Bradykinin, applied locally to the airways, is a weak bronchoconstrictor agent in guinea pigs in vivo and it may cause constriction or dilatation of guinea pig airways smooth muscle in vitro. We examined the motor effect of bradykinin perfused through the lumen of isolated guinea pig tracheal tubes with or without nitric oxide (NO) synthase inhibitors. In the presence of NG-nitro-D-arginine methyl ester (D-NAME) or NG-monomethyl-D-arginine (D-NMMA) intraluminal bradykinin caused a moderate concentration-dependent relaxation. In contrast, in the presence of NG-nitro-L-arginine methyl ester (L-NAME) or NG-monomethyl-L-arginine (L-NMMA) tracheas developed a sustained increase in tone, and bradykinin caused a marked, concentration-dependent contraction, both effects being reversible by pretreatment with L-arginine, but not with D-arginine. The ability of bradykinin to relax (in the presence of D-NAME) or contract (in the presence of L-NAME) guinea pig tracheal tubes was not affected by indomethacin. Bradykinin contracted epithelium-denuded tracheas in the presence of either L-NAME or D-NAME. Both contraction and relaxation by bradykinin were blocked by the kinin B2 receptor antagonist, HOE 140. Baseline production of guanosine 3',5'-cyclic monophosphate (cyclic GMP) in strips of guinea pig trachealis in vitro was markedly reduced by L-NAME, but not by D-NAME. Bradykinin increased baseline cyclic GMP concentration. These results indicate that bradykinin releases NO or a NO-related molecule, which, possibly by increasing cyclic GMP concentrations, mediates relaxation and opposes contraction induced by bradykinin itself, and further, that bradykinin releases NO from the tracheal epithelium.