Contributions Of Endothelin In The Process Of The Noise-induced Injury Of Cochlea

Objective: To study the pathological alteration of the cochlear microcirculationand the role of endothelin(ET)in the process of the noise -induced injury of cochlea.Methods: Thirty rats were randomly divided into five groups: control group and1d, 4d, 8d and 15 d noise exposure group (115dB SPL, white noise, 8h daily). Thecilium of hair cell was observed by scanning electron microscope, the conditon ofcochlear microcirculation was determined by stretched preparation of the striavascularis. The Level of ET in plasm was measured through radio-immunity .Thedistribution of ET-1,ETA,ETB ,Actinα-smooth muscle in cochlea were detectedthrough immunohistochemistry staining.Results: In the 4d,8d,15d group, severe ischemia appeared on the capillary ofstria vascularis of the basal turn, and the cilia of outer hair cells displayedsignificantly disorder. The Level of ET in plasm rose significantly in the 4d group, butdecreased to the normal level in the 8d group. Immunohistochemistry staining showedthat ET-1 activity distributed widely in the rat cochlea and strong positive stainingwere observed in all the groups, there was no significant difference between thecontrol group and the noise exposure groups. In all the groups, immunoreactive Actinα-smooth muscle localized in the capillary walls of the stria vascularis and the spiralligament, and appeared weak positive staining. ETA expressed in the plasm of theintermediate cells and the capillary walls in the stria vascularis. The control group andthe 1d group showed weak positive staining, while the 4d,8d,15d group showedstrong positive . The increase of the staining intensity was most significant in thebasal turn of the cochlea. The ETB activity distributed on the membrane of theendothelial cells of the capillary of stria vascularis and the alteration of the stainingintensity was similar to the manifestation of ETA Conclusions: Severe disturbance of the cochlear circulation occurred during thecourse of the noise injury to the rat cochlea. At the same time, the activity of the ETsystem of the cochlea stepped up significantly, it occurred at the same part of thecochlea with the ischemia of the stria vascularis. These findings suggest that ETsystem may play an important role in the process of the cochlear microcirculationdisorder caused by noise.