[An ultrastructural study of capillaries of rabbit ovarian follicles during ovulatory process (author's transl)].

The observations that perifollicular capillaries of the ovary become engorged with prominent edema in the theca interna and externa around the time of ovulation, suggest a preovulatory increase in permeability of perifollicular capillaries. In order to obtain an ultrastructural evidence for this increased capillary permeability, we examined the perifollicular capillaries in the theca interna by using mature rabbit ovaries at various time intervals after the hCG injection for induction of ovulation. We observed a capillary engorgement at 9, 10, 12 hours after the hCG injection, most prominent at 9 hours, and edema in the pericapillary space at 10, 12 hours. Pinocytotic vesicles were seen through the all stages of follicular development and they did not show any significant changes in their size, number and distribution. Fenestrations were observed at 0, 3, 4, 6 hours after the hCG injection, most frequent at 4 hours. Intercellular gaps (500 approximately 1,200 A) between two endothelial cells were demonstrated at 10, 12 hours, and thrombocytes in these gaps were also noticed. The present observations suggest that increased permeability of perifollicular capillaries just prior to ovulation were mainly due to the formation of gaps between the endothelial cells.