Effects of pirenzepine on omeprazole-induced gastrin gene expression in rat antral tissues.

Pirenzepine has inhibitory effects on gastrin secretion both in vivo and in vitro. The aim of this study was to determine the mechanism responsible for the suppression of omeprazole-induced hypergastrinemia that occurs with pirenzepine treatment. The effects were measured in rats treated with oral omeprazole plus intraperitoneal pirenzepine or saline once daily for seven days in the antrum. The serum gastrin level increased significantly by more than sixfold with omeprazole treatment; additional treatment with pirenzepine suppressed this increase by 48%. Pirenzepine treatment did not change the level of gastrin mRNA but significantly increased the level of somatostatin mRNA. Combination treatment with omeprazole plus pirenzepine significantly decreased the gastrin mRNA level to half and significantly increased the somatostatin mRNA level up to 1.4-fold of the levels achieved with omeprazole treatment alone. These results suggest that the stimulatory effect of omeprazole on gastrin synthesis is partially blocked by pirenzepine via mediation of somatostatin synthesis in the antrum.