Uterine vasculature of the pregnant pig: a scanning electron microscope study.

Colored cold setting acrylic cement was injected through catheters into the arteries and veins of sixteen gravid uteri obtained from pigs at various stages of pregnancy. After the cement had set hard, the reproductive tracts were macerated in concentrated acid and the vascular casts resulting were washed clean of digested tissues. Small pieces of cast were coated with gold and viewed by means of a scanning electron microscope. Early in pregnancy the capillary network consists of low parallel ranks of ridges and troughs; later, cross ridging was observed which developed in complexity as pregnancy progressed. The density of capillaries comprising the microvascular network also increased towards term. No comparable changes were noted in the relatively less well vascularized areas surrounding the mouths of the uterine glands. This technique surmounted the problems of obtaining an adequate depth of focus for viewing the capillary network of the gravid uterus with the light microscope. The relationships that the blood vessels bore to the overlying epithelial layers were discussed and the inference tentatively drawn that blood flow at the capillary level was from ridge top to trough base.