Metabolic coupling, cumulus expansion and meiotic resumption in mouse cumuli oophori cultured in vitro in the presence of FSH or dcAMP, or stimulated in vivo by hCG.

The temporal changes of metabolic coupling between the mouse oocyte and the cumulus cells which follow hCG injection in vivo and FSH treatment in vitro were studied by measuring what fraction of [3H]uridine taken up by cumulus cells was transferred to the oocyte. Meiotic resumption and a partial coupling loss (to 35% of the initial value) spontaneously occurred in cumuli cultured in control medium. The addition of 1 microgram FSH/ml in vitro, or the injection of hCG in vivo caused a delay of about 3 h in both phenomena and a near total uncoupling, together with cumulus expansion. FSH caused uncoupling even if cumulus expansion was prevented by the addition of heparin. The presence of 2 mM-dcAMP prevented meiotic resumption in cumulus-enclosed oocytes and maintained a high level of co-operation for at least 6 h. The slow uncoupling observed at later times was due to cumulus expansion, because it was totally prevented by heparin. We suggest that metabolic co-operation with the cumulus oophorus and meiotic resumption are both regulated by FSH through variations of intracellular levels of cAMP.