Ovulation in the isolated perfused rat ovary as documented by intravital microscopy

Surface cell changes at the apices of preovulatory follicles and ovulations were documented in isolated perfused ovaries from immature rats treated with pregnant mare serum gonadotropin (20 IU) and 48 h later with human chorionic gonadotropin (hCG) (10 IU). A video camera coupled to an inverted microscope and a video recorder captured the preovulatory and ovulatory events at a cellular level. At around 8 h post-hCG, the follicular apex changed from a smooth and optically homogeneous appearance into a rough surface with bleb formation and extrusions of single cells through minute perforations (early stigma formation). At approximately 10 h, a sticky material formed a basketlike structure with trapped cells (late stigma formation). At 12 to 15 h, ovulation took place at a constant speed and with no contractions of the follicular wall. This indicates that ovulation can occur with no visible circumfollicular muscular activity. Furthermore, the observations of a leakage of cells over an extended period of time indicates that the follicular wall is partly digested several hours before ovulation occurs.