Studies of the metabolism of glucose by the preimplantation mouse embryo

Wasantha Rohini Edirisinghe

The results of an investigation of the metabolism of glucose by the preimplantation mouse embryo, with particular reference to the synthesis and turnover of embryonic glycogen are presented in this thesis. The synthesis of glycogen pools as well as other biochemical pools were studied using incorporation of radioisotopically labelled glucose in vitro. Degradation of these biochemical pools both in vitro and in vivo were studied using pulse/chase techniques. As previous studies have shown that freshly collected late preimplantation mouse embryos contain less glycogen than embryos cultured to similar stages in vitro, an attempt has been made in the present study to find an explanation for these differences. Incorporation studies showed that, in vitro, considerable amounts of labelled glucose entered the acid-soluble glycogen pool at the morula and blastocyst stages. In the case of acid-insoluble glycogen an increase in incorporation occurred up to the morula stage but was followed by a decrease with the development of the blastocyst. Pulse/chase experiments showed that a greater degradation of acid-soluble glycogen occurred in vivo than in vitro. Studies using ovariectomized recipients maintained with ovarian steroids showed that progesterone but not oestrogen given to the recipients promoted this degradation. In order to study some of the effects of the uterine environment on the metabolism of glycogen, the concentrations of energy substrates and major cations in the uterine fluid of mice were determined. The direct effects of these constituents and other possible environmental factors on the embryo, including hormones involved in glycogen metabolism, were studied. Of these factors, only elevated potassium levels, similar to those found in the uterine lumen, had any depressing effect on the synthesis of glycogen. The magnitude of this effect was small and it is suggested that other, as yet unknown, factors in the uterus control glycogen degradation. Finally, the cellular distribution of glycogen synthesized in vitro was studied using autoradiographic and histochemical techniques. Trophoblast cells accumulated large amounts of glycogen in comparison to inner cell masses. Incorporation studies using inner cell mass cells isolated by immunosurgery also indicated a low rate of synthesis of glycogen by these cells.

Studies of the metabolism of glucose by the preimplantation mouse embryo

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