Antagonist binding reveals two heterogenous B2 bradykinin receptors in rat myometrial membranes

In rat myometrial membranes, two bradykinin binding sites with K1 values of 18 pM and 5.6 nM were identified. Three potent bradykinin antagonists were tested for their ability to compete for [3H]bradykinin binding. Two of them, D-Arg[Hyp3,Thi5.8,D-Phe7]bradykinin and [Hyp3,Thi5.8,D-Phe7]bradykinin, also bound to both the high- (KH) and the low-affinity (KL) site whereas [Thi5.8,D-Phe7]bradykinin identified only the low-affinity bradykinin receptor. There is a close correlation between the antagonistic potencies and the KL site affinities.