Alterations in cochlear function during induced acute hyperinsulinemia in an animal model

Roberto Dihl Angeli,Alexandre Dolganov,Luiz Lavinsky

doi:10.1590/s1808-86942009000500024

Abstract

Hyperinsulinism secondary to peripheral insulin resistance has been described as the most frequent etiologic factor in cochlear and vestibular syndromes. AIM: This experimental study recorded and analyzed evoked auditory potential changes using transtympanic electrocochleography (EcochG) during induced acute hyperinsulinism in an animal model. MATERIALS AND METHODS: Six adult male sheep were randomly divided into 2 groups. The animals were submitted to EcochG under general anesthesia, and a peripheral blood sample was collected to measure glycemia and insulinemia. Animals in the intervention group (n=3) received regular human insulin IV (0.1 U/kg). The control group (n=3) received saline solution. Glycemia and insulinemia were measured simultaneously with the recording of evoked potentials at 10-minute intervals during 90 minutes. RESULTS: The intervention group experienced a progressive suppression in action potential amplitude when compared to the control group (p=0.001). CONCLUSION: Data strongly suggest that acute induced hyperinsulinism suppresses cochlear function. Results may be attributed to loss of Na+K+ATPase activity in the stria vascularis, leading to loss of endocochlear potential and subsequent depolarization of cochlear hair cells as well as of neural cells in the auditory portion of cranial nerve VIII.

Highlights

Many experimental and clinical studies have demonstrated the effect of carbohydrate metabolism on inner ear function
Baseline data for both groups were similar in terms of insulinemia, blood glucose, and amplitude of the cochlear action potential (AP)
Electrocochleography was applied to monitor the response to acute hyperinsulinemia

Summary

Introduction

Many experimental and clinical studies have demonstrated the effect of carbohydrate metabolism on inner ear function. Hyperinsulinemia is an early change in peripheral resistance to insulin.[8,9] classified as a mild disorder, it may affect significantly the inner ear metabolism and fluid concentrations.[10]. The inner ear is not able to store much energy.[11,12] Paradoxically, it has a high metabolic activity, especially for maintaining endolymph ionic concentrations.[13,14] Mendelsohn and Roderique showed that induction of hypoglycemia in rodents reduces significantly endolymph potassium concentrations.[15] Most of these studies have shown that hyperinsulinemia is the most frequent metabolic alteration associated with cochleo-vestibular disease.[1,2,3,4,5,6] D’Avila and Lavinsky studied the glucose profile of patients with Ménière’s disease and showed that 72% of these cases had variables degrees of hyperinsulinemia that could be detected by the 5-hour glucose tolerance test.[7]

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