Pseudomonas aeurignosa exotoxin A and Haemophilus influenzae type b endotoxin. Effect on the inner ear and passage through the round window membrane of the chinchilla

Pseudomonas aeruginosa exotoxin A was applied to the round window membrane of the chinchilla in concentrations ranging from 1 μg/ml to 1 mg/ml. Haemophilus influenzae type b endotoxin (45,000 endotoxin units/ml) was applied in the same way. Five animals were also subjected to blocking of the Eustachian tube, 3 to 8 months earlier, resulting in serous otitis media and exotoxin A (1 mg/ml) was applied into the round window niche of these animals. Effects on the inner ear was recorded with quantitative morphology (hair cell counting) and electrophysiologically (action potential threshold measurements) 4 weeks after application of exotoxin A. Concentrations of exotoxin A in perilymph was measured with ELISA and concentration of endotoxin in perilymph was measured with Limulus Amoebocyte Lysate and Quantitative Chromogenic Limulus Amebocyte Lysate. Four weeks after application of exotoxin A at a concentration of 10 μg/ml severe inner ear damage could be demonstrated. No inner ear damage was demonstrated when lower concentrations were used. Passage into the inner ear could only be demonstrated after exposure of the round window membrane to an exotoxin A concentration of 1 mg/ml. Round window membranes affected by chronic inflammation were shown to be less permeable to exotoxin A, thus indicating that thickening of the round window membrane may have a protective effect on the inner ear. A low passage rate into the inner ear was demonstrated after endotoxin exposure. It may be concluded that small amounts of exotoxin A passing through the round window membrane may cause inner ear damage. The passage rates, however, for both exotoxin A and endotoxins are low.