The ototoxic effects induced in rats by treatment for 12 weeks with 2-butenenitrile, 3-butenenitrile and cis-2-pentenenitrile.

Brainstem auditory and visual evoked-potentials were studied in male Sprague-Dawley rats during subchronic oral treatment with three unsaturated aliphatic nitriles. The rats were given, by gastric intubation, doses of 10, 20 and 40 mg x kg(-1) 3-butenenitrile (allyl cyanide) and 25, 50 and 100 mg x kg(-1) of either cis/trans-2-butenenitrile (crotononitrile) or cis-2-pentenenitrile once a day, 5 days per week for 12 weeks. Oral administration of the three unsaturated nitriles produced deafness and absence of reaction when the animals were subject to droptest. Rats in the high dosage groups exhibited a complete disappearance of the five waves of the auditory evoked-potentials. There was a decrease in the amplitudes of the 2nd component of the auditory evoked-potentials. Those changes were not reversible at the 8th week of the recovery period. A dose-dependent effect on inner and outer hair cells was observed in the organ of Corti. The basal part of the cochlea was the most affected. Though no measurements were made of systemic exposure, a tentative ranking of decreasing ototoxicity of these three unsaturated nitriles might be proposed based on the electrophysiological deficiencies and histological losses observed: 3-butenenitrile >cis-2-pentenenitrile >cis/trans-2-butenenitrile. Moreover, rats treated with those nitriles showed a corneal opacity as well as a decrease in the amplitude and lengthening of the peak latencies of the visual evoked-potentials. These latter changes were reversible by the end of the 8th week of the recovery period and appeared to be related to the opacity of the cornea.