Abstract
PURPOSE: It is now well established that, even in the absence of food intake, a large proportion of muscle glycogen (MG) stores are replenished during recovery from high intensity exercise (HIE), and that this process occurs to a large extent at the expense of lactate. The two metabolic pathways with the capacity to convert lactate into MG are the Cori cycle and muscle lactate glyconeogenesis (MLG), but their relative contributions to this process in mammals is still a matter of dispute. The purpose of this study was to establish the contributions of these pathways by determining the post-exercise pattern of carbon labelling of [13C]glucosyl-glycogen from muscles pre-labelled with [1 −13C]glucosyl-glycogen.
METHODS: A group of post-absorptive male Wistar rats previously fed with [1−13C]glucose were subjected to a 3-min high intensity swim and their muscles, plasma and liver sampled under halothane anaesthesia either prior to or at time intervals (0, 15 and 30 min) after exercise. The samples were extracted and assayed for metabolite levels, and NMR spectral analyses performed to determine the pattern of [13C] labelling of muscle glycogen.
RESULTS: were analysed using a one-way ANOVA with repeated measures followed by a Tukey test.
RESULTS: In response to HIE, MG stores were significantly depleted and both muscle and plasma lactate levels rose significantly. By 30 min post-exercise, 73% of glycogen was replenished concomitant with a fall in both plasma and muscle lactate to pre-exercise levels, and [1 −13C]glucosyl-glycogen units of skeletal muscle returned to 59% of pre-exercise levels, with the greatest increase in labelling occurring at C-1 and C-6 of the glucosyl-glycogen units. On this basis, it was calculated that during the initial 15 min of recovery, the relative contributions of MLG and blood glucose derived from Cori cycle were at the most 58.0% and 31.7%, respectively, but during the subsequent 15 min, the contribution of MLG decreased to 36.4%, whereas that of blood glucose increased to 55.3%.
CONCLUSION: Our findings provide the first evidence that during recovery from HIE, there is a temporal shift in the relative contributions of MLG and the Cori cycle to muscle glycogen synthesis.