Fate of exogenous hyaluronic acid in the middle ear.

The fate of exogenous high-molecular-weight hyaluronic acid applied in the middle ear was studied in rats. Tritium-labelled hyaluronic acid was deposited, and its disappearance through the eustachian tube was followed by analysis of nasopharyngeal secretions. Radioactivity in the secretions reached a peak after three hours and approached zero after 12 hours, indicating that almost all hyaluronic acid had been removed. The middle ears were all empty when opened 24 hours after the deposition of hyaluronic acid. The fate of hyaluronic acid after obstruction of the eustachian tube was followed both with radioactive hyaluronic acid and subsequent autoradiography and by direct analysis of the hyaluronic acid concentration and the hyaluronic acid molecular weight distribution. Radioactive hyaluronic acid was confined to the obstructed middle ear, and no uptake into surrounding tissues could be detected between three hours and four days after the deposition. The amount of hyaluronic acid deposited could be recovered to about the same extent for up to six days. Analysis of the molecular weight distribution of the deposited material indicated only a slow degradation, if any, during the same time period.