AJP - Endocrinology and Metabolism, Vol 273, Issue 1 E139-E148, Copyright © 1997 by American Physiological Society
In vivo NMR investigation of intramuscular glucose metabolism in conscious rats
B. M. Jucker, A. J. Rennings, G. W. Cline, K. F. Petersen and G. I. Shulman
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520-8020, USA.
In vivo 13C nuclear magnetic resonance (NMR) spectroscopy was used to
determine quantitatively the flux of muscle glycolysis, glycogen synthesis,
pyruvate dehydrogenase, and pyruvate carboxylation in the hindlimb of
conscious rats. 13C NMR spectroscopy was used to observe [1-13C]glucose
label precursor incorporation into intramuscular [1-13C]glycogen,
[3-13C]lactate, and [3-13C]alanine during a hyperglycemic (approximately 11
mM)-hyperinsulinemic (10 mU.kg-1.min-1) clamp. The glycogen synthesis rate
was calculated to be 224 +/- 23 nmol.g-1.min-1. The kinetic data obtained
from the label turnover in the intramuscular C-3 lactate and C-3 alanine
metabolite pools, as well as in plasma 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.min-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 (Vpc). The pyruvate dehydrogenase flux (Vpdh) was calculated
after a steady-state flux correction for Vpc. Calculated values of Vpc and
Vpdh were 24.8 +/- 4.3 and 110.0 +/- 18.7 nmol.g-1.min-1, respectively. In
addition, [2-13C]acetate was used in a separate study to determine that
pyruvate carboxylation was the major pathway for anaplerosis in skeletal
muscle under conditions of hyperglycemia-hyperinsulinemia.
