Effects of kinins on isolated stomachs of control and transgenic knockout B2 receptor mice

The aim of this study was to investigate the pharmacological profile of the kinin B-1 and B-2 receptors in isolated stomachs from wild-type control and B-2 receptor knockout mice. Isometric contractions evoked by bradykinin (BK) (9 nM) and desArg(9)BK (28 nM) were shown to be different. The contraction induced by desArg(9)BK had a longer duration than that evoked by BK and increased during incubation in vitro in stomachs of wild-type controls, while in the transgenic B-2 receptor knockout mice, the contractions evoked by desArg(9)BK and BK were similar and followed the B-1 receptor agonist pattern. BK but not the carboxypeptidase-resistant analog, [Phe(8) Psi(CH2-NH)Arg(9)]BK, was found to be active in the stomach of B-2 receptor knockout mice. BK-induced contractions were prevented by mergetpa (a carboxypeptidase M inhibitor) (10 mu M) and by a the B-1 receptor antagonist, AcLys[D beta Nal(7),Ile(8)]desArg(9)BK (R 715) (0.88 mu M), while not being influenced by the B-2 receptor antagonist HOE 140 (0.38 mu M). BK and [Phe(8) Psi(CH2-NH)Arg(9)]BK were potent contractants of the wild-type mice stomach and their effects were not influenced by mergetpa or by the B-1 receptor antagonist: they were reduced by HOE 140. After incubation in vitro for 3-4 hours, the tissues were treated with HOE 140 (4 mu M) and FR-173657 (17 mu M) to eliminate B-2 receptor function. In these tissues, BK evoked a B-1-like contraction which was inhibited by mergetpa (10 mu M) and antagonized by R 715 (8 mu M). The results indicate that BK acts primarily on B-2 receptors. However, after intramural conversion to desArg(9)BK, activation of B-1 receptors of the mice stomach occurs. In the tissues of B-2 receptor knockout mice, BK behaves as a pure B-1 receptor agonist while in stomachs of control animals, the B-2 receptor contribution is overwhelming. After complete blockade of the B-2 receptor, BK is able to evoke B-1-mediated responses similar to those observed in tissues of B-2 receptor knockout mice. It is concluded that the disruption of the B-2 receptor gene eliminates the B-2 receptor without influencing the B-1 receptor system.