GASTRIC EFFECTS OF THE CCK-B GASTRIN RECEPTOR-LIGAND CI-988 IN CYNOMOLGUS MONKEYS

We have previously demonstrated that the CCK-B/gastrin receptor ligand CI-988 induces gastric gland degeneration and atrophy in cynomolgus m onkeys, an effect consistent with gastrin receptor antagonism and inhi bition of gastrin's trophic effects on oxyntic mucosa. However, gastri n receptor ligands of the dipeptoid chemical series to which CI-988 be longs have been reported to act as agonists or antagonists towards gas trin-related events, depending on the animal model and the functional endpoint examined. To investigate further these apparently conflicting data, basal gastric acid secretion was monitored acutely in conscious monkeys given CI-988 orally at 10 mg/kg or intravenously at 0.01 mu m ol/kg/hr and histological changes in gastric mucosa were evaluated in monkeys given CI-988 orally at 5, 25 or 75 mg/kg/day for 4 weeks. Dege neration and atrophy of gastric glands occurred at 25 and 75 mg/kg wit h statistically significant decrements in gastric mucosal height at 75 mg/kg. In addition, CI-988 stimulated gastric acid secretion when giv en either orally or intravenously. Co-administration of the structural ly unrelated CCK-B/gastrin antagonist L-365 260 completely blocked CI- 988-stimulated acid secretion, confirming that CI-988's agonist effect on acid secretion is mediated by the gastrin receptor. Assuming that gastric mucosal degeneration is the result of inhibition of gastrin's trophic activity, CI-988 appears to induce paradoxical agonist and ant agonist gastrin-receptor mediated effects. (C) 1998 Elsevier Science L td. All rights reserved.