Hypoxaemia increases the accumulation of inosine monophosphate (IMP) in human skeletal muscle during submaximal exercise

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Abstract
The effect of hypoxaemia on the muscle content of inosine monophosphate (IMP) during short-term, low-intensity exercise has been investigated. Six men cycled twice for 5 min at 120 .+-. 6 W (mean .+-. SE), which corresponded to .apprx. 50% of their maximal normoxic O2 utpake , breathing air (N) on one occasion and 11% O2 in N2 (H) on the other. Oxygen uptake at the end of the exercise period was similar between treatments. No significant difference was observed between H and N in the muscle metabolite contents at rest. Muscle content of phosphocreatine (PCr) decreased and lactate increased during exercise. Post-exercise PCr during H was 80% of the value during N (P > 0.05) and post-exercise muscle lactate was fourfold higher during H than during N (P < 0.001). Post-exercise muscle content of ADP was significantly higher during H than during N (P < 0.01), while ATP and AMP remained constant under both H and N exercise (P > 0.05 H vs N). IMP was not detectable in pre-exercise muslce samples (< 0.01 mmol kg-1 dry wt) but increased during N exercise (0.03 .+-. 0.01 mmol kg-1 dry wt, P < 0.05) and even more during H exercise (0.16 .+-. 0.05 mmol kg-1 dry wt, P < 0.05, H vs N). Post-exercise IMP was negatively related to PCr (r= - 0.90) and positively related to lactate (r = 0.88). It is concluded that hypoxaemia results in an enhanced accumulation of IMP during submaximal exercise and that the IMP level is related to the degree of anaerobic energy utilization.