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Cerebral metabolism of [1,2‐ 13 C 2 ]glucose and [U‐ 13 C 4 ]3‐hydroxybutyrate in rat brain as detected by 13 C NMR spectroscopy
Author(s) -
Künnecke Basil,
Cerdan Sebastian,
Seelig Joachim
Publication year - 1993
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/nbm.1940060406
Subject(s) - metabolism , glutamate receptor , citric acid cycle , biochemistry , glutamine , nuclear magnetic resonance spectroscopy , tricarboxylic acid , pyruvate carboxylase , in vivo , pyruvate dehydrogenase complex , chemistry , biology , stereochemistry , amino acid , enzyme , receptor , microbiology and biotechnology
The metabolism of [1,2‐ 13 C 2 ]glucose and [U‐ 13 C 4 ]3‐hydroxybutyrate was studied in rat brain with in vivo and in vitro 13 C NMR spectroscopy, taking advantage, in particular, of homonuclear 13 C‐ 13 C spin coupling patterns. After infusion of [1,2‐ 13 C 2 ]glucose or [U‐ 13 C 4 ]3‐hydroxybutyrate into rats, the uptake of the substrates in brain and their metabolism to [1‐ 13 C]bicarbonate could be detected with in vivo 13 C NMR spectroscopy. At the end of the infusion experiment, methanol/HCI/HCIO 4 extracts of the brain tissue were further analysed by high resolution 13 C NMR spectroscopy. The 13 C spin coupling patterns revealed entirely different isotopomer distributions for the closely related cerebral metabolites glutamate, glutamine and 4‐aminobutyric acid. A quantitative analysis of the 13 C spectra demonstrated (i) the existence of two kinetically distinct pools of glutamate, (ii) a pronounced CO 2 fixation via pyruvate carboxylase in the glial cells accounting for as much as 38% of the oxaloacetate synthesis in the glial tricarboxylic acid cycle, (iii) a cerebral pyruvate recycling system contributing maximally 17% of the pyruvate metabolism through the pyruvate dehydrogenase in neurons, and (iv) a predominant production of 4‐aminobutyric acid from glutamate synthesized in the neurons. In addition, the labelling pattern of N ‐acetyl aspartate upon infusion of labelled glucose or 3‐hydroxybutyrate provided insight into the synthesis of this compound in mammalian brain. While the acetyl moiety originates from the metabolic equivalent of the C‐1–C‐2 part of cerebral glutamate, the aspartyl moiety is not in direct contact with the intermediates of glycolysis or of the tricarboxylic acid cycles.