Glucose Inhibits Development of Hamster 8-Cell Embryos in Vitro1

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Abstract
Relative preferences of energy substrates (glucose, pyruvate, and lactate) for in vitro development of hamster 8-cell embryos were investigated. Using protein-free modified Tyrode''s medium (TLP-PVA) containing 10 mM lactate (L), 0.1 mM pyruvate (P), and amino acids (Phe, Ile, Met and Gln), we found that development of hamster 8-cell embryos to blastocysts was supported better in the absence of glucose than in medium containing (standard) 5 mM glucose (88.1% and 50%, respectively). Addition of even 0.25 mM glucose to the medium significantly inhibited blastocyst formation (54.1%). Medium T-PVA, containing 5 mM glucose as sole energy substrate (without pyruvate, lactate, and amino acids), very poorly supported embryo development (.ltoreq. 7.9% blastocysts), but addition of 0.1 mM pyruvate enhanced blastocyst formation (52%). Elimination of pyruvate in TL-PVA medium containing 5 mM glucose and amino acids markedly reduced blastocyst formation by 4-fold (13.5%); the optimal pyruvate concentration was 0.2 mM. However, if the same medium was devoid of glucose, blastocyst formation was high both in the absence (71.1%) and presence (83.3%) of 0.1 mM pyruvate. Similarly, in glucose-free T-PVA medium, addition of either 10 mM lactate or amino acids supported 8-cell embryo development to blastocysts (61.7% and 60.5%, respectively) as opposed to 18.8% and 30.6%, respectively, in the presence of 5 mM glucose. This augmented development in the absence of glucose is suggested to be due to the efficient conversion of lactate to pyruvate and of amino acids to amphibolic intermediates and hence their utilization via the Krebs cycle. Glucose by itself not only inhibited development but also inhibited lactate/amino acids-mediated development. These results imply that hamster 8-cell embryos employ the Krebs cycle, not the glycolytic pathway, for their major energy production during development. The data reveal striking differences in the energy substrate requirements of hamster 8-cell embryos compared with mouse embryos.