Elevated skeletal muscle glucose transporter levels in exercise-trained middle-aged men.
Exercise training has been proposed to improve whole body insulin sensitivity through a postreceptor adaptation in skeletal muscle. This study examined if levels of the insulin-responsive muscle glucose transporter protein (GLUT-4) were associated with improved insulin sensitivity in trained vs. sedentary middle-aged individuals. Muscle GLUT-4 levels and oral glucose tolerance test (OGTT) responses were obtained in age-matched trained and sedentary men (n = 11). Plasma insulin levels during the OGTT were significantly lower (P less than 0.01) in the trained men, whereas no differences were seen in plasma glucose responses. GLUT-4 protein content was approximately twofold higher in the trained men (2.41 +/- 0.17 vs. 1.36 +/- 0.11 micrograms standard, P less than 0.001). OGTT responses and GLUT-4 levels were not altered 15-18 h after a standard exercise bout in six representative sedentary subjects. These data suggest that GLUT-4 levels are increased in conjunction with insulin sensitivity in chronically exercise-trained middle-aged men. This finding suggests a possible mechanism for the improved insulin sensitivity observed with exercise training in humans.
Houmard
J A
JA
Human Performance Laboratory, School of Medicine, East Carolina University, Greenville, North Carolina 27858.
Egan
P C
PC
Neufer
P D
PD
Friedman
J E
JE
Wheeler
W S
WS
Israel
R G
RG
Dohm
G L
GL
D000328:Adult; D000368:Aged; D001786:Blood Glucose / Q000032:analysis; D005951:Glucose Tolerance Test; D006801:Humans; D007328:Insulin / Q000097:blood / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism*; D010806:Physical Education and Training; D013997:Time Factors
D001786:Blood Glucose; D007328:Insulin; D009004:Monosaccharide Transport Proteins