PARTITIONING OF GLUCOSE CARBON IN POST-COMPACTION OVINE EMBRYOS

Day 5 sheep embryos (late morulae and early blastocysts) were surgical ly recovered from superovulated ewes. Groups of embryos (four to seven ) were incubated for 24 h at 39-degrees-C under humidified 5% CO2, 5% O2, 90% N2 in 50-mul microdrops of a substrate-free synthetic oviduct fluid (SOF) medium (12 mg ml-1 bovine serum albumin, m-SOF) containing 1.0 mM glucose and +/- 1.0 mM glutamine. Following incubation, embryo s were washed in m-SOF and stored at -70-degrees-C until fractionation . Embryos were fractionated into acid-soluble (glycogen/non-glycogen) and acid-insoluble (desmoglycogen/non-glycogen) fractions. To further characterise glucose carbon partitioning in the acid-soluble fraction, carbohydrates were separated by high performance liquid chromatograph y (HPLC). Incorporation of glucose into glycogen or desmoglycogen in p ost-compaction sheep embryos was negligible. The presence of glutamine tended to accelerate morphological development over the 24 h culture period, but had no significant effect on glucose incorporation. Most g lucose carbon was associated with the acid-soluble non-glycogen fracti on. HPLC revealed that this was predominantly glucose (approximately 4 0%), in addition to other metabolic intermediates. It is concluded tha t, unlike the mouse embryo, sheep embryos produce negligible glycogen from exogenous glucose and that most of the glucose carbon incorporate d in the embryo is in the form of low molecular weight metabolites or unmetabolised glucose.