Apoptosis of postovulatory cumulus granulosa cells of the rat

The process of apoptosis in the postovulatory cumulus granulosa cells was investigated in pregnant rats. Mature female Wistar rats, exhibiting a regular 4-day oestrous cycle, were placed with males on the day of pro-oestrus. The following day, on which spermatozoa were found in vaginal smears, was designated day 1 of pregnancy. The animals were killed just before ovulation (24.00 hours), on days 1 (5.00, 11.00, and 18.00 hours), and 2 ( 11.00 hours) of pregnancy. Excised ovaries and oviducts were submitted to a routine histological procedure and paraplast sections were subjected to detection of apoptotic cells using the TUNEL method. The cumulus granulosa cells of preovulatory follicles (24.00 hours) were negative for apoptotic staining. However, 5 h later a positive staining was observed in the oviduct ampulla and included the cumulus granulosa cells lying in the peripheral parts of postovulatory cumuli oophori, and the oviductal epithelial cells of this region. On the evening of day 1 almost all cumulus granulosa cells showed strong immunostaining while on day 2 at 11.00 hours only immunonegative clusters of remnants of cumulus granulosa cells were present in the distended ampulla region, while naked, two or more cell embryos were present in the further parts of oviduct. These results indicate that in the rat apoptosis of cumulus granulosa cells starts shortly after ovulation in the peripheral region. Epithelial ampullary cells surrounding ovulated cumuli show a massive apoptosis.