Recovery from 24 h of anaerobiosis was investigated in Sipunculus nudus L. by monitoring changes in the concentrations of anaerobic metabolites in the musculature and in the coelomic plasma. The metabolic events in animals collected during March and October were compared.
Anaerobiosis led to an increase of succinate, propionate and acetate in the muscle tissues and the coelomic plasma. Strombine, octopine and alanine (predominantly l- rather than d-alanine) accumulated in the musculature, whereas aspartate and phospho-l-arginine levels decreased. A higher metabolic rate was observed during anaerobiosis in October than in March animals, as indicated by the higher amounts of strombine, octopine and acetate formed. An increase in metabolic rate appears to entail an increase of flux through the Embden-Meyerhof pathway which favours the accumulation of direct derivatives of pyruvate.
During recovery, regeneration of phospho-l-arginine occurred during the first 3 h, whereas disposal of succinate, octopine and propionate was observed during the entire 24-h period of recovery. Strombine, alanine and, to a lesser extent, acetate contents remained elevated. The concentration of d-alanine approached that of Lalanine during recovery, indicating the activity of alanine racemase. Malate levels increased transiently, possibly linked to the repletion of the aspartate pool.
In October animals, strombine seemed to accumulate transiently during initial recovery, indicating that the energy demand was not met by aerobic metabolism alone. In contrast to the situation in March animals, however, anaerobic glycolysis during recovery obviously becomes important only when the metabolic rate during anaerobiosis was high enough.