The responses of the rat isolated stomach fundus to bradykinin (BK) and des-Arg9-BK (DA-BK) have been examined. In rat isolated stomach fundus pre-contracted with BaCl2 (0.5-1 mM), BK caused concentration-dependent biphasic responses characterized by relaxation followed by contraction. DA-BK also caused marked relaxations, but, unlike BK, induced only small contractions. Removal of the mucosal layer initially abolished the relaxant responses to BK and both responses to DA-BK without affecting BK-induced contractions, but repeated challenges with BK or DA-BK revealed a time-dependent reappearance of the relaxant response, suggesting "de novo" synthesis of BK receptors. Pretreatment of rat stomach fundus with tetrodotoxin (1 microM), atropine (1 microM), captopril (3 microM), prazosin (1 microM) or glibenclamide (1 microM) did not significantly modify the biphasic responses to BK (300 nM). The biphasic responses to DA-BK were antagonized selectively by the B1 receptor antagonist des-Arg9-[Leu 8]-BK (DAL-BK) (1 microM). In contrast, the biphasic responses to BK were unaffected by DAL-BK or by several selective peptide antagonists of B2 receptors including NPC 431 (Thi5,8, D-Phe7)-BK, NPC 349 (D-Arg Hyp3,Thi5,8,D-Phe7)-BK, NPC 567 (D-Arg-Hyp3,D-Phe7)-BK and NPC 361 (D-Phe7)-BK (3 to 10 microM). These results are consistent with the view that the biphasic responses of the rat isolated stomach fundus to BK appear to be mediated by a novel BK receptor which is insensitive to blockade by B1 and B2 selective BK receptor antagonists.