Oxygen radicals in capsaicin-induced bronchoconstriction

The role of oxygen radicals in capsaicin-induced bronchoconstriction was investigated using scavengers of the radicals. A total of 48 guinea pigs weighing 293 +/- 7 g were employed in this study, which consisted of two phases. In phase 1, 35 anesthetized paralyzed animals were divided into five groups: group 1A, control (n = 6); group 1B, chronic dimethylthiourea (DMTU, n = 12); group 1C, acute DMTU (n = 6); group 1D, superoxide dismutase (n = 4); and group 1E, catalase (n = 7). All animals were injected with capsaicin (16 micrograms/kg iv), and changes in respiratory compliance and maximal expiratory flow rate were used as indicators of bronchoconstriction. The capsaicin injection caused a marked airway spasm that was significantly ameliorated by chronic DMTU pretreatment, but no amelioration was noted with the other treatments. An additional study for group 1C was performed using a double dose of DMTU. Again no amelioration was found. In phase 2, 13 animals were divided into two groups: group 2A, substance P (SP, n = 7) and group 2B, chronic DMTU + SP (n = 6). There was no significant difference in SP-induced bronchoconstriction between animals in these two groups. These data suggest that capsaicin-induced airway constriction is modulated by oxygen radicals which may augment mainly on the biosynthesis and/or axonal transport of tachykinins.