Involvement of bradykinin B1 and B2 receptors in relaxation of mouse isolated trachea

1. The aim of the present study was to investigate the effects of bradykinin and [des-Arg⁹]-bradykinin and their relaxant mechanisms in the mouse isolated trachea.
2. In the resting tracheal preparations with intact epithelium, bradykinin and [des-Arg⁹]-bradykinin (each drug, 0.01–10 μM) induced neither contraction nor relaxation. In contrast, bradykinin (0.01–10 μM) induced concentration-dependent relaxation when the tracheal preparations were precontracted with methacholine (1 μM). The relaxation induced by bradykinin was inhibited by the B₂ receptor antagonist, D-Arg⁰-[Hyp³,Thi⁵,D-Tic⁷,Oic⁸]-bradykinin (Hoe 140, 0.01–1 μM) in a concentration-dependent manner whereas the B₁ receptor antagonist, [des-Arg⁹,Leu⁸]-bradykinin (0.01–1 μM), had no inhibitory effect on bradykinin-induced relaxation. [des-Arg⁹]-bradykinin (0.01–10 μM) also caused concentration-dependent relaxation after precontraction with methacholine. The relaxation induced by [des-Arg⁹]-bradykinin was concentration-dependently inhibited by the B₁ receptor antagonist, [des-Arg⁹,Leu⁸]-bradykinin (0.01–1 μM), whereas the B₂ receptor antagonist, Hoe 140 (0.01–1 μM) was without effect.
3. In the presence of the cyclo-oxygenase inhibitor, indomethacin (0.01–1 μM), the relaxations induced by bradykinin and [des-Arg⁹]-bradykinin were inhibited concentration-dependently.
4. Two nitric oxide (NO) biosynthesis inhibitors N^G-nitro-L-arginine methyl ester (L-NAME, 100 μM) and N^G-nitro-L-arginine (L-NOARG, 100 μM) had no inhibitory effects on the relaxations induced by bradykinin and [des-Arg⁹]-bradykinin. Neither did the selective inhibitor of the soluble guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 μM) inhibit the relaxations induced by bradykinin and [des-Arg⁹]-bradykinin.
5. Prostaglandin E₂ (PGE₂, 0.01–33 μM) caused concentration-dependent relaxation of the tracheal preparations precontracted with methacholine. Indomethacin (1 μM) and ODQ (10 μM) exerted no inhibitory effects on the relaxation induced by PGE₂.
6. The NO-donor, sodium nitroprusside (SNP; 0.01–100 μM) also caused concentration-dependent relaxation of the tracheal preparations precontracted with methacholine. ODQ (0.1–1 μM) concentration-dependently inhibited the relaxation induced by SNP.
7. These data demonstrate that bradykinin and [des-Arg⁹]-bradykinin relax the mouse trachea precontracted with methacholine by the activation of bradykinin B₂-receptors and B₁-receptors, respectively. The stimulation of bradykinin receptors induces activation of the cyclo-oxygenase pathway, leading to the production of relaxing prostaglandins. The NO pathway is not involved in the bradykinin-induced relaxation. The relaxation caused by NO-donors in the mouse trachea is likely to be mediated via activation of soluble guanylate cyclase.