SPIN TRAP PROTECTION AGAINST LEAD INDUCED OTOTOXICITIES

U.Tuncel, L.Yang, R O.Jones, W.J.Clerici

Ankara Numunune Hospital

Ankara-Turkey

Lead exposures damage various organ systems including that of the inner ear. This study investigated the differential ototoxicities induced by exposures to solutions containing lead acetate (LA) and tetraethyl lead (TEL) of equivalent Pb content, and the efficacy of alpha-phenyl-teri-butyl-nitrone (PBN) a spin trap for reactive oxygen species (ROS), to prevent the cochlear dysfunction induced by these agents.

Anaesthetized guinea pigs were surgically prepared and baseline compound action potential (CAP) thresholds and 1.0 mV RMS cochlear Microphonics (CM) isopotential curve values to 11 pure tone frequencies were recorded. The animals (n=5l group) were administered PBN (100 mg/kg, ip) or an equal volume of 0.9% saline, followed in 30 min. by an ip injection of LA (50 mg/kg), TEL (42.7 mg/kg) or an equal volume of a vehicle. CM and CAP responses were recorded 120 min later and changes in cochlear functions were evaluated.

Group mean CAP threshold values did not differ significantly (p>0.5) between pre and post exposure in control groups. Mean CAP threshold shifts in the group receiving saline followed by LA were greater than shifts in control animals at mid-high frequencies. Group mean CAP shift values in guinea pigs receiving PBN prior to LA were not significantly different from values in animals receiving saline prior to LA at ally frequency. CAP threshold shifts in the group receiving saline prior to TEL were significantly greater than those in the control groups at 12 to 30 kHz and also greater than those in the group receiving saline followed by LA, indicating that TEL was more ototoxic than was LA of equal Pb content. Mean CAP threshold shifts were significantly smaller for mid-high frequencies in the group receiving PBN prior to TEL than in the group receiving saline prior to TEL.CM shift values did not differ significantly among any of the groups (p>0.5). These data suggest that under these conditions organic lead is more ototoxic than inorganic lead, and that, ROS generation may be partially responsible for TEL induced CAP threshold disruption.

Supported by Ankara Numune Hospital, the Division of O-HNS, UK.