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Department of Diabetes Biology, Novo Nordisk, 2880 Bagsvaerd, Denmark
We examined whether acute
activation of 5'-AMP-activated protein kinase (AMPK) by
5'-aminoimidazole-4-carboxamide-1-
-D-ribonucleoside (AICAR) ameliorates insulin resistance in isolated rat skeletal muscle.
Insulin resistance was induced in extensor digitorum longus (EDL)
muscles by prolonged exposure to 1.6 mM palmitate, which inhibited
insulin-stimulated glycogen synthesis to 51% of control after 5 h
of incubation. Insulin-stimulated glucose transport was less affected
(22% of control). The decrease in glycogen synthesis was accompanied
by decreased glycogen synthase (GS) activity and increased GS
phosphorylation. When including 2 mM AICAR in the last hour of the 5-h
incubation with palmitate, the inhibitory effect of palmitate on
insulin-stimulated glycogen synthesis and glucose transport was
eliminated. This effect of AICAR was accompanied by activation of AMPK.
Importantly, AMPK inhibition was able to prevent this effect. Neither
treatment affected total glycogen content. However, glucose 6-phosphate
was increased after inclusion of AICAR, indicating increased influx of
glucose. No effect of AICAR on the inhibited insulin-stimulated GS
activity or increased GS phosphorylation by palmitate could be
detected. Thus the mechanism by which AMPK activation ameliorates the
lipid-induced insulin resistance probably involves induction of
compensatory mechanisms overriding the insulin resistance. Our results
emphasize AMPK as a promising molecular target for treatment of insulin resistance.
insulin sensitivity; 5'-aminoimidazole-4-carboxamide-1-
-D-ribonucleoside; glycogen synthesis; palmitate
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