The protective effect of intratympanic dexamethasone on streptomycin ototoxicity in rats.

The purpose of this experimental study was to investigate the protective role of intratympanically administered dexamethasone on the inner ears of rats that were exposed to streptomycin ototoxicity. Twenty-four adult Wistar albino rats were separated into 4 groups: Group 1 (only streptomycin), Group 2 (only intratympanic dexamethasone), Group 3 (streptomycin and intratympanic dexamethasone), and Group 4 (streptomycin and intratympanic saline). All rats were evaluated with distortion product otoacoustic emissions (DPOAE) tests before the start of treatment and on the day it ended. On the 45th day, after the final DPOAE tests, animals of all groups were sacrificed under general anesthesia. The differences between the amplitudes of DPOAE results were determined, and hearing results were statistically analyzed. Also, the cochleas of each rat were histopathologically evaluated under a light microscope with hematoxylin and eosin staining. In the intratympanic dexamethasone group it was observed that cochlear hair cells were mostly protected. No significant difference was seen between the DPOAE results before and after treatment (p >0.05). On the other hand, loss was observed in the hearing functions and hair cells of the rats that received streptomycin and streptomycin plus intratympanic saline (p <0.05). In the streptomycin plus intratympanic dexamethasone group, the cochlear hair cells were partially protected. A significant difference was observed when the DPOAE results (DP-grams) of the streptomycin plus intratypmanic dexamethasone group were compared to those of the streptomycin plus intratympanic saline group (p <0.05). After the experimental study, ototoxic effects of the administration of streptomycin and intratympanic dexamethasone were observed on the rats' cochlear hair cells. We conclude that intratympanic dexamethasone has protective effects against this cochlear damage in rats.