Nitric oxide synthase inhibitor reduces noise-induced cochlear damage in guinea pigs

CONCLUSION: The results obtained in this study indicate that NG-nitro-L-arginine methyl ester (L-NAME) protects cochlear damage from acoustic trauma through reducing the production of nitric oxide (NO). OBJECTIVES: This study aimed to explore whether NO synthase inhibitor L-NAME could reduce cochlear damage in acoustic trauma. MATERIALS AND METHODS: Seventy guinea pigs (300-350g) were divided randomly into four groups (n=20 in groups I, III, and IV; n=10 in group II). Two days consecutively and 30min before noise exposure (4kHz octave band, 115dB SPL 5h), subjects received an injection of 5ml saline/kg (groups I and III) or 10mg/kg L-NAME (groups II and IV). Sham-exposed guinea pigs were listed as groups I and II. Protection was assessed physiologically by the change in auditory brainstem response (ABR) threshold and histologically by survival of outer hair cells (OHCs). NO level of cochlear tissue was assayed 3days after noise exposure. RESULTS: Group III showed significantly greater OHC loss, threshold shifts and NO level compared with group I and group IV. Compared with group III, noise-induced elevation in NO level in the cochlea was significantly attenuated by L-NAME (p<0.001).