GRP-PREFERRING BOMBESIN RECEPTOR SUBTYPE MEDIATES CONTRACTILE ACTIVITY IN CAT TERMINAL ILEUM

Mammalian bombesin-like peptides, such as gastrin-releasing peptide an d neuromedin B, are known to increase motility of different segments i n the gut. The present study was carried out to identify the receptor subtype mediating these contractions of ileal longitudinal muscles in cats, in vitro. Both gastrin-releasing peptide (GRP) and neuromedin B (NMB) evoked concentration-dependent contractions of the strips. [D-Ph e(6)]Bombesin(6-13)-methyl-ester, a highly selective GRP-preferring re ceptor antagonist, competitively inhibited contractions induced by eit her agonist. On the other hand, D-Nal-Cys-Tyr-D-Trp-Lys-Val-Cys-Nal-NH 2, a selective NMB receptor antagonist, did not affect the actions of either gastrin-releasing peptide or neuromedin B. Our results suggest that bombesin-like peptides contract cat terminal ileum via activating GRP receptors.