Papain-induced emphysema: the influence of preliminary oxygenation

Rats were exposed for 7 days to an oxygen concentration of 85% and then submitted to an aerosol of papain, immediately, 3, 7 or 15 days after this exposure. The number of animals dying increased as the time between the administration of papain and the end of the exposure to oxygen increased. The quantification of emphysema was made by measurement of the mean linear intercept (LM). The LM does not differ between animals pretreated with oxygen and which have received papain, immediately or after 3 days, and the controls in air not having received papain. On the contrary, the animals pretreated with oxygen and having received papain 7 or 15 days later show a significantly higher LM than do the controls in air having received papain. The protection of the lung against the elastolytic effect of papain by a preliminary stay in 85% O2 is short-term; its mechanism is discussed.