EXCITATORY AMINO-ACID SYNTHESIS IN HYPOXIC BRAIN-SLICES - DOES ALANINE ACT AS A SUBSTRATE FOR GLUTAMATE PRODUCTION IN HYPOXIA

Excitatory amino acids are an important cause of cell death in the hyp oxic and ischaemic brain. Neuronal glutamate stores are depleted rapid ly in hypoxia, but alanine production rises under such conditions and has been suggested to be a potential precursor of glutamate, To test t his hypothesis, we have investigated amino acid metabolism using C-13 NMR With superfused guinea pig cortical slices subjected to varying de grees of hypoxia. During severe hypoxia, brain slices metabolising 5 m M [2-C-13]pyruvate exported [2-C-13]alanine into the superfusion fluid . The metabolic fate of alanine during normoxia and hypoxia was tested by superfusion of brain slices with 10 mM glucose and 2 mM [2-C-13,N- 15]alanine. Metabolism of exogenous alanine leads to the release of as partate into the superfusion fluid. The pattern of labelling of aspart ate indicated that it was synthesised via the glial-specific enzyme py ruvate carboxylase, C-13-labelled glutamate was produced with both nor moxia and hypoxia, but concentrations were 30-fold lower than for labe lled aspartate. Thus, although substantial amounts of glutamate ape no t synthesised from alanine in hypoxia, there is significant production of aspartate, which also may have deleterious effects as an excitator y amino acid.