Wang Xu, Qiao Shiyan, Yin Yulong, Yue Longyao, Wang Zongyi, Wu Guoyao
National Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China.
J Nutr. 2007 Jun;137(6):1442-6. doi: 10.1093/jn/137.6.1442.
Dietary threonine imbalance is known to reduce the growth of the small intestine, liver, and skeletal muscle in young animals, but the underlying mechanism is largely unknown. Using the pig model, this study was conducted to test the hypothesis that either a deficiency or an excess of dietary threonine impairs protein synthesis in these tissues. Young pigs (25 d of age) were fed diets containing 0.37, 0.74 (current NRC requirement) or 1.11% true ileal digestible threonine (TIDT) (n = 6/diet). Pigs receiving the 0.74 and 1.11% TIDT diets were pair-fed with the same amount of feed as pigs receiving the 0.37% TIDT diet. After a 14-d dietary treatment, the fractional synthesis rate (FSR) of protein in tissues was measured using a flooding dose of l-phenylalanine plus L-[ring-(2)H(5)]phenylalanine. The results indicated that the FSR of protein in liver was reduced (P < 0.05) in pigs fed the 0.37% TIDT diet compared with pigs fed the 0.74 or 1.11% TIDT diet, and did not differ between pigs fed the 0.74 and 1.11% TIDT diets. The FSR of protein in longissimus muscle, jejunal mucosa, and mucins was reduced (P < 0.05) in pigs fed the 0.37 or 1.11% TIDT diet compared with pigs fed the 0.74% TIDT diet. The absolute synthesis rate of protein in the jejunal mucosa and muscle was also reduced (P < 0.01) in pigs fed the 0.37 and 1.11% TIDT diets compared with the controls. The absolute synthesis rate of hepatic protein was lower (P < 0.01) in pigs fed the 0.37% TIDT diets when compared with pigs fed the 0.74% TIDT diet. Protein synthesis in skeletal muscle as well as jejunal mucosa and mucins was reduced to a greater extent than that in liver in response to an imbalance of dietary threonine. Collectively, these results indicate that either an excess or a deficiency of dietary threonine decreases protein synthesis in rapidly growing tissues of young pigs. The findings provide a mechanism for the low growth performance of animals fed a threonine-imbalanced diet.
已知日粮苏氨酸失衡会降低幼龄动物小肠、肝脏和骨骼肌的生长，但潜在机制 largely 未知。本研究采用猪模型来检验以下假设：日粮苏氨酸缺乏或过量会损害这些组织中的蛋白质合成。给幼猪（25 日龄）饲喂含 0.37%、0.74%（当前 NRC 需求量）或 1.11%真回肠可消化苏氨酸（TIDT）的日粮（每组 n = 6）。接受 0.74%和 1.11% TIDT 日粮的猪与接受 0.37% TIDT 日粮的猪按相同采食量进行配对饲喂。经过 14 天的日粮处理后，使用大剂量的 L-苯丙氨酸加 L-[环-(2)H(5)]苯丙氨酸测定组织中蛋白质的分数合成率（FSR））。结果表明，与饲喂 0.74%或 1.11% TIDT 日粮的猪相比，饲喂 0.37% TIDT 日粮的猪肝脏中蛋白质的 FSR 降低（P < 0.05），而饲喂 0.74%和 1.11% TIDT 日粮的猪之间无差异。与饲喂 0.74% TIDT 日粮的猪相比，饲喂 0.37%或 1.11% TIDT 日粮的猪背最长肌、空肠黏膜和黏蛋白中蛋白质的 FSR 降低（P < 0.05）。与对照组相比，饲喂 0.37%和 1.11% TIDT 日粮组猪的空肠黏膜和肌肉中蛋白质的绝对合成率也降低（P < 0.01）。与饲喂 0.74% TIDT 日粮的猪相比，饲喂 0.37% TIDT 日粮的猪肝脏蛋白质的绝对合成率更低（P < 0.01）。日粮苏氨酸失衡时，骨骼肌以及空肠黏膜和黏蛋白中的蛋白质合成比肝脏中的蛋白质合成减少幅度更大。总体而言，这些结果表明，日粮苏氨酸过量或缺乏都会降低幼猪快速生长组织中的蛋白质合成。这些发现为饲喂苏氨酸失衡日粮的动物生长性能低下提供了一种机制。
