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

This research article studies and documents the ovulation process in immature rat ovaries, showing how ovulation can occur without visible muscular activity around the follicular wall and how the follicular wall begins breaking down hours before ovulation happens.

Research Methodology

• The researchers used the ovaries of immature rats that were treated with pregnant mare serum gonadotropin (20 IU), followed by human chorionic gonadotropin (hCG) (10 IU) 48 hours later.
• To record this process, a video camera was attached to an inverted microscope, and a video recorder was used to capture the pre-ovulatory and ovulatory events at a cellular level.

Findings and Observations

• Approximately 8 hours after hCG administration, the researchers observed a change in the follicular apex, which shifted from a smooth, optically homogeneous appearance to a rough surface with bleb formation. Moreover, the extrusions of single cells through tiny perforations (an early sign of stigma formation) were noticed.
• After about 2 more hours (at around 10 hours post-hCG), they noticed the formation of a sticky substance, which created a basket-like structure with trapped cells (indicative of late stigma formation).
• The actual ovulation event took place between 12 and 15 hours after the administration of hCG, and it occurred at a constant speed without any contractions of the follicular wall.

Significance of the Findings

• The study demonstrates that ovulation can proceed without any noticeable circumfollicular muscular activity. This negates the general belief that visible muscular contractions are necessary for ovulation to occur.
• It was observed that there was a constant leakage of cells over a long period, which suggests that the follicular wall starts to break down or is partly digested several hours before the actual ovulation occurs. This observation provides a deeper understanding of the cellular processes involved in ovulation.