Effect of morphology on placentome size, vascularity, and vasoreactivity in late pregnant sheep.

Ovine placentomes vary in shape, with type A placentomes being concave, type D convex, and types B and C intermediate in morphology. It has been speculated that as placentomes advance in type they differ in vascularity and nutrient transport capacity. Our objective was to determine cellularity and vascularity measurements, angiogenic factor expression, and arterial vasoactivity within different morphologic types of placentomes. On Day 130 of gestation, placentomes were collected from multiparous ewes (n = 38) and were evaluated for size, cellularity estimates, angiogenic factor mRNA expression, capillary vascularity (capillary size, capillary surface density [CSD], capillary number density [CND], and capillary area density [CAD]), and vasoreactivity to potassium chloride and angiotensin II. The average weight and size of type A and B placentomes were less (P < 0.01) than those of type C and D placentomes. Placentome morphology did not affect (P > or = 0.24) cotyledonary or caruncular cellularity estimates or percentage of cellular proliferation. Placentome morphology affected (P > or = 0.41) neither caruncular CAD, CND, CSD, or capillary size nor cotyledonary CND, CSD, or capillary size. Cotyledonary CAD was increased (P < 0.01) in type B and D placentomes compared with type A placentomes. Furthermore, placentome type did not affect (P > or = 0.06) angiogenic factor gene expression in the cotyledon or the caruncle. Size, but not morphologic type of placentome, was associated with greater caruncular artery contractility to potassium chloride and angiotensin II (P < 0.01 for both). Placentome size, but not morphologic type, may be important for vascularity and nutrient transfer in the placenta of the pregnant ewe.