Incorporation of glucose by the sheep conceptus between days 13 and 19 of pregnancy

Abstract

Incorporation of glucose into the internal biochemical pools of the sheep embryo and samples of extraembryonic membranes was measured during a 2.5 h incubation in the presence of radiolabelled glucose. Very little glucose was incorporated into the glycogen pools by either the embryo or its membranes and never represented more than 5% of total incorporation. Approximately 65% of label was isolated in the non-glycogen acid-soluble fraction of samples and the remainder was incorporated into non-glycogen macromolecules. The embryonic disc of the day-13 conceptus had the highest rate of incorporation per mg dried weight of any structure studied. Synthesis of non-glycogen macromolecules by the day-13 disc was five to six times that of either day-15 or day-17 embryos. On day 19 very low rates of incorporation into the isolated embryo were found during culture. Evidence suggests that this was a result of limitations on the diffusion of substrate into the embryo because incubation of fragmented embryos produced rates similar to those found on days 15 and 17. Incorporation of glucose into the intracellular pools of extraembryonic membranes per mg dried weight remained relatively low and stable over the period studied and there were only minor differences in the rate of incorporation between membranes. Incorporation of glucose by embryos and extraembryonic membranes was equally as good in phosphate-buffered media as in bicarbonate-buffered solutions and was unaffected by changes in the concentration of lactate and pyruvate in the culture medium.