Nishio M L, Jeejeebhoy K N
Department of Physiology, University of Toronto, Ontario, Canada.
JPEN J Parenter Enteral Nutr. 1992 May-Jun;16(3):219-25. doi: 10.1177/0148607192016003219.
The effect of malnutrition on the functional properties of fast- and slow-twitch muscles from rats was studied using aerobic and anaerobic preparations. A 2-day fast and hypocaloric feeding to a weight loss of 25% were used as models of malnutrition. Soleus (slow-twitch) and extensor digitorum longus (EDL) (fast-twitch) muscles were studied using an in situ preparation with the blood supply intact and an in vitro preparation to which cyanide had been added to render the muscles anaerobic. We found that a 2-day fast had little effect on the function of muscles stimulated in situ, whereas anaerobic stimulation produced a decrease in force per gram of muscle weight in the soleus, but not in the EDL, compared with control values. Hypocaloric feeding resulted in a slowed relaxation rate, an increased Fs/Fmax ratio, and an upward shift of the force-frequency curve relative to controls when studied in situ. Under anaerobic conditions, soleus muscles from hypocaloric rats continued to show a slow relaxation rate and demonstrated a loss of force per gram of muscle weight compared with controls, particularly at low stimulation frequencies. EDL muscles from hypocaloric rats had an increased relaxation rate and were able to maintain force with anaerobic stimulation. Soleus and EDL muscles from the fasted and hypocaloric groups had lower activities of phosphofructokinase. We conclude that slow-twitch muscles from malnourished rats are at a disadvantage when required to function under anaerobic conditions. These findings suggest that muscle performance may be impaired in malnourished patients subjected to hypoxia.
采用有氧和无氧制备方法，研究了营养不良对大鼠快肌和慢肌功能特性的影响。以2天禁食和低热量喂养导致体重减轻25%作为营养不良模型。使用完整保留血液供应的原位制备方法以及添加氰化物使肌肉处于无氧状态的体外制备方法，对比目鱼肌（慢肌）和趾长伸肌（EDL，快肌）进行研究。我们发现，2天禁食对原位刺激肌肉的功能影响不大，而与对照值相比，无氧刺激使比目鱼肌每克肌肉重量的力量下降，但对趾长伸肌没有影响。低热量喂养导致原位研究时，肌肉舒张速率减慢、Fs/Fmax比值增加以及力量-频率曲线相对于对照向上偏移。在无氧条件下，低热量喂养大鼠的比目鱼肌继续表现出舒张速率缓慢，并且与对照相比，每克肌肉重量的力量有所下降，尤其是在低刺激频率下。低热量喂养大鼠的趾长伸肌舒张速率增加，并且在无氧刺激下能够维持力量。禁食和低热量喂养组的比目鱼肌和趾长伸肌磷酸果糖激酶活性较低。我们得出结论，营养不良大鼠的慢肌在无氧条件下发挥功能时处于劣势。这些发现表明，营养不良且处于缺氧状态的患者肌肉性能可能受损。
