Non-competitive Pharmacological Antagonism at the Rabbit B(1) Receptor

The B(1) receptor for kinins, stimulated by kinin metabolites without the C-terminal Arg residue (e.g., des-Arg(9)-bradykinin (BK) and Lys-des-Arg(9)-BK), is an increasingly recognized molecular target for the development of analgesic and anti-inflammatory drugs. Recently developed antagonists of this receptor were compared to a conventional antagonist, Ac-Lys-[Leu(8)]-des-Arg(9)-BK, in pharmacological assays based on the rabbit B(1) receptor. B-9858 (Lys-Lys-[Hyp(3), Igl(5), D-Igl(7), Oic(8)]des-Arg(9)-BK) and three other analogues possessing the alpha-2-indanylglycine(5) (Igl(5)) residue (order of potency B-9858 approximately B-10146>B-10148>B-10050) were partially insurmountable antagonists of des-Arg(9)-BK in the contractility assay based on rabbit aortic rings. B-9858-induced depression of the maximal effect was more pronounced in tissues treated with the protein synthesis inhibitor cycloheximide to block the spontaneous increase of response attributed to the post-isolation formation of B(1) receptors, and only partly reversible on washing. By comparison, Ac-Lys-[Leu(8)]des-Arg(9)-BK was a surmountable antagonist (pA(2) 7. 5), even in cycloheximide-treated tissues. B-9958 (Lys-[Hyp(3), CpG(5), D-Tic(7), CpG(8)]des-Arg(9)-BK) was also surmountable (pA(2) 8.5). The binding of [(3)H]-Lys-des-Arg(9)-BK to recombinant rabbit B(1) receptors expressed in COS-1 cells was influenced by two of the antagonists: while Ac-Lys-[Leu(8)]des-Arg(9)-BK competed for the radioligand binding without affecting the B(max), B-9858 decreased the B(max) in a time-dependent and washout-resistant manner. B-9858 and analogues possessing Igl(5) are the first reported non-competitive, non-equilibrium antagonists of the kinin B(1) receptor.