Oxidative utilization of glucose, acetate and lactate by early preimplantation sheep, mouse and cattle embryos

Abstract

The production of radiolabelled CO2 from [U-14C]glucose, [1-14C]lactate, and [U-14C]acetate was used to study the oxidative metabolism of embryos recovered from sheep, mice and cattle. Sheep embryos showed an increasing capacity to oxidize glucose after the 4- to 8-cell stage and oxidative turnover of this substrate at the blastocyst stage was four times that at the early stages. Decarboxylation of carbon-1 of lactate followed a pattern similar to that seen for glucose oxidation, but acetate oxidation was low and did not follow the trends with development seen for the other substrates. Furthermore, estimates of incorporation of acetate into the macromolecules of sheep embryos were low compared with similar estimates for glucose and, unlike glucose, did not increase with development. Oxidation of all three substrates by mouse embryos increased with development but the rate of CO2 production from acetate was low compared with that from the other substrates. A combination of lactate or glucose with acetate had no influence on the utilization of acetate by mouse morulae/early blastocysts, nor did acetate influence utilization of the other substrates. Cattle morulae/early blastocysts also produced more CO2 from glucose and lactate than from acetate and the incorporation of carbon from acetate into the macromolecules of these embryos was less than from glucose. Overall, cattle embryos showed the greatest ability to metabolize acetate but were not as effective in using the other substrates as either sheep or mouse embryos at the same stage.

Glucose and Pyruvate Metabolism of Preimplantation Goat Blastocysts followingIn VitroFertilization and Parthenogenetic Activation

“…Measurement of glucose uptake per se does not therefore give an accurate indication of glucose metabolism. Similarly, sheep embryos showed an increasing capacity to oxidize glucose after the four-and eight-cell stage, with oxidative turnover at the blastocyst stage being four times that at the early stages (Waugh and Wales, 1993). Glucose alone was unable to support development of mouse embryos before the eight-cell stage.…”

Utilization of [U-14C] Glucose by Preimplantation Rat Embryo Cultured In Vitro.

“…The increasing capacity to oxidize glucose as development proceeds appears to be a general phenomenon with mammalian embryos and is also seen in mouse [5], rabbit [17], human [18], cow [19] and sheep [20] embryos. This increasing incorporation and CO 2 production of [U-14 C] glucose could arise from the increased pentose phosphate pathway (PPP) activity, increased TCA cycle processing, or a combination of both.…”

“…Waugh and Wales [20] reported that the major incorporation of glucose carbon by cattle embryos occurs in the acid-soluble, non-glucose pool, and approximately 70% of total incorporation is found in this fraction with most of the remainder in non-glycogen macromolecules. The present data indicated that preimplantation rat embryos can incorporate the labels from [U-14 C] glucose into lipids.…”

Altering nutrient utilization in animals through transgenesis

“…Acetyl-CoA is unlikely to be in short supply in an adult ruminant because the abundant supply of acetate produced by the rumen micro-organisms is readily converted to acetyl-CoA by the enzyme acetylCoA synthase (EC 6.2.1.1) (Van Soest, 1982). However, this is not the case in the embryo during early development because, as found in most mammalian embryos, acetyl-CoA synthase activity is very low (Waugh & Wales, 1993). This does not cause any dif®culties in embryos which can convert glucose to lactate, but this option is blocked in the ruminant blastocyst by a low activity of the enzyme pyruvate kinase (EC 2.7.1.40) (Rieger & Guay, 1988).…”