NUTRITION AND MYOFIBRILLAR PROTEIN METABOLISM IN OLD AGE

长期目标是了解营养因素是如何影响 肌肉蛋白质代谢，以及这些因素可能如何影响损失 与衰老相关的肌肉群。三个假设将是 检查：1.肌原纤维蛋白的合成与 恒定能量摄入的蛋白质摄入量；2.肌原纤维蛋白 在蛋白质摄入量不变的情况下，合成与能量摄入成正比； 3.高蛋白或高能量饮食刺激肌原纤维 参加抗阻训练计划的受试者的蛋白质合成。 受试者为健康的男性和女性，年龄在60-75岁之间。在第一个 研究将随机分配给他们食用以下其中一种食物 在肌原纤维蛋白合成研究前一周的饮食：低 蛋白质(能量的5%)、正常蛋白质(能量的15%)或高蛋白 (能源的25%)。在第二项研究中，受试者将被随机分配 在摄入蛋白质前一周接受下列饮食之一 综合研究：低能量(50%体重维持)，正常能量 (100%保持体重)，高能量(150%保持体重)。 在第三项研究中，高蛋白/正常能量，高 能量/正常蛋白质，正常蛋白质/正常能量饮食将 提供给参加抵抗训练计划的受试者。 稳定同位素L-[1-13C]亮氨酸掺入肌原纤维 从股外侧肌活检中分离出的蛋白质 肌肉，将测定以评估肌原纤维蛋白的合成。 编码最丰富的肌原纤维蛋白的mRNAs水平， 肌球蛋白头链和肌动蛋白将在这些活检样本中被确定 评估饮食或锻炼是否会影响蛋白质合成 翻译前过程。将使用3-甲基组氨酸的排泄 作为全身肌原纤维蛋白降解的指标。因为肌肉 纤维的大小取决于蛋白质合成和蛋白质合成之间的平衡。 蛋白质降解，这些研究将提供重要的新的 有助于预测营养策略以优化 老年时的肌肉群。

The long term goal is to understand how nutritional factors influence muscle protein metabolism, and how these factors might influence the loss of muscle mass associated with old age. Three hypotheses will be examined: 1. That myofibrillar protein synthesis is proportional to protein intake at a constant energy intake; 2. That myofibrillar protein synthesis is proportional to energy intake at a constant protein intake; 3. That a high protein or a high energy diet stimulate myofibrillar protein synthesis in subjects engaged in a resistance exercise program. Subjects will be healthy men and women, 60-75 years old. In the first study they will be randomly assigned to consume one of the following diets for one week before the myofibrillar protein synthesis study: low protein (5% of energy), normal protein (15% of energy), or high protein (25% of energy). In the second study, subjects will be randomly assigned to receive one of the following diets for one week before the protein synthesis study: low energy (50% of weight-maintenance), normal energy (100% of weight-maintenance), high energy (150% of weight maintenance). In the third study, the high protein/normal energy, the high energy/normal protein, and the normal protein/normal energy diets will be given to subjects who are engaged in a resistance exercise program. Incorporation of the stable isotope L-[1-13C]leucine into myofibrillar proteins, isolated from muscle biopsies taken from the vastus lateralis muscle, will be determined to evaluate myofibrillar protein synthesis. Levels of the mRNAs that encode the most abundant myofibrillar proteins, myosin head chain and actin, will be determined in these biopsy samples to evaluate whether diet or exercise affects protein synthesis through pretranslational processes. Excretion of 3-methylhistidine will be used as an index of wholebody myofibrillar protein degradation. Because muscle fiber size is determined by the balance between protein synthesis and protein degradation, these studies will provide significant new information that could help to predict nutritional strategies to optimize muscle mass in old age.