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Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908
After confirming that adrenalectomy per se
does not affect skeletal muscle protein synthesis rates, we examined
whether endogenously produced glucocorticoids modulate the effect of
physiological insulin concentrations on protein synthesis in
overnight-fasted rats 4 days after either a bilateral adrenalectomy
(ADX), ADX with dexamethasone treatment (ADX + DEX), or a sham
operation (Sham; n = 6 each). Rats received a 3-h
euglycemic insulin clamp (3 mU · min
1 · kg
1).
Rectus muscle protein synthesis was measured at the end of the clamp,
and the phosphorylation states of protein kinase B (Akt), eukaryotic
initiation factor 4E-binding protein 1 (4E-BP1), and ribosomal protein
S6 kinase (p70S6K) were quantitated before and after the
insulin clamp. The basal phosphorylation states of Akt, 4E-BP1, and
p70S6K were similar between ADX and Sham rats. Insulin
significantly enhanced the phosphorylation of Akt (P < 0.03), 4E-BP1 (P = 0.003), and p70S6K
(P < 0.002) in ADX but not in Sham rats. Protein
synthesis was significantly greater after insulin infusion in ADX than
in Sham rats (P = 0.01). Glucocorticoid replacement
blunted the effect of insulin on Akt, 4E-BP1, and p70S6K
phosphorylation and protein synthesis. In conclusion, glucocorticoid deficiency enhances the insulin sensitivity of muscle protein synthesis, which is mediated by increased phosphorylation of
translation initiation-regulatory proteins.
dexamethasone; translation initiation; protein kinase B; eukaryotic initiation factor 4E-binding protein-1; p70 S6 kinase
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