Abstract
In the present study, using radioisotope we observed functionally the changes in submucosal microvascular permeability of the middle ear and response to histamine after occlusion of the eustachian tube in rabbits with experimentally induced otitis media with effusion. Results obtained were compared with results of histopathological study performed simultaneously.
As experimental animals 22 adult rabbits were used. Thirteen of these animals were subjected to functional study by use of radioisotope and 9 animals to histopathological study. Otitis media with effusion was induced by pretreating the animals with an insertion of laminalia prepared in wedge form into the pharyngeal orifice of the eustachian tube to occlude it. At 1, 7 and 14 days after the treatment animals were subjected to experiments. The animals with untreated eustachian tube served as the controls. Prior to experiments, a hole as large as possible was made in the tympanic membrane and the middle ear cavity was perfused via the external auditory canal. Also tritium water was administered through intravenous injection and transference of this tritium water into the middle ear cavity was measured by the radioactivity of the middle ear perfusate. From the results obtained, microvascular permeability of submucosa of the middle ear cavity was determined at various periods after establishment of otitis media. Moreover, histamine was added to the fluid for perfusion to determine whether vascular permeability is increased by histamine or not. Radioactivity levels were measured using a scintillation counter.
The vascular permeability as measured at 1, 7 and 14 days after occlusion of the eustachian tube increased in function with time. A histopathological study of otitis media with effusion induced by the same procedure indicated a remarkable increase in permeability such as edematous hypertropy of the submucosal tissue of the middle ear. The intensity of the response (increase in vascular permeability) of the mucosa of the middle ear to histamine decreased gradually after occulusion of the eustachian tube, while the effect of the histamine tended to have a long duration. In this tendency no dose-respond relation was seen.
From these findings it was demonstrated that the mucosal membrane of the middle ear induced of otitis media with effusion shows a remarkable increase in vascular permeability which persists at least until 14 days after treatment. Moreover it was indicated that histamine increase vascular permeability of not only submucosal micro blood vessels of the mucosa of the normal middle ear cavity but also these in already established otitis media with effusion, suggesting its involvement in the persistence of this disease.
Similar to histamine, the vascular permeating factors present in the fluid of the middle ear easily enter into the mucosa through inflammed tissue to further increase microvascular permeability, making chronic inflammation and irreversible. The remarkable proliferation and organization tendency of the connective tissue as revealed by the histopathological observation made at 7 and 10 weeks after treatment of the eustachian tube reflect the above described process.
Therefore, in otitis media with effusion which persists for a prolong time and in which the mucosa of the middle ear consistently exposed to the retained fluid containing various factors such as the vascular permeability increasing factor, it is difficult to find a cure of otitis media with conservative treatment such as administration of drugs. We confirmed it is again important under these conditions to employ surgical treatment such as removal of retained fluid as early as possible, namely myringotomy and transtympanic insertion of a drainage tube.
