A study of the possible role of vasopressin in the formation of the endolymphatic hydrops

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1) New device to measure vestibular-ocular reflex (VOR) of guinea pigs was developed. This system consists of an infra-red eye camera, a small velocity sensor, a frequency modulator and a computer-controlled turn-table wit a head holder for small animals. Eye movement against sinusoidal rotation was carried out by a personal computer. VOR analysis was possible if pigment guinea pigs are used as experimental animals.2) The influence of vasopressin on the rat inner ear was investigated morphologically and molecular-biologically. Vasopressin was subcutaneously applied with an osmotic mini-pump. Chronic application of vasopressin produced endolymphatic hydrops and a significant increase in aquaporin-2 mRNA expression both in the cochlea and in the endolymphatic sac (p<0.01).3) The influence of V2-antagonist (OPC-31260) on experimentally-induced endolymphatic hydrops and on a regulation of AQP2 mRNA expression in the rat inner ear was investigated. The infusion of 3% OPV-31260 into the scala tympani decreased experimentally-induced endolymphatic hydrops in guinea pigs. In the PCR study, quantitative analyses of AQP2 mRNA expression were performed with the LightCycler analysis software (version 3.3, Roche Diagnostics). An intrvenous injection of OPC-31260 resulted a significant decrease in the ratio of AQP2 and β-actin mRNA both in the cochlea and in the endolymphatic sac (t-test). These results indicated that water homeostasis in the inner ear is regulated via vasopressin-aquaporin2 (VP-AQP2) system, and that V_2-antagonist (OPC-31260) is the promising drug for the therapy of Meniere's disease.