The B(1) receptor for
kinins is selectively stimulated by
bradykinin-related fragments lacking the C-terminal
arginine, des-arginine(9)-bradykinin (des-Arg(9)-BK), and
Lys-des-Arg(9)-BK. The latter
peptide is the optimal agonist at the human and rabbit receptor. The B(1) receptor is inducible as a function of inflammatory conditions in the vasculature. We studied the effect of endogenously expressed
peptidases on the potency of
ligands of this receptor in an established bioassay, the rabbit aorta contractility. The potency measured for agonists (EC(50)) or antagonists (pA(2) scale) in this assay was compared with the affinity of each agent determined using [(3)H]Lys-des-Arg(9)-BK binding competition in cultured aortic smooth muscle cells and with the competition K(i) for the hydrolysis of the
aminopeptidase chromogenic substrate L-Ala-p-nitroanilide by smooth muscle cell membranes. The contractile potency of the agonist
Lys-des-Arg(9)-BK is decreased by in situ metabolism, and
aminopeptidase N mediates most of the distortion (inhibited by
amastatin but not efficiently by
puromycin). At the other end of the spectrum, the fully protected agonist Sar-[D-Phe(8)]des-Arg(9)-BK is not significantly potentiated by
peptidase inhibitors. A similar distortion of apparent potency was observed for some
peptide antagonists used in the contractility assay, B-10350 (
Lys-Lys-[Hyp(3), Igl(5), d-
Tic(7), CpG(8)]des-Arg(9)-BK) and Lys-[Leu(8)]des-Arg(9)-BK being intensely potentiated by
amastatin treatment and effective L-Ala-p-nitroanilide competitors. N-Protected
peptide antagonists or a nonpeptide antagonist of the B(1) receptor were not potentiated by
amastatin. The coexpression of
aminopeptidase N and the
kinin B(1) receptor in rabbit arterial tissue is of interest for the inactivation of the high-affinity agonist
Lys-des-Arg(9)-BK and for the design of hydrosoluble antagonist drugs.