Cardioprotective effect of acclimatization to sustained hypobaric hypoxia

With the aim of developing a model to study the mechanisms involved in physiological and long-lasting cardioprotection, the basal parameters of contractile function and their response to hypoxia/ reoxygenation were measured under isometric conditions in papillary muscles of rats submitted to 53.8 kPa in a hypobaric chamber for various periods and in their controls at 101.3 kPa. Developed tension (DT) was 34-64 % higher in rats exposed to hypoxia for 10, 26, and 45 wk than in their age-matched controls. Maximal rates of contraction and relaxation showed a similar pattern as DT. Recovery of all three parameters after hypoxia/reoxygenation was also improved in adult hypoxic rats. Heart acclimatization was lost after 74 wk of exposure. Results may contribute to explain the cardioprotection observed in high altitude people.