CATABOLIC UTILIZATION OF GLUCOSE BY THE SHEEP CONCEPTUS BETWEEN DAYS 13 AND 19 OF PREGNANCY

The production of carbon dioxide and lactate from glucose by sheep emb ryos 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, t he utilization of glucose per unit weight fell as development progress ed from Day 13 to Day 19 of pregnancy. Both oxidation of glucose and g lycolysis by the extraembryonic tissues, expressed as activity per mug dried tissue, fell progressively with development. The rate of declin e in CO2 production was greater than the rate for glycolysis and, as a consequence the contribution of glycolysis to the estimated energy yi eld from the catabolism of glucose rose with time. In the embryo, both glucose oxidation and glycolysis peaked on Day 15 with estimates of a denosine triphosphate (ATP) production from glucose per mug dried tiss ue 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 sim ilar for structures of the same developmental age except that, at Day 19, it was calculated that the rate of ATP production by embryos was d ouble that by the extraembryonic membranes. In incubations using 5.56 mm glucose as sole exogenous energy source, glucose turnover by embryo s and embryonic membranes tended to be higher in a bicarbonate-buffere d 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 s ignificantly higher in this medium than in the others. Glucose turnove r by the embryo and its membranes in bicarbonate-buffered medium conta ining 0.56 mm glucose plus the alternate substrates, lactate and pyruv ate, was severely depressed. Further experiments using samples of trop hoblast and yolk sac indicated that both reduction in glucose concentr ation and the presence of the other substrates contributed to this sup pression. Furthermore, an interaction between these factors was eviden t with the effects of alternative substrates being exaggerated when gl ucose concentration was low.