Characterization of the receptors responsible for the diphasic effect of bradykinin in rat duodenum.

The response of the rat duodenum to bradykinin (BK) consists of relaxant and contractile components, which have been attributed to different receptor types. To characterize the receptors responsible for this diphasic response we studied the effects of BK analogues known to act on B1 or B2 receptors in other systems. DesArg9-Leu8-BK and Thi5,8DPhe7-BK presented only relaxant and only contractile effects, respectively, whereas DArg0Hyp3Thi5,8DPhe7-BK was a potent antagonist of the relaxation (but not of the contraction) induced by BK. Our results show that the relaxant and contractile components of the rat duodenum's response to BK are due to B2 and B1 receptor subtypes, respectively.