Abstract des Autors

Twelve male Sprague-Dawley rats (21 days old) were randomly assigned into two experimental groups: sea level control (CONT) and hypobaric hypoxia (HYPO). The HYPO rats were kept in an hypobaric chamber maintaining a simulated altitude of 4000 m (61.1 kPa). After 10 weeks of treatment, the rat hindlimb muscles (soleus (SOL) and extensor digitorum longus (EDL)) were subjected to histochemical and electro-mechanical analyses. Results indicated that compared to CONT the HYPO SOL muscle had a significantly greater relative distribution of fast-twitch-oxidative-glycolytic (FOG) fibres (28.9 SEM 2.0 vs 18.3 SEM 1.8) with a significant decrease in slow twitch oxidative fibre distribution (69.5 SEM 2.4 vs 82.9 SEM 3.1). Compared to CONT the HYPO EDL muscle also manifested a significant increase in FOG fibre distribution (51.6 SEM 0.8 vs 46.6 SEM 1.1), but this was accompanied by a significant decrease in fast twitch glycolytic fibres (44.3 SEM 0.9 vs 49.2 SEM 1.7). These histochemical fibre type transformations accompanied significant and expected changes in the electro-mechanical parameters tested in situ, e.g. maximal twitch force, maximal rate of force development, contraction time, half relaxation time, force: frequency curve, and fatigability. It was concluded that chronic hypobaric hypoxia could have a potent influence upon the phenotype expression of muscle fibres.