The effects of high dose creatine feeding (5 g kg(-1) BW day(-1), 5 days) on creatine content, glucose transport, and glycogen accumulation in white gastrocnemius, red gastrocnemius and soleus muscles of the rat was investigated. Isolated rat hindquarters of creatine fed and control rats were perfused with a standard medium containing either insulin alone (0, 100 or 20 000 microU mL(-1)) or in combination with creatine (2 or 10 mmol L(-1)). Furthermore, plasma insulin concentration was measured in normal rats during creatine feeding, as well as in anaesthetized rats during intravenous creatine infusion. Five days of creatine feeding increased (P < 0.05) total creatine content in soleus (+ 20%) but not in red gastrocnemius (+15%, n.s.) and white gastrocnemius (+ 10%, n.s.). In parallel, glycogen content was markedly elevated (P < 0.05) in soleus (+ 40%), less (P < 0.05) in red gastrocnemius (+ 15%), and not in white gastrocnemius (+ 10%, n.s.). Glucose transport rate, muscle GLUT-4 content, glycogen synthase activity in perfused muscles and glycogen synthesis rate were not significantly altered by creatine feeding in either muscle type. Furthermore, high dose creatine feeding raised (P < 0.05) plasma creatine concentration fivefold but did not alter circulating insulin level. It is concluded that short-term high dose creatine feeding enhances creatine disposal and glycogen storage in rat skeletal muscle. However, the creatine and glycogen response to creatine supplementation is markedly greater in oxidative than in glycolytic muscles.
"The authors demonstrated that postexercise muscle glycogen storage can be augmented by CR and carbohydrate supplementation following exercise compared with carbohydrate ingestion alone. Thereafter, it has been shown that CR-supplemented subjects, during a phase of rehabilitation from immobilization-induced muscle atrophy, had larger muscle glycogen content when compared with non-supplemented subjects (650 versus 520 mmol/kg dry weight) . Accordingly, an 18% increase in muscle glycogen content has been reported as a result of 5 days of concomitant CR and carbohydrate supplementation compared with placebo ingestion . "
[Show abstract][Hide abstract] ABSTRACT: The effects of creatine (CR) supplementation on glycogen content are still debatable. Thus, due to the current lack of clarity, we investigated the effects of CR supplementation on muscle glycogen content after high intensity intermittent exercise in rats.
First, the animals were submitted to a high intensity intermittent maximal swimming exercise protocol to ensure that CR-supplementation was able to delay fatigue (experiment 1). Then, the CR-mediated glycogen sparing effect was examined using a high intensity intermittent sub-maximal exercise test (fixed number of bouts; six bouts of 30-second duration interspersed by two-minute rest interval) (experiment 2). For both experiments, male Wistar rats were given either CR supplementation or placebo (Pl) for 5 days.
As expected, CR-supplemented animals were able to exercise for a significant higher number of bouts than Pl. Experiment 2 revealed a higher gastrocnemius glycogen content for the CR vs. the Pl group (33.59%). Additionally, CR animals presented lower blood lactate concentrations throughout the intermittent exercise bouts compared to Pl. No difference was found between groups in soleus glycogen content.
The major finding of this study is that CR supplementation was able to spare muscle glycogen during a high intensity intermittent exercise in rats.
Journal of the International Society of Sports Nutrition 01/2010; 7(1):6. DOI:10.1186/1550-2783-7-6 · 1.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: INTRODUCTION: Fluorescence recovery after photobleaching (FRAP) is a confocal microscopy- based technique widely used for in vivo quantification of intracellular molecular movements and interactions. FRAP is very useful for elucidating several fundamental but complicated cellular activities, such as cell membrane diffusion and protein binding. AIM: The aim of this study was to investigate whether it is possible to develop stochastic simulation strategies for interpretation of FRAP kinetics. METHODS: A simulation algorithm based on a stochastic simulation of the time evolution of coupled reaction-diffusion biochemical systems was developed for investigating and interpreting FRAP experiments in terms of diffusion and binding. The proposed algorithm was compared with standard deterministic methods that are currently being used for analysis of FRAP curves. RESULTS AND DISCUSSION: Predictions of recovery times of FRAP curves and sum of residuals revealed a good agreement (Table I), at the level of both timescale and intensity, between the proposed model and the standard deterministic methods. The stochastic simulation algorithm presents a firmer physical basis that its deterministic counterparts and might be used to successfully model probabilistic events in the cell, deciphering information in FRAP experiments that cannot be computed using deterministic models.
[Show abstract][Hide abstract] ABSTRACT: The effect of oral creatine supplementation on high-intensity exercise performance has been extensively studied over the past ten years and its ergogenic potential in young healthy subjects is now well documented. Recently, research has shifted from performance evaluation towards elucidating the mechanisms underlying enhanced muscle functional capacity after creatine supplementation. In this review, we attempt to summarise recent advances in the understanding of potential mechanisms of action of creatine supplementation at the level of skeletal muscle cells. By increasing intracellular creatine content, oral creatine ingestion conceivably stimulates operation of the creatine kinase (CK)/phosphocreatine (PCr) system, which in turn facilitates muscle relaxation. Furthermore, evidence is accumulating to suggest that creatine supplementation can beneficially impact on muscle protein and glycogen synthesis. Thus, muscle hypertrophy and glycogen supercompensation are candidate factors to explain the ergogenic potential of creatine ingestion. Additional issues discussed in this review are the fibre-type specificity of muscle creatine metabolism, the identification of responders versus non-responders to creatine intake, and the scientific background concerning potential side effects of creatine supplementation.
Canadian journal of applied physiology = Revue canadienne de physiologie appliquée 02/2001; 26 Suppl(S1):S79-102. DOI:10.1139/h2001-045 · 1.30 Impact Factor
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