Effects of high-energy phosphates on morphological and functional development in rat muscles

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Effects of chronic depletion or loading of high-energy phosphate contents in skeletal muscles by feeding either beta-guanidinopropionic acid (beta-GPA) or creatine were studied in Wistar rats. The contractile properties in both soleus and extensor digitorum longus (EDL) were shifted toward slower type by feeding beta-GPA.The fatigue resistance in these muscles, especially EDL,was also improved. Transition of myosin isoforms in fast-twitch plantaris muscle was induced by administration of beta-GPA.Greater glucose uptake and the maximum binding capacity of beta-adrenoceptor, due to an increased receptor number, were further observed in the musles of beta-GPA group. Administration of creatine induced, generally, opposite phenomena. It is suggested that chronic depletion of high-energy phosphates stimulates the mitochondrial energy metabolism and shifts the muscle towerd slower type. It is also indicated that maintenance of high-energy phosphates at higher levels may not be essential for the greater fatigue resistance, if the capacity of adenosine triphosphate synthesis is improved.