Utilization of glucose by the implanting mouse blastocyst activated by oestrogen

Blastocysts from mice in an experimental delay of implantation increased their oxidation rate of both glucose and fructose when implantation was initiated by an injection of oestrogen. About 18 h after the injection, the rate of glucose oxidation was significantly higher than that of fructose oxidation. Simultaneously with the increase in the rate of glucose oxidation, glycogen granules appeared in the trophoblast cells. In uterine flushings, the amount of glucose increased already at 6 h. This time corresponds to the period when the blastocyst gets activated for implantation. Determination of glucose utilization by the blastocysts demonstrated that 3 h after the oestrogen injection, the utilization was low but that it was markedly increased at 6 and 18 h. It is concluded that at the initiation of implantation, mouse blastocysts prefer glucose to fructose and that the presence of glucose in the secretion and the increased utilization of glucose by blastocysts at this time suggest that this substrate could be one important nutrient for the blastocyst at early implantation. Glucose, however, cannot be the sole factor critical for the activation of the delayed blastocyst.