Effect of hydrogen peroxide on guinea‐pig tracheal smooth muscle <i>in vitro</i>: role of cyclo‐oxygenase and airway epithelium

Hydrogen peroxide (H 2 O 2 ) (0.1 μ m ‐3 mM) induced variable contractions of guinea‐pig isolated trachea which were attenuated by catalase (100 u ml −1 ) and mannitol (15 mM) suggesting that contractions were induced by H 2 O 2 and/or the hydroxyl anion. Epithelial removal potentiated contractile responses of tracheal preparations to H 2 O 2 with a leftward shift of the concentration‐response curve and an increase in the maximal response. Indomethacin (3 μ m ) inhibited contractions to H 2 O 2 of intact preparations and preparations without epithelium suggesting that contractions may be mediated by cyclo‐oxygenase products. Intact preparations (but not preparations without epithelium) contracted in response to high concentrations (&gt;0.1 mM) of H 2 O 2 in the presence of indomethacin suggesting that other excitatory factor(s) released by the epithelium may induce contraction. Preincubation of intact tracheal preparations with H 2 O 2 (1 mM) for 1 h had no effect on responses to histamine or isoprenaline. These results suggest that hydrogen peroxide generated during the inflammatory process may play a role in bronchoconstriction.