[Protective effect of nitric oxide against hydrogen peroxide-induced hearing loss]

Previous research showed that reactive oxygen species (ROS) play an important role in ototoxity. The present research was to investigate whether nitric oxide, an important neurotransmitter in the inner ear, could prevent hydrogen peroxide-induced hearing loss through the nitric oxide/cyclic GMP pathway in guinea pig cochlea. Fifty adult pigmented guinea pigs (250~350 g) of either sex with positive prier reflex were randomly divided into five groups. All of the animals underwent whole cochlear perfusion for two hours. The solution that was perfused into the cochlear of different group was artificial perilymph (AP) for group 1200 micromol/L H2O2 for group 2100 micromol/L L-Arg for group 3, H2O2+L-Arg for group 4 and H2O2+L-Arg+L-NNA for group 5 respectively. Compound action potential (CAP, evoked by click) and cochlear microphonic (CM, evoked by tone burst) were recorded every thirty minutes to show the effects of different reagents on cochlear function. In order to assess cell viability after perfusion, the fluorescent dyes Hoechst that stains all cell nuclei and propidium iodide (PI) that specifically stains nuclei of dead cells, were used. The CAP threshold shifts and CM amplitude decreased after perfusion with H2O2+L-Arg. They were significantly lower than those of H2O2 group. No obvious cell death was noticed after H2O2+L-Arg perfusion, while only 54% of hair cells were alive after H2O2 perfusion. There were no significant differences between the group of H2O2 and that of H2O2+L-Arg+L-NNA group. Our results suggest that nitric oxide may partly be able to protect guinea pigs from hydrogen peroxide-induced hearing loss.