The purpose of this study was to determine whether hyperinsulinemia alters
myosin heavy chain (MHC) gene expression in human skeletal muscle. A biopsy
from the vastus lateralis was obtained in young, lean [age 24.6 +/- 1.0 (S
E) yr, body fat 11.9 +/- 1.9%, body mass index 26.1 +/- 1.1 kg/m(2); n = 10
] men before and after 3 h of hyperinsulinemia (hyperinsulinemic-euglycemic
clamp). Muscle was analyzed for mRNA of type I, IIa, and IIx MHC isoforms.
Hyperinsulinemia (mean of 1,065.7 +/- 9.8 pmol/l during minutes 20 to 180)
did not change (P > 0.05) the mRNA concentration of either the type I MHC
or type IIA MHC isoforms. In contrast, type IIX MHC mRNA increased (P < 0.0
5) with hyperinsulinemia compared with the fasted condition. These data ind
icate that hyperinsulinemia rapidly increases type IIx MHC mRNA in human sk
eletal muscle.