Morphological studies of the microcirculatory system of periovulatory ovine follicles

Thecal vascular tissue and blood cells were studied by light, transmission, and scanning electron microscopy during ovulation in the ewe. Cross-sectional areas of vascular lumens increased after the preovulatory surge in luteinizing hormone, decreased before ovulation, and then increased again as corpora lutea formed. Numbers of blood vessels per unit area of thecal tissue declined just before ovulation, then increased during luteinization. The follicular stigma that develops near the time of ovulation was completely void of blood vessels. These findings were paralleled chronologically by evidence of vasodilation, increased vascular permeability, tissue edema, congestion, ischemia, vascular injury, and angiogenesis. Neutrophils and eosinophils migrated out of the vascular compartment before ovulation. Around the time of ovulation, there were masses of extravasated blood in thecal tissue, and numerous platelets adhered to damaged vascular endothelium. Extravasated monocytes/macrophages were evident after ovulation. Numbers of extravascular lymphocytes remained relatively constant, but the lymphocytes were often marginated along endothelium in ovulatory and postovulatory follicles. Basophilic cells accumulated in association with the development of new capillaries during luteinization. Our observations are consistent with the concept that periovulatory follicular processes include acute inflammation, tissue damage, glandular transformation, and healing.