OXYGEN-CONSUMPTION AND ENERGY-METABOLISM OF THE EARLY MOUSE EMBRYO

Oxygen consumption of preimplantation and early postimplantation mouse embryos has been measured using a novel noninvasive ultra micro fluor escence technique, based on an oil-soluble, nontoxic quaternary benzoi d compound pyrene, whose fluorescence is quenched in the presence of o xygen. Pyruvate and glucose consumption, lactate production, and glyco gen formation from glucose were also measured. Preimplantation mouse e mbryos of the strain CBA/Ca x C57BL/6 were cultured in groups of 10-30 in 2 mu l of modified M2 medium containing 1 mmol 1(-1) glucose, 0 mm ol 1(-1) lactate, and 0.33 mmol 1(-1) pyruvate, for between 4-6 hr. Da y 6.5 and 7.5 embryos were cultured singly in 40 mu l M2 medium far be tween 2-3 hr. Oxygen consumption was detected at all stages of develop ment, including, for the first time, in the early postimplantation emb ryo. Consumption remained relatively constant from zygote to morula st ages before increasing in the blastocyst and day 6.5-7.5 stages. When expressed as QO(2) (mu l/mg dry weight/hr), oxygen consumption was rel atively constant from the one-cell to morula stages before increasing sharply at the blastocyst stage and declining to preblastocyst levels on days 6.5 and 7.5. Pyruvate was consumed during preimplantation stag es, with glucose uptake undetectable until the blastocyst stage. Gluco se was the main substrate consumed by the 6.5 and 7.5 day embryo. The proportions of glucose accounted for by lactate appearance were 81%, 8 6%, and 119% at blastocyst, day 6.5, and day 7.5 stages, respectively. The equivalent figures for glucose incorporated into glycogen were 10 .36%, 0.21%, and 0.19%, respectively. The data are consistent with a s witch from a metabolism dependent on aerobic respiration during early preimplantation stages to one dependent on both oxidative phosphorylat ion and aerobic glycolysis at the blastocyst stage, a pattern which is maintained on days 6.5 and 7.5. Our technique for measuring oxygen co nsumption may have diagnostic potential for selecting viable embryos f or transfer following assisted conception techniques in man and domest ic animals. (C) 1996 Wiley-Liss, Inc.