Superoxide dismutase in in vitro cultures of middle ear fibroblasts from the rabbit.

The present study was undertaken to establish whether intra- and extracellular concentrations of the antioxidative enzyme superoxide dismutase (SOD) in cultures of rabbit middle ear and skin fibroblasts were affected by increasing normal oxygen tensions from 7% to 21% and cause structural damage. The DNA amount was measured fluorometrically and intra- and extracellular concentrations of SOD were determined spectrophotometrically by the inhibition of formazan absorbance. Results demonstrated that SOD was located primarily intracellularly in middle ear fibroblasts and that exposure to atmospheric air gave rise to a significant increase in the SOD concentration from the 6th day following altered oxygen tension (P < 0.0044). Extracellular SOD was sparse in cultures at 7% oxygen whereas atmospheric air induced a significant increase in formazan absorbance from 5% to 60% (P < 0.0163). Inhibition studies indicated that the latter was partly the result of compounds with reducing capabilities similar to superoxide anions. These findings suggest that exposure of middle ear fibroblasts to atmospheric air may involve generation of oxygen-derived free radicals in vitro as well as in vivo but the complexity and significance of these changes need further investigation.