Distortion product otoacoustic emissions in an animal model of induced hyperinsulinemia.

The existence of a relationship between abnormal insulin levels and the occurrence of labyrinth disorders has been demonstrated in several works. Among many metabolic alterations, such studies indicate that hyperinsulinemia is one of the most frequent causes of cochlear and vestibular syndromes. In this study, we monitored distortion product evoked otoacoustic emission thresholds during induced acute hyperinsulinemia in sheep so as to identify the occurrence of electrophysiological changes in cochlear outer hair cells. In the study group, seven sheep received a bolus of 0.1 U/kg of regular human insulin. In the control group, seven sheep received saline solution. We measured insulin and glucose levels simultaneously with the recording of distortion product otoacoustic emissions at 10-minute intervals over 90 minutes. We successfully induced hypoglycemia and hyperinsulinemia. We detected no changes in distortion product thresholds in the control group during the 90 minutes of the experiment. In the study group, we recorded a reduction in distortion product thresholds in relation to the control group at frequencies above 1,500 Hz and after 60 minutes (p < .001). We observed significant electrophysiological changes in cochlear outer hair cells reflected in the variation of distortion product thresholds at high frequencies after 60 minutes.