OBJECTIVETo study the pathological alteration of the cochlear microcirculation and the role of endothelin (ET) in the process of the noise-induced injury of inner ear.

METHODSThirty rats were randomly divided into five groups: control group and 1, 4, 8, 15 d noise exposure groups (115 dB, white noise, 8 h daily). The cilium of hair cell was observed by scanning electron microscope, the cochlear microcirculation was determined by stretched preparation of the stria vascularis. The level of ET in plasma was measured through radio-immunity. The distribution of ET-1, ETA, ETB, in cochlea were detected through immunohistochemistry staining.

RESULTSIn the 4, 8, 15 d group, severe ischemia appeared on the capillary of stria vascularis and the cilium of hair cell displayed significantly disorder. The level of ET in plasma rose temporarily in the 4 d group. ET-1 activity distributed widely in the rat cochlea, there was no significant difference between the control group and the noise exposure groups. ETA expressed in the plasma of the intermediate cells and the capillary walls in the stria vascularis. The control group and the 1 d group showed weak positive staining, while the 4, 8, 15 d groups showed strong positive. The ETB, activity distributed on the endothelial cells of the capillary of stria vascularis and the alteration of the staining intensity was similar to the manifestation of ETA.

CONCLUSIONSSevere disturbance of the cochlear circulation occurred during the course of the noise injury to the inner ear. At the same time, the activity of the ET system of the cochlea stepped up significantly. It coincided with the ischemia of the stria vascularis. These findings suggest that ET may play an important role in the process of the cochlear microcirculation disorder caused by noise.