Effect of indomethacin on preovulatory changes in the ultrastructure of rabbit Graafian follicles

This investigation uses electron microscopy to examine the effect of prostaglandins on follicular tissue during the ovulatory process. The ultrastructure of follicles from indomethacin-treated rabbits was compared to the ultrastructure of normal ovulatory follicles in order to determine the morphological differences between follicles with negligible and normal prostaglandin synthesis, respectively. The most obvious difference between the two groups of follicles was that the tissue at the apex of normal follicles began to thin out significantly by 9 h post coitus (near the time of ovulation), whereas the follicles from indomethacin-treated animals showed no signs of thinning, even as late as 12 h post coitus. It appeared that the fibroblasts in the follicles with limited prostaglandin synthesis failed to undergo the normal ovulatory transformation from a quiescent to a proliferative state. Otherwise, the prostaglandin-deficient follicles had a number of morphological features similar to those which usually occur in ovulatory tissue. There was detectable loosening of the connective tissue elements and some indication of edema at the apex of the mature follicles. Also, granulocytes became localized in the vascular compartment of these follicles. In addition, there tended to be an increase in the multivesicular structures which protrude from the fibroblasts, as well as an increase in the dense granules which accumulate in the cytoplasm of the surface epithelial cells. Collectively, these data suggest that normal prostaglandin synthesis in ovulatory follicles may be important in the connective tissue decomposition and ultimate thinning of the follicle wall.