In vivo 13C NMR assessment of brain glycogen concentration and turnover in the awake rat

Brain glycogen metabolism was recently observed in vivo and found to be very slow in the lightly alpha-chloralose anesthetized rat [J. Neurochem. 73 (1999) 1300]. Based on that slow turnover, the total glycogen content in the awake rat brain and its turnover time were assessed after administering C-13-labeled glucose for 48 h. Label incorporation into glycogen, glucose, amino acid, and N-acetyl-aspartate (NAA) resonances was observed. The amount of C-13 label incorporated into glycogen was variable and did not correlate with that in glutamate (r = -0.1, P > 0.86). However, the amount of C-13 label incorporated into glycogen was very similar to that in NAA (r = 0.93), implying similar turnover times between brain glycogen and NAA (similar to10h). Absolute quantification of the total concentration of brain glycogen in the awake, normoglycemic rat yielded 3.3 +/- 0.8 mumol/g (n = 6, mean +/- S.D.). (C) 2003 Elsevier Science Ltd. All rights reserved.