GLYCOGEN SUPERCOMPENSATION MASKS THE EFFECT OF A TRAINING-INDUCED INCREASE IN GLUT-4 ON MUSCLE GLUCOSE-TRANSPORT

Endurance exercise training induces a rapid increase in the GLUT-4 iso form of the glucose transporter in muscle. In fasted rats, insulin-sti mulated muscle glucose transport is increased in proportion to the inc rease in GLUT-4. There is evidence that high muscle glycogen may decre ase insulin-stimulated glucose transport. This study was undertaken to determine whether glycogen supercompensation interferes with the incr ease in glucose transport associated with an exercise-induced increase in GLUT-4. Rats were trained by means of swimming for 6 h/day for 2 d ays. Rats fasted overnight after the last exercise bout had an approxi mately twofold increase in epitrochlearis muscle GLUT-4 and an associa ted approximately twofold increase in maximally insulin-stimulated glu cose transport activity. Epitrochlearis muscles of rats fed rodent cho w after exercise were glycogen supercompensated (86.4 +/- 4.8 mu mol/g wet wt) and showed no significant increase in maximally insulin-stimu lated glucose transport above the sedentary control value despite an a pproximately twofold increase in GLUT-4. Fasting resulted in higher ba sal muscle glucose transport rates in both sedentary and trained rats but did not significantly increase maximally insulin-stimulated transp ort in the sedentary group. We conclude that carbohydrate feeding that results in muscle glycogen supercompensation prevents the increase in maximally insulin-stimulated glucose transport associated with an exe rcise training-induced increase in muscle GLUT-4.