Biphasic contraction of isolated guinea pig tracheal chains by superoxide radical

The effects of free radicals on the isolated tracheal chains from guinea pigs were examined in in vitro experiments. When isolated tracheal chains were exposed to the hypoxanthine plus xanthine oxidase system, biphasic contraction was observed. This contraction was prevented by adding superoxide dismutase. However, catalase, mannitol, and indomethacin were ineffective in preventing the contraction due to free radicals. The uric acid plus uricase system had no effect on tracheal muscle tension. These results suggest that superoxide radical contracts tracheal chains.