Hydroxyl radical formation in the perilymph of asphyxic guinea pig

To elucidate the role of hydroxyl radical (.OH) species in the generation mechanism of the cochlear pathology induced by transient asphyxia and subsequent re-ventilation, the concentrations of 2,3-hydroxybenzoic acid (DHBA) and 2,5-DHBA, major products arising from the attack of .OH upon salicylate, were measured in the perilymph of the guinea pig by the high performance liquid chromatography-electrochemical/UV method. The mean value of 2, 3-DHBA concentration in the perilymph significantly increased from the pre-asphyxic level (6.4 microM) to 7.6 microM and 8.8 microM during asphyxia of 3 min duration and at 5 min after the onset of re-ventilation, respectively. The 2,5-DHBA concentration was 7.9 microM before asphyxia, and also significantly increased to 11.5 microM and 16.2 microM during and after asphyxia, respectively. These results strongly indicated that .OH was generated in the perilymph of the asphyxic and re-ventilated guinea pig cochlea, and the significance of this increased .OH in generating anoxia and re-perfusion injury is discussed with respect to iron and oxygen-derived free radicals.