SKELETAL-MUSCLE GLUT-4 AND GLUCOSE-UPTAKE DURING EXERCISE IN HUMANS

The present study examined the relationship between total skeletal mus cle GLUT-4 protein level and glucose uptake during exercise. Eight act ive non-endurance-trained men cycled at 72 +/- 1% peak pulmonary oxyge n consumption for 40 min, with rates of glucose appearance and disappe arance (Rd) determined by utilizing a primed continuous infusion of [3 -H-3]glucose commencing 2 h before exercise. Muscle glycogen content a nd utilization, citrate synthase activity, and total GLUT-4 protein we re measured on muscle biopsy samples obtained from the vastus laterali s. A direct relationship existed between preexercise muscle glycogen c ontent and glycogen utilization during exercise (r = 0.76, P < 0.05). Citrate synthase activity and glucose Rd at the end of exercise averag ed 21.9 +/- 3.0 mu mol . min(-1) . g(-1) and 27.3 +/- 2.5 mu mol . kg( -1) . min(-1), respectively. There was a direct correlation between ci trate synthase activity and GLUT-4 protein (r = 0.78, P < 0.05); howev er, at the end of exercise, glucose Rd was inversely related to both G LUT-4 (r = -0.89, P < 0.01) and citrate synthase activity (r = -0.72, P < 0.05). Plasma insulin, which decreased during exercise, was not re lated to glucose Rd. In conclusion, glucose uptake during 40 min of ex ercise at 72% peak pulmonary oxygen consumption was inversely related to the total muscle GLUT-4 protein level. This suggests that factors o ther than the total GLUT-4 protein level are important in the regulati on of glucose uptake during exercise.