Effect of cumulus cell mass and follicle quality on in-vitro maturation of cynomolgus monkey oocytes

Cynomolgus monkey oocytes were recovered from healthy or atreticfollicles > 1000 µm in diameter at day 8 of gonadotrophinstimulated cycles and cultured in vitro, cumulus enclosed orcumulus free, for 2 days. Germinal vesicle breakdown (GVBD)occurred in 26.7% of healthy cumulus enclosed oocytes (n= 60)compared to 52.6% of atretic cumulus enclosed oocytes (n = 38).The mechanical removal of the cumulus cell mass increased theGVBD rate of the healthy oocytes (56.5%, n = 23) and acceleratedthe passage of the atretic oocytes (n = 23) from metaphase I(4.3%) to metaphase II (47.8%). In the healthy primate follicle,the dktyate stage could be maintained by aninhibitory substancesecreted by the cumulus; foUicular atresia could either decreasethe synthesis of this substance and/or induce the metabolismof a stimulatory substance.