Studies on the equine placenta II. Ultrastructure of the placental barrier

Samuel, Carole A.; Allen, W. R.; Steven, D. H.

doi:10.1530/jrf.0.0480257

Cited by 63 publications

(29 citation statements)

References 5 publications

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“…9; Samuel et al, 1975). Further development persists throughout gestation to maximize the area of contact between the fetal and maternal epithelial layers for haemotrophic transfer of nutrients and waste products, and the exchange process is aided by the indentation of blood capillaries into the bases of these epithelial layers on both the fetal and maternal sides of the interface (Samuel et al, 1976;Macdonald et al, 2000). Each microcotyledon is supplied by a sizeable artery on the maternal side and an equivalent placental artery on the fetal side to maximize the haemotrophic exchange process (Fig.…”

Section: Placentationmentioning

confidence: 99%

Fetomaternal interactions and influences during equine pregnancy

Allen

2001

Reproduction

115

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The equine embryo takes 6 days to traverse the oviduct and, when it finally enters the uterus, it remains spherical in shape and moves continually throughout the uterine lumen until day 17 after ovulation to deliver its maternal recognition of pregnancy signal to the entire endometrium. Between day 25 and day 35 after ovulation, the trophoblast cells of a discrete annulate portion of the chorion multiply rapidly and acquire an invasive phenotype and, between day 36 and day 38, migrate deeply into the maternal endometrium to form the equine-unique endometrial protuberances known as endometrial cups. These cups secrete large quantities of a gonadotrophic hormone (eCG) into the maternal circulation which, in conjunction with pituitary FSH, stimulates the development of accessory luteal structures in the maternal ovaries to supplement the supply of progesterone to maintain the pregnancy until the placenta can assume this role at about day 100. The non-invasive allantochorion extends slowly to fill the uterus by days 80-85 and its microcotyledonary architecture, which provides both haemotrophic and histotrophic nutrition for the growing fetus, is not fully established until days 120-140. The fetoplacental unit synthesizes large quantities of steroid hormones during the second half of pregnancy, using fetal C-19 precursors secreted by the enlarged fetal gonads for the production of oestrogens and maternal C-21 precursors for the synthesis of progesterone and large quantities of 5alpha-reduced progestagens. Near term, additional pregnenelone is secreted by the fetal adrenal glands so that the mare exhibits the unusual phenomenon of foaling while maternal serum progestagen concentrations are increasing and oestrogen concentrations are decreasing.

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Section: Placentationmentioning

confidence: 99%

Fetomaternal interactions and influences during equine pregnancy

Allen

2001

Reproduction

115

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“…(Amoroso, 1961;Bjorkman, 1970;Friess et al, 1980;Samuel et al, 1976;King, 1984a). It is a common feature in terminal villi of mature monkey and human placentas and, from a functional point of view, serves to decrease the diffusional distance between maternal and fetal bloodstreams.…”

Section: Origin Of Angioblastic Tissuementioning

confidence: 99%

Ultrastructural differentiation of stromal and vascular components in early macaque placental villi

King

1987

Am. J. Anat.

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In this study, closely staged placental villi from rhesus monkeys between 19 and 60 days of gestation were used to examine 1) the origin of endothelial cells and the mechanism of angiogenesis in villi; 2) the origin of placental macrophages (Hofbauer cells), and 3) the origin of the reticular cells that compartmentalize the stroma. The results did not support the concept that early stromal cells in the villi were derived by in situ delamination from cytotrophoblast. The extraembryonic mesodermal (mesenchymal) cells at the earliest of ages examined contained considerable granular ER. These cells organized into groups and formed primitive intercellular junctions, thus giving rise to the early angioblastic masses. The angioblastic masses were cellular, not syncytial; and lumen formation was not the result of intracellular vacuolization, but rather was the result of the acquisition of junctionally defined spaces. The earliest capillaries lacked intravascular blood cells and a basal lamina. Later, blood cells were evident in the lumina. At about 45-50 days of gestation, fetal capillaries began to indent the basal surface of the trophoblast. The basal lamina of the fetal capillaries still had not developed by 60 days of gestation. Between 35 and 40 days of gestation, significant morphological changes took place in the villous stroma. Evidence was obtained that the mesenchymal cells differentiated into the reticular cells that subdivided the stroma into fibril-rich and fibril-free compartments. At the same time, Hofbauer cells were observed for the first time; they occupied the fibril-free regions of the stroma. We did not observe any clear indications of intermediate stages of differentiation between other stromal cell types and Hofbauer cells. It is suggested that placental macrophages may have an origin independent of other stromal types; one possibility is that they are derived from blood monocytes as in other tissues. It is further suggested that the activities of the macrophages and reticular cells may be important in remodeling the extracellular matrix and may be related to the process of branching morphogenesis in the villi.

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“…CG secretion appears to occur mainly through the villi of the human syncytiotrophoblast and also the equine endometrial cup cells [1,3,46–48]. It was shown that the CTP, and particularly the O-linked oligosaccharides of the domain, route the hCGβ subunit through the apical side of polarized MDCK cells [34].…”

Section: Discussionmentioning

confidence: 99%

The recombinant equine LHβ subunit combines divergent intracellular traits of human LHβ and CGβ subunits

2015

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The pituitary LHβ and placental CGβ subunits are products of different genes in primates. The major structural difference between the two subunits is in the carboxy-terminal region, where the short carboxyl sequence of hLHβ is replaced by a longer O-glycosylated carboxy-terminal peptide (CTP) in hCGβ. In association with this structural deviation, there are marked differences in the secretion kinetics and polarized routing of the two subunits. In equids, however, the CGβ and LHβ subunits are products of the same gene expressed in the placenta and pituitary (eLH/CGβ), and both contain a CTP. This unusual expression pattern intrigued us and led to our study of eLH/CGβ subunit secretion by transfected CHO and MDCK cells. In continuous labeling and pulse chase experiments, the secretion of the eLH/CGβ subunit from the transfected CHO cells was inefficient (medium recovery of 16–25%) and slow (t1/2 >6.5 hrs). This indicated that, the secretion of the eLH/CGβ subunit resembles that of hLHβ rather than hCGβ. In MDCK cells grown on Transwell filters, the eLH/CGβ subunit was preferentially secreted from the apical side, similar to the hCGβ subunit secretory route (~65% of the total protein secreted). Taken together, these data suggested that secretion of the eLH/CGβ subunit integrates features of both hLHβ and hCGβ subunits. We propose that the evolution of this intracellular behavior may fulfill the physiological demands for biosynthesis of the eLH/CGβ subunit in the pituitary as well as in the placenta.

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Studies on the equine placenta II. Ultrastructure of the placental barrier

Cited by 63 publications

References 5 publications

Fetomaternal interactions and influences during equine pregnancy

Fetomaternal interactions and influences during equine pregnancy

Ultrastructural differentiation of stromal and vascular components in early macaque placental villi

The recombinant equine LHβ subunit combines divergent intracellular traits of human LHβ and CGβ subunits

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