THE PROTECTIVE EFFECTS OF ALLOPURINOL AND SUPEROXIDE-DISMUTASE ON NOISE-INDUCED COCHLEAR DAMAGE

Several studies have demonstrated that noise exposure may result in lo cal vasoconstriction of cochlear vessels. The subsequent decrease in c ochlear blood flow may lead to hypoxia and predispose to the formation of free oxygen radicals (FORs). If hypoxia occurs in response to nois e exposure, then drugs that scavenge or block the formation of FORs sh ould protect the cochlea from damage resulting from hypoxic or ischemi c events as well as noise trauma. Rats were exposed to 60 hours of con tinuous brood-band noise (90 dB SPL) and treated with superoxide dismu tase-polyethylene glycol (SOD-PEG), allopurinol, or a control vehicle. Exposure to noise resulted in significant threshold shifts at each fr equency tested (3, 8, 12, and 18 kHz) as measured by tone burst-evoked compound action potentials and cochlear microphonics recorded from th e round window. Both of these thresholds in drug-treated animals were attenuated compared with animals exposed to noise alone. These finding s show that SOD-PEG and allopurinol may preserve cochlear sensitivity associated with noise exposure. This suggests that noise-induced damag e to the cochlea may be related to the activity of FORs.