Non-invasive measurement of glucose and pyruvate uptake by individual human oocytes and preimplantation embryos

Pyruvate and glucose uptake by 73 indivudial human oocytes andpreimplantation embryos was measured non-invasively, using anultramicrofluorescence assay to analyse changes in substratelevels in microdroplets of culture medium. The uptake of bothsubstrates was measured over successive daily incubations betweendays 1(unfertilized oocytes)or 2 (‘spare’ embryoswhich were not transferred) and day 6 (dat 0= day of insemination).Under these conditions, 58% (25/43) of fertilized embryos withtwo pronuclei on day 1 developed to the blastocyst stage byday 6. The pyruvate uptake of these embryos increased from 28 to a maximum of 40 pmol/ embryo/h between days 2.5 and 4.5.Similarly, glucose uptake increased from 8 to 14 pmol/embryo/hbetween days 2.5 and 4.5, but then increased further to 24 pmol/embryo/hon day 5 at the blastocyst stage. The pyruvate uptake of fertilized4.5, but then increased further to 24 pmol/embryo/h on day 5at the blastocyst stage. The pyruvate uptake of fertilized embryoswhich arrested at cleavage stages was significantly lower thanfor those which developed to the blastocyst stage. Polyspermicand parthenogenetic embryos, and unfertilzed oocytes also hadlower pyruvate uptakes at later stages. The glucose uptake ofunfertilized oocytes and abnormal embryos never reached thelevel of fertilized embryos at the blastocyst stage on day 5.5.Non-invasive measurement of pyruvate uptake before embryo transfermay provide a valuable functional criterion for the selectionof viable embryos capable of developing to the blastocyst stage