Effects of hyperbraic oxygen pretreatment on the ultrastructure in acute hypoxia rats

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Objective To observe the effects of hyperbaric oxygen (HBO) pretreatment on the ultrastructure of heart,brain and lung induced by acute hypoxia (altitude of 7 000 m) in rats and changes of water content in the tissues involved.Methods Fifty SD rats were randomly divided into 6 groups:3 HBO groups (the HBO group 1,the HBO group 2,and the HBO group 3) and 3 control groups (the control group 1,the control group 2,and the control group 3).The HBO groups were all pretreated with HBO for 7 days.The HBO group 1 (n =10),HBO group 2 (n =10),and HBO group 3 (n =10) were exposed to an altitude of 7 000 m in the hypobaric chamber for durations of 12 h,24 h,and 72 h respectively,following HBO pretreatment.The control group 1 (n =6),control group 2(n =7) and the control group 3 (n =7) stayed in the hypobaric chamber for durations of 12 h,24 h,and 72 h respectively.The rats in all the groups were quickly sacrificed in the hypobaric chamber and frontal cortex,heart and lung samples were collected for optical microscopy and electron microscopy.Wet weight of the left brain and lung were measured and dried to calculate water contents of the tissues.Results Water contents in the tissues of the rats in the HBO groups were all decreased markedly than those in the control groups,with statistical significance (P ＜ 0.05 or 0.01).Tissue water contents increased with the prolonging of exposure time during acute hypoxia within 72 h.In rats with acute hypoxia,lung tissue structure was in disorder,pulmonary capillary vessels were congested significantly,alveolar wall was thickened,pink alveolar exudation was clearly visible in some areas,and significant interstitial pulmonary edema and alveolar pulmonary edema were also present.Myocardial nucleuses were deformed with cloudy swelling,vacuolar degeneration and myocardial interstitial edema.Brain nuclear membrane was indistinct with an unsmooth surface.Tissue injury aggravated with prolonged hypoxia.However,for the animals in the HBO pretreatment groups,things were different:lung tissue structure was in proper order,alveolar wall was slightly thickened,myocardial cells were slightly swollen with the exception of a few neurons,cell circumscription was slightly irregular,brain cell membranes and nucleolemma were intact with uniform nucleoplasm.Conclusions HBO pretreatment could prevent cerebral edema and lung edema induced by acute hypoxia,and could produce good protective effect on the tissues affected by hypoxia. Key words: Rats ; Hyperbaric oxygen ; Acute hypoxia; Ultrastructure ; Water content