Hu Q, Agarwal U, Bequette B J
Department of Animal and Avian Sciences, University of Maryland-College Park, 20742
Department of Animal and Avian Sciences, University of Maryland-College Park, 20742.
Poult Sci. 2017 Feb 1;96(2):414-424. doi: 10.3382/ps/pew249. Epub 2016 Aug 2.
We aimed to quantify the rate of gluconeogenesis (GNG), non-essential amino-acid (NEAA) synthesis, and substrate partitioning to the Krebs cycle in embryonic (e) day e14 and e19 chicken embryos. An in ovo continuous tracer infusion approach was employed to test the hypotheses that GNG and NEAA synthesis in developing chicken embryo increases from e14 to e19. [C]Glucose or [C]glycerol was continuously infused (8 h) into the chorio-allantoic compartment of eggs on e14 and e19. Glucose entry rate, Cori cycling, and GNG were higher (P < 0.05) in e19 compared to e14 embryos, presumably to support higher glycogen deposition in liver and muscle. Whereas de novo synthesis of alanine, aspartate, and glutamate via glycolysis and the Krebs cycle was higher (P < 0.01) in e14 embryos, synthesis of these NEAA from glycerol was higher (P < 0.05) in e19 compared to e14 embryos. These patterns of glucose and glycerol utilization suggest a metabolic shift to conserve glucose for glycogen synthesis and an increased utilization of yolk glycerol (from triacylglyceride) after e14. Although the contribution of glycerol to GNG in e19 embryos was higher (P < 0.05) than that in e14 embryos, the contribution of glycerol to GNG (1.3 to 6.0%) was minor. Based on [C]glucose tracer kinetics, the activities of both pyruvate carboxylase (PC) and pyruvate dehydrogenase (PDH) in the liver were higher (P < 0.05) in e19 embryos; whereas the higher (P < 0.01) relative activity of liver PC compared to PDH in e14 embryos suggests a greater anaplerotic flux into the Krebs cycle. In summary, the in ovo continuous tracer infusion approach allowed for a measurement of chicken embryo whole body and liver metabolism over a shorter window of development. This study provided quantitative estimates of the developmental shifts in substrate utilization, GNG, and NEAA synthesis by chicken embryos, as well as qualitative estimates of the activities of enzymes central to the Krebs cycle, glucose, and fatty acid metabolism.
我们旨在量化胚胎期（e）第14天和第19天鸡胚的糖异生（GNG）速率、非必需氨基酸（NEAA）合成以及进入三羧酸循环的底物分配情况。采用胚内连续示踪剂输注方法来检验以下假设：发育中的鸡胚中GNG和NEAA合成从第14天到第19天会增加。在第14天和第19天，将[C]葡萄糖或[C]甘油连续输注（8小时）到鸡蛋的尿囊绒毛膜腔中。与第14天的胚胎相比，第19天胚胎的葡萄糖进入速率、科里循环和GNG更高（P<0.05），这可能是为了支持肝脏和肌肉中更高的糖原沉积。虽然通过糖酵解和三羧酸循环从头合成丙氨酸、天冬氨酸和谷氨酸在第14天胚胎中更高（P<0.01），但与第14天胚胎相比，第19天胚胎中由甘油合成这些非必需氨基酸的量更高（P<0.05）。这些葡萄糖和甘油利用模式表明，在第14天后发生了代谢转变，以保存葡萄糖用于糖原合成，并增加了对卵黄甘油（来自三酰甘油）的利用。虽然甘油对第19天胚胎中GNG的贡献高于第14天胚胎（P<0.05），但甘油对GNG的贡献较小（1.3%至6.0%）。基于[C]葡萄糖示踪动力学，第19天胚胎肝脏中丙酮酸羧化酶（PC）和丙酮酸脱氢酶（PDH）的活性均更高（P<0.05）；而与第14天胚胎相比，肝脏PC相对于PDH的相对活性更高（P<0.01），这表明进入三羧酸循环的回补通量更大。总之，胚内连续示踪剂输注方法能够在较短的发育窗口期内测量鸡胚的全身和肝脏代谢。本研究提供了鸡胚底物利用、GNG和NEAA合成发育变化的定量估计，以及对三羧酸循环、葡萄糖和脂肪酸代谢核心酶活性的定性估计。
