Requirement for glucose during in vitro culture of sheep preimplantation embryos

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Abstract
Glucose utilization by sheep embryos was examined in 8‐cell (N = 36) and blastocyst (N = 36) stages, by measuring conversion of [5−3H]glucose to 3H2O. Fifty percent glucose utilization occurred at 0.79 ± 0.69 mM for 8‐cell embryos and ∼0.06 ± 0.15 mM for blastocysts. Development of 1‐ and 2‐cell sheep embryos (N = 264) was examined under different glucose concentrations (0, 1.5, 3, or 6 mM) and in the presence or absence of 0.33 mM pyruvate and 3.3 mM lactate (PL). Overall, the presence of glucose was detrimental (P < 0.001) to embryonic development. By contrast, the presence of pyruvate and lactate was beneficial (PP P ±0.1). Development to the blastocyst stage was observed in medium when supplemented with amino acids and albumin alone. Thus, glucose metabolism is not critical for embryonic development, but beneficial at low concentrations. High concentrations can inhibit development, possibly by inhibiting the tricarboxylic acid (TCA) cycle. Sheep embryos may also be using amino acids as an energy source for development.