ENDOLYMPHATIC SAC MORPHOLOGY AFTER INSTILLATION OF HYPEROSMOLAR HYALURONAN IN THE ROUND WINDOW NICHE

One hundred and sixty-eight mice were injected with hyaluronan (HA) of varying tonicity in the middle ear and compared with 81 control anima ls to study the effects of hypertonic solutions in the middle ear on i nner ear fluid homeostasis and endolymphatic sac (ES) response. Six ho urs after 1.9% HA and 4, 6 and 8 h after 4% HA deposition there was a significant increase in the proportion of granule-containing light epi thelial cells in the ES as compared with controls indicating an enhanc ed secretory activity from the epithelial lining. Six, 8 and 10 h afte r deposition of 4% HA, the ES volume was significantly reduced. The se cretory activity and the ability of the ES to vary its volume could be specific responses to dehydration of the inner ear resulting from the high colloid osmotic pressure exerted by concentrated HA. The secreti on of high-molecular substances into the ES may serve to keep the ES l umen patent and thus ensure a proper ES function and/or to regulate th e intralabyrinthine volume and fluid pressure. Whether the findings ma y have clinical relevance for Meniere's patients remains to be elucida ted.