was 8.3-fold less potent than cimetidine when given p.o. Moreover, the ED50 value for L-365,260, given i.v., in prevention of aspirin-induced gastric damage (11.5 mg/kg) agreed well with its ED50 value for inhibition of basal acid secretion (12.6 mg/kg). At doses as great as 100 mg/kg p.o., neither L-365,260 nor cimetidine had an effect on ethanol-induced gastric damage. L-365,260, although p.o. less bioavailable relative to cimetidine in the aspirin gastric damage model, was as potent as cimetidine in the prevention of cysteamine-induced duodenal ulcers in the rat. We conclude that the gastrin/CCK-B receptor antagonist L-365,260, at doses supramaximal for the inhibition of pentagastrin-stimulated secretory responses in vivo, inhibits gastrointestinal damage in models of peptic ulcer disease by an antisecretory mechanism of action.