UPTAKE AND METABOLISM OF PYRUVATE AND LACTATE DURING PREIMPLANTATION DEVELOPMENT OF THE MOUSE EMBRYO IN VITRO

Abstract

Summary. The incorporation of substrate carbon from pyruvate and lactate has been measured at all stages of preimplantation development in the mouse embryo using substrates labelled at the C2 position. Embryos were cultured for 24 hr in medium containing pyruvate (0·5 mm) or lactate (5 mm), alone or in combination and the accumulation of label in various intracellular fractions was measured. The incorporation of both pyruvate and lactate carbon increased with increasing development of the embryos. Before the morula stage, the presence of unlabelled lactate in the medium depressed the incorporation of C2 of pyruvate whereas the opposite effect occurred when embryos were cultured in [2-14C]lactate in the presence of unlabelled pyruvate. The combined incorporation of carbon from both pyruvate and lactate was greater than that from either substrate alone at all stages of development. Lactate contributed a greater proportion to the combined incorporation of substrate carbon than pyruvate at all stages of development. The increased incorporation of substrate carbon into cultured two-cell embryos in the combination of pyruvate and lactate was almost entirely due to the stimulated accumulation of carbon in the protein fraction of the embryos. Incorporation into this fraction contributed proportionately less to the increased total incorporation into the embryos at the later stage of development. Alanine, glutamic acid and aspartic acid accounted for most of the carbon incorporated into the basic compounds of the acid-soluble fraction of the embryos. Labelled malate and citrate were found in the acidic compounds of this fraction when two-cell embryos were cultured in [2-14C]pyruvate. After the eight-cell stage, labelled lactate, as well as malate and citrate, accumulated in embryos cultured in medium containing pyruvate, lactate or their combination. Labelled pyruvate only accumulated in these embryos during culture in media containing [2-14C]pyruvate alone or [2-14C]lactate and unlabelled pyruvate.