FISH MUSCLE ENERGY-METABOLISM MEASURED DURING HYPOXIA AND RECOVERY - AN IN-VIVO P-31-NMR STUDY

Three fish species were exposed to graded hypoxia levels and allowed t o recover. Levels of high-energy phosphate compounds in epaxial white muscle were monitored by in vivo P-31 nuclear magnetic resonance (NMR) spectroscopy. Furthermore, O-2 consumption of the animals was measure d. With increasing hypoxia load, metabolic parameters started to chang e in the following order: phosphocreatine (PCr)-to-P-i ratio (decrease ), O-2 consumption (decrease), [PCr] (decrease), intracellular pH (pH( i); decrease), P-i (increase), free ADP concentration ([ADP](free); in crease), [ATP] (decrease). PCr levels fell with the P-O2. After each i ncrement, the [PCr] reached a stable plateau value while, in some case s, a recovery was observed. This recovery could be explained because t he balance between anaerobic and aerobic metabolism is continuously fl uctuating during hypoxia as a consequence of changes in the activity o f the fish. Consequently the [ADP](free) are fluctuating, resulting in an activation of the creatine kinase reaction and the anaerobic glyco lysis. In all three species, anaerobic glycolysis was activated, but i n contrast to anoxia exposure, metabolic suppression was absent. The c hanges of [ADP](free) and [H+] (which influences the position of the c reatine kinase equilibrium) are species dependent. Species differences observed in the other parameters were small. It is concluded that the pattern of the activation of anaerobic metabolism under deep hypoxia is different from that under anoxia.