MUSCLE GLYCOGEN REPLETION FROM ENDOGENOUS CARBON-SOURCES DURING RECOVERY FROM HIGH-INTENSITY EXERCISE IN THE FASTED RAT

During recovery from high intensity exercise. substantial and rapid mu scle glycogen repletion from endogenous carbon sources is reported in a variety of vertebrate species, the rat being the only reported excep tion. The major aim of this study was to re-examine the process of gly cogen repletion during recovery from high intensity exercise in the ra t. In response to 3 min of vigorous swimming, muscle glycogen concentr ations decrease markedly from initial levels of 20.2+/-1.5 and 21.2+/- 0.9 mu mol g(-1) to 6.4+/-1.1 and 7.9+/-1.4 mu mol g(-1) in the tibial is anterior and plantaris muscles respectively, The equivalent of 58% of the glycogen carbons mobilized during exercise by the plantaris and 73% of that mobilized by the tibialis anterior muscle is repleted wit hin 1 h following exercise. Using the hepatectomized rat as experiment al model, a secondary aim of the study was to evaluate whether the liv er is essential for the repletion of muscle glycogen. Although the abs ence of significant differences in the magnitude of post-exercise musc le glycogen repletion between sham-operated and hepatectomized rats su ggests that the resynthesis of muscle glycogen can take place in the a bsence of hepatic gluconeogenesis. the present study identifies severa l limitations in the use of acute hepatectomy. Overall, the present st udy indicates that, in contrast to published views, the rat resembles other vertebrates in that it can support extensive muscle glycogen rep letion from endogenous carbon sources during the recovery phase follow ing high intensity exercise.