Paradoxical effects of gastrin releasing peptide on gastrin release and gastric secretion in the rat.

The effects of gastrin releasing peptide (GRP) on gastrin release and gastric secretion were studied in anesthetized rats. Intravenous infusion of GRP (1-16 micrograms/kg/hr) caused a dose-dependent increase in serum gastrin level, however, it had no effect on basal gastric secretion in the lumen-perfused stomach preparation. Furthermore, GRP inhibited gastric secretion stimulated by pentagastrin or histamine dose-dependently, but not by carbachol. Simultaneous infusion of GRP and a beta adrenergic blocking agent, propranolol, an inhibitor of somatostatin release, did not alter the inhibitory effect of GRP on pentagastrin-stimulated gastric secretion. These results suggest that the inhibitory effect of GRP on gastric secretion in a stimulated condition is mediated via peptide hormones coreleased by GRP, and not via beta-adrenergic pathways.