Hydrophobic lining of the eustachian tube imparted by surfactant.

The eustachian tubes were excised from nine rabbits and one pig, and the hydrophobic nature of each luminal surface was determined by placing upon it a drop of saline. Each surface resisted wetting, with the droplet "beading up" to give a mean contact angle between the tissue-fluid and fluid-air interfaces of 50.1 degrees for the rabbits and 49 degrees for the pig. Each measurement was determined by a goniometer. The hydrophobicity was eliminated by lipid solvents and largely by aspirin, which desorb surface-active phospholipids. These results are consistent with the hypothesis that surfactants identified in the eustachian tubes are absorbed to the luminal surfaces as adhesives to oppose the strongly adhesive nature of the proteins and thus maintain patency and ventilation of the middle ear. This concept implies that an inadequate layer of adsorbed phospholipid could lead to serous otitis.