Light and ultrastructure of intra-ovarian oocyte release in infantile rats

Follicular ruptures with intra-ovarian oocyte release (IOR) were studied in 17, 21 and 24-day-old rats by morphological methods. Using a light microscope, it was seen that IOR occurred at all times and the IOR frequency did not change. IOR developed in preantral follicles. Their oocytes were mostly found within the follicular compartment (incomplete IOR). Using an electron microscope, a circumscribed dissolution of the basal lamina was observed. IOR granulosa cells appeared activated. They rarely underwent typical necrosis after herniation into the extrafollicular area. Herniated granulosa cells tended either to stay intact or to shed cytoplasmic components into the extracellular space, whilst nuclei of active cell function were maintained. Tissue adjacent to an IOR seemed inactive with the exception of endothelial cells. Some endothelial cells underwent necrosis. Additionally, the endothelium was discontinuous. The morphological data support the hypothesis that the mechanism of follicular rupture represents an inside to outside process.