Alltech Inc., Brookings, SD 57006, USA.
J Anim Sci. 2011 Dec;89(12):3954-72. doi: 10.2527/jas.2010-3597. Epub 2011 Jul 1.
Data from species other than cattle indicate that ghrelin and GH secretagogue receptor (GHS-R) could play a key role in fat deposition, energy homeostasis, or glucose metabolism by directly affecting liver and adipose tissue metabolism. Beef steers (n = 72) were used to test the hypothesis that plasma ghrelin and leptin concentrations and abundance of the GHS-R in liver, muscle, and adipose tissues differ in steers exhibiting differences in composition of gain. At trial initiation (d 0), 8 steers were slaughtered for initial carcass composition. The remaining 64 steers were stratified by BW, allotted to pen, and treatment was assigned randomly to pen. Steers were not implanted with anabolic steroids. Treatments were 1) a low-energy (LE) diet fed during the growing period (0 to 111 d) followed by a high-energy (HE) diet during the finishing period (112 to 209 d; LE-HE) or 2) the HE diet for the duration of the trial (1 to 209 d; HE-HE). Eight steers per treatment were slaughtered on d 88, 111, 160, and 209. Carcass ninth, tenth, and eleventh rib sections were dissected for chemical composition and regression equations were developed to predict compositional gain. Liver, muscle, and subcutaneous adipose tissues were frozen in liquid nitrogen for subsequent Western blotting for GHS-R. Replicate blood samples collected before each slaughter were assayed for ghrelin and leptin concentrations. When compared at a common compositional fat end-point, the rate of carcass fat accretion (g·kg of shrunk BW(-1)) was greater (P < 0.001) in HE-HE steers whereas the rate of carcass protein accretion (g·kg of shrunk BW(-1)) was less (P < 0.001) compared with LE-HE steers. When compared at a common compositional fat end-point, plasma leptin, ghrelin, and insulin concentrations were greater (P < 0.05) for HE-HE compared with LE-HE steers. Abundance of the GHS-R, to which ghrelin binds, increased over time in liver and adipose tissue but did not differ as a result of treatment. Plasma ghrelin concentrations were increased for cattle continuously fed the HE diet as they became increasingly fatter; however, abundance of the GHS-R in liver, muscle, and subcutaneous adipose tissue was not different between treatment groups. The role of ghrelin in cattle metabolism warrants further investigation as it could have a significant effect on composition of BW gain, feed efficiency, and metabolic disorders such as ketosis and fatty liver.
来自牛以外物种的数据表明，ghrelin 和生长激素促分泌素受体 (GHS-R) 通过直接影响肝脏和脂肪组织代谢，可能在脂肪沉积、能量平衡或葡萄糖代谢中发挥关键作用。本试验选用 72 头肉牛来验证以下假设：在增重组成存在差异的牛中，血浆 ghrelin 和瘦素浓度以及肝脏、肌肉和脂肪组织中 GHS-R 的丰度存在差异。试验开始时（d0），屠宰 8 头牛以测定初始胴体组成。其余 64 头肉牛按体重进行分层，分配到栏中，并随机分配到栏中进行处理。牛未植入合成代谢类固醇。处理为 1）在生长阶段（0 至 111d）饲喂低能量（LE）日粮，然后在育肥阶段（112 至 209d）饲喂高能量（HE）日粮（LE-HE），或 2）在整个试验期间（1 至 209d）饲喂 HE 日粮（HE-HE）。每个处理组有 8 头牛在 d88、111、160 和 209 时屠宰。屠宰后对牛的第 9、10 和 11 肋骨进行化学组成剖分，并建立回归方程以预测组成增益。将肝脏、肌肉和皮下脂肪组织在液氮中冷冻，随后进行 GHS-R 的 Western blot 分析。在每次屠宰前采集重复的血液样本，测定 ghrelin 和瘦素浓度。当在脂肪含量相同的终点进行比较时，与 LE-HE 组相比，HE-HE 组的体脂沉积率（g/kg 去脂体重）更高（P<0.001），而体蛋白沉积率（g/kg 去脂体重）更低（P<0.001）。当在脂肪含量相同的终点进行比较时，与 LE-HE 组相比，HE-HE 组的血浆瘦素、ghrelin 和胰岛素浓度更高（P<0.05）。GHS-R（ghrelin 的结合受体）的丰度随着时间的推移在肝脏和脂肪组织中增加，但未因处理而不同。随着牛持续饲喂 HE 日粮变得越来越肥胖，血浆 ghrelin 浓度增加；然而，肝脏、肌肉和皮下脂肪组织中 GHS-R 的丰度在处理组之间没有差异。ghrelin 在牛代谢中的作用值得进一步研究，因为它可能对 BW 增重组成、饲料效率以及酮症和脂肪肝等代谢紊乱产生重大影响。
