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(cAMP) is involved in the maintenance of meiosis in a number
of species (Downs, 1995a; review) and arises from ATP by
the action of adenylate cyclase. During spontaneous maturation
in vitro, cAMP levels decrease in oocytes (Downs, 1995a),
and this is associated with a decrease in ATP levels (Downs,
1995b). It is possible that once the oocyte is irreversibly
committed to mature, cAMP is no longer required to maintain
meiotic arrest, ATP requirements fall and pyruvate uptake
decreases. Interestingly, pyruvate uptake by oocytes which
failed to mature remained high throughout the 24 h period.
Maturation of human oocytes in vitro is accompanied
by changes in the aggregation patterns of mitochondria
(Sathananthan and Trounson, 2000; Wilding et al., 2001),
which may reflect changing metabolic needs of the oocyte in
preparation for fertilization. These changes in mitochondrial
distribution may also account for the lower pyruvate uptake
that was observed during later stages of nuclear maturation.
This work has shown for the first time that it is possible to
measure pyruvate uptake and lactate production by individual,
maturing human oocytes non-invasively. It also demonstrates
that the metabolism of human oocytes can be significantly
influenced by both the composition of the in-vitro culture
medium and the cellular event taking place within the oocyte
nucleus. The fact that the culture environment affects metabol-
ism during human oocyte maturation suggests that the choice
of culture medium for clinical IVM could be critical for
embryonic and possibly fetal health. Further work is needed
to investigate how substrate utilisation by maturing oocytes
relates to subsequent development.
Gardner, D.K. and Lane, M. (1993) Amino acids and ammonium regulate
mouse embryo development in culture. Biol. Reprod., 48, 377–385.
Acknowledgements
Gardner, D.K., Lane, M., Calderon, I. and Leeton, J. (1996) Environment of
the preimplantation human embryo in vivo: metabolite analysis of oviduct
and uterine fluids and metabolism of cumulus cells. Fertil. Steril., 65,
349–353.
The authors are grateful to members of the IVF Unit for their help.
The authors would like to thank J.Stark for help with the statistical
analysis. This study was funded by Wellbeing.
Gott, A.L., Hardy, K., Winston, R.M. and Leese, H.J. (1990) Non-invasive
measurement of pyruvate and glucose uptake and lactate production by
single human preimplantation embryos. Hum. Reprod., 5, 104–108.
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