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Noninvasive Measurements of [1‐ 13 C] Glycogen Concentrations and Metabolism in Rat Brain In Vivo
Author(s) -
Choi InYoung,
Tkáčc Ivan,
Ugurbil Kâmil,
Gruetter Rolf
Publication year - 1999
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1999.0731300.x
Subject(s) - glycogen , glycogen phosphorylase , endocrinology , medicine , chemistry , metabolism , in vivo , glycogen branching enzyme , glycogen synthase , mole , carbohydrate metabolism , glycogenesis , biochemistry , biology , microbiology and biotechnology
: Using a specific 13 C NMR localization method, 13 C label incorporation into the glycogen C1 resonance was measured while infusing [1‐ 13 C]glucose in intact rats. The maximal concentration of [1‐ 13 C]glycogen was 5.1 ± 0.6 μmol g ‐1 (mean ± SE, n = 8). During the first 60 min of acute hyperglycemia, the rate of 13 C label incorporation (synthase flux) was 2.3 ± 0.7 μmol g ‐1 h ‐1 (mean ± SE, n = 9 rats), which was higher ( p <0.01) than the rate of 0.49 ± 0.14 μmol g ‐1 h ‐1 measured ≥2 h later. To assess whether the incorporation of 13 C label was due to turnover or net synthesis, the infusion was continued in seven rats with unlabeled glucose. The rate of 13 C label decline (phosphorylase flux) was lower (0.33 ± 0.10 μmol g ‐1 h ‐1 ) than the initial rate of label incorporation ( p < 0.01) and appeared to be independent of the duration of the preceding infusion of [1‐ 13 C]glucose ( p > 0.05 for correlation). The results implied that net glycogen synthesis of ~3 μmol g ‐1 had occurred, similar to previous reports. When infusing unlabeled glucose before [1‐ 13 C]glucose in three studies, the rate of glycogen C1 accumulation was 0.46 ± 0.08 μmol g ‐1 h ‐1 . The results suggest that steady‐state glycogen turnover rates during hyperglycemia are ~1% of glucose consumption.