Up-regulation of cochlear aquaporin-3 mRNA expression after intra-endolymphatic sac application of dexamethasone.

The final aim of the present study is to see if the endolymphatic sac is really available as a drug delivery system to have effect on the inner ear organs. In the present study, we examined effects of a single insertion of dexamethasone into the rat unilateral endolymphatic sac on mRNA expression of the inner ear aquaporin (AQP) family, transmembrane water transporters and putative endolymphatic fluid modulators, by means of real-time quantitative PCR. Only AQP-3 mRNA expression in the ipsilateral cochlea was significantly up-regulated in comparison with controls and the up-regulation was demonstrated both in dose-dependent and time-dependent manners. These findings suggest that the intra-endolymphatic sac steroids could make regulatory effects on the inner ear AQP-3 expression via vestibular aqueduct and modulate the homeostasis of endolymphatic fluids, encouraging the possibility that the endolymphatic sac could be a therapeutic window for the inner ear disease.