Protective Effects of α-Tocopherol on ABR Threshold Shift in Rabbits Exposed to Noise and Carbon Monoxide

Noise induced hearing loss (NIHL) is one of the most important occupational disease worldwide. NIHL has been found potentiate by simultaneous carbon monoxide (CO) exposure. Free radicals have been implicated in cochlear damage resulted from the exposure to noise and due to the CO hypoxia. This study examined whether α-tocopherol administration, as a free radical scavenger, causes the attenuation of auditory brainstem response (ABR) threshold shifts resulting from noise exposure and noise plus CO exposure. Forty-two rabbits were divided into seven groups including control, noise + saline, noise + CO + saline, noise + α-tocopherol, noise + CO + α-tocopherol , CO + α-tocopherol and α-tocopherol alone. ABR was assessed before exposure, 1 h and 14 days post exposure. The administration of 50 mg/Kg of α-tocopherol prior, following and post exposure to noise or noise plus CO recovered permanent ABR threshold shift at 1 and 2 KHz almost to the baseline and provided significant attenuation in permanent ABR threshold shift at 4 and 8 KHz in subjects which were exposed to noise but it did not block the potentiating of threshold elevation by CO exposure (extra threshold loss by combined exposure) at 4 and 8 KHz. α-Tocopherol provides protective effect against the hearing loss resulting from noise exposure and simultaneous exposure to noise plus CO.