Morioka I., Minami Y., Yamamoto H., Kawai T., Miyashita K.

The effect of styrene or furosemide alone and the interaction between both substances on the auditory function of the guinea pig were studied by auditory brainstem response (ABR) and scanning electron microscopy (SEM). In the first and second experiments, the animals were exposed to 700 or 900 ppm styrene alone (8 h/day for 21 days) and to 60, 80 or 100 mg/kg/day furosemide alone for 14 days. In the third experiment, they were exposed to 900 ppm styrene alone (8 h/day for 21 days) and in combination with furosemide at 60 or 80 mg/kg/day for 14 days, beginning with the eighth day of the exposure of styrene. In the first experiment, ABR results showed significant threshold shifts at 4 and 16 kHz frequencies, and SEM showed that some outer hair cells were disrupted in the 900 ppm styrene group. In the second experiment, there was a significant threshold shift at the 8 kHz frequency in the 100 mg/kg furosemide group in ABR, but SEM results showed no damage among the in any of the animal groups. In the third experiment, there were interactions between exposure dose and time at 4 and 8 kHz frequencies in ABR, and histological findings by SEM indicated that the combined exposure caused more severe cochlear damage than the exposure to styrene alone. The results suggested that styrene and furosemide synergistically impair auditory function.