Effect of creatine supplementation on creatine and glycogen content in ratskeletal muscle

The effects of high dose creatine feeding (5 g kg(-1) BW day(-1), 5 days) o n creatine content, glucose transport, and glycogen accumulation in white g astrocnemius, red gastrocnemius and soleus muscles of the rat was investiga ted. Isolated rat hindquarters of creatine fed and control rats were perfus ed with a standard medium containing either insulin alone (0, 100 or 20 000 muU mL(-1)) or in combination with creatine (2 or 10 mmol L-1). Furthermor e, plasma insulin concentration was measured in normal rats during creatine feeding, as well as in anaesthetized rats during intravenous creatine infu sion. Five days of creatine feeding increased (P < 0.05) total creatine con tent in soleus (+20%) but not in red gastrocnemius (+15%, n.s.) and white g astrocnemius (+10%, n.s.). In parallel, glycogen content was markedly eleva ted (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, mus cle GLUT-4 content, glycogen synthase activity in perfused muscles and glyc ogen synthesis rate were not significantly altered by creatine feeding in e ither muscle type. Furthermore, high dose creatine feeding raised (P < 0.05 ) plasma creatine concentration fivefold but did not alter circulating insu lin level. It is concluded that short-term high dose creatine feeding enhan ces 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.