Measurement of amino acid metabolism derived from 1-13Cglucose in the rat brain using13C magnetic resonance spectroscopy

摘要

To clarify the unique characteristics of amino acid metabolism derived from glucose in the central nervous system (CNS), we injected 1-13Cglucose intraperitoneally to the rat, and extracted the free amino acids from several kinds of tissues and measured the amount of incorporation of13C derived from 1-13Cglucose into each amino acid using13C-magnetic resonance spectroscopy (NMR). In the adult rat brain, the intensities of resonances from13C-amino acids were observed in the following order: glutamate, glutamine, aspartate, γ-aminobutyrate (GABA) and alanine. There seemed no regional difference on this labeling pattern in the brain. However, only in the striatum and thalamus, the intensities of resonances from 2-13CGABA were larger than that from 2,3-13Caspartate. In the other tissues, such as heart, kidney, liver, spleen, muscle, lung and small intestine, the resonances from GABA were not detected and every intensity of resonances from13C-amino acids, except13C-alanine, was much smaller than those in the brain and spinal cord. In the serum,13C-amino acid was not detected at all. When the rats were decapitated, in the brain, the resonances from 1-13Cglucose greatly reduced and the intensities of resonances from 3-13Clactate, 3-13Calanine, 2, 3, 4-13CGABA and 2-13Cglutamine became larger as compared with those in the case that the rats were sacrificed with microwave. In other tissues, the resonances from 1-13Cglucose were clearly detected even after the decapitation. In the glioma induced by nitrosoethylurea in the spinal cord, the large resonances from glutamine and alanine were observed; however, the intensities of resonances from glutamate were considerably reduced and the resonances from GABA and aspartate were not detected. These results show that the pattern of13C label incorporation into amino acids is unique in the central nervous tissues and also suggest that the metabolic compartmentalization could exist in the CNS through the metabolic trafficking between neurons and astroglia