Summary. This study was undertaken to create an in-vitro model using granulosa cell monolayers to replace the role of the follicle in the maturation of bovine oocytes. Cumulus–oocyte complexes were co-incubated with fresh or 7-day granulosa cell cultures (with new or conditioned medium) or with conditioned medium alone, in the presence or absence of IBMX (isobutylmethylxanthine), adenosine or heparin. Progression to the metaphase-II stage was significantly affected by the co-culture of oocytes with bovine granulosa cell monolayers and to a lesser degree when cultured with supernatant alone (conditioned medium). The oocytes attached rapidly to the monolayer, suggesting that the intimate contact between the granulosa cells and the cumulus–oocyte complexes is an important signal for the maintenance of meiotic arrest. Heparin did not prevent maturation itself, but prevented attachment of cumulus–oocyte complexes to monolayers, thereby reducing their inhibitory effect. Adenosine prevented cumulus expansion and reduced maturation and IBMX was an effective inhibitor only in the presence of additional granulosa cells.
Keywords: oocyte; meiosis; granulosa cells; in vitro; cattle