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

采用Wistar大鼠，研究了β -胍基丙酸（β - gpa）或肌酸对骨骼肌中高能磷酸盐含量的长期消耗或负荷的影响。给药后比目鱼肌和指长伸肌（EDL）的收缩特性向慢速型转移。这些肌肉的抗疲劳性，特别是EDL，也得到了改善。β - gpa可诱导快速收缩跖肌肌球蛋白亚型的转变。由于受体数量的增加，在β - gpa组肌肉中进一步观察到更大的葡萄糖摄取和β -肾上腺素能受体的最大结合能力。肌酸的施用通常会引起相反的现象。这表明，长期消耗高能磷酸盐刺激线粒体能量代谢，使肌肉向较慢类型转移。研究还表明，如果三磷酸腺苷合成能力得到改善，维持较高水平的高能磷酸盐可能不是提高抗疲劳能力所必需的。

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.