Degradation of biochemical pools labelled with [14C]glucose during culture of 8-cell and morula--early blastocyst-stage mouse embryos in vitro and in vivo.

When 8-cell mouse embryos were chase cultured for 24 h in vitro or in vivo (in uteri of pseudopregnant mice) there was no indication of utilization of the small amount of acid-soluble glycogen synthesized during the pulse. At the morula-early blastocyst stage of development almost 50% of the label incorporated during the pulse was found in the acid-soluble glycogen fraction. The biochemical pools at this stage were relatively stable in vitro and in vivo during a short (5 h) chase period. However, marked degradation of the acid-soluble glycogen pool occurred during long periods of exposure to the uterine environment and, over 48 h in utero, almost all of the label was lost from this pool. By contrast, embryos cultured in vitro for the same period retained greater than 60% of their acid-soluble glycogen. Utilization of glucose carbon in the acid-insoluble glycogen fraction occurred during in-vitro and in-vivo chase but there was a suggestion that the change in vivo was less than that in vitro. The non-glycogen macromolecular pool was relatively stable except during extended chase culture of morulae-early blastocysts when some utilization occurred. Under these conditions utilization was less in utero than in vitro. The experiments show that the uterine environment has a marked influence on the metabolism, particularly of glycogen, of the embryo and indicate that some factor in the uterus causes net degradation of acid-soluble glycogen by the embryo at the late preimplantation stage of development.