A morphological study of the development of the placenta of the rat; an outline of the development of the placenta of the white rat

Contribution of placental 11β-HSD2 to the pathogenesis of preeclampsia

Preeclampsia, a major human pregnancy-specific disorder, leads to maternal and fetal morbidity and mortality. Here we reported that 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2), an enzyme that degrades active glucocorticoids, is one of the key factors that contributes to preeclampsia development. In the pregnant rat model, we firstly confirmed that administration of 11β-HSD2 inhibitor carbenoxolone (CBX) subcutaneously or by placenta-targeted delivery system could lead to a decrease in placental 11β-HSD2 expression and activity and an increase in corticosterone level in placenta and maternal circulation. Then, we showed that subcutaneous administration and placenta-targeted delivery of CBX resulted in the hallmark of preeclampsia-like features including hypertension, proteinuria, renal damages as well as elevated circulatory soluble fms-like tyrosine kinase 1 (sFlt1) and increased sFlt1/placental growth factor (PlGF) ratio in pregnant rats. These animals displayed decreased trophoblast invasion in uterus, impaired spiral artery remodeling, and reduced placental blood flow. Preeclampsia-like features could also be induced by administration of dexamethasone in pregnant rats. In the cultured human trophoblast models, we found that cortisol only inhibited migration and invasion of the extravillous trophoblasts with 11β-HSD2 knockdown, and promoted sFlt1 release in the cultured syncytiotrophoblasts with 11β-HSD2 knockdown. Furthermore, we elucidated that cortisol stimulated a disintegrin and metalloprotease (ADAM)17 expression in placentas, thereby promoting sFlt1 release in placenta. Collectively, our study provided the evidence that placental 11β-HSD2 dysfunction plays a key role in the development of preeclampsia and immediately identified innovative target to counteract preeclampsia.

Endopolyploid and proliferating trophoblast cells express different patterns of intracellular cytokeratin and glycogen localization in the rat placenta

The presence of keratin intermediate filaments is a characteristic of trophoblast differentiation. Meantime, their intracellular localization in the functionally different subtypes of placental trophoblast is poorly investigated in rodent, whereas their placentae are being broadly investigated in recent years as a model of the feto-maternal interaction. The purpose was to study the intracellular distribution of cytokeratin filaments in correlation with glycogen deposits, both being important constituents of the trophoblast cells in rat placenta. Different rat trophoblast cell populations exhibited different patterns of cytokeratin immunolocalization. The most intensive immunostaining was observed in the highly endopolyploid SGTCs (secondary giant trophoblast cells) at the border with decidua basalis. The most prominent cytokeratin-positive threads were found at the periphery of cytoplasm and in the extensive system of cytoplasmic sprouts by which the SGTC connect each other. Similar cytokeratin intensity and distribution was detected in the TSC (trabecular spongiotrophoblast cells) of the junctional zone of placenta that line the lacunae with the maternal blood. Clusters of highly proliferative pre-glycogen as well as glycogen cells showed some weaker cytokeratin signals mostly in the perinuclear and peripheral zones of cytoplasm. At the 11.5th to the 13.5th day of gestation, the interstitial and endovascular invasive endopolyploid TGTCs (tertiary giant trophoblast cells) prove the intensive cytokeratin staining throughout the cytoplasm and its sprouts. Meantime, the TGTCs were glycogen negative. By contrast, glycogen was heavily accumulated in the glycogen cells that belong both to the junctional zone of placenta and the cuff of the central arterial channel underlying the monolayer of endovascularly invading TGTCs. Thus, the TGTCs that are first to penetrate into the depth of the uterine wall do not contain glycogen but are accompanied by the glycogen-rich cells. The SGTC also contained the prominent deposits of glycogen at the periphery of cytoplasm and in the cytoplasmic sprouts. At the 16th day of gestation, an extensive interstitial invasion of the cytokeratin-positive glycogen trophoblast cells from the junctional zone was observed. The patterns of cytokeratin and glycogen intracellular localization are specific for each subtype of the rat trophoblast; that is, most probably, accounted for by the functional diversity of different trophoblast populations, i.e. patterns of invasion/phagocytosis and their involvement in a barrier at the feto-maternal interface.

Trophoblast glycogen cells differentiate early in the mouse ectoplacental cone: putative role during placentation

The role of differentiated trophoblast glycogen cells (GCs) in the ectoplacental cone (EPC) has not been elucidated yet. Recently, GC progenitors have been shown to be present from embryonic day 7.5 (E7.5), but glycogen is found in GC only from E10.5. Herein, we investigated the origin, localization and characterization of mouse GCs in EPC and their relationship with blood cells and trophoblast giant cells (TGCs) during placentation. Implantation sites (E5.5-E12.5) were processed for histological studies, histochemical detection (glycogen) and immunohistochemical staining (Ki67). Three-dimensional reconstruction of the EPC was obtained from suitably oriented embryos at E7.5. Our findings evidence that GCs are present and assembled in clusters from E6.5 to E12.5, and that they exhibit the classic vacuolated appearance and contain PAS-positive glycogen, which is amylase-sensitive and acetylation-resistant. In fact, only GCs were stained after acetylation, confirming unequivocally their presence in tissues. At E6.5, GCs showed numerous mitoses and vacuoles with scattered glycogen particles. At E7.5, GCs showed low numbers of mitoses and abundant vacuoles full of glycogen. During E7.5-E8.5, GCs were in close proximity to TGCs, and cells were intercalated by thin maternal blood spaces; placental GCs lost maternal blood contact during E9.5-E12.5. Our results indicate that GCs are originated and proliferate in the upper portion in the midregion of EPC at E6.5, and that at E7.5-E8.5 they show consistent glycogen deposits, which are likely metabolized to glucose. This compound may be directly transferred to circulating maternal blood, and used as a source of energy by GCs and TGCs during placentation.

Interstitial trophoblast invasion in the decidua and mesometrial triangle during the last third of pregnancy in the rat

Like other species with haemochorial placentation, pregnant rats show marked invasion of the uterine wall by trophoblast. While an endovascular pathway of invasion has been recognized for a long time, only recently, by application of cytokeratin immunostaining, the existence of an interstitial pathway of invasion has been established. Interstitial invasion is mainly effected by glycogen cell-like trophoblast arising from glycogen cell islands of the trophospongium opening up into the decidua, and from glycogen cell sheaths surrounding the intraplacental maternal arterial channels which are connected with the spiral arteries in decidua and mesometrial triangle. Quantitative evaluation of interstitial invasion in both maternal compartments was carried out on days 15-21, using PAS staining and cytokeratin and alpha-actin immunostaining for detecting trophoblast and defining maternal tissue compartments. Measurements of compartment size, cytokeratin-positive areas and invasion extent were performed using the KS400 image analysis system. A distinct pattern of interstitial trophoblast invasion emerged, starting from central decidual areas around the maternal arterial channels, and mushrooming into the mesometrial triangle reaching a peak at day 18, followed by gradual regression of the invaded areas. These measurements may serve as a basis for further experiments to evaluate factors which may influence the depth of trophoblast invasion.

Placental lesions caused by experimental infection of Sprague-Dawley rats with Mycoplasma pulmonis

PROBLEM

Sprague-Dawley (SD) rats infected during pregnancy with Mycoplasma pulmonis display adverse pregnancy outcomes that are similar to those observed in women with chorioamnionitis and may provide a good model system for this disease. The placental lesions caused by this microorganism, however, have not been thoroughly characterized.

METHOD OF STUDY

Rats were infected with 10(7) colony-forming units (CFU) M. pulmonis or vehicle control on gestation day (gd) 14 and were euthanized on gd 16-18. Tissues were fixed in 10% neutral buffered formalin, embedded in paraffin, sectioned at 4 microm, and stained with hematoxylin and eosin (H & E). The slides were coded and examined by a blinded pathologist using light microscopy.

RESULTS

Infection with M. pulmonis was associated with necrosis of trophoblast giant cells at gd 18. Significantly more neutrophils were observed in the decidual region of the apex of the placenta in M. pulmonis infected animals. The vast majority of neutrophils, however, were observed in the decidua in the lateral regions of the placenta and in the adjacent endometrium.

CONCLUSIONS

Infection of SD rats with M. pulmonis resulted in histological placentitis similar to that described in deciduitis of humans and represents a good model system for investigations into the pathophysiology of intrauterine infection. The influx of neutrophils seems to migrate from the endometrium towards the lateral regions of the placenta near Reichert's membrane and the divergence of the parietal yolk sac.

Evolutionary transformations of chorioallantoic placental characters in rodentia with special reference to hystricognath species

The aim of this paper is to reconstruct the evolution of chorioallantoic placental characters in Rodentia. The analysis is based on pre-existing hypotheses of rodent relationships and the tracing of character evolution. Data on 64 rodent species of 49 genera are derived from the literature. New results refer to the hystricognath species Petromus typicus A. Smith, 1831 and Octodon degus (Molina, 1782). This comprehensive analysis confirms that the stem species pattern of Rodentia is characterised by a haemochorial placenta which is divided horizontally. Inside the placental labyrinth, fetal vessels and their trophoblastic external border build up a network through which the maternal blood flows. The trophoblastic tissue is one-layered, syncytial and possess a considerable surface extension. Within Rodentia, evolutionary transformations occurred on the macroscopic as well as the fine structural level. The results suggest that the stem species of Hystricognathi underwent transformations only on the macroscopic level, i.e., forming a ring-shaped arrangement of placental regions with centrally situated maternal arteries and the acquisition of a subplacenta. By contrast, in Muridae the chorioallantoic placenta shows derived features only in regard to the fine structure of the labyrinth, i.e. the interhaemal membrane is modified in composition, and the fetal capillary endothelium is fenestrated. Geomyoidea underwent transformations on both levels. Macroscopically, their placenta is modified into a hillock shape. Microscopically, the interhaemal membrane is formed by the cytotrophoblast. In addition to the mentioned transformations, some aspects of other fetal membrane differentiation in Rodentia are briefly discussed.

Pregnancy dating in the rat: placental morphology and maternal blood parameters

The rat is commonly used as a model in studies on embryology and reproduction toxicology. Surprisingly, the current literature does not provide a comprehensive reference data set on placental development in rat. Therefore, we have evaluated morphological changes of the placenta and maternal blood parameters during pregnancy of the Sprague-Dawley rat. The morphologic data presented in this study may be useful as reference material. This study revealed that placental development in the rat is a well-defined process, characterized by key synchronized morphological events at specific points in time, convenient for laboratory practice and provides the toxicologist with a sensitive tool to distinguish between normal and abnormal placental development and to detect fetal and placental mismatches. During rat pregnancy, significant changes were observed in maternal blood parameters strongly reminiscent of those observed in pregnant women. These changes included: (a) decreased blood cell volume as a result of hemodilution, (b) increased white blood cell counts reflecting the response of the mother to the fetal allograft, (c) increased blood clotting values, (d) decreased plasma glucose and increased lipid content maximizing fetal glucose availability and maternal energy conservation, and (e) decreased electrolyte values reflecting plasma volume expansion. It was concluded that the combined data set on placental morphology and maternal blood parameters in pregnant rats provides powerful tools for recognition of abnormal pregnancies.

Demonstration of extracellular acid phosphatase activity in the involuting, antimesometrial decidua in fed and acutely fasted mice by combined cytochemistry and electron microscopy

An ultrastructural cytochemical study of acid phosphatase activity in the antimesometrial decidua on days 9-11 of pregnancy was performed in fed and acutely fasted mice. Specimens were fixed in a buffered mixture of paraformaldehyde and glutaraldehyde and were incubated in a buffered medium containing sodium beta-glycerophosphate and cerium chloride for ultrastructural localization of acid phosphatase activity. Fed and fasted animals showed extracellular acid phosphatase reaction product in the decidual-trophoblast interface, in the region of loosely and tightly packed, mature decidual cells, and in the region of predecidual cells. Reaction product was absent in the region of nondecidualized stromal cells. Extracellular acid phosphatase activity was more conspicuous in the region of mature decidual cells in fasted mice than in fed mice, and it was apparently similar in the region of predecidual cells in both fed and fasted mice. Acid phosphatase reaction product was also observed in lysosomes in all cells studied. Because acid phosphatase activity reflects the presence of lysosomal hydrolases in general, our results suggest that there is matrix degradation by lysosomal enzymes in both fed and fasted mice. These events may be part of the process of tissue remodeling in regions of predecidual cells and mature decidual cells. However, it is also possible that, in the region of mature decidual cells, breakdown of matrix constituents is a mechanism to provide nutrients for the growing fetus. This mechanism is probably enhanced in fasted mice.

Insulin-like growth factor binding protein gene expression in the pregnant rat uterus and placenta

While the insulin-like growth factor (IGF) system plays a fundamental role in regulating embryonic and placental growth, the specific contributions of the six IGF binding proteins (IGFBPs 1-6) to these processes are not well understood. We here focus on IGFBP expression in the extraembryonic environment, which both supports and constrains embryonic growth, and have used in situ hybridization to determine sites of IGFBP mRNA synthesis in the pregnant rat uterus and placenta. We find that all IGFBPs are expressed in distinct, changing patterns in the uterine endometrium, at the decidual boundary, in the decidual vasculature, and in the myometrium during pregnancy. Within the endometrium, the most prominent change is that expression of IGFBP-1 begins in some, but not all, endometrial glands prior to implantation and then expands to include all secretory epithelia shortly after implantation. During the period of rapid decidual proliferation that follows implantation, IGFBP-3, -4, and -5 transcripts are all detected in a laminar array at the boundary between the decidua and the nondecidualized endometrium. In the decidual vasculature at Day (d) 8.0, both IGFBP-3 and IGFBP-4 mRNAs are detected in dilating blood vessels, with BP-3 most prominent in the antimesometrial plexus and BP-4 primarily at the mesometrial pole. Later (d11.5), all decidual vessels express high levels of IGFBP-3 and lower levels of IGFBP-4 mRNAs. Finally, changes in expression of several IGFBPs also occur within the myometrium during pregnancy. For example, IGFBP-2 is expressed in the inner circular layer shortly after implantation, and expression increases through late gestation. In contrast, IGFBP-5 hybridization occurs over both myometrial layers before implantation, but decreases in intensity and spatial distribution as pregnancy proceeds. Finally, and most strikingly, IGFBP-6 expression, barely detectable in the d7.0 myometrium, gradually increases until it is very strongly transcribed during the placental stages. Taken together, these observations suggest multiple roles for IGFBPs in supporting implantation, regulating the extent of decidualization, modulating local levels of vascular IGFs, and regulating uterine muscular growth.

Expression of a novel member of estrogen response element-binding nuclear receptors is restricted to the early stages of chorion formation during mouse embryogenesis

Members of the nuclear hormone receptor gene family of transcription factors have been shown to be expressed in characteristic patterns during mouse organogenesis and postnatal development. Using an RT-PCR based screening assay, we have identified nuclear receptors expressed in embryonal carcinoma stem cells. One of the cDNAs characterized, mERR-2, was found to be expressed exclusively during a narrow developmental window in trophoblast progenitor cells between days 6.5 and 7.5 post coitum (p.c.). From 8.5 days p.c. and onwards, the mERR-2 gene activity evaded detection as analysed by in situ hybridization. We also show that the mERR-2 gene product and the estrogen receptor share a common target DNA-sequence recognition specificity unique among members of the gene family. Furthermore, efficient homodimerization and DNA-binding of the orphan receptor mERR-2 was found to be dependent on interaction with the heat shock protein 90, a molecular chaperone hitherto recognized to interact only with the steroid hormone receptor subgroup of nuclear receptors. Based on our results we suggest that the mouse orphan receptor mERR-2 has the potential to regulate overlapping gene networks with the estrogen receptor and may participate in signal transduction pathways during a short developmental period coinciding with the formation of the chorion.

Changes in the pattern of expression of alkaline phosphatase in the mouse uterus and placenta during gestation

The development of the rodent chorio-allantoic placenta is a complicated process that results in the formation of a transport system capable of sustaining embryonic and fetal growth and development. Intimately linked to this process is alkaline phosphatase (AP), a cell-surface glycoprotein that possibly functions as a transport protein. In the present study, we have mapped the location of AP-expressing cells in the mouse utero-placental unit during the development of the chorio-allantoic placenta by use of enzyme histochemistry and in situ hybridization histochemistry. We found that at implantation the expression of the tissue non-specific AP (TNAP) gene is located exclusively in the decidua and that most of this decidual expression ceases as the placenta starts to form. One exception is a mesometrially located marginal zone of the decidua, which continues to express the TNAP gene until day 12 and the active protein until at least day 16. Trophoblasts of the chorion already express AP before the time of fusion with the ectoplacental cone, after which AP is expressed by trophoblasts of the resulting ectoplacental plate. AP expression in the mature chorio-allantoic placenta is localized in the placental labyrinth and spongy zones. In the latter zone, expression ceases on about day 14. Giant trophoblasts start to express AP on about day 10, with some cells still positive for AP at day 16. The yolk sac does not express AP at any developmental stage. The results show that AP expression during placental development is neither restricted to cells known to be involved in transport, nor expressed in all cells thought to be involved in this transport. This may indicate that AP is not merely a transport protein but has additional functions.

Giant and binucleate trophoblast cells of mammals

The cellular origin, structure, and function of trophoblastic giant cells (GC) and binucleate cells (BNC) are reviewed. Mammals in which these cells have received the greatest attention include rodents, rabbits, and humans (GCs), and ruminants and equids (BNCs). In almost all cases these cells arise from the cytotrophoblast. All are large cells and contain either two diploid nuclei (BNCs), multiple nuclei (human placental bed GCs), or single nuclei with amplified DNA content (rodent and rabbit GCs). Giant and binucleate cells typically exhibit the capacity for migration or invasion, although the degree of migratory activity varies between species. While most end up within, or at the interface with, endometrial tissue, in some instances the GCs or BNCs contribute directly to the interhemal membrane of the placenta. Hormone production is a property which most GC-BNC populations have in common. Lactogen or gonadotropin has been documented in almost all cells of this type examined to date, and in some animals they are also steroidogenic (e.g., rats and sheep). In spite of some common features, both structural and functional differences remain and it is suggested that use of terms such as mononuclear giant cells, multinucleate giant cells, and binucleate cells be continued rather than assuming that these cells are all members of a single trophoblastic subtype.

Chorioallantoic placenta formation in the rat: II. Angiogenesis and maternal blood circulation in the mesometrial region of the implantation chamber prior to placenta formation

Rat gestation sites were examined on days 7 through 9 of pregnancy by light microscopy and transmission and scanning electron microscopy to determine the extent of vascular modifications in the vicinity of the mesometrial part of the implantation chamber (mesometrial chamber). At a later time, the mesometrial chamber is, in conjunction with the uterine lumen, the site of chorioallantoic placenta formation. On day 7, in the vicinity of the mesometrial chamber, vessels derived from a subepithelial capillary plexus and venules draining the plexus were dilating. By early day 8, this network of thin-walled dilated vessels (sinusoids) was further enlarged and consisted primarily of hypertrophied endothelial cells with indistinct basal laminas. Sinusoids were frequently close to the mesometrial chamber's luminal surface which was devoid of epithelial cells but was lined by decidual cell processes and extracellular matrix. By late day 8, cytoplasmic projections of endothelial cells extended between healthy-appearing decidual cells and out onto the mesometrial chamber's luminal surface, and endothelial cells were sometimes found on the luminal surface indicating that endothelial cells were migrating. The presence of maternal blood cells in the mesometrial chamber lumen suggested that there was continuity between the chamber and blood-vessel lumens. On day 9, the mesometrial chamber was completely lined with hypertrophied endothelial cells, and sinusoid lumens were clearly continuous with the lumen of the mesometrial chamber. Mesometrial sinusoids and possibly the mesometrial chamber lumen were continuous with vessels in vicinity of the uterine lumen that were fed by mesometrial arterial vessels. Clearing of the mesometrial chamber lumen during perfusion fixation via the maternal vasculature indicated the patency of this luminal space and its confluence with mesometrial arterial vessels and sinusoids. The conceptus occupied an antimesometrial position in the implantation chamber on days 7 through 9, and it was not in direct contact with uterine tissues in the vicinity of the mesometrial chamber. These observations suggest that angiogenesis, not trophoblast invasion or decidual cell death, plays a major role in the opening of maternal vessels into the mesometrial chamber lumen before the formation of the chorioallantoic placenta.

Chorioallantoic placenta formation in the rat: I. Luminal epithelial cell death and extracellular matrix modifications in the mesometrial region of implantation chambers

On days 7 and 8 of pregnancy, mesometrial regions of rat gestation sites were examined by light microscopy and transmission electron microscopy to determine what changes occur before the chorioallantoic placenta forms in that region. By day 7, gestation sites contained a uterine lumen mesometrially and an antimesometrial extension of the uterine lumen, the implantation chamber. The implantation chamber consisted of a mesometrial chamber between the uterine lumen and the conceptus, an antimesometrial chamber that contained the conceptus, and a decidual crypt antimesometrial to the conceptus. Stromal cells that formed the walls of the implantation chamber were closely packed decidual cells, while those that surrounded the uterine lumen were loosely arranged. Late on day 7, a portion of the epithelium lining the mesometrial chamber was degenerating, but this area of initial degeneration was never adjacent to the antimesometrial chamber. By early day 8, most of the epithelial cells lining the mesometrial chamber were degenerating and were being sloughed into the chamber lumen. Although degeneration of these epithelial cells morphologically resembled necrosis, it was precisely controlled, since adjacent epithelial cells lining the uterine lumen remained healthy. The space that separated the denuded luminal surface of the mesometrial chamber from underlying decidual cells became wider and was occupied by an extracellular matrix rich in cross-banded collagen fibrils. Decidual cell processes, that earlier had penetrated the basal lamina beneath healthy epithelial cells, protruded into this matrix and penetrated the basal lamina at the luminal surface. By late day 8, large areas of denuded chamber wall were covered with decidual cell processes, little remained of the basal lamina, and cross-banded collagen fibrils were scarce in the area occupied by decidual cell processes. During the times studied, uterine tissues that formed the walls of the mesometrial chamber were not in direct contact with the conceptus. This study indicates that trophoblast does not play a direct role in epithelial degeneration, basal lamina penetration, or extracellular matrix modifications in the mesometrial region of implantation chambers where part of the chorioallantoic placenta forms, although trophoblast may be required to trigger or modulate some of the changes.

Chemically induced alterations in maternal homeostasis and histology of conceptus: their etiologic significance in rat fetal anomalies

Possible relationships between maternal acid-base-electrolyte imbalance, histological changes in the maternal/extraembryonic tissues (decidua, placenta, membranes enclosing cavities), and fetal anomalies induced by maternotoxic doses of ethylene glycol, sodium salicylate, and cadmium chloride in rats were investigated. Acid-base-electrolyte, histologic and, teratologic studies were conducted concurrently with, as far as feasible, a similar protocol. Ethylene glycol caused 1) maternal homeostatic changes including metabolic acidosis and hyperosmolality, 2) extraembryonic lesions with degeneration of allantois and reduced villigenesis being more prevalent, and 3) materno-fetal effects such as decreases in fetal and maternal body weights, decreased maternal food intake, and fetal abnormalities (vertebral, rib, and sternebral defects). Few of these changes occurred when NaHCO3, an endogenous agent known to correct metabolic acidosis, was coadministered with ethylene glycol. Ethylene glycol-induced maternal metabolic acidosis, concurrent with hyperosmolality, was suspected to contribute toward reduction in villigenesis and fetal anomalies, including body weight reductions. Sodium salicylate induced the following: 1) mild maternal acidosis, hypokalemia, and hypophosphatemia with no significant change in pH; 2) maternal hemorrhage in extraembryonic cavities, papillary proliferation of the visceral yolk sac endoderm, and failure to form the chorioallantoic labyrinth; and 3) resorptions, hydrocephaly, rib defects, and fetal body weight reduction. Upon simultaneous treatment with sodium salicylate, NaHCO3 significantly reduced, and NH4Cl enhanced the incidence of the above histologic and teratologic effects, without significantly altering acid-base values. An etiologic association between the above salicylate-induced maternal and extraembryonic lesions and teratogenicity was likely. Cadmium chloride, whether administered by the intraperitoneal (ip) or intravenous (iv) route, caused 1) hydrocephaly, anophthalmia, vertebral and rib defects, reduction in fetal body weight, resorptions and maternal toxicity (acute peritonitis by the ip route only), and 2) extensive necrosis and hemorrhage in the decidua basalis, hemorrhage in the ectoplacental cone and around Reichert's membrane, and absence of chorioallantoic labyrinth. An etiologic relationship between these teratologic and histologic effects seemed probable, since both were dose-related. From the above studies, it was hypothesized that maternal factors--metabolic acidosis, hyperosmolality, hemorrhages in the ectoplacental cone, extraembryonic cavities, and around Reichert's membrane, and necrosis of decidua basalis--may have, directly or indirectly, reduced fetal nutrition and materno-embryonic gaseous exchange, which ultimately altered fetal development.

Cellular localization of rat placental lactogen II and rat prolactin-like proteins A and B by in situ hybridization

In situ hybridizations using 35S-labelled antisense and sense RNA probes of rPLII, rPLP-A and rPLP-B were carried out on developing rat placenta to determine which cell types synthesized each specific mRNA. Cellular localization of the sites of synthesis of these placental RNAs would help to decide whether these proteins were functioning in the mother of the fetus. The cells of the basal zone are known to have access only to the maternal blood supply, while the labyrinth region is supplied by both maternal and fetal blood vessels. The data in this paper show that at day 12 of pregnancy the rPLII mRNA is synthesized in the primary and secondary giant cells. At later days, hybridization is seen in both the giant cells of the basal zone, and cells in the labyrinth, suggesting that rPLII has a function not only in the mother, but also in the fetus. The rPLP-A mRNA is synthesized in both the giant cells and the cytotrophoblasts of the basal zone. No hybridization is seen to any cells in the labyrinth, even at the later days when it appears that all cytotrophoblasts synthesize rPLP-A mRNA. The rPLP-B mRNA is synthesized exclusively by the cytophoblasts of the fetal placenta. Like rPLP-A, all these cells synthesize this mRNA in the late term placenta. The synthesis of the rPLP-A and rPLP-B mRNAs in cells which have access only to the maternal circulation suggest that they have a role in the mother.

Cadmium and zinc concentrations in fetal and maternal rat tissue after parenteral administration of cadmium during pregnancy

Cadmium (Cd) and zinc (Zn) concentrations were determined by solid sampling atomic absorption spectrometry (AAS) in rat maternal and fetal tissues after exposure to cadmium. Cadmium was administered subcutaneously as CdCl2 in saline daily during pregnancy. Two experiments were performed. In expt. I we investigated the tissue concentration at day 19 (gestational age) after administration of several doses: 0, 1.1, 2.2, 4.4, and 8.8 mumol Cd/kg/day. In expt. II the course of the Cd and Zn concentrations during pregnancy was investigated by collecting samples at days 14, 16, 18 and 20, after daily injections of 4.4 mumol Cd/kg. Cadmium concentrations in blood, maternal liver, placenta and fetal liver increased with dose and duration of exposure. Cadmium was heavily accumulated in the liver and transferred to the fetus only in small amounts. The zinc concentration in the maternal liver was positively correlated with the cadmium concentration. In the placenta the zinc concentration was not affected. Zinc in fetal liver was decreased from day 18 onward. Despite relatively high cadmium levels and decreased zinc levels in the fetus, we observed no adverse effects on various reproduction parameters, such as birth weights and obvious malformations.

Involution of the antimesometrial decidua in the mouse. An ultrastructural study

Involution of the antimesometrial decidua was analysed by electron microscopy on days 9, 10 and 11 of pregnancy in the mouse. During this period, the width of the antimesometrial decidua decreases considerably. Involution begins in the decidual cells situated closest to the embryo (internal decidua) and proceeds towards the myometrium. The cells of the internal decidua showed signs of deterioration characterized by accumulation of clumps of chromatin in the nuclei and dilation of the perinuclear cisterna and endoplasmic reticulum cisternae. Autophagosomes and heterophagosomes accumulated in the cytoplasm of these cells. Cells particularly strongly affected became spherical and were devoid of their plasma membrane. Some cells near the trophoblast as well as the mature decidual cells situated farther from the embryo showed a normal morphology. The trophoblastic cells established close contact with healthy decidual cells and engulfed fragments of disorganized decidual cells. It is suggested that the death of decidual cells is a type of programmed cell death and that it is not due to a direct lytic action by the trophoblast.

The metrial gland

The information available about the metrial gland of the pregnant rodent uterus with its content of granulated metrial gland (GMG) cells is reviewed. Recent research shows that GMG cells differentiate from bone marrow cells and supports the suggestion that GMG cells are involved in the immunological relationship between mother and foetus. There is probably a complex association between GMG cells and stromal cells of the metrial gland, and it is suggested that the association between GMG cells and the placental labyrinthine cells represents a functional interaction.

Trophoblast-decidual cell interactions and establishment of maternal blood circulation in the parietal yolk sac placenta of the rat

Implantation sites from rats were studied on days 6, 7, and 8 of pregnancy to determine the sequence of events in the formation of blood spaces in the trophoblast that is part of the parietal wall of the yolk sac placenta and to determine how trophoblast gains access to maternal blood. The maternal blood flowing through these spaces is the source of nutrients that reach the embryo via the visceral endoderm. Tissues were prepared for light microscopy, scanning electron microscopy, and transmission electron microscopy. Trophoblast blood spaces are derived from the lateral intercellular spaces of trophoblast cells and are present in a collapsed condition until day 8, when maternal vessels are tapped by trophoblast. These spaces then contain circulating maternal blood, and trophoblast cells reflect adaptations for metabolic exchange including thinning of trophoblast covering Reichert's membrane and the appearance of numerous fenestrations, with and without diaphragms, in the areas where trophoblast is attenuated. Between days 6 and 7 decidual cells appear to form a barrier between the maternal circulation and trophoblast. On day 7, however, decidual cell processes penetrate the residual uterine luminal epithelial basal lamina, and then the decidual cells that are juxtaposed to trophoblast undergo degradative changes that resemble apoptosis. There is condensation of cytoplasmic contents, fragmentation of the cells, and phagocytosis of the fragments by trophoblast. Some decidual cells are interposed between endothelial cells in the walls of maternal vessels as early as day 7. Trophoblast may gain access to the maternal vessels by replacing decidual cells or by direct imposition of trophoblast cell processes between endothelial cells.

The rat placenta expresses paternal class I major histocompatibility antigens

The expression of paternally inherited class I MHC antigens on the placental trophoblast of the rat has been investigated using a mouse anti-rat monoclonal antibody (MN4-91-6) in an indirect immunoperoxidase labelling assay on cryostat sections. Strong specific staining was obtained on the spongy zone trophoblast of the mature placenta from DA male (RT1a) X PVG female (RT1c) matings. In marked contrast, no staining was observed on the labyrinthine trophoblast nor on the trophoblastic giant cells at any stage of gestation from 8 to 19 days post-coitum. None of the trophoblastic cell populations at any stage of gestation were reactive with an anti-class II monoclonal antibody. Class I positive endovascular cytotrophoblast cells were present in the maternal arterial sinusoids of the decidua. These findings imply that maternal immunoregulatory mechanisms must be essential for the survival of the placenta and fetus.

Localization and synthesis of the tumor protein oncomodulin in extraembryonic tissues of the fetal rat

The calcium-binding protein oncomodulin, previously found only in tumors, has been detected during rat development. Specific antisera to purified rat hepatoma oncomodulin (MW 11,500) were used to detect oncomodulin by radioimmunoassay (RIA) and by avidin-biotin-peroxidase complex (ABC) immunohistochemistry. Using RIA, oncomodulin was found to increase in placenta from below the limits of detection (2 ng/mg protein) on Day 13 to approximately 25 ng/mg on Day 16 of pregnancy, and to remain high through to the end of gestation. Determinations on separated inner and outer placenta showed the increase to be greater in the outer placenta (basal zone and decidua) than in the inner placenta (labyrinth). The ABC technique on paraffin sections produced positive staining for oncomodulin throughout the placenta, with the most intense staining occurring in the outer placenta (cytotrophoblast and giant cells of the basal zone). Parietal and visceral yolk sac, and amnion also stained positively, while fetal organs did not. Oncomodulin synthesis measured by [35S]methionine incorporation into immunoprecipitates occurred in isolated inner and outer placenta, whole placenta, the separated trophectoderm and endoderm of the parietal yolk sac, and amnion. No oncomodulin synthesis could be measured in visceral yolk sac, fetal liver, or 16-day embryo. This occurrence in developing and transformed tissues demonstrates that oncomodulin is an oncodevelopmental protein.

The immunohistochemical localization of pregnancy-specific beta 1-glycoprotein in postimplantation rat trophoblast

Pregnancy-specific beta 1-glycoprotein (SP1) was identified by peroxidase-antiperoxidase (PAP) immunohistochemistry in the placenta of inbred strains of rat between 10 and 21 days of gestation. SP1 was located predominantly in basal zone trophoblast and in intravascular trophoblast of decidual vessels, but it was absent from labyrinthine trophoblast. No perivascular cells were identified by SP1 staining, but occasional clusters of interstitial trophoblast stained for SP1. The results suggest that basal and labyrinthine trophoblast are functionally different.

Occlusion and reformation of the rat uterine lumen during pregnancy

Implantation sites were obtained from rats at various stages of pregnancy and were studied by light microscopy and scanning electron microscopy. Early in pregnancy the uterine luminal epithelium and the decidual cells in the implantation site formed an implantation chamber containing the conceptus. The epithelial cells lining the chamber and the mouth of the chamber degenerated, and the uterine lumen that was mesometrial to the conceptus was obliterated such that the uterine lumen became discontinuous, and the luminal epithelia of intersite areas were isolated. As the conceptus continued to grow, the decidua-conceptus unit bulged into the intersite areas and was partially covered by an epithelium that eventually became discontinuous and degenerated. Once this had occurred, the luminal epithelium of the intersite areas reestablished contact antimesometrial to the decidua-conceptus unit, and the uterine lumen was again continuous. However, the epithelium lining the lumen was not complete in the mesometrial region because of the vascular connections between the uterine stroma and the placenta. Factors influencing the restructuring of the uterine luminal epithelium were discussed.

Review article: trophoblast invasion and the establishment of haemochorial placentation in man and laboratory animals

Trophoblast invasion is an essential component of haemochorial placentation and has to be considered to relation to reactive changes in the maternal uterine tissues. Some comparative aspects of human and laboratory rodents are discussed and, although there is an obvious phylogenetic gap between the two, many characteristics of placental development are found to be analogous. Trophoblast growth into the uterus is different in different species: localized trophoblast growth forming a bulky tissue (mouse, rat, hamster) contrast with a dispersion of independent trophoblastic elements, forming an interstitial invasion (guinea pig, man). In the rat, mouse, hamster and man retrograde intra-arterial trophoblast migration occurs in maternal vessels supplying blood to the developing placenta. Early changes in maternal tissue might influence trophoblast behaviour. Decidualization probably is a key phenomenon, and the relation of decidual necrosis to trophoblast invasion is considered. Some kind of controlled immune response by the mother also may be involved. These considerations apply to stromal or interstitial invasion as well as to intravascular trophoblast migration but, for the latter, haemodynamic factors probably influence tissue reactions.

On the developing rat placenta. I. Differentiation and junctional alterations of labyrinthine layers II and III

The differentiation of chorionic layers II and III and alterations of intercellular junctions within the developing placental labyrinth were investigated in rats. Between the 14th and 16th day of gestation, the trabecular structures of the labyrinth alter and increasing numbers of primary, secondary, and tertiary lamellae develop. Trophoblastic layer I remains multicellular. Layer III rearranges and cytoplasmic fusions result in a continuous cytoplasmic barrier intervening between the already syncytial trophoblastic layer II and fetal capillaries. Simultaneously, most of the "undifferentiated" cells within the labyrinth disappear. Thin sectioning anf freeze-fracturing reveal multiple images of intercellular junctions, particularly gap and tight junctions in the cellular and syncytial parts of layers II and III. Continuous and regularly arranged tight junctions occur as well as fragmented structures which are spaced irregularly. Gap junctions are occasionally found between the juxtasinusoidal regions of layers II and III on the 14th day. More often they occur within restricted areas near the center of the trabeculae, integrated within extensive tight junctional strands. Gap junctions increase in later stages of pregnancy and eventually become distributed between the interfaces of layers II and III in the primary lamellae.

Ultrastructural changes in the rat metrial gland in the latter half of pregnancy

The ultrastructural changes occurring in the metrial gland in the latter half of pregnancy in the rat have been studied. Typical palely stained granulated cells are present in the metrial gland up to day 20 but many granulated cells show variations in appearance which may be associated with degeneration. In some the cytoplasm is more darkly stained and such cells often have apparently empty areas of cytoplasm adjacent to the granules. From day 14 onwards many areas of the gland show cellular debris, apparently resulting from lysis of the granulated cells. However, occasionally normal granulated cells are present in blood vessels and have been observed apparently penetrating the vascular endothelium. A variety of changes was also noted in the stromal cell population. Inclusions became apparent in many of these cells; some of these consisted of lipid while others resembled granules from the typical granulated cells. Other cells with numerous inclusions appeared to be macrophages. Lysis of granulated cells in situ is compatible with suggestions that the metrial gland produces a holocrine secretion, though some normal granulated cells enter blood vessels. The stromal cells may have a phagocytic role in late pregnancy but evidence for this was inconclusive.

Localization of rabbit gamma globulins in the mouse visceral yolk sac placenta

The yolk sac placenta has been implicated previously in transmission of passive immunity to the fetus. This work uses an immunohistochemical technique devised by Sternberger et al. ('69) to study this problem. Rabbit serum containing gamma globulins was injected into the uterine lumen of the White Swiss mouse during the last third of pregnancy. Two or four hours later yolk sacs were removed and fixed in 2% paraformaldehyde or freeze-dried and fixed with paraformaldehyde vapors. Finely chopped tissue was treated with (1) sheep antiserum to rabbit serum gamma globulin, (2) an antigen-antibody complex consisting of horseradish peroxidase and rabbit anti-horseradish peroxidase and (3) hydrogen peroxide and 3,3'-diaminobenzidine. Reaction product was heavily concentrated in visceral yolk sac endodermal cells, frequently deposited in endothelial cells of vitelline vessels, and rarely in the serosal basement membrane and mesothelial cells which border the exocoelomic cavity. This supports evidence of other workers that the yolk sac membrane rapidly absorbs substances with which it comes in contact, transport into vitelline vasculature is a route of transfer from mother to fetus, and possible transfer into the exocoelomic cavity and thence to the amniotic cavity may occur in mice.

Histologic characteristics of cells cultured from rat placental tissue

Laboratory animals, especially rats, have provided a comparative model for extensive research on maternal-fetal relationships. To identify individual placental cells for subsequent immunologic analysis, cultures of rat placentas were studied. Five cell types were observed, including: two histologically distinct giant cells, mononucleate and multinucleate, apparently formed by amitosis and fusion, respectively; small round cells; polygonal cells, probably cytotrophoblasts. Of particular interest are the small round cells which are phagocytic and morphologically similar to macrophages, cells known to be important in the immune response.

Effects of amethopterin (methotrexate) on the evolution of pregnancy in rats

Amethopterin (4-amino-N-10-methyl-glutamic acid) was given to pregnant rats in varying doses at different periods of gestation to evaluate its effects upon both the mother and the fetoplacental unit. The maternal organism is more sensitive to this drug at days 14 to 17 than at a larger stage of gestation. When administered to rats from day 14 to day 18 of pregnancy the drug is capable of inducing a series of deleterious effects: maternal weight loss, resorption, abortion or hypotrophy of fetuses. Day 16 appears to be a critical moment in the evolution of rat pregnancy, after which injection of amethopterin does no longer impair fetoplacental growth. Before this date, the drug directly inhibits fetal weight gain, whereas the sensitivity of the placenta is only transient at day 16 resulting in maximum weight decrease of this organ 24 h later. Its action on rat pregnancy follows a direct dose-effect relationship reflecting increasing damage to the products of conception (resorption, abortion and hypotrophy).