Preovulatory changes in cumulus-oocyte complex of the hamster.

An orderly series of associations was found between the cumulus and the stages of nuclear development in the hamster oocyte as the oocyte-cumulus complex underwent preovulatory maturation. Ten hours prior to ovulation meiotic resumption was first seen in the oocyte. The onset of cumulus dissociation with corresponding morphological changes in cumulus cells was observed eight hours prior to ovulation. Completion of the first meiotic division in the oocyte and full cumulus dissociation occurred 2 hours prior to ovulation. Cumulus dissociation was found to occur only in vesicular follicles destined to ovulate and not in follicles undergoing atresia. Cells with large vacuolar inclusions with distorted, hyperchromatic nuclei were found in the maturing cumulus.