Taillandier D, Bigard X, Desplanches D, Attaix D, Guezennec C Y, Arnal M
Laboratoire d'Etude du Métabolisme Azoté, Institut National de la Recherche Agronomique, Centre de Recherches de Clermont-Ferrand-Theix, Ceyrat, France.
J Appl Physiol (1985). 1993 Sep;75(3):1226-32. doi: 10.1152/jappl.1993.75.3.1226.
Protein turnover in skeletal muscle is very sensitive to protein intake. To examine whether protein intake is able to affect protein synthesis in the atrophied soleus muscle, the effects of a high-protein (30%, HP) and a medium-protein (15%, MP) diet were studied in rats after 21 days of hindlimb unweighting. Three weeks of unweighting induced a sharp decrease in food intake (30%). The fractional rate of protein synthesis (ks) was determined in vivo in the slow-twitch soleus muscle by use of a flooding-dose method. With respect to pair-fed animals, a significant reduction in ks occurred (33%) in MP non-weight-bearing rats, whereas it was of lesser magnitude and not significant in HP rats. In the atrophied soleus muscle of non-weight-bearing MP rats, a large decrease (42%) in type I fiber distribution was accompanied by an increase in intermediate and type IIa fibers. By contrast, a higher percentage of type I fiber was maintained with the HP diet. However, the HP diet had no beneficial effect in preventing the decrease in either type I fiber cross-sectional area (65%) or the average decrease in absolute myofibrillar and mitochondrial volumes (69 and 52%, respectively). These results demonstrate that an HP intake did not prevent soleus muscle atrophy but may sustain protein synthesis and partly preserve fiber type distribution without affecting the ultrastructural composition of fibers. Because the circulating level of free 3,5,3'-triiodothyronine was reduced by 14% with the HP diet, this effect on fiber type distribution, and possibly protein synthesis, may involve thyroid hormones.
骨骼肌中的蛋白质周转对蛋白质摄入非常敏感。为了研究蛋白质摄入是否能够影响萎缩比目鱼肌中的蛋白质合成，在大鼠后肢去负荷21天后，研究了高蛋白（30%，HP）和中等蛋白（15%，MP）饮食的影响。三周的去负荷导致食物摄入量急剧下降（30%）。通过使用灌注剂量法在体内测定慢肌比目鱼肌中的蛋白质合成分数率（ks）。与配对喂养的动物相比，MP非负重大鼠的ks显著降低（33%），而HP大鼠的降低幅度较小且不显著。在非负重MP大鼠萎缩的比目鱼肌中，I型纤维分布大幅下降（42%），同时中间纤维和IIa型纤维增加。相比之下，HP饮食能维持更高比例的I型纤维。然而，HP饮食在预防I型纤维横截面积下降（65%）或肌原纤维和线粒体绝对体积的平均下降（分别为69%和52%）方面没有有益作用。这些结果表明，高蛋白摄入并不能预防比目鱼肌萎缩，但可能维持蛋白质合成并部分保留纤维类型分布，而不影响纤维的超微结构组成。由于HP饮食使游离3,5,3'-三碘甲状腺原氨酸的循环水平降低了14%，这种对纤维类型分布以及可能对蛋白质合成的影响可能涉及甲状腺激素。
