Differential ototoxicities induced by lead acetate and tetraethyl lead¹

Lead poisoning disrupts many biological structures and functions, including those of the auditory system. This study examined the ototoxic effects of lead acetate (LA) and tetraethyl lead (TEL) of equal lead content on cochlear function and the ability of α-phenyl-tert-butyl-nitrone (PBN) to attenuate such effects. Baseline 1.0 μV cochlear microphonic (CM) and compound action potential (CAP) responses were recorded and animals administered either PBN (100 mg/kg, i.p.) or an equal volume of 0.9% saline, followed by an i.p. injection of LA (50 mg/kg) in an ethanol vehicle, TEL (42.7 mg/kg) in a corn oil vehicle, corn oil or ethanol vehicle alone. Two hours after administration, post-exposure CM and CAP responses were recorded. CAP threshold shifts in the saline-LA group were elevated by 5-10 dB at mid to high frequencies relative to controls (20-24 kHz, P < 0.05). Mean CAP threshold shifts in the saline-TEL were significantly greater than those of both control groups at all tested frequencies except 2 kHz (P < 0.001). However, threshold shifts in the group receiving PBN prior to TEL were significantly smaller than shifts in the group receiving saline prior to TEL (P < 0.01). These data suggest that TEL is more ototoxic than is LA and that free radicals partially mediate TEL-induced CAP disruption.