Lapierre H, Bernier J F, Dubreuil P, Reynolds C K, Farmer C, Ouellet D R, Lobley G E
Dairy and Swine Research and Development Centre, Agriculture and Agri-Food Canada, Lennoxville, Qc, Canada.
J Anim Sci. 2000 Apr;78(4):1084-99. doi: 10.2527/2000.7841084x.
The effect of feed intake level (.6, 1.0, and 1.6 x maintenance energy and protein requirements, M) on splanchnic (portal-drained viscera [PDV] plus liver) metabolism was evaluated in six multicatheterized beef steers (398 +/- 27 kg), using a double 3 x 3 Latin square design. On the last day of each 21-d experimental period, six hourly blood samples were collected from arterial, portal, and hepatic vessels. Due to catheter patency, PDV fluxes were measured on five steers, and liver and splanchnic fluxes on four steers. Increasing intake elevated (P < .01) splanchnic release of total (T) amino acids (AA), through increases (P < .01) in PDV release of both essential (E) and nonessential (NE) AA, in spite of a tendency (P < .20) for increased liver removal of NEAA. The PDV release of AA N represented 27 and 51% of digested N for 1.0 and 1.6 x M, respectively. At 1.0 and 1.6 x M, the liver removed 34% of total AA released by the PDV. For individual AA, portal flux of most EAA increased (P < .05) with feed intake, and the increase (P < .10) in splanchnic flux was accompanied by increased arterial concentration for all EAA except histidine, lysine, and methionine. This suggests that these might be limiting AA for this diet. On a net basis, most individual NEAA were released by the PDV except glutamate and glutamine, which were removed by the digestive tract. There was a net removal of NEAA by the liver, except for aspartate and especially glutamate, which were released. Ammonia release by the PDV tended (P < .20) to increase with intake and represented 69, 53, and 45% of digested N at .6, 1.0, and 1.6 x M, respectively. Urea removed by the PDV, unaffected by intake, represented 32, 33, and 21% of the digested N. Arterial glucose concentration increased linearly (P < .01) with greater intake, whereas net liver and splanchnic glucose release increased in a quadratic (P < .05) manner. Net PDV glucose release represented 26% of net glucose hepatic release at 1.6 x M. Intake elevated (P < .10) both insulin and glucagon arterial concentrations, resulting from a larger increment of portal release (P < .01) than hepatic removal (P < .05). Intake-based variations in IGF-I and NEFA arterial concentrations (P < .05) were not related to changes in splanchnic metabolism. These results clearly show the crucial role of the splanchnic tissues in regulating the profile and quantity of AA and concentrations of glucose and pancreatic hormones reaching peripheral tissues.
采用双3×3拉丁方设计，在6头多导管安装的肉牛（398±27千克）中评估采食量水平（维持能量和蛋白质需要量的0.6、1.0和1.6倍，即M）对内脏（门静脉引流内脏[PDV]加肝脏）代谢的影响。在每个21天实验期的最后一天，从动脉、门静脉和肝血管每小时采集6份血样。由于导管通畅，对5头牛测定了PDV通量，对4头牛测定了肝脏和内脏通量。尽管肝脏对非必需氨基酸（NEAA）的清除有增加趋势（P<0.20），但随着采食量增加，内脏总（T）氨基酸（AA）释放量升高（P<0.01），这是由于必需（E）和非必需（NE）氨基酸的PDV释放量均增加（P<0.01）。对于1.0倍和1.6倍M的采食量，PDV释放的AA N分别占消化N的27%和51%。在1.0倍和1.6倍M时，肝脏清除了PDV释放的总AA的34%。对于单个氨基酸，大多数必需氨基酸的门静脉通量随采食量增加而增加（P<0.05），除组氨酸、赖氨酸和蛋氨酸外，所有必需氨基酸的内脏通量增加（P<0.10）伴随着动脉浓度升高。这表明这些可能是该日粮的限制性氨基酸。从净量来看，除谷氨酸和谷氨酰胺被消化道清除外，大多数单个非必需氨基酸由PDV释放。肝脏对非必需氨基酸有净清除，除天冬氨酸尤其是谷氨酸被释放外。PDV释放的氨有随采食量增加的趋势（P<0.20），在0.6倍、1.0倍和1.6倍M时分别占消化N的69%、53%和45%。PDV清除的尿素不受采食量影响，分别占消化N的32%、33%和21%。动脉葡萄糖浓度随采食量增加呈线性增加（P<0.01），而肝脏和内脏葡萄糖净释放量呈二次方增加（P<0.05）。在1.6倍M时，PDV葡萄糖净释放量占肝脏葡萄糖净释放量的26%。采食量升高（P<0.10）了动脉胰岛素和胰高血糖素浓度，这是由于门静脉释放量的增加幅度更大（P<0.01），而肝脏清除量增加幅度较小（P<0.05）。基于采食量的胰岛素样生长因子-I（IGF-I）和非酯化脂肪酸（NEFA）动脉浓度变化（P<0.05）与内脏代谢变化无关。这些结果清楚地表明了内脏组织在调节到达外周组织的氨基酸的组成和数量、葡萄糖浓度以及胰腺激素方面的关键作用。
