Follicular microvasculature in the porcine ovary.

The microvasculature of porcine ovaries, with special regard to the follicles in the interstitial-stromal tissue, was studied by scanning electron microscopy (SEM) of vascular corrosion casts. Porcine ovaries displayed several coiled arteries in the hilus and many branches with small diameters and a tightly spiraling configuration in the cortical areas. However, small arterioles became straight before entering vascular complexes of follicles and finally divided into capillaries. Vascular baskets of various sizes (150-9,900 micro m in diameter) and architecture related to follicles in various developmental stages were observed in the ovarian cortex. Small follicles (150-300 micro m in diameter) began with a polygonal meshwork of a few large capillary meshes and developed to an obvious spherical microvascular network with a thin single layer of capillaries when reaching 500-700 micro m in diameter. The microvascular architecture of follicles 1,000-2,000 micro m in diameter developed further and had a three-layer vascular plexus. With a diameter of more than 2,000 micro m, the microvasculature of antral follicles was arranged as an inner vascular plexus of about 25 micro m, a middle plexus of about 100 micro m, and an outer capillary plexus of about 30 micro m in thickness. The present observations indicate that follicular vascular baskets of diverse sizes and architecture in various developmental stages support the gradual increase of follicular blood flow during follicle growth in the pig.