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1 Copenhagen Muscle Research Center, Department of Human Physiology, Institute of Exercise and Sport Sciences, University of Copenhagen, DK-2400 Copenhagen; 2 Copenhagen Muscle Research Center, Department of Neurology, Rigshospitalet, DK-2100 Copenhagen, Denmark; 3 Institute for Exercise and Environmental Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75216; and 4 Diabetes Research Laboratory, Winthrop University Hospital, Mineola, New York 11501
Insulin action is decreased by high
muscle glycogen concentrations in skeletal muscle. Patients with
McArdle's disease have chronic high muscle glycogen levels and might
therefore be at risk of developing insulin resistance. In this study,
six patients with McArdle's disease and six matched control subjects
were subjected to an oral glucose tolerance test and a
euglycemic-hyperinsulinemic clamp. The muscle glycogen concentration
was 103 ± 45% higher in McArdle patients than in controls. Four
of six McArdle patients, but none of the controls, had impaired glucose
tolerance. The insulin-stimulated glucose utilization and the
insulin-stimulated increase in glycogen synthase activity during the
clamp were significantly lower in the patients than in controls
(51.3 ± 6.0 vs. 72.6 ± 13.1 µmol · min
1 · kg lean body
mass
1, P < 0.05, and 53 ± 15 vs.
79 ± 9%, P < 0.05, n = 6, respectively). The difference in insulin-stimulated glycogen synthase
activity between the pairs was significantly correlated
(r = 0.96, P < 0.002) with the
difference in muscle glycogen level. The insulin-stimulated increase in
Akt phosphorylation was smaller in the McArdle patients than in
controls (45 ± 13 vs. 76 ± 13%, P < 0.05, respectively), whereas basal and insulin-stimulated glycogen synthase
kinase 3
and protein phosphatase-1 activities were similar in the
two groups. Furthermore, the ability of insulin to decrease and
increase fat and carbohydrate oxidation, respectively, was blunted in
the patients. In conclusion, these data show that patients with
McArdle's glycogen storage disease are insulin resistant in terms of
glucose uptake, glycogen synthase activation, and alterations in fuel oxidation. The data further suggest that skeletal muscle glycogen levels play an important role in the regulation of insulin-stimulated glycogen synthase activity.
glycogen synthase; protein phosphatase; glycogen synthase kinase 3; glucose clamp technique; glycogen storage disease type V
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