Abstract
The effect of ethacrynic acid upon the cochlear microphonics was studied by the differential electrode technique. The following results were obtained.
1. With intravenous doses of 1mg/kg ethacrynic acid, the cochlear microphonics caused a slight depression accompanied by a gradual recovery. CM increased rapidly 50 minutes after the injection and then decreased gradually.
2. With intravenous doses of 10mg/kg ethacrynic acid, the cochlear microphonics caused a rapid decrease to 63.3 % of the initial value within 30 minutes, to 49.3 % within 80 minutes, and then a gradual decrease to 43.7 % within 3 hours. It did not cause any recovery within 3 hours. But one of 5 cases caused the same variation of CM that the injection of 1mg/kg ethacrynic acid produced.
Recent experimental evidence indicates that ethacrynic acid causes the damage of the intermediate cell layers of the stria vascularis and the outer hair cells. It is also known that ethacrynic acid causes an increase in the endolymphatic sodium concentration and a decrease in the endolymphatic potassium concentration. Therefore it was concluded that the depression of the cochlear microphonics caused by ethacrynic acid would be due to the ionic changes in the endolymph which is produced by the inhibition of the active sodium transport in the stria vascularis.
