Effect of gastrin-releasing peptide analogues on gastrin and somatostatin release from isolated rat stomach

A differential biological potency of bombesin (BBS), compared with its mammalian counterpart gastrin-releasing peptide (GRP), has been reported in several biological systems in rodents. In the present study we have examined the relative potency of BBS, GRP-(1-27) (GRP-L), and GRP-(14-27) (GRP-S) on the release of gastrin and somatostatin (SRIF) from the isolated perfused rat stomachs. Male rats were fasted overnight and the stomachs perfused via the celiac artery. Increasing doses of BBS, GRP-L, and GRP-S were perfused for 15 min each and the effluent collected for measurement of gastrin and SRIF. The release of gastrin and SRIF in response to the GRP analogues was biphasic, with a peak increase occurring within the first 5 min, followed by a sustained increased secretion. The release of gastrin in response to 10^-10-10^-9 M concentrations of the peptides was strongest with GRP-S (1.5-2.0 times higher than that released by BBS and GRP-L), although at higher concentrations (10^-8 M), the response to all three analogues was similar. The release of SRIF, on the other hand, was significantly higher in the presence of BBS compared with that in response to GRP-S, while GRP-L was ineffective. These studies indicate that the biological potency of BBS compared with its mammalian counterpart, GRP, is different on the two cell populations [gastrin (G) and SRIF (D)].