Influence of intense sound exposure on glutathione synthesis in the cochlea

Previous studies have shown that depletion of endogenous glutathione (GSH) potentiates noise-induced hearing loss (NIHL), whereas replenishment of GSH attenuates NIHL (Yamasoba et al., Brain Res. 784 (1998) 82-90). Since these findings indicate an important role of GSH in protection from NIHL, we assessed the influence of intense sound exposure (broadband noise, 105 dB SPL, 5 h) on GSH and cysteine levels in the guinea pig cochlea using high performance liquid chromatography. GSH levels were significantly increased in the lateral wall 2 and 4 h post-exposure and returned to normal 6 h post- exposure. GSH levels in the sensory epithelium and modiolus did not show significant changes following noise. Cysteine levels were unchanged in any of the cochlear segments. For the cochlea as a whole, intense sound exposure did not significantly change GSH or cysteine levels throughout the 6-h measurement period post-exposure. These results indicate that GSH synthesis is markedly upregulated selectively in the lateral wall by noise exposure, presumably in response to the robust consumption of GSH, as it is utilized in scavenging reactive oxygen species.