Department of Animal Sciences, University of Illinois, Urbana.
Department of Veterinary Medicine, Ajinomoto Animal Nutrition North America Inc., Chicago, IL.
J Anim Sci. 2019 Oct 3;97(10):4282-4292. doi: 10.1093/jas/skz259.
An experiment was conducted to test the hypothesis that excess dietary Leu affects metabolism of branched-chain amino acids (BCAA) in growing pigs. Forty barrows (initial body weight [BW]: 30.0 ± 2.7 kg) were housed individually in metabolism crates and allotted to 5 dietary treatments (8 replicates per treatment) in a randomized complete block design. The 5 diets were based on identical quantities of corn, soybean meal, wheat, and barley and designed to contain 100%, 150%, 200%, 250%, or 300% of the requirement for standardized ileal digestible Leu. Initial and final (day 15) BW of pigs were recorded. Daily feed consumption was also recorded. Urine and fecal samples were collected for 5 d following 7 d of adaptation to the diets. At the end of the experiment, blood and tissue samples were collected to analyze plasma urea N (PUN), plasma and hypothalamic serotonin, tissue BCAA, serum and tissue branched-chain α-keto acids, and messenger ribonucleic acid abundance of genes involved in BCAA metabolism. Results indicated that acid detergent fiber, average daily feed intake, and gain-to-feed ratio decreased (linear, P < 0.05) as dietary Leu increased. A trend (linear, P = 0.082) for decreased N retention and decreased (linear, P < 0.05) biological value of dietary protein was also observed, and PUN increased (linear, P < 0.05) as dietary Leu increased. A quadratic reduction (P < 0.05) in plasma serotonin and a linear reduction (P < 0.05) in hypothalamic serotonin were observed with increasing dietary Leu. Concentrations of BCAA in liver increased (linear, P < 0.001), whereas concentrations of BCAA in skeletal muscle decreased (linear, P < 0.05) as dietary Leu increased. Concentration of α-ketoisovalerate was reduced (linear and quadratic, P < 0.001) in liver, skeletal muscle, and serum, and α-keto-β-methylvalerate was reduced (linear, P < 0.001; quadratic, P < 0.001) in skeletal muscle and serum. In contrast, α-keto isocaproate increased (linear, P < 0.05) in liver and skeletal muscle and also in serum (linear and quadratic, P < 0.001) with increasing dietary Leu. Expression of mitochondrial BCAA transaminase and of the E1α subunit of branched-chain α-keto acid dehydrogenase increased (linear, P < 0.05) in skeletal muscle as dietary Leu increased. In conclusion, excess dietary Leu impaired growth performance and nitrogen retention, which is likely a result of increased catabolism of Ile and Val, which in turn reduces availability of these amino acids resulting in reduced protein retention, and excess dietary Leu also reduced hypothalamic serotonin synthesis.
进行了一项实验，以检验以下假设：过量的膳食亮氨酸会影响生长猪支链氨基酸（BCAA）的代谢。将 40 头阉公猪（初始体重[BW]：30.0±2.7kg）单独饲养在代谢笼中，并按随机完全区组设计分配到 5 种膳食处理（每种处理 8 个重复）。这 5 种日粮以相同数量的玉米、豆粕、小麦和大麦为基础，并设计成含有标准化回肠可消化亮氨酸需求的 100%、150%、200%、250%或 300%。记录猪的初始和终末（第 15 天）BW。还记录了每日饲料消耗量。适应日粮 7 天后，收集尿液和粪便样本 5 天。实验结束时，采集血液和组织样本，以分析血浆尿素氮（PUN）、血浆和下丘脑 5-羟色胺、组织 BCAA、血清和组织支链α-酮酸以及涉及 BCAA 代谢的基因的信使核糖核酸丰度。结果表明，随着日粮亮氨酸的增加，酸性洗涤纤维、平均日采食量和饲料增重比降低（线性，P<0.05）。还观察到氮保留减少的趋势（线性，P=0.082）和膳食蛋白质生物学价值降低（线性，P<0.05），随着日粮亮氨酸的增加，PUN 增加（线性，P<0.05）。随着日粮亮氨酸的增加，血浆 5-羟色胺呈二次降低（P<0.05），下丘脑 5-羟色胺呈线性降低（P<0.05）。随着日粮亮氨酸的增加，肝脏中 BCAA 的浓度增加（线性，P<0.001），而骨骼肌中 BCAA 的浓度降低（线性，P<0.05）。肝脏、骨骼肌和血清中α-酮异戊酸的浓度降低（线性和二次，P<0.001），骨骼肌和血清中α-酮-β-甲基戊酸的浓度降低（线性，P<0.001；二次，P<0.001）。相反，随着日粮亮氨酸的增加，肝脏和骨骼肌以及血清中的α-酮异己酸增加（线性，P<0.05）。随着日粮亮氨酸的增加，骨骼肌中线粒体 BCAA 转氨酶和支链α-酮酸脱氢酶 E1α 亚基的表达增加（线性，P<0.05）。总之，过量的膳食亮氨酸会损害生长性能和氮保留，这可能是由于异亮氨酸和缬氨酸的分解代谢增加所致，这反过来又减少了这些氨基酸的可用性，导致蛋白质保留减少，过量的膳食亮氨酸还会减少下丘脑 5-羟色胺的合成。
