R-PHENYLISOPROPYLADENOSINE ATTENUATES NOISE-INDUCED HEARING-LOSS IN THE CHINCHILLA

Reactive oxygen species, which are cytotoxic to living tissues, are th ought to be partly responsible for noise-induced hearing loss. In this study R-phenylisopropyladenosine (R-PIA), a stable non-hydrolyzable a denosine analogue which has been found effective in upregulating antio xidant enzyme activity levels, was topologically applied to the round window of the right ears of chinchillas, Physiological saline was appl ied to the round window of the left ears (control). The animals were t hen exposed to a 4 kHz octave band noise at 105 dB SPL for 4 h, Inferi or colliculus evoked potential thresholds and distortion product otoac oustic emissions (DPOAE) were measured and hair cell damage was docume nted, The mean threshold shifts immediately after the noise exposure w ere 70-90 dB at frequencies between 2 and 16 kHz. There were no signif icant differences in threshold shifts at this point between the R-PIA- treated and control ears. By 4 days after noise exposure, however, the R-PIA-treated ears showed 20-30 dB more recovery than saline-treated ears at frequencies between 4 and 16 kHz. More importantly, threshold measurements made 20 days after noise exposure showed 10-15 dB less pe rmanent threshold shifts in R-PIA-treated ears. The amplitudes of DPOA E also recovered to a greater extent and outer hair cell losses were l ess severe in the R-PIA-treated ears, The results suggest that adminis tration of R-PIA facilitates the recovery process of the outer hair ce ll after noise exposure.