Department of Animal Science, Iowa State University, Ames 50011.
Department of Animal Science, Iowa State University, Ames 50011.
J Dairy Sci. 2019 Apr;102(4):3584-3597. doi: 10.3168/jds.2018-15627. Epub 2019 Jan 17.
Experimental objectives of this study were to characterize the systemic and intracellular metabolic response to continuous lipopolysaccharide (LPS) infusion in mid-lactation Holstein cows (169 ± 20 d in milk; 681 ± 16 kg of body weight). Following 3 d of acclimation, cows were enrolled in 2 experimental periods (P). During P1 (3 d), cows were fed ad libitum and baseline data were collected. In P2 (8 d), cows were assigned to 1 of 2 treatments: (1) saline-infused and pair-fed (CON-PF; i.v. sterile saline at 40 mL/h; n = 5) or (2) LPS-infused and fed ad libitum (LPS-AL; Escherichia coli O55:B5 at 0.017, 0.020, 0.026, 0.036, 0.055, 0.088, 0.148, and 0.148 µg/kg of body weight per hour for d 1 through 8, respectively; n = 6). During P2, CON-PF cows were pair-fed to LPS-AL cows to eliminate confounding effects of dissimilar nutrient intake. Blood samples were collected on d 1 and 2 of P1 and d 1, 3, 5, and 7 of P2. Following the P2 d 7 a.m. milking, adipose tissue, skeletal muscle, and liver biopsies were collected for reverse transcription quantitative PCR and Western blot analysis. To assess whole-body nutrient trafficking, an i.v. glucose tolerance test (GTT) was performed following the a.m. milking on P2 d 8; 4 h after the GTT, cows received an epinephrine challenge. During P2, there were no treatment differences in circulating glucose. Relative to P1, CON-PF cows had or tended to have decreased plasma β-hydroxybutyrate and insulin (29 and 47%, respectively) during P2, whereas neither variable changed in LPS-AL cows, leading to an overall increase in β-hydroxybutyrate and insulin (41 and 140%, respectively) relative to CON-PF cows. Circulating nonesterified fatty acids were increased from d 1 to 3 and subsequently decreased from d 3 to 7 in cows from both treatments. Blood urea nitrogen gradually decreased in CON-PF cows and increased in LPS-AL cows from d 1 to 5 of P2, resulting in an overall 25% increase in LPS-AL versus CON-PF cows. In response to the GTT, the glucose and insulin area under the curve were increased 33 and 56%, respectively, in LPS-AL compared with CON-PF cows; changes reflective of whole-body insulin resistance. However, protein abundance of insulin signaling markers within muscle, liver, and adipose tissue were similar between treatments. There were no observable treatment differences in the glucose or nonesterified fatty acids response to the epinephrine challenge. No treatment differences were observed in hepatic mRNA abundance of key gluconeogenic or lipid export enzymes. In conclusion, chronic LPS exposure altered multiple parameters of basal and stimulated metabolism, but did not appear to affect the molecular machinery evaluated herein.
本研究的实验目的是描述持续内毒素（LPS）输注对泌乳中期荷斯坦奶牛（泌乳天数 169±20 天；体重 681±16kg）的全身和细胞内代谢的影响。适应期 3 天后，奶牛被分为 2 个实验期（P）。在 P1（3 天）期间，奶牛自由采食，并收集基线数据。在 P2（8 天）期间，奶牛被分配到以下 2 种处理之一：（1）生理盐水输注和等热量限制（CON-PF；静脉注射无菌生理盐水 40ml/h；n=5）或（2）LPS 输注和自由采食（LPS-AL；大肠杆菌 O55:B5 分别在第 1 天至第 8 天以 0.017、0.020、0.026、0.036、0.055、0.088、0.148 和 0.148μg/kg 体重/小时的速度输注；n=6）。在 P2 期间，CON-PF 奶牛被等热量限制喂养以消除不同营养摄入的混杂影响。在 P1 的第 1 天和第 2 天以及 P2 的第 1、3、5 和 7 天采集血液样本。在 P2 第 7 天上午挤奶后，采集脂肪组织、骨骼肌和肝脏活检组织，进行逆转录定量 PCR 和 Western blot 分析。为了评估全身营养转运，在 P2 第 8 天上午挤奶后进行静脉内葡萄糖耐量试验（GTT）；GTT 后 4 小时，奶牛接受肾上腺素挑战。在 P2 期间，两组奶牛的循环葡萄糖无差异。与 P1 相比，CON-PF 奶牛在 P2 期间的血浆β-羟丁酸和胰岛素分别下降了 29%和 47%（分别），而 LPS-AL 奶牛的这两个变量均无变化，导致β-羟丁酸和胰岛素分别增加了 41%和 140%（分别）。两组奶牛的循环非酯化脂肪酸从第 1 天到第 3 天增加，然后从第 3 天到第 7 天减少。CON-PF 奶牛的血尿素氮逐渐下降，而 LPS-AL 奶牛从第 1 天到第 5 天增加，导致 LPS-AL 与 CON-PF 奶牛相比增加了 25%。与 CON-PF 奶牛相比，LPS-AL 奶牛的 GTT 葡萄糖和胰岛素曲线下面积分别增加了 33%和 56%；这反映了全身胰岛素抵抗。然而，肌肉、肝脏和脂肪组织中胰岛素信号标志物的蛋白丰度在处理之间相似。肾上腺素挑战时，两组奶牛的葡萄糖和非酯化脂肪酸反应均无差异。肝脏中关键糖异生或脂质输出酶的 mRNA 丰度在两组间无差异。总之，慢性 LPS 暴露改变了基础和刺激代谢的多个参数，但似乎没有影响本文评估的分子机制。
