We compared the chronic effect of intermittent
hypoxia and
endurance training on the
glucose tolerance and
GLUT4 protein expression in rat skeletal muscle. Thirty-two Sprague-Dawley rats were matched for weight and assigned to one of the following four groups: control,
endurance training,
hypoxia, or
hypoxia followed by
endurance training. Hypoxic treatment consisted of breathing 14% O2 for 12 h/day under normobaric conditions, and the training protocol consisted of making animals swim 2 times for 3 h/day. At the end of the 3rd week, an oral
glucose tolerance test (OGTT) was performed 16 h
after treatments. At the end of the 4th week,
GLUT4 protein,
mRNA, and
glycogen storage in skeletal muscle were determined.
Endurance training significantly improved OGTT results.
Glycogen content and
GLUT4 protein expression in the plantaris and red gastrocnemius, but not in the soleus or white gastrocnemius muscles, were also elevated. Chronic intermittent
hypoxia also improved OGTT results, but did not alter
GLUT4 protein expression. Additionally,
hypoxia followed by exercise training produced significant increases in
GLUT4 protein and
mRNA in a greater number of muscles compared to
endurance training alone. Both exercise training and
hypoxia significantly reduced body mass, and an additive effect of both treatments was found. In conclusion, chronic intermittent
hypoxia improved
glucose tolerance in the absence of increased
GLUT4 protein expression. This treatment facilitated the exercise training effect on muscle GLUT4 expression and
glycogen storage. These new findings open the possibility of utilizing intermittent
hypoxia, with or without exercise training, for the prevention and clinical treatment of
type 2 diabetes or
insulin resistance.