Wales R G, Waugh E E
School of Veterinary Studies, Murdoch University, W.A.
Reprod Fertil Dev. 1993;5(1):111-22. doi: 10.1071/rd9930111.
The production of carbon dioxide and lactate from glucose by sheep embryos and samples of extraembryonic membranes was measured during a 2.5 h incubation period. Both embryos and their membranes were active in the glycolytic and oxidative utilization of glucose and, in general, the utilization of glucose per unit weight fell as development progressed from Day 13 to Day 19 of pregnancy. Both oxidation of glucose and glycolysis by the extraembryonic tissues, expressed as activity per microgram dried tissue, fell progressively with development. The rate of decline in CO2 production was greater than the rate for glycolysis and, as a consequence, the contribution of glycolysis to the estimated energy yield from the catabolism of glucose rose with time. In the embryo, both glucose oxidation and glycolysis peaked on Day 15 with estimates of adenosine triphosphate (ATP) production from glucose per microgram dried tissue on this day being 50% above those on Day 13 and 100% above those on Day 17. In general, the estimated yields of ATP from glucose were similar for structures of the same developmental age except that, at Day 19, it was calculated that the rate of ATP production by embryos was double that by the extraembryonic membranes. In incubations using 5.56 mM glucose as sole exogenous energy source, glucose turnover by embryos and embryonic membranes tended to be higher in a bicarbonate-buffered medium than in HEPES (4-(2-hydroxyethyl)-1-piperazincethane sulfonic acid) and phosphate-buffered media. As a result, the estimate of ATP yield plus the contribution of oxidative pathways to this yield were significantly higher in this medium than in the others. Glucose turnover by the embryo and its membranes in bicarbonate-buffered medium containing 0.56 mM glucose plus the alternate substrates, lactate and pyruvate, was severely depressed. Further experiments using samples of trophoblast and yolk sac indicated that both reduction in glucose concentration and the presence of the other substrates contributed to this suppression. Furthermore, an interaction between these factors was evident with the effects of alternative substrates being exaggerated when glucose concentration was low.
在2.5小时的孵育期内，测定了绵羊胚胎和胚外膜样本从葡萄糖产生二氧化碳和乳酸的情况。胚胎及其膜在葡萄糖的糖酵解和氧化利用方面都很活跃，一般来说，随着怀孕从第13天到第19天的进展，单位重量的葡萄糖利用率下降。胚外组织对葡萄糖的氧化和糖酵解，以每微克干燥组织的活性表示，随着发育而逐渐下降。二氧化碳产生的下降速率大于糖酵解的速率，因此，糖酵解对葡萄糖分解代谢估计能量产生的贡献随时间增加。在胚胎中，葡萄糖氧化和糖酵解在第15天达到峰值，这天每微克干燥组织从葡萄糖产生的三磷酸腺苷（ATP）估计量比第13天高50%，比第17天高100%。一般来说，相同发育年龄结构从葡萄糖产生的ATP估计产量相似，只是在第19天，计算得出胚胎产生ATP的速率是胚外膜的两倍。在使用5.56 mM葡萄糖作为唯一外源能量来源的孵育中，胚胎和胚膜的葡萄糖周转率在碳酸氢盐缓冲培养基中往往高于在HEPES（4-(2-羟乙基)-1-哌嗪乙磺酸）和磷酸盐缓冲培养基中。因此，这种培养基中ATP产量的估计值加上氧化途径对该产量的贡献明显高于其他培养基。在含有0.56 mM葡萄糖以及替代底物乳酸和丙酮酸的碳酸氢盐缓冲培养基中，胚胎及其膜的葡萄糖周转率严重降低。使用滋养层和卵黄囊样本的进一步实验表明，葡萄糖浓度的降低和其他底物的存在都导致了这种抑制。此外，这些因素之间存在相互作用，当葡萄糖浓度较低时，替代底物的影响会被放大。
