Inhibition of meiotic maturation in growing pig oocytes by factor(s) from cumulus cells.

Total inhibition of germinal vesicle breakdown (GVBD) was observed in growing pig oocytes (internal diameter 80, 90 and 100 microns) when they were cultured in a medium conditioned by cumulus oocyte complexes (COCs) of fully grown oocytes. In denuded growing oocytes, only partial inhibition was observed. The inhibitory effect was fully reversible. The addition of heparin (300 IU/ml) could overcome the effect of the conditioned medium. Transient exposure (6 h) of oocytes to dibutyryl cyclic adenosine monophosphate (dbcAMP) (1 mg/ml) could also partly reverse the effect of factor (s) produced by cumulus cells of fully grown oocytes. Follicle-stimulating hormone (5 micrograms/ml) was able to increase the percentage of maturing oocytes. The addition of luteinizing hormone (5 micrograms/ml) had no effect on GVBD inhibition by cumulus-conditioned medium.