Gluconeogenesis and substrate utilization in chicken embryos during later development determined by in ovo continuous infusion of [13C6]glucose and [13C3]glycerol
We aimed to quantify the rates of gluconeogenesis (GNG) and substrate partition to the Krebs cycle in embryonic (e) day e14 and e19 chicken embryos (n=5-6 per group). An in ovo continuous tracer infusion approach was employed to test the hypotheses that GNG and non-essential amino acid (NEAA) synthesis increase from e14 to e19. [13C6]Glucose or [13C3]glycerol was continuously infused (8 h) into the chorio-allantoic compartment on e14 and e19. Based on [13C6]glucose infusion, glucose entry rate, Cori cycling and GNG were higher (P < 0.05) in e19 than in e14 embryos, presumably to support greater deposition of glycogen in the muscle and liver in preparation for pipping and hatching. In the liver, the contribution of glucose to alanine, aspartate, and glutamate synthesis was greater (P < 0.05) in e14 than in e19 embryos whereas the synthesis of NEAA from glycerol was higher (P < 0.05) in e19 than in e14 embryos. These patterns of glucose and glycerol utilisation by the liver suggest a metabolic shift to conserve glucose for glycogen synthesis and an increased utilisation of yolk glycerol (triacylglycerides) after e14. Although the contribution of glycerol to GNG in e19 embryos was greater (P < 0.05) than in e14 embryos, the contribution of glycerol to GNG (1.3−6.0%) was minor. Based on [13C6]glucose tracer kinetics, the activities of both pyruvate carboxylase (PC) and pyruvate dehydrogenase (PDH) in the liver were higher (P < 0.05) on e19; however, the higher (P < 0.05) relative activity of PC vs PDH on e14 suggests a greater anaplerotic flux into the Krebs cycle of the e14 liver. In conclusion, the in ovo continuous tracer infusion approach allowed for measurement of chicken embryo whole body and liver metabolism over a shorter window of development compared to our previous approach of dosing tracer in ovofor 3 to 4 d. Lastly, this study provided quantitative estimates of the developmental shifts in substrate utilisation, GNG and NEAA synthesis by chicken embryos, as well as qualitative estimates of the activity of enzymes central to the Krebs cycle, and glucose and fatty acid metabolism.
chicken, embryo, metabolism