Indirect evidence using nitric oxide (NO) synthase (NOS) inhibitors suggests that in guinea-pig airways bradykinin releases bronchoprotective NO. In this study, using a recently developed electrochemical method of NO measurement based on a porphyrinic microsensor, we investigated whether bradykinin releases NO from guinea-pig airways and whether the epithelium is the main source of NO. Further, the Ca(2+)-dependence of bradykinin-induced NO release was assessed stimulating airway preparations with bradykinin in Ca(2+)-free conditions. We also studied the immunohistochemical distribution of the Ca(2+)- dependent constitutive isoforms of NOS (constitutive NOS [cNOS]: neuronal and endothelial [ecNOS]) in our preparations. The porphyrinic microsensor was placed in the bathing fluid onto the mucosal surface of tracheal or main bronchial segments. Addition of bradykinin vehicle (0.9% saline) did not cause any detectable change of the baseline signal. Addition of bradykinin caused an upward shift of the baseline that reached a maximum within 1 to 2 s. The amplitude of the response to bradykinin was concentration-dependent between the range 1 nM to 10 microM, with a maximum effect at 10 microM. Bradykinin-induced NO release was higher in tracheal than in main bronchial segments. The selective bradykinin B(2) receptor antagonist D-Arg(0)-[Hyp(3), Thi(5), D-Tic(7), Oic(8)]bradykinin (1 microM) inhibited NO release induced by a submaximum concentration of bradykinin (1 microM). The ability of bradykinin to release NO was markedly reduced in epithelium-denuded segments, and abolished in Ca(2+)-free conditions and after pretreatment with N(G)-monomethyl-L-arginine (100 microM), but not with N(G)-monomethyl-D-arginine. Both cNOS isoforms were present in trachea and main bronchi, ecNOS being the predominant isoform in the epithelium. The study shows that bradykinin via B(2) receptor activation caused a rapid and Ca(2+)-dependent release of NO, mainly, but not exclusively, derived from the epithelium. It also shows that both cNOS isoforms may be involved in bradykinin-evoked NO release.