Analysis of Fetal and Maternal Microvasculature in Ruminant Placentomes by Corrosion Casting

Vascular corrosion casting is a useful tool for studying the vascular architecture of complex organs. The synepitheliochorial placenta of ruminants is composed of two closed blood circuits, a fetal and a maternal one. The microvasculature of each circuit has the shape of the corresponding cotyledon (villous trees) and caruncle (crypts). These two compartments interdigitate with each other in a complementary fashion. Understanding three-dimensional vascular arrangements is facilitated by scanning electron microscopy of vascular corrosion casts. Methods to be used in the generation of vascular casts from fetal and maternal placentomal blood vessels are described, with special emphasis on casting resins and corrosion using potassium hydroxide. The procedure of splitting larger casts following gelatin embedding and freezing is also presented.