Frank Jason W, Escobar Jeffery, Suryawan Agus, Kimball Scot R, Nguyen Hanh V, Jefferson Leonard S, Davis Teresa A
U.S. Department of Agriculture/Agriculture Research Service, Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA.
J Nutr. 2005 Jun;135(6):1374-81. doi: 10.1093/jn/135.6.1374.
Limited data suggest that the growth of low-birth-weight infants is enhanced by feeding a high-protein diet; however, the mechanisms involved in the effect have not been delineated. To identify these mechanisms, 34 pigs were fed from 2 to 7 d of age [60 g dry matter/(kg body weight . d)] isocaloric milk diets that contained levels of dietary protein that were marginal, adequate, and in excess of the piglets protein requirement (21, 33, and 45% of dry matter, respectively). Dietary protein replaced lactose and fat on an isocaloric basis. Fractional protein synthesis rates, various biomarkers of translational regulation, and plasma glucose and insulin levels were measured in overnight food-deprived and fed pigs. Mean daily weight gain of pigs fed the 33 and 45% protein diets was greater than that of pigs fed the 21% protein diet (P < 0.01). Plasma glucose (P = 0.07) and insulin (P < 0.01) levels decreased as dietary protein increased 60 min after feeding. Protein synthesis rates in longissimus dorsi, gastrocnemius, masseter, heart, liver, kidney, jejunum, and pancreas were greater in the fed than in the food-deprived state (P < 0.01). Protein synthesis in skeletal muscle did not change with protein intake in the fed state, but decreased quadratically (P < 0.01) with increasing dietary protein in the food-deprived state. Protein kinase B, ribosomal protein S6 kinase 1(S6K1), and eukaryotic initiation factor (eIF) 4E binding protein-1 (4E-BP1) were more phosphorylated, and assembly of the inactive eukaryotic initiation factor 4E . 4E-BP1 complex in muscle and liver was reduced in the fed state (P < 0.001) and were not consistently affected by dietary protein level. The results suggest that feeding stimulates protein synthesis, and this is modulated by the activation of initiation factors that regulate mRNA binding to the ribosomal complex. However, the provision of a high-protein diet that exceeds the protein requirement does not further enhance protein synthesis or translation initiation factor activation.
有限的数据表明，喂养高蛋白饮食可促进低体重婴儿的生长；然而，这种效应所涉及的机制尚未明确。为了确定这些机制，给34头仔猪从2日龄至7日龄饲喂等热量的牛奶日粮[60克干物质/（千克体重·天）]，日粮中的蛋白质水平分别为略低于、充足和超过仔猪蛋白质需求量（分别为干物质的21%、33%和45%）。日粮蛋白质在等热量基础上替代乳糖和脂肪。在禁食过夜和喂食后的仔猪中测量了蛋白质合成率、翻译调控的各种生物标志物以及血浆葡萄糖和胰岛素水平。饲喂33%和45%蛋白质日粮的仔猪平均日增重高于饲喂21%蛋白质日粮的仔猪（P<0.01）。喂食60分钟后，随着日粮蛋白质增加，血浆葡萄糖（P = 0.07）和胰岛素（P<0.01）水平降低。喂食状态下，背最长肌、腓肠肌、咬肌、心脏、肝脏、肾脏、空肠和胰腺中的蛋白质合成率高于禁食状态（P<0.01）。在喂食状态下，骨骼肌中的蛋白质合成不会随蛋白质摄入量而变化，但在禁食状态下会随着日粮蛋白质增加呈二次方下降（P<0.01）。蛋白激酶B、核糖体蛋白S6激酶1（S6K1）和真核起始因子（eIF）4E结合蛋白-1（4E-BP1）的磷酸化程度更高，并且在喂食状态下肌肉和肝脏中无活性的真核起始因子4E·4E-BP1复合物的组装减少（P<0.001），且未受到日粮蛋白质水平的一致影响。结果表明，喂食可刺激蛋白质合成，这是由调节mRNA与核糖体复合物结合的起始因子的激活所调节的。然而，提供超过蛋白质需求量的高蛋白饮食并不会进一步增强蛋白质合成或翻译起始因子的激活。
