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THE METABOLISM OF SPECIFICALLY LABELLED LACTATE AND PYRUVATE BY TWO-CELL MOUSE EMBRYOS

Summary.: The accumulation and utilization of substrate carbon by two-cell mouse embryos incubated in media containing combinations of lactate and pyruvate were studied. The results were consistent with utilization of the two substrates by common metabolic pathways. The intracellular accumulation of substrate carbon was greater when pyruvate as well as lactate was present in the medium. The evidence also suggests that pyruvate is more effective in maintaining the activity of the tricarboxylic acid cycle than lactate alone.

Fractionation of substrate carbon accumulated in embryos during a 30-min incubation period indicated that approximately 10% of this carbon had entered the acid-insoluble (protein) fraction. This accumulation was increased substantially when a combination of lactate and pyruvate, rather than either substrate alone, was present in the incubation medium.

The major organic acids found to accumulate intracellularly from substrate were malate and citrate. The intracellular accumulation of lactate was confined to embryos incubated in medium containing this substrate. Base-containing compounds accounted for a substantial portion of the substrate carbon in embryos. Glutamic acid was the major amino acid identified in this component. Alanine accumulated from pyruvate or its combination with lactate but not from lactate alone. Small amounts of aspartate accumulated from both substrates.

The effect of the interaction of lactate and pyruvate on the development of two-cell mouse embryos to the blastocyst stage was confirmed. Although pyruvate was effective over a limited range of concentration, the effective range of concentration of lactate was not as limited. The present studies suggest that the beneficial effect of combinations of lactate and pyruvate could be due to a stimulation of the metabolism of the embryos and a more favourable level of macromolecule synthesis.

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