Combined effects of simultaneous exposure to toluene and ethanol on auditory function in rats

Three experimental groups and one control group of Long-Evans rats were used to study the combined effects of toluene and ethanol on auditory function. The first experimental group was exposed to toluene vapors (1750 ppm, 6 h/day, 5 days/week, 4 weeks), the second one was daily gavaged with a saline solution of ethanol (4 g/kg, 4 weeks), and the last group was simultaneously exposed to both toluene and ethanol. Auditory function was tested by recording brain stem (inferior colliculus) auditory-evoked potentials for audiometric frequencies ranging from 2 to 32 kHz. Urinary hippuric acid was dosed to check the toluene metabolism during the experiments. Ethanol clearly modified the toluene metabolism in the present experimental conditions. As a result, the hearing loss induced by a simultaneous exposure to both ethanol and toluene was larger than that induced by exposure to toluene alone.