Bm. Jucker et al., IN-VIVO NMR INVESTIGATION OF INTRAMUSCULAR GLUCOSE-METABOLISM IN CONSCIOUS RATS, American journal of physiology: endocrinology and metabolism, 36(1), 1997, pp. 139-148
In vivo C-13 nuclear magnetic resonance (NMR) spectroscopy was used to
determine quantitatively the flux of muscle glycolysis, glycogen synt
hesis, pyruvate dehydrogenase, and pyruvate carboxylation in the hindl
imb of conscious rats. C-13 NMR spectroscopy was used to observe [1-C-
13]glucose label precursor incorporation into intramuscular [1-C-13]gl
ycogen, [3-C-13]lactate, and [3-C-13]alanine during a hyperglycemic (s
imilar to 11 mM)-hyperinsulinemic (10 mu.kg(-1).min(-1)) clamp. The gl
ycogen synthesis rate was calculated to be 224 +/- 23 nmol.g(-1).min(-
1). The kinetic data obtained from the label turnover in the intramusc
ular C-3 lactate and C-3 alanine metabolite pools, as well as in plasm
a C-3 lactate and C-3 alanine, were combined with a steady-state rate
analysis to determine the glycolytic flux (67.4 +/- 10.1 nmol.g(-1).mi
n(-1)). Steady-state isotopomer analysis of glutamate and pyruvate in
skeletal muscle tissue extracts was used to determine the anaplerotic
contribution of substrate via pyruvate carboxylation (V-pc). The pyruv
ate dehydrogenase flux (V-pdh) was calculated after a steady-state flu
x correction for V-pc. Calculated values of V-pc and V-pdh were 24.8 /- 4.3 and 110.0 +/- 18.7 nmol.g(-1).min(-1), respectively. In additio
n, [2-C-13]acetate was used in a separate study to determine that pyru
vate carboxylation was the major pathway for anaplerosis in skeletal m
uscle under conditions of hyperglycemia-hyperinsulinemia.