Disaturated phosphatidylcholine in rabbit eustachian tube surfactant.

A chemical analysis of phospholipids in rabbit Eustachian tube and in its lavages shows phosphatidylcholine (PC) as being the predominating compound, followed by sphingomyelin and phosphatidylethanolamine. As in the lung surfactant, the majority of tubal PC is represented by its disaturated form dipalmitoylphosphatidylcholine (DPPC), known as a powerful surface-active agent. The concentration of PC and DPPC is higher in tubal washing than in the whole tissue, suggesting the existence of an active secretory process. Incubation of tubal mucosa with 14C-choline resulted in the biosynthesis of radiolabelled PC and DPPC at a ratio similar to the lung. These data provide further evidence for the existence of a surface-active agent in the Eustachian tube, chemically similar to the lung surfactant and probably produced through similar metabolic pathways.

Presence of phospholipidic lamellar bodies on the mucosa of rabbit eustachian tube. Ultrastructural aspects.

Electron microscopy of the rabbit eustachian tube showed the presence of osmiophilic lamellar bodies in the cytoplasm of secretory cells and of osmiophilic free lamellar membranes in the lumen of tubal glands or above the epithelium. Similar structures have been reported in other parts of the respiratory system and in the pulmonary alveoli. The functional significance of these morphological observations is suggestive of a surface-tension-lowering effect on the mucosal lining layer of the eustachian tube and of a possible relationship to the phospholipid surfactant of the lung.

Location of intravenously injected kanamycin sulfate in the middle ear mucosa.

Twelve guinea pigs were treated with intravenous kanamycin sulfate (KM) and sacrificed 2, 5, 10, and 30 min later to investigate its location in the middle ear mucosa, especially in the Eustachian tube (ET). Immunological examinations evidenced KM in the epithelial and subepithelial layers of the ET on each occasion of observation. But, it was never recognized in the tubal gland. These observations might indicate that clinically used drugs easily get to the ET except for the tubal gland which might have some barrier mechanism against foreign bodies.

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.

Histologic architecture of submucosal connective tissues in human eustachian tube with supplemental reference to the effects of aging.

Serial sections of 74 human eustachian tubes from 37 autopsy cases were examined microscopically to determine the histologic architecture of submucosal connective tissues. Abundant elastic fibers ran just beneath the mucosal epithelium of the eustachian tube. Two kinds of layers of collagenous fiber were observed an inner circular layer and an outer longitudinal layer. An "elastic fiber band" perfectly encircled the tubal lumen at the pharyngeal part of the eustachian tube. This band became less sharply defined at the osseous part. The two layers of collagenous fiber were contiguous, especially in the upper part of the tube, and ran from the pharyngeal orifice to the isthmus. Submucosal connective tissues were found to be undeveloped in fetal eustachian tubes. In children as well, elastic fibers were not fully developed, and circular banding of collagenous fibers was less marked. With advancing age, elastic fibers increased in number and became large and brittle. Both layers of collagenous fibers became thicker. The present data indicate that the submucosal connective tissues may play an important role in the elasticity of the eustachian tube itself and in the maintenance of the tubal framework. Gerontologic changes in the eustachian tube stroma have been considered pathophysiologically.