Placentation in the Hottentot golden mole, Amblysomus hottentotus (Afrosoricida: Chrysochloridae)

The placentation of the Hottentot golden mole (Amblysomus hottentotus) has been examined using light and electron microscopy and lectin histochemistry of nine specimens at both mid and late gestation. The placentae were lobulated towards the allantoic surface and the lobules contained roughly parallel arrays of labyrinthine structures converging on a central spongy zone. At mid gestation, the arrays were composed of an inner cellular and outer syncytial trophoblast layer, the inner layer enclosing scant connective tissue and fetal capillaries. Maternal blood spaces coursed through the outer trophoblast and were lined by trophoblastic microvilli; the blood spaces were narrow in mid gestation but enlarged near term, while the inner trophoblast layer became thinner and seemed to be syncytial. These features were confirmed by transmission electron microscopy. The microvillous surfaces and dispersed cytoplasmic particles were heavily glycosylated, as shown by lectin histochemistry, and exhibited changes with maturation, particularly a loss in N-acetyl glucosamine oligomers bound by Phytolacca americana lectin on the microvilli lining the maternal blood spaces and outer trophoblast particles. A substantial yolk sac was present both in mid and late gestation stages. It was clearly unattached to the uterus in the later stages. These morphological features are discussed in relation to the phylogenetic position of Amblysomus with respect to other members of Afrosoricida and Afrotheria.

Diabetes and cardiovascular disease: related disorders created by disturbances in the endogenous clock

The factors underpinning the development of type 2 diabetes mirror closely the presentation of atherothrombotic risk factors that enhance risk of macrovascular disease. It has been postulated that this relationship is so tight as to indicate that diabetes and cardiovascular disease are the same condition with common genetic and environmental antecedents ('the common soil hypothesis'). The huge Increase in prevalence of type 2 diabetes in the Asia-Pacific region in recent years has raised serious concerns regarding the cardiovascular consequences for these populations. For example, in the UK, subjects of S. Asian origin have a higher prevalence of type 2 diabetes with a relative risk of macrovascular disease of -1.5 compared to the Indigenous population. Current opinion favours the view that the development of obesity is associated with an insulin resistant phenotype that promotes vascular risk. Our endogenous clock is regulated centrally in the hypothalamus by light exposure and in peripheral tissues to place our metabolic needs in time with day length and the seasons. Evidence from animal and cellular studies with early data from human studies indicates that disruption of the endogenous clock as can occur with obesity, is associated with a metabolic syndrome phenotype. The adaption of western lifestyles by S Asian subjects may promote disruption of circadian rhythms with associated increases in both diabetes and cardiovascular disease.

Alanine aminotransferase is associated with atherothrombotic risk factors in a British South Asian population

BACKGROUND

Alanine aminotransferase (ALT) predicts the development of Type 2 diabetes mellitus and cardiovascular disease in Caucasian subjects.

OBJECTIVES

This study aimed to determine the incidence of an elevated ALT and its relationship to metabolic and atherothrombotic risk factors in a healthy British South Asian population.

PATIENTS/METHODS

One hundred and forty-three participants from the West Yorkshire community were recruited randomly from general practice registers and were grouped according to whether their ALT was above or within the normal range (cut-off 35 IU L(-1)) and examined for differences in metabolic and atherothrombotic risk factors. All participants were originally from South Asia, with their grandparents being born in India, Pakistan, or Bangladesh.

RESULTS

The incidence of a raised ALT was 24%. Those with a raised ALT had a more adverse metabolic profile, with significantly higher body mass index, waist/hip ratio, fasting insulin, glucose, homeostasis model assessment homeostasis model assessment insulin resistance (HOMA-IR), and triglycerides, and lower high-density lipoprotein (HDL) cholesterol. Fifty per cent had the metabolic syndrome [International Diabetes Federation (IDF) criteria]. They also had a more adverse atherothrombotic profile, with higher tissue-type plasminogen activator and plasminogen activator inhibitor-1 (PAI-1) antigen. In accordance, the group as a whole showed a positive correlation of ALT (age-adjusted) with waist/hip ratio, insulin, glucose, triglycerides, PAI-1 antigen, factor XIII B subunit, and FXII, and a negative correlation with HDL cholesterol.

CONCLUSION

Raised ALT is common in apparently healthy British South Asians, and is significantly associated with an adverse metabolic and atherothrombotic risk profile.

Sources for comparative studies of placentation I. embryological collections

A rich source of material for comparative studies of the placenta is the collections made by pioneers in the field such as H.W. Mossman, A.A.W. Hubrecht and J.P. Hill. This overview gives a brief description of collections known to be available and information on how each can be accessed. Included are some of the major series of human and animal embryos, such as the Boyd and Carnegie collections, as these also house placental material.

Placentation in cloned cattle: Structure and microvascular architecture

To elucidate the morphological differences between placentas from normal and cloned cattle pregnancies reaching term, the umbilical cord, placentomes and interplacentomal region of the fetal membranes were examined macroscopically as well as by light and scanning electron microscopy. In pregnancies established by somatic nucleus transfer (NT), the umbilical cord and fetal membranes were edematous. Placentomal fusion was common, resulting in increased size and a decreased number of placentomes. Extensive areas of the chorioallantoic membrane were devoid of placentomes. An increased number of functional or accessory microcotyledons (<1 cm) were present at the maternally oriented surface of fetal membranes. Extensive areas of extravasated maternal blood were present within the placentomes and in the interplacentomal region. The crypts on the caruncular surface were dilated and accommodated complexes of more than one primary villus, as opposed to a single villus in non-cloned placentae. Scanning electron microscopy of blood vessel casts revealed that there was also more than one stem artery per villous tree and that the ramification of the vessels failed to form dense complexes of capillary loops and sinusoidal dilations as in normal pregnancies. At the materno-fetal interface, however, the trophoblast and uterine epithelium had normal histology. In conclusion, the NT placentas had a range of pathomorphological changes; this was likely associated with the poor clinical outcome of NT pregnancies.

Placental Diversity in Malagasy Tenrecs: Placentation in Shrew Tenrecs (Microgale spp.), The Mole-Like Rice Tenrec (Oryzorictes hova) and The Web-Footed Tenrec (Limnogale mergulus)

Placentation in tenrecs of the subfamily Oryzorictinae, family Tenrecidae, has not been described previously. The structure of the placenta of this group and especially of the genus Microgale was investigated to determine its similarity or dissimilarity to previously described placentas of the tenrec subfamilies Potamogalinae and Tenrecinae. Fifteen specimens of the genus Microgale ranging from an early yolk sac stage to near term were available for study. Placentation in Microgale was found to be different from other tenrecids in that there is an early simple lateral rather than central haemophagous region. In addition, a more villous portion of the placental disk forms before the formation of a more compact labyrinth. Although the definitive placenta is cellular haemomonochorial, it lacks the spongy zone found in the Tenrecinae. Neither does it resemble the endotheliochorial condition found in the Potamogalinae. Of the two genera of the subfamily Oryzorictinae represented by single specimens, the placenta of Limnogale resembled that of the Microgale but Oryzorictes had several differences including a lobulated placental disk. It is concluded that there is more variation in placentation both within the subfamily Oryzorictinae and within the family Tenrecidae than would ordinarily be expected.

Evolution of the Placenta in Eutherian Mammals

We review recent advances in our understanding of placental evolution with particular focus on the interhaemal barrier. It seems likely that the non-invasive, epitheliochorial placentation of living eutherians is a derived state. However, there is disagreement on whether the last common ancestor of eutherian mammals had an endotheliochorial placenta or a haemochorial one. Research has been stimulated by improved understanding of the relations between the orders of mammals provided by molecular phylogenetics. In part, the uncertainties arise from doubt about how to root the mammalian tree. Resolution of this issue will require improved taxon sampling in molecular analyses. At the same time, we need to foster research in comparative placentation on relevant taxa, particularly at the ultrastructural level. Only then can we ensure that information available about the placenta is adequate to capitalise on future advances in molecular phylogenetics. Examples are given of recent findings that could benefit cladistic analysis of placental evolution.

Ethnic differences in cardiovascular risk factors in healthy Caucasian and South Asian individuals with the metabolic syndrome

BACKGROUND

The metabolic syndrome is a cluster of atherothrombotic risk factors that are commonly associated with insulin resistance.

OBJECTIVES

The aim of this study was to investigate ethnic differences in insulin resistance and non-traditional cardiovascular risk factors in relation to the International Diabetes Federation (IDF) definition of the metabolic syndrome.

PATIENTS AND METHODS

A total of 245 healthy South Asians and 245 age- and sex-matched Caucasians were studied. C-reactive protein (CRP), complement C3, plasminogen activator inhibitor-1 (PAI-1) and tissue plasminogen activator (t-PA) were measured and homeostasis model assessment-insulin resistance (HOMA-IR) was calculated from fasting plasma glucose and insulin levels.

RESULTS

Fifty Caucasian (20%) and 95 (39%) South Asian subjects had the metabolic syndrome as defined by the IDF. In South Asian subjects, HOMA-IR, CRP, C3, PAI-1 and t-PA were significantly higher in subjects with the metabolic syndrome. In contrast, in Caucasian individuals there was no difference in HOMA-IR or C3 levels and only CRP, PAI-1 and t-PA were higher in subjects with the metabolic syndrome. In a logistic regression model, plasma levels of CRP and PAI-1 were independent predictors of the metabolic syndrome in Caucasians, whereas plasma levels of C3 and t-PA as well as HOMA-IR were independent predictors of the metabolic syndrome in South Asian subjects.

CONCLUSIONS

In the cohort of individuals studied, the IDF definition of the metabolic syndrome was associated with insulin resistance in the South Asian but not the Caucasian population. This work also showed ethnic differences in non-traditional cardiovascular risk factors in the presence of the metabolic syndrome.

Animal models of human placentation--a review

This review examines the strengths and weaknesses of animal models of human placentation and pays particular attention to the mouse and non-human primates. Analogies can be drawn between mouse and human in placental cell types and genes controlling placental development. There are, however, substantive differences, including a different mode of implantation, a prominent yolk sac placenta, and fewer placental hormones in the mouse. Crucially, trophoblast invasion is very limited in the mouse and transformation of uterine arteries depends on maternal factors. The mouse also has a short gestation and delivers poorly developed young. Guinea pig is a good alternative rodent model and among the few species known to develop pregnancy toxaemia. The sheep is well established as a model in fetal physiology but is of limited value for placental research. The ovine placenta is epitheliochorial, there is no trophoblast invasion of uterine vessels, and the immunology of pregnancy may be quite different. We conclude that continued research on non-human primates is needed to clarify embryonic-endometrial interactions. The interstitial implantation of human is unusual, but the initial interaction between trophoblast and endometrium is similar in macaques and baboons, as is the subsequent lacunar stage. The absence of interstitial trophoblast cells in the monkey is an important difference from human placentation. However, there is a strong resemblance in the way spiral arteries are invaded and transformed in the macaque, baboon and human. Non-human primates are therefore important models for understanding the dysfunction that has been linked to pre-eclampsia and fetal growth restriction. Models that are likely to be established in the wake of comparative genomics include the marmoset, tree shrew, hedgehog tenrec and nine-banded armadillo.

Comparative Placentation: Some Interesting Modifications for Histotrophic Nutrition – A Review

In considering the diversity of Eutherian mammalian placental structure, it is helpful to keep in mind that both phylogenetically and ontogenetically a functional yolk sac placenta precedes development of the chorioallantoic placenta. Usually the chorioallantoic placenta progressively displaces the area of contact of the yolk sac placenta with the endometrium. It is also closely applied to the endometrium, increasing respiratory efficiency but tending to decrease histotrophic nutrition. Catarrhine primates have minimal histotrophic uptake, using haemotrophic mechanisms throughout most of gestation. Rodents, by using partial or complete inversion of the yolk sac, have extensive regions available to histotroph in later pregnancy. Most mammals, however, have developed specialized regions of the chorioallantoic placenta for ingestion of uterine secretions, cell debris and erythrocytes. These regions vary from simple saccular areolae to more complex areolae such as the chorionic vesicles of prosimian primates to specialized haemophagous areas. All such structures are consistently lined by columnar cellular trophoblast. Examples of these structures, many of which can ingest both glandular secretions and erythrocytes (i.e. they are heterophagous), can be found in species whose definitive placenta is epitheliochorial. They are common but not universal in species whose definitive placenta is endotheliochorial and are even found in a few species with definitive haemochorial placentas. Restriction of phagocytosis to regions of columnar cells provides polarized cells appropriately oriented for ingestion, breakdown and transport, and limits the type of ingestion of both beneficial and potentially toxic materials to expendable individual cells.

The Expression of Insulin-like Growth Factor and Insulin-like Growth Factor Binding Protein mRNAs in Mouse Placenta

Insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) are paracrine regulators of tissue growth and development, and are expressed at the sites of biological action. To study the role of the IGFs and IGFBPs in mouse placental development, we determined the temporal and spatial expression patterns of the mRNAs at embryonic days 10.5 to 18.5 by in situ hybridization. IGF-II mRNA was expressed strongly in mesoderm and fetal blood vessels of early placenta and in labyrinthine trophoblast of later placenta. In the junctional zone, IGF-II mRNA was expressed first in spongiotrophoblasts, later strongly in glycogen cells and variably in giant cells. IGFBP-2 mRNA was expressed weakly in spongiotrophoblasts and glycogen cells. IGFBP-2, -5 and -6 mRNAs were detected in the stroma of the metrial gland. Myometrium expressed IGFBP-2 mRNA strongly, IGFBP-6 mRNA moderately and IGFBP-5 mRNA weakly. The endothelium of maternal blood vessels in decidua expressed IGFBP-3 and -5 mRNAs, and some deeper vessels expressed IGFBP-4 mRNA. In the yolk sac, IGF-II mRNA was expressed in endoderm and mesoderm, whereas IGFBP-1, -2 and -4 mRNAs were expressed only in endoderm, and IGFBP-4 mRNA in mesoderm. Strong expression of IGF-II mRNA in glycogen cells suggests a role in the autocrine/paracrine regulation of invasion. Similar to rat and guinea pig, but in contrast to man and primates, IGFBP mRNAs, except IGFBP-4, were not expressed in mouse decidua. However, IGFBP-3, -4 and -5 mRNAs were expressed in endothelium of maternal blood vessels, and IGFBP-2 and -6 mRNAs in myometrium, where IGFBPs may play a critical role in regulating trophoblast invasion. These findings suggest possible biological roles of the peptides at the feto-maternal interface.

The Fetal Membranes of the Otter Shrews and a Synapomorphy for Afrotheria

The otter shrews of mainland Africa are the closest relatives of the Madagascar tenrecs. We sought for similarities in placentation between the two groups and, in a wider context, with other mammals of the Afrotheria clade. Specimens of the Nimba otter shrew (Micropotamogale lamottei) were obtained from the Ivory Coast and examples of the giant otter shrew (Potamogale velox) from the Hill Collection. The Nimba otter shrew has a central haemophagous organ similar to that in tenrecs. The labyrinth of the Nimba otter shrew, however, is endotheliochorial with syncytial trophoblast enclosing the maternal vessels. On the other hand tenrecs have cellular haemomonochorial placentae and an associated spongy zone, which is not present in the Nimba otter shrew. The placenta of the giant otter shrew is also endotheliochorial. The central region of its placenta is particularly interesting, since the juxtafetal portion is clearly a haemophagous region whereas the labyrinth feeding this region is endotheliochorial. Thus there is considerable variation in placental morphology within Tenrecidae. Importantly, however, both otter shrews have a large allantoic sac divided into four intercommunicating lobes by two pairs of septal folds. A similar arrangement has been described for representatives of each of the remaining five orders within Afrotheria. This is significant because previous anatomical studies have failed to establish a single synapomorphy in support of Afrotheria.

Placentation in the rock cavy, Kerodon rupestris (Wied)

Rock cavies are rodents found in the semi-arid caatinga of Brazil. We studied the structure of the rock cavy placenta by light and transmission electron microscopy. The exchange area of the labyrinth was organized in lobes separated by interlobular areas. The interhaemal barrier was syncytial haemomonochorial. The syncytiotrophoblast had recesses in the basal membrane and some invaginations of the apical membrane, but transtrophoblastic channels could not be found. The interlobular regions comprised syncytiotrophoblast, enclosing maternal venous blood channels, and cytotrophoblast. There was a prominent subplacenta composed of cytotrophoblast and syncytiotrophoblast. Microvilli projected into spaces between the cytotrophoblasts and into lacunae within the syncytiotrophoblast. The yolk sac epithelium exhibited coated pits, endocytotic vesicles and larger vacuoles, consistent with a role in protein uptake from the uterine lumen. Tight junctions between these cells provided a barrier to diffusion by the intercellular route. The reproductive biology of the rock cavy differs from other members of the family, including the guinea pig, but the architecture of the placenta remains remarkably constant.

Metformin reduces C-reactive protein but not complement factor C3 in overweight patients with Type 2 diabetes mellitus

AIMS

To determine the influence of metformin treatment on plasma C-reactive protein (CRP) and complement factor C3.

METHODS

A double-blind, placebo-controlled trial of metformin in patients with poorly controlled Type 2 diabetes mellitus and body mass index > 25 kg/m2. CRP and C3 were analysed in stored plasma samples by in-house ELISAs. Patients attended two baseline visits before randomization and subsequently attended at 3, 6, 12 and 24 weeks post randomization. All patients gave informed consent according to a protocol approved by the Leeds Teaching Hospitals Research Ethics Committee.

RESULTS

Baseline CRP in the patients randomized to placebo [1.33 (0.79, 2.25) mg/l] and metformin [1.24 (0.89, 1.71) mg/l] were similar (P = 0.8). Baseline CRP correlated with baseline C3 (r = 0.366) and HbA1c (r = 0.327). The difference in ratios of CRP levels at each visit to baseline between placebo- (n = 16) and metformin-treated (n = 26) subjects was significantly different at the 12-week (P = 0.002) and 24-week (P = 0.03) visits. The difference in CRP ratios between the two treatment groups remained significant after accounting for glycaemic control at both visits (P = 0.001 and P = 0.003, respectively). Baseline C3 was correlated with CRP. Baseline C3 was lower in the placebo-treated group [0.97 (0.88, 1.05) mg/ml] compared with the metformin-treated group [1.09 (1.02, 1.17) mg/ml, P = 0.03]. There was no difference in the mean change in C3 at any visit from baseline between placebo- and metformin-treated groups.

CONCLUSION

Metformin may have a specific interaction with mechanisms involved in CRP synthesis or secretion, not directly related to improved insulin sensitivity and dampening of chronic inflammation.

Placentation in an American mole, Scalopus aquaticus

In 1938 Mossman reported that epitheliochorial placentation occurred in an insectivore, the Eastern mole. This led to a radical change in his thinking about placental evolution, yet 40 years would pass before the appearance of a definitive description. Unpublished papers in the Mossman Collection at the University of Wisconsin Zoological Museum tell a fascinating story about this delay. The Scalopus material was studied by Mossman's graduate student, M.R.N. Prasad, who concluded that the placenta was initially endotheliochorial and that subsequent re-epithelialization of the uterus led to the definitive epitheliochorial condition. Mossman withheld publication of these findings pending electron microscopic studies. The definitive publication described the ultrastructure of the interhaemal region. Although based on a single specimen, this seemed to justify the conclusion that an epitheliochorial condition was maintained throughout gestation. These findings are discussed in relation to subsequent work on the European mole and current thinking about placental evolution.

Structure of the Ovaries of the Nimba Otter Shrew, Micropotamogale lamottei, and the Madagascar Hedgehog Tenrec, Echinops telfairi

The otter shrews are members of the subfamily Potamogalinae within the family Tenrecidae. No description of the ovaries of any member of this subfamily has been published previously. The lesser hedgehog tenrec, Echinops telfairi, is a member of the subfamily Tenrecinae of the same family and, although its ovaries have not been described, other members of this subfamily have been shown to have ovaries with non-antral follicles. Examination of these two species illustrated that non-antral follicles were characteristic of the ovaries of both species, as was clefting and lobulation of the ovaries. Juvenile otter shrews range from those with only small follicles in the cortex to those with 300- to 400-microm follicles similar to those seen in non-pregnant and pregnant adults. As in other species, most of the growth of the oocyte occurred when follicles had one to two layers of granulosa cells. When larger follicles became atretic in the Nimba otter shrew, hypertrophy of the theca interna produced nodules of glandular interstitial tissue. In the tenrec, the hypertrophying theca interna cells in most large follicles appeared to undergo degeneration. Both species had some follicular fluid in the intercellular spaces between the more peripheral granulosa cells. It is suggested that this fluid could aid in separation of the cumulus from the remaining granulosa at ovulation. The protruding follicles in lobules and absence of a tunica albuginea might also facilitate ovulation of non-antral follicles. Ovaries with a thin-absent tunica albuginea and follicles with small-absent antra are widespread within both the Eulipotyphla and in the Afrosoricida, suggesting that such features may represent a primitive condition in ovarian development. Lobulated and deeply crypted ovaries are found in both groups but are not as common in the Eulipotyphla making inclusion of this feature as primitive more speculative.

Adrenomedullin expression during hypoxia in fetal sheep

AIM

We asked how adrenomedullin (AM), a vasodilator peptide, was distributed in fetal sheep organs and whether expression of AM would be upregulated in response to moderate acute fetal hypoxia in vivo.

METHODS

In four sheep at day 126-130 of gestation, nitrogen was added to the inspired air by tracheal infusion to reduce fetal arterial oxygen content for a period of 4 h. Control fetuses were from four ewes given a tracheal infusion of room air. Fetal and maternal blood samples were taken prior to and during hypoxia/sham hypoxia. Fetal tissue samples were frozen for RNA analysis and fixed for immunohistochemistry.

RESULTS

In hypoxic fetuses, arterial oxygen content was significantly reduced to 50% compared with sham fetuses with no change in arterial pH in either group. Plasma ACTH levels rose significantly at 2 and 4 h in hypoxic fetuses only. Initial plasma concentrations of AM in control and hypoxic fetuses were 457 +/- 20 and 430 +/- 35 pg mL(-1) and did not change during the experiment. The relative abundance of AM mRNA was placental cotyledons >> lung > cerebral cortex approximately equal to renal cortex > left ventricle approximately equal to right ventricle > adrenal gland > renal medulla > aorta approximately equal to liver. Immunohistochemical staining for AM confirmed distinct labelling in organs with significant expression. AM mRNA level increased significantly in cerebral cortex of hypoxic fetuses.

CONCLUSION

Our results show expression of AM in placenta and in several fetal organs in late gestation sheep. AM may participate in the cerebral vasodilatation that is an integral part of the fetal response to hypoxia.

Development of the haemophagous region and labyrinth of the placenta of the tenrec, Echinops telfairi

Our purpose was to determine how the central haemophagous region and cellular haemomonochorial labyrinth of the tenrec placenta are formed. The haemophagous region is preceded by a region of invasion of the endometrium by trophoblast comprising a cytotrophoblast layer covered by syncytial trophoblast and contiguous with numerous masses of multinucleate trophoblast. The trophoblast intrudes into the endometrium, eliminating the stroma, although small vessels and clumps of glandular epithelium persist. This extensive central region is connected to the forming disk by a ring of chorioallantois covered by a single layer of columnar trophoblast. Later the multinucleate masses and syncytial trophoblast degenerate. The unilaminar cytotrophoblast remains, is elaborated into folds, and phagocytoses glandular secretion, cell debris and erythrocytes. As the central area is transforming, fetal capillaries move into the cytotrophoblast pads surrounding the central zone. Prior to this, the cytotrophoblast has formed a multilayered structure and interrupted maternal vessels to create an anastomotic network of blood spaces lined by cytotrophoblast. The invasion of fetal capillaries transforms this preplacental pad into a cellular haemomonochorial labyrinth with the uninvaded portion forming an underlying spongy zone. Thus interaction of the trophoblast with the endometrium is substantially different in the central zone compared to the area of the preplacental pad.

Altered expression of IGFs and IGF-binding proteins during intrauterine growth restriction in guinea pigs

The IGF system is one of the most important endocrine and paracrine growth factor systems that regulate fetal and placental growth. We hypothesized that intrauterine growth restriction (IUGR) in guinea pigs is mediated by the altered expression of IGFs and/or IGF binding protein (BP) mRNAs in tissues and is related to growth of specific tissues. IUGR was induced by unilateral uterine artery ligation on day 30 of gestation, and fetal plasma, amniotic fluid and tissue samples were collected at 55-57 days (term about 68 days) from paired IUGR and control fetuses (n=6). Western ligand blotting and immunoblotting were used to compare IGFBP levels in plasma and amniotic fluid. Total RNA was extracted from placenta and fetal tissues, and the relative abundance of IGF-II and IGFBP-1-6 mRNA was determined by Northern blotting, using species-specific probes where available. IUGR fetuses had decreased (P<0.01, by Student's t-test) placental weight and body weight with an increase in the brain:liver weight ratio. The principal IGFBPs in fetal plasma migrated at 40-35, 30 and 25 kDa and were identified as IGFBP-3, -2 and -4 respectively. IUGR was associated with elevated plasma IGFBP-2 and IGFBP-4 and reduced IGFBP-3 levels. IGFBPs were detected at low levels in amniotic fluid of control fetuses but at higher levels in IUGR fetuses. In IUGR placentae, there was a small increase in IGFBP-4 mRNA (P<0.05). IGFBP-2 mRNA increased (P<0.001) in liver of IUGR fetuses. IGF-II and IGFBP mRNA expression did not change in fetal muscle. The results are consistent with reduced IGF action, directly or through inhibition by IGFBPs, particularly by circulating and tissue IGFBP-2, as a potential causal factor in decreased growth of the placenta and certain fetal tissues.

Placenta and fetal membranes of the four-toed elephant shrew, Petrodromus tetradactylus

The four-toed elephant shrew is the only extant member of the genus Petrodromus. Some features of its placentation are found in other elephant shrews and may be important in consolidating the elephant shrews in the order Macroscelidea. These include implantation in an embryo chamber at the caudal end of the uterine horn; a large yolk sac; a large, lobulated allantoic sac; a distinct layer of proliferative trophoblastic cells between the labyrinthine and spongy zones of the placenta; an accessory epitheliochorial placenta; and the formation of a mesoplacenta by the decidua basalis. Of particular note are the large granulated cells that occupy the walls of decidual, myometrial and mesometrial arteries. They appear to be uterine natural killer cells. The persistence of a relatively large yolk sac and a large lobulated allantoic sac is a feature which Petrodromus and other elephant shrews share with other members of the superordinal clade Afrotheria.

Placentation in species of phylogenetic importance: the Afrotheria

Afrotheria, one of four mammalian superorders, comprises elephants, sea cows, hyraxes, aardvark, elephant shrews, tenrecs and golden moles. Their placentas either form an equatorial band or are discoid in shape. The interhemal region, separating fetal and maternal blood, is endotheliochorial in elephants, aardvark and possibly the sea cows, but hemochorial in the remaining orders. There is a secondary epitheliochorial placenta in elephant shrews while a similar structure in tenrecs erodes maternal tissues. Specialized hemophagous regions are a striking characteristic of some of these placentas yet absent in hyraxes, elephant shrews, and golden moles. It is possible that the common ancestor of the Afrotheria had an endotheliochorial placenta. Establishment of a hemochorial condition, as seen in rock hyraxes, elephant shrews, tenrecs, and golden moles, would be a more recent development. The elephant, manatee, and aardvark all have circumferential placentas. Thus the formation of a discoid placenta with a more or less extensive secondary placenta in elephant shrews and tenrecs would also be a derived state.