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  • Title: Effects of long-term exposures to 100% oxygen at selected simulated altitudes on the pulmonary surfactant in mice.
    Author: Sheffield PJ.
    Journal: Aviat Space Environ Med; 1975 Jan; 46(1):6-10. PubMed ID: 1172927.
    Abstract:
    The purpose of this investigation was to evaluate the effects on pulmonary surfactant in mice after long-duration exposure to 100% oxygen at various partial pressures equivalent to 842 mb (632) mmHg) or less. Six-month-old female CBA mice, weighing 25-35 g, were exposed to the pure oxygen environment. The effect on pulmonary surfactant was evaluated in two groups of 16 experimental animals and compared with control groups which were maintained in a similar environmentally controlled chamber at sea level conditions. Group I was exposed to pure oxygen at 842 mb (632 mmHg), a level known to be toxic and lethal. Group II was initially exposed for 60 d to pure oxygen at 420 mb (315 mmHg), a level not expected to be lethal, and the oxygen partial pressure gradually increased in steps over a 150-d period until an oxygen partial pressure at 842 mb (632 mmHg) was reached. In Group I, 12 out of 16 mice died of respiratory distress within 7 d. One died on the 10th day and three survived to complete 15 d of exposure but were euthanized because of severe despiratory distress. Mice in Group II which were exposed to pregressively increasing oxygen partial pressures survived. Pulmonary surfactant was obtained by saline lavage of the lungs. Chloroform/methanol extracted samples from oxygen-exposed mice in Group I displayed lower surfactant activity than Group II or controls. In fact, surfactant activity of mice dying in respiratory distress after 7 d was markedly lower than that of all other animals. Mice in Group II exhibited significantly lower(p less than 0.05) surfactant activity than controls, X = 34.71 and 38.58 respectively. This lower surfactant activity was consistent for Group II throughout the 150-d exposure except at the 90-d and 150-d exposures. The findings of this investigation support preceding studies which contend that the lung is the most vulnerable target for oxygen toxicity at altitude. It appears that an adaptive process involving both quantitative and qualitative changes in the pulmonary surfactant enabled animals in Group II to survive the progressively increasing ocygen partial pressures in an environment where survival would not normally be possible.
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