Activities of carbonic anhydrase in the cochleae of guinea pigs with early experimental endolymphatic hydrops.

Normal auditory function depends on maintenance of the unique ion composition in the endolymph. Carbonic anhydrase in the inner ear has been suggested to play an important role in maintaining the ion concentration and regulating fluids of the inner ear. Cochlear dysfunction may indicate changes in the biochemical components and osmotic pressure of the inner ear fluids as well as inadequate generation of intracellular metabolic energy. Dysfunction of the inner ear was investigated in the early stages of endolymphatic hydrops. Normal adult albino guinea pigs were operated on to obliterate the endolymphatic ducts and sacs of the right ears to induce endolymphatic hydrops. The auditory function of experimental guinea pigs was assessed according to the difference between the preoperative and postoperative hearing thresholds of the auditory brainstem response (ABR). Vibratome sections of the hydropic cochlea (right) and control cochlea (left) were stained histochemically for the activities of carbonic anhydrase in this study. Decreased activity of this enzyme was not shown consistently in the stria vascularis and organ of Corti of the hydropic cochlea in the early stage of endolymphatic hydrops whereas auditory dysfunction in the hydropic ear was noted from the ABR threshold for the experimental animals with 2 months survival. The results of the present study suggest that further investigation concerning the role of carbonic anhydrase in the cochlear auditory function is necessary.