The three‐dimensional feto‐maternal vascular interrelationship during early bovine placental development: a scanning electron microscopical study

Abstract

Both the fetal and maternal microvasculature of bovine placentomes was examined by scanning electron microscopy of vascular casts. So far the development of the vascular architecture of the bovine placentome in early gestation has only been studied 2-dimensionally due to technical difficulties arising from the fragility of the early placental blood vessels. Repeated experiments led to the selection of the microvascular corrosion casts presented here. The vasculature of the maternal compartment is supplied by large caruncular stalk or spiral arteries, which release short maternal stem arteries. In the 3rd month of gestation, these arteries branch into several arterioles at their base, thus providing the vascular framework for the lower part of the septal walls of the primary crypts. In the 4th month, due to progressive longitudinal growth of the stem arteries, branching into arterioles occurs not only at the base, but over the whole length of the stem arteries. These arterioles supply the capillary complexes of the septa which resemble the major part of the septal vasculature and face the secondary crypts. Further indentation results in the formation of tertiary crypt capillary complexes, encircling the earlier secondary unit. From the 6th month of gestation the architecture resembles the fully developed maternal placenta with stem arteries running directly to the fetal side to branch into 4 to 6 arterioles, which turn back to enter secondary and tertiary septa. Maternal venules, collecting the blood from the capillary bed of secondary and tertiary septa, converge onto stem veins leaving the caruncle via branches of the uterine vein. The fetal part of the placentome is supplied by the cotyledonary arteries, which branch into fetal stem arteries that are the tributary to single villous trees. Over their whole course towards the maternal side, these give off arterioles entering secondary villi. The tertiary or terminal villous vasculature consists of capillaries, which are organised in serial capillary loops. This system is progressively elaborated in the course of gestation. In the 4th month there are only finger-like loops, whereas from the 6th month large fan-like structures can be observed. In early gestation the maternal and fetal blood vessels meet predominantly in a countercurrent fashion, changing to the less efficient crosscurrent exchange when the tertiary unit develops. These results indicate the development of a highly elaborated fetomaternal villous-crypt exchange system, already established in the 1st half of gestation, thus meeting the increasing needs of the fetus.

Cytoskeletal filaments and associated proteins during restricted trophoblast invasion in bovine placentomes: light and transmission electron microscopy and RT-PCR

“…In vitro, the transmembrane accumulation of talin and a-actinin at the apical surface of ovine luminal epithelial and conceptus trophectoderm cells upon contact with osteopontin-coated beads has revealed that functional integrin activation and cytoskeletal reorganization might occur during embryo implantation in sheep . The presence of actin in fetal and maternal endothelia is not surprising, since endothelial cell migration is a common feature during angiogenesis (Risau 1997), which takes place in the fetal and maternal compartments of the bovine placenta throughout gestation (Leiser et al 1997;Pfarrer et al 2001).…”

Integrin Activation in Bovine Placentomes and in Caruncular Epithelial Cells Isolated from Pregnant Cows

“…The bovine placentome is a complex placental structure that provides restricted trophoblast invasion and maximal vascular exposure for the transport of molecules across the epitheliochorial feto-maternal interface [20]. By colocalizing aggregates of ITGB1, phosphorylated tyrosine, PTK2, TLN1, and ACTN, we have for the first time conclusively shown that the activation of ITGB1-integrin leads to formation of focal adhesions in caruncular epithelial cells that inhabit the fetomaternal interface.…”

Placental development during early pregnancy in sheep: vascular growth and expression of angiogenic factors in maternal placenta

“…Moreover, in compromised pregnancies (that is, pregnancies in which fetal or placental growth, or both, is affected), placental angiogenesis is also abnormal at mid to late periods , Reynolds et al 2005a, 2005b, 2005c, 2010, Burton et al 2009). Although the importance of vasculogenesis and angiogenesis during early pregnancy is well recognized (Pfarrer et al 2001, Sherer & Abulafia 2001, Mayhew 2002, Demir et al 2007, Reynolds et al 2010, limited data are available concerning the timing of initiation of placental angiogenesis, changes in vascular development and expression of angiogenic factors during this period. Previously, we have reported changes in vascular growth during early pregnancy in sheep (Reynolds & Redmer 1992, Zheng et al 1996; however, relatively few days were studied, and therefore, we recognized the need for a more detailed analysis as in the present study.…”