Permeability of the round window membrane to horseradish peroxidase in experimental otitis media.

The permeability of the round window membrane (RWM) was studied by using horseradish peroxidase (HRP) in the different stages of otitis media developed in guinea pigs, and it was compared with normal RWM under transmission electron microscopic examination. The experimental model of otitis media was developed by inoculation of a Pseudomonas aeruginosa suspension. When HRP could penetrate into the inner layer of a normal RWM, the duration of HRP instillation into the round window niche was 10 minutes. The permeability of the RWM in otitis media was as follows: 3-day animals showed penetration of HRP into the middle layer. In 1-week animals, HRP had penetrated into the inner layer in all 10 ears. In 2-week animals, HRP had penetrated into the inner layer in 6 of 11 ears. In 4-week animals, however, HRP was not seen in 6 of 7 ears. HRP had penetrated through the damaged focus of the epithelial cells by inflammation. These results suggest that any derangement of the epithelial linings could increase the penetration of HRP and also ototoxic materials into the inner ear through the RWM.