DETERMINANTS OF OOCYTE AND PREIMPLANTATION EMBRYO QUALITY - METABOLICREQUIREMENTS AND THE POTENTIAL ROLE OF CUMULUS CELLS

This review examines the metabolic requirements of the oocyte and prei mplantation embryo and the potential of the cumulus oophorus to influe nce events in the follicular and luteal phases, Mammalian oocytes and early preimplantation embryos generate ATP aerobically, oxidizing subs trates such as pyruvate, lactate, amino acids and possibly fat, with g lucose consumption increasing sharply as the blastocyst stage is reach ed. The major product of glucose metabolism is lactate produced by aer obic glycolysis. Several methods are described for the measurement of oxygen consumption by oocytes and early embryos, since this provides a good indication of their overall capacity to generate energy. The ori gin of the energy substrates utilized by oocytes and eat ly embryos, f rom follicular fluid and tubal fluid, is also discussed. The cumulus o ophorus is shown to interact with the developing oocyte and to influen ce events following ovulation, Preliminary data from the authors' labo ratories show that cumulus cells in vitro produce pyruvate in sufficie nt quantity to satisfy the metabolic requirements of human oocytes and preimplantation embryos, Cumulus cells also exhibit steroidogenic act ivity, with this activity being maintained in vitro for up to 10 weeks . Steroidogenic activity was shown to vary between cumulus complexes a ssociated with oocytes from the same cohort. Preliminary data suggest that oestradiol production by cumulus cells in vitro is significantly higher in pregnant than in non-pregnant cycles.