Influence of hyperoxia on in vitro growth of rabbit middle ear epithelium and auditory meatal epithelium

The oxygen partial pressure of middle ear gas increases more than 3-fold upon insertion of ventilation tubes, while the carbon dioxide partial pressure decreases. Whereas the middle ear gas is normally equilibrated to venous gases and has an oxygen partial pressure of 43 mmHg, 138 mmHg is measured in ventilated ears. The present study was undertaken to compare the effects of these oxygen tensions on in vitro growth and glycoprotein secretion of rabbit middle ear epithelium and for comparison auditory meatal epithelium. Cultures were incubated in atmospheres of 7, 21 or 75% O2 in 5% CO2 and the remnant N2. The cell layer protein mass, [3H]thymidine-incorporation, DNA content and [3H]glucosamine-incorporation was measured in identical subcultures every third day during a 15-day period. In middle ear epithelium the DNA content, DNA synthesis and cell layer protein mass were significantly higher at 7% oxygen compared to 21% and 75%. In conclusion hyperoxia leads to decreased growth of middle ear epithelium in vitro. If applicable to in vivo conditions, this might contribute to the mechanism of action of ventilation tubes. Moreover the proliferation rate of auditory meatal epithelium exceeds that of middle ear epithelium both at 7 and 21% oxygen, an interesting point with regards to cholesteatoma pathogenesis.