EFFECT OF DETRAINING ON GLUT-4 PROTEIN IN HUMAN SKELETAL-MUSCLE

The present study was undertaken to examine the effect of 10 days of d etraining on levels of GLUT-4 protein expression and citrate synthase (CS) activity in the vastus lateralis of trained men. During the cours e of normal training, seven endurance-trained (T) men and eight age- a nd weight-matched active but untrained (UT) men underwent an oral gluc ose tolerance test (OGTT) after an overnight fast. Muscle samples were obtained from the vastus lateralis by needle biopsy for measurement o f GLUT-4 protein and CS activity. The tests were repeated on six of th e T subjects after 10 days of detraining (DT men). The area under the insulin response curve during OGTT was lower in T men than in DT and U T men (22.4 +/- 2.8, 32.1 +/- 5.9, and 39.9 +/- 4.7 X10(-3) pmol . 1(- 1) . min(-)1, respectively; P < 0.05). There were no differences betwe en groups in the glucose responses to OGTT. GLUT-4 protein levels and CS activity were higher in T men than in DT and UT men (GLUT-4: 4.37 /- 0.40, 2.92 +/- 0.53, and 1.71 +/- 0.22 arbitrary standard units and CS: 47.12 +/- 4.75, 33.63 +/- 3.98, and 24.51 +/- 2.97 mu mol . min(- 1) . g(-1), respectively; both P < 0.05). Muscle GLUT-4 protein conten t was correlated with CS activity in all three groups (r = 0.64, 0.68, and 0.96 for UT, T, and DT men, respectively). These results suggest that muscle GLUT-4 protein content and oxidative capacity undergo para llel adaptations after detraining in previously well-trained men.