Cochlear Potentials and Electrolyte Contents in Endolymph in Experimentally Induced Endolymphatic Hydrops

Abstract

It has been reported that surgical obliteration of the endolymphatic duct and sac brought about the endolymphatic hydrops in guinea pigs [R. S. Kimura, Ann. Otol. Rhinol. Laryngol. 76, 665 (1967)]. In order to reveal functional disturbances in endolymphatic hydrops, we undertook measurements of cochlear potentials and sodium and potassium contents in the endolymph in guinea pigs with obstruction of the endolymphatic duct. The sodium and potassium contents in the endolymph were determined in 19 cases of endolymphatic hydrops and the cochlear potentials were measured in 12 animals. The endocochlear potential (EP) and the cochlear microphonics (CM) were recorded from the scala media of the basal and third turns. The results obtained were compared with those obtained in sham operations. In all guinea pigs in which the endolymphatic duct and sac were obliterated successfully, endolymphatic hydrops were observed 5 to 10 weeks postoperatively. In these animals EP was markedly decreased (62.9±14.0 mV). The average EP was 86.4±8.2 mV in the sham operation group. In addition, the endolymphatic hydrops resulted in significant loss of CM in the third turn and, to a lesser degree, in the basal turn. A slight rise in sodium content (1.7±1.9 mEq/L) was observed, compared with 0.9±0.6 mEq/L in the sham operation group. The average potassium content was 162.1 mEq/L in the endolymphatic hydrops and 161.5 mEq/L in the sham operation. The relationship between morphological and functional changes was discussed.