Evidence of a bradykinin B1 receptor in human ileum: pharmacological comparison to the rabbit aorta B1 receptor.

Bradykinin B1 receptors have been identified in a limited number of human tissues and may have implications in pathological states of chronic inflammation. In the present study, longitudinal strips of postmortem human ileum displayed a strong contractile response to the B2 receptor agonist, bradykinin (EC50 = 7.0 nM). Noninduced ileum strips contracted only to high concentrations (1 and 10 microM) of the B1 receptor agonists, des-Arg9-BK and Lys0des-Arg9-BK. After incubation overnight at 37 degrees C the potency of des-Arg9-BK and Lys0des-Arg9-BK dramatically increased (EC50 = 183 and 13.2 nM, respectively). The increase in B1 agonist potency was inhibited by the protein synthesis inhibitor, puromycin. Similarly, rabbit aorta strips displayed a protein synthesis-dependent induction of the B1 agonist response. Incubated human ileum and rabbit aorta exhibited a reproducible response to des-Arg9-BK over time, whereas responses to Lys0des-Arg9-BK were not reproducible, having reduced potency and magnitude over time. Lys0[Leu8]des-Arg9-BK was a more potent antagonist at the B1 receptor in both tissues compared with [Leu8]des-Arg9-BK. The B2 antagonist, HOE-140, was a very weak inhibitor of the B1 response in human ileum and inactive in rabbit aorta. In conclusion, incubation of isolated human ileum overnight induces expression of a B1 receptor through a mechanism that depends on de novo protein synthesis. The potency profile of selected B1 agonists and antagonists indicates pharmacological similarities between the inducible B1 receptor in both the human ileum and rabbit aorta.