Doepel L, Lobley G E, Bernier J F, Dubreuil P, Lapierre H
Département des Sciences Animales, Université Laval, Québec, Quebec, Canada, G1K 7P4.
J Dairy Sci. 2007 Sep;90(9):4325-33. doi: 10.3168/jds.2007-0124.
The suggestion that glutamine (Gln) might become conditionally essential postpartum in dairy cows has been examined through increased postruminal supply of Gln. Net nutrient flux through the splanchnic tissues and mammary gland was measured in 7 multiparous Holstein cows receiving abomasal infusions of water or 300 g/d of Gln for 21 d in a crossover design. Milk yield increased significantly (by 3%) in response to Gln supplementation, but the 2.4% increase in milk protein yield was not statistically significant. Glutamine treatment had no effect on portal or hepatic venous blood flows. Net portal appearance of Gln and Glu was increased by Gln supplementation, accounting for 83% of the infused dose with, therefore, only limited amounts available to provide additional energy to fuel metabolism of the portal-drained viscera. The extra net portal appearance of Gln was offset, however, by a corresponding increase in hepatic removal such that net Gln splanchnic release was not different between treatments. Nonetheless, the Gln treatment resulted in a 43% increase in plasma Gln concentration. Infusions of Gln did not affect splanchnic flux of other nonessential amino acids or of essential amino acids. Glutamine supplementation increased plasma urea-N concentration and tended to increase net hepatic urea flux, with a numerical increase in liver hepatic O2 consumption. There were no effects on glucose in terms of plasma concentration, net portal appearance, net liver release, or postliver supply, suggesting that Gln supplementation had no sparing effect on glucose metabolism. Furthermore, mammary uptake of glucose and amino acids, including Gln, was not affected by Gln supplementation. In conclusion, this study did not support the hypothesis that supplemental Gln would reduce glucose utilization across the gut or increase liver gluconeogenesis or mammary glutamine uptake to increase milk protein synthesis.
通过增加瘤胃后谷氨酰胺（Gln）的供应量，对奶牛产后Gln可能成为条件必需氨基酸这一观点进行了研究。采用交叉设计，对7头经产荷斯坦奶牛进行真胃灌注水或300 g/d Gln，持续21天，测定内脏组织和乳腺的净营养通量。补充Gln后，产奶量显著增加（增加3%），但乳蛋白产量增加2.4%无统计学意义。Gln处理对门静脉或肝静脉血流量无影响。补充Gln后，门静脉中Gln和Glu的净出现量增加，占注入剂量的83%，因此，仅有有限量可用于为门静脉引流内脏的代谢提供额外能量。然而，Gln额外的门静脉净出现量被肝脏清除的相应增加所抵消，使得不同处理间Gln内脏净释放量无差异。尽管如此，Gln处理使血浆Gln浓度增加了43%。输注Gln不影响其他非必需氨基酸或必需氨基酸的内脏通量。补充Gln增加了血浆尿素氮浓度，并倾向于增加肝脏净尿素通量，肝脏耗氧量有数值上的增加。在血浆浓度、门静脉净出现量、肝脏净释放量或肝脏后供应量方面，对葡萄糖均无影响，表明补充Gln对葡萄糖代谢无节约作用。此外，补充Gln不影响乳腺对葡萄糖和氨基酸（包括Gln）的摄取。总之，本研究不支持补充Gln会减少肠道对葡萄糖的利用或增加肝脏糖异生或乳腺对谷氨酰胺的摄取以增加乳蛋白合成这一假说。
