Effect of gestational age and hypoxia on activity of ribonucleic acid polymerase in fetal guinea pig brain

OBJECTIVE: The aim of this study was to determine the effect of gestational age and hypoxia on the activity of ribonucleic acid polymerase in fetal guinea pig brain. STUDY DESIGN: Fetal cerebral cortical neuronal nuclei were isolated at 40, 50, and 60 days (term) of gestation to determine the effect of gestational age on the activity of ribonucleic acid polymerase I, II, and III. Pregnant guinea pigs at 60 days' gestation were randomly assigned to a normoxic or hypoxic group to determine the effect of hypoxia on ribonucleic acid polymerase activity. The fetal neuronal nuclei were pooled from 6 pregnant animals in each group. In the normoxic group the pregnant guinea pigs were exposed to room air before delivery. In the hypoxic group delivery occurred after the pregnant guinea pig had been exposed to 7% oxygen for 60 minutes. The fetuses were delivered by cesarean, and the fetal cerebral cortical neuronal nuclei were isolated immediately. Ribonucleic acid polymerase activity was determined with nuclei suspended in a buffer containing adenosine triphosphate, guanosine triphosphate, cytidine triphosphate, and tritiated uridine triphosphate. Dactinomycin (actinomycin D) and polydeoxyadenylic-thymidylic acid were used to determine the activity of bound and free ribonucleic acid polymerase. alpha-Amanitin was used to determine the activity of ribonucleic acid polymerase II. RESULTS: The activity of total (bound and free) ribonucleic acid polymerase I and III increased from 85.4 +/- 9.4 fmol of tritiated uridine triphosphate incorporated per milligram of protein per hour at 40 days' gestation to 233.3 +/- 82.1 fmol at 50 days and to 343.4 +/- 231.6 fmol at 60 days (P =.02). Total ribonucleic acid polymerase II activity increased from 19.9 +/- 6.0 fmol of tritiated uridine triphosphate incorporated per milligram of protein per hour at 40 days to 123.8 +/- 53.0 fmol at 50 days and to 200.9 +/- 77.8 fmol at 60 days (P <.01). In the term fetal guinea pig brain the activity of bound ribonucleic acid polymerase I and III decreased from 116.8 +/- 107.2 fmol of tritiated uridine triphosphate incorporated per milligram of protein per hour under normoxic conditions to 92.8 +/- 76.0 fmol in hypoxic fetal brain, a decrease of 20.5%. Free ribonucleic acid polymerase I and III activity decreased from 199.2 +/- 115.2 fmol of tritiated uridine triphosphate incorporated per milligram of protein per hour in normoxic fetal brain to 132.0 +/- 66.4 fmol in hypoxic fetal brain, a decrease of 33.8%. Free ribonucleic acid polymerase II activity decreased from 62.4 +/- 70.4 fmol of tritiated uridine triphosphate incorporated per milligram of protein per hour in normoxic fetuses to 13.6 +/- 9.6 fmol in hypoxic fetal brain, a decrease of 78.2%. In contrast, however, in term fetal guinea pig brain, bound ribonucleic acid polymerase II activity increased from 8.0 +/- 10.4 fmol of tritiated uridine triphosphate incorporated per milligram of protein per hour under normoxic conditions to 35.2 +/- 8.8 fmol in hypoxic fetal brain, an increase of 340% (P <.01). CONCLUSION: The activity of ribonucleic acid polymerases I, II, and III increases throughout the latter half of gestation, from 40 to 60 days, in the fetal guinea pig brain. Hypoxia in utero is associated with a decrease in ribonucleic acid polymerase I and III activity. Although hypoxia is associated with a decrease in free ribonucleic acid polymerase II activity, we observed a marked increase in bound ribonucleic acid polymerase II activity, which may represent a hypoxia-induced alteration of gene expression.     

Developmental changes in taurine and other sulfur-containing amino acid concentrations in fetal and neonatal rats

The concentrations of taurine and other sulfur-containing amino acids in the fetal, neonatal and maternal liver, placenta, and whole fetal body between the 15th day of gestation and the 14th day after birth were determined using an automatic amino acid analyzer. In the fetal liver and placenta, the taurine concentration was the highest among all ninhydrin positive compounds. In these tissues the concentration of taurine increased significantly with the number of gestational days. Moreover, the total amount of taurine per fetus increased markedly up to term after the 15th day of gestation, and reached almost the same value as the total amount for adult rat liver. A striking difference in the changes in taurine concentrations during gestation between the fetal and maternal rat liver was observed: In contrast to the increase in the fetal liver, a significant decrease in the maternal liver was observed near term. But in these organs, no significant change in methionine, cystathionine and cysteine concentrations was observed during the perinatal period. These results suggest that taurine is supplied to the developing rat fetus from the maternal liver throughout gestation.     

Intrauterine growth retardation and diabetic pregnancy: two types of fetal malnutrition

Placental transfer of alpha-aminoisobutyric acid and methylglucose was studied near term in normal guinea pigs carrying growth-retarded fetuses and in streptozotocin-treated diabetic guinea pigs. Compared with their normal littermates, growth-retarded fetuses had lower placental weights and a diminished transfer of both nutrient analogues in proportion to the reduction in fetal weight. Fetuses from diabetic animals had normal fetal weight and placental methylglucose transfer but reduced litter size and a 40% reduction in placental alpha-aminoisobutyric acid transfer. These data suggest that intrauterine growth retardation in an otherwise normal pregnancy is associated with a small placenta and a reduced transfer of nutrients. Diabetic pregnancy may represent a different type of fetal malnutrition due to amino acid deprivation. It is speculated that birth weight does not necessarily reflect the degree of fetal malnutrition in diabetic pregnancy since fetal growth may be maintained by glucose and fat deposition.     

Delayed amplification of cytomegalovirus infection in the placenta and maternal tissues during late gestation

To stimulate first-trimester human cytomegalovirus infection, pregnant guinea pigs were inoculated with a low dose of guinea pig cytomegalovirus during the first trimester of pregnancy. Maternal viremia, which was cleared by 2 weeks after inoculation, was found to reappear near the time of delivery in one third of the animals tested. The virus, first detected in the placenta during initial maternal viremia, replicated after the time when maternal blood was cleared of virus, although high titers of maternal serum antibodies were present. In the last week of gestation (43 to 48 days after inoculation), the virus was detected in 95% of placentas and was present at high titers. Fetal infection first appeared on day 25 after inoculation and reached an incidence of 37% in the last week of gestation despite the presence of fetal antibody. These results suggest that the placenta may amplify cytomegalovirus infection late in human gestation, even after low-dose infection in the first trimester.     

The localization of SP1-like substance in the rat placenta by immunohistochemical method

A protein which reacted with an anti-serum to pregnancy specific beta 1-glycoprotein (SP1) was found in rat placenta by the immunohistochemical method, and is tentatively called SP1-like substance in this paper. By means of a PAP method, the localization of SP1-like substance in the placentae of mice and rats was investigated. Placentae were fixed with 10% neutralized formaldehyde and Bouin's fluid. In mice placentae, SP1-like substance could not be detected with either fixation procedure. In rat placentae, however, the substance was observed to be fixed with Bouin's fluid; the strongly stained substance for anti-SP1 serum was localized at the cytoplasma in tertiary giant cells of the junctional zone near the labyrinth. The animals were examined at 12-13 days, 15-16 days and 19-20 days of gestation. The SP1-like substance was not stained at 12-13 days gestation, but stained weakly at 19-20 days gestation and strongly at 15-16 days gestation in the rat's placentae. These results probably reflect the change in placental aging.     

The effects of repeated endotoxin exposure on placental structure in sheep

Intrauterine infection has been associated with fetal brain injury and preterm birth. We have recently shown that repeated exposure to bacterial endotoxin leads to hypoxia and brain injury in the preterm ovine fetus and we considered it possible that endotoxin could also damage the placenta. Our aim therefore was to assess placental structure following repeated exposure to endotoxin. Endotoxin was administered on 3-5 occasions (1 microg/kg, i.v.) over 5 days from 95-99 days of gestation (term approximately 147 days) to 6 fetal sheep and placental structure assessed at 105 days. In LPS-exposed animals there was a 17 per cent reduction (P<0.05) in placental weight and the average cross-sectional area of placentomes was reduced (P<0.05) by 20 per cent. In addition, all LPS-exposed placentae showed significant injury as evidenced by calcium deposits associated with areas of infarcted tissue. We conclude that repeated endotoxin exposure results in damage to the placenta which could lead to persistent alterations in placental exchange function.     

Permeability of the near-term rat placenta to hydrophilic solutes

The permeability of the rat placenta at 21 days' gestation (term is 23 days) has been measured with fetuses intact in situ and by perfusion of the fetal circulation. Intact measurements were made by removal of fetuses at known time intervals after injection of radioisotopes to the anaesthetized mother and measurement of their radioactivity content. Unidirectional clearance (Kmf) was calculated and found to be in proportion to the diffusion coefficient in water (Dw) for [14C]mannitol, [14C]sucrose, [51Cr]EDTA and [3H]inulin but was relatively high for 22Na and low for [125I]albumin. The high value for 22Na is partially explained by transfer across the yolk sac placenta; cautery of the vitelline vessels significantly reduced the Kmf for 22Na but not that for [51Cr]EDTA or [125I]albumin. The low [125I]albumin value is explained on the basis of restricted diffusion of this tracer. Perfused permeability measurements were made by injection of radioisotope into the anaesthetized mother and measurement of the radioactive content of fetal perfusate samples. Although the Kmf for Na+ was significantly (P less than 0.01) reduced by 25 per cent, there was no other significant difference between results with the perfused placentae compared with those from the intact placentae. Comparison of the intact data with similar measurements in guinea pig and human confirms the similar permeability properties of the haemochorial placentae as a whole; the extra trophoblast layers in the rat make no discernible difference.     

The effect of a reversible period of adverse intrauterine conditions during late gestation on fetal and placental weight and placentome distribution in sheep

Adverse intrauterine conditions occurring during early to mid-gestation or throughout the whole of gestation influence placental weight and the distribution of placentome types in sheep. However, no study to date has investigated the effect of a reversible period of adverse intrauterine conditions during late gestation upon fetal and placental weight and placentome distribution in sheep. Twenty-two sheep fetuses were chronically instrumented with an inflatable cord occluder, amniotic and vascular catheters and with a Transonic flow probe around an umbilical artery. At 125 days (term isca.145 days) the occluder was inflated to reduce umbilical blood flow by ca.30 per cent for 3d in 12 fetuses (umbilical cord compressed, UCC). The occluder was then deflated and umbilical blood flow allowed to return to baseline. The remaining 10 fetuses acted as sham-operated controls in which the occluder remained deflated at all times. At 135-137dGA ewes were humanely killed and tissues collected, weighed and placentomes classified. A reduction in umbilical blood flow by approximately 30 per cent from baseline for 3 days in UCC fetuses led to mild fetal asphyxia throughout the period of cord-compression. After deflation of the occluder cuff, umbilical blood flow returned to a level that was significantly greater than that measured during baseline. Umbilical cord compression had no effect on fetal body weight but significantly increased fetal adrenal weight relative to body weight. While the total number of placentomes was not altered by cord-compression, total placentome weight and the total weight of C/D-type placentomes were both reduced in UCC relative to control placentae. In addition, the mean weight of placentomes, and of C/D-type placentomes specifically, was significantly lower in UCC relative to control placentae. When expressed as a percentage of the total number of placentomes in the placenta, there was a significantly lower percentage of C/D-type placentomes in UCC relative to control placentae. In addition, there was a significant relationship between the total number of placentomes and the percentage C/D-type placentomes in control, but not UCC, placentae. The data suggest that a temporary, reversible period of adverse intrauterine conditions occurring late in gestation in sheep has persisting effects upon the placenta, mean placentome weight and placentome distribution.     

Release of lipid from the equine placenta during in vitro incubation

An in vitro incubation technique was used to examine release of lipids from the equine placenta. Placental tissue was obtained at term (n=5, term=320–365 days) and earlier in gestation (n=8, mean=266 days). Term placentae were incubated at two temperatures, 4°C (control) and 37°C for 2 h. Pre-term placentae were incubated at 37°C with two different concentrations of fatty acid in the medium. Tissues and media were analysed for their lipid concentrations.Term and pre-term placentae released free fatty acid (FFA) and phospholipid into the incubation medium during incubation at 37°C. Long chain polyunsaturated fatty acids derived from the essential fatty acids were released into the media. The fatty acid profiles of the lipids released during incubation more closely resembled those of fetal plasma than maternal plasma lipids as measure in previous studies.These data are consistent with the view that the equine placenta is a source of both FFA and phospholipid for the fetus and that the placenta may provide long chain polyunsaturated fatty acids for the fetal foal.     

The evolutionary significance of placental interdigitation in mammalian reproduction: Contributions from comparative studies

The placenta is fundamental to mammalian reproduction and is surprisingly diverse in gross morphology among species. Whether and how this diversity affects maternal investment and fetal growth is still poorly understood. Contrary to suggestions that highly invasive hemochorial placentation is beneficial to fetal development, recent comparative studies have revealed that interdigitation - the degree of contact between maternal and fetal tissues at the area of exchange - strongly influences fetal growth rates. Species with labyrinthine placentae give birth to neonates of similar size to those of species with villous or trabecular placentae but in less than half the time. These findings suggest that there might be tradeoffs between fetal growth rates (higher with greater interdigitation) and gestation time (shorter with greater interdigitation), in association with type of interdigitation. Such tradeoffs might be the results of maternal-offspring conflict over the allocation of maternal resources, with paternal genes favouring greater interdigitation and so higher fetal growth, and maternal genes responding by reducing gestation time. These results emphasize the role of interdigitation as a means to increase the surface area for exchange, and are consistent with within species studies demonstrating that a higher surface area for exchange is associated with heavier neonates. Further studies could investigate the role of other traits in the evolution of placental diversity and their impact on fetal development.     

Placental hormones: II. Immunofluorescence studies of the localization of prolactin/placental lactogen- and human chorionic gonadotrophin-receptors in human and rat placenta

Human term placentae and rat placentae of gestation day 15 and 17 were examined for the localization of prolactin (PRL)/placental lactogen (PL) and human chorionic gonadotrophin (hCG) receptors by means of an immunofluorescence technique in order to determine possible target cells for PRL/PL and hCG and to obtain indirect evidence for the localization of steroid producing cells. In the human placenta, PRL/PL- and hCG-receptors were observed in the syncytiotrophoblast of the chorionic villi and in the giant cells of placental septa and cytotrophoblastic islands in the intervillous space. In the rat placenta, PRL/PL- and hCG-binding was localized mainly to the giant cells and vacuolated glycogen cells of the basal zone.     

Placental permeability for morphine-3-beta-D-glucuronide in the guinea pig

The fetal Vd and the PS of the major metabolite of morphine, M3G, were studied in pregnant guinea pigs during the last half of gestation. Fetal Vd was determined to be 0.334 ml/g of fetal plus placental weight and did not vary as the gestation progressed. The mean +/- s.e. PS for M3G was 3.7 +/- 0.3 X 10(-5) ml/sec/g and was independent of anaesthesia. This value was consistent with previous studies of other hydrophilic compounds, indicating that diffusion governs the placental passage of M3G. The PS value increased with increasing fetal weight which was consistent with structural changes in the guinea pig placenta as fetal age progresses in late gestation.     

Perfusion with lipopolysaccharide differently affects the secretion of interleukin-1 beta and interleukin-1 receptor antagonist by term and preterm human placentae

The aim of the present study was to examine the effect of lipopolysaccharide (LPS) on the secretion of the pro-inflammatory cytokine interleukin-1beta (IL-1beta) and of its natural inhibitor interleukin-1 receptor antagonist (IL-1Ra), by perfused human term and preterm placental tissue. Eight term and eight preterm placentae were collected immediately after delivery; four term and four preterm placentae were perfused with control medium (without LPS) and the other four term and four preterm placentae were perfused with medium containing LPS. The release of IL-1beta into the maternal compartment by term placenta was significantly higher than the release by preterm placenta (p<0.001). However, there were no significant differences between IL-1beta levels released into the fetal compartments of term and preterm placentae. No significant differences were observed in the release of IL-1Ra into the maternal and fetal compartments of term placenta, when compared to preterm placenta. Exposure to LPS significantly decreased the capacity of term placenta to release IL-1beta into the maternal compartment (p<0.001) and increased the capacity of term placenta to release IL-1Ra into the maternal and fetal compartments (p<0.001 and p=0.017, respectively). However, the capacity of preterm placentae to release IL-1beta and IL-Ra into the maternal and fetal compartments was not affected by LPS. IL-1beta was expressed by both term and preterm placentae before and after perfusion (+/- LPS), by epithelial cells of the amnion, chorion, by syncytiotrophoblast and stromal cells of villous tissue and by the decidua. IL-1Ra in term and preterm placentae was expressed before perfusion mainly in epithelial cells of the amnion. After perfusion of term placentae (+/- LPS), additional IL-1Ra expression was seen in epithelial cells of the amnion and in syncytiotrophoblast and stromal cells of villous tissue and by the decidua. However, perfusion of preterm placentae (+/- LPS) did not affect IL-1Ra expression. The localization of IL-1beta and IL-1Ra in both term and preterm human placental tissue suggests a their physiologic role. The data presented indicates that the IL-1 system in term and preterm placentae seems to be differently affected by LPS. Down-regulation in the release of the pro-inflammatory cytokine IL-1beta and the up-regulation of its antagonist (IL-1Ra) may be a part of the inflammatory response to infection in human term, but not preterm, placentae. The IL-1 system in term and preterm placentae seems to be differently affected by LPS.     

Ultrasonic detection and developmental changes in calcification of the placenta during normal pregnancy in mice

High resolution ultrasound imaging of the mouse placenta during development revealed highly echogenic foci localized near the materno-placental interface in early gestation and, near term, in the placental labyrinth (the exchange region of the placenta). Echogenic foci and calcium deposits identified in histological sections using Alizarin red staining showed similar localization and changes with gestation. Calcium deposits caused the echogenic foci because incubating uteri in a decalcifying solution eliminated both the deposits and echogenic foci. Transmission electron microscopy, X-ray microanalysis, and electron diffraction were used to show that deposits were calcium hydroxyapatite crystals. Calcium deposits were extensive and densely packed at days 7.5-9.5 of gestation at the border between the maternal decidua and the fetal trophoblast giant cells of ectoplacental cone. After the formation of the chorio-allantoic placenta (approximately day 10.5), calcification deposits appeared larger and more rarefied but were still localized at the border between the maternal decidua and the fetal trophoblast giant cells of the placenta. Calcification deposits were not observed in the labyrinthine region of the mouse placenta until > or = day 15.5 (day 18.5 is full term). We conclude that deposits of calcium hydroxyapatite crystals in the mouse placenta are detectable by high resolution ultrasound imaging. These deposits provide an ultrasound detectable marker of the maternal-placental interface that is particularly prominent during the establishment of the chorio-allantoic placenta between days 7.5 and 9.5 of gestation.     

Relation between placental morphometry and fetal growth]

Forty-eight placentae of full term infants, 21 placentae from appropriate for gestational age infants (AGA) and 27 placentae from small for gestational age infants (SGA) were measured by morphometric technic using the automatic image analyzer, in order to find out the extent of fetomaternal exchange which determines the transfer of oxygen and nutrition from mother to fetus and fetal growth. The results of measurement correlated well both with infant birth weight and placental weight. They demonstrated striking quantitative differences when the placentae of SGA were compared with those of AGA. The placenta weights in the group of SGA were notably less than those in the group of AGA. It seems that low birth weight relates to low functional tissue mass of placenta. This reduction of functional tissue is accompanied by diminution of the area for exchange between mother and fetus, both at the villous surface area and at fetal capillary surface area. Thus, the ability of transferring oxygen and nutrition from mother to fetus is curtailed. The results show that the rate of fetal growth is limited by placental function as well as its weight.     

Incorporation of labeled ribonucleic acid precursors into maternal and fetal rat tissues during pregnancy

Tritium-labeled ribonucleic acid precursors, including cytidine, uridine, and orotic acid, were injected into rats with dated pregnancies (14 to 21 days) and virgin rats. The acid-insoluble counts indicating incorporation into fetal and placental tissues showed that the highest incorporation occurred with cytidine, particularly earlier in pregnancy. In contrast, uridine demonstrated a minor degree of incorporation but displayed facile and enhanced transplacental passage with duration of pregnancy as represented by acid-soluble counts. Orotic acid was minimally used by both fetal and placental tissues. The incorporation of labeled precursors into maternal liver, heart, and kidney demonstrated varying responses during the course of pregnancy.     

Comparison of intrauterine prostaglandin metabolism during pregnancy in man, sheep and guinea pig.

Metabolism of prostaglandin F2 alpha (PGF2 alpha) was studied in uterine tissues from pregnant women (n = 10), sheep (n = 6) and guinea pigs (n = 6). Two maternal tissues, myometrium and decidua or maternal placenta, and two fetal tissues, fetal placenta and membranes, were studied in each species. PGF2 alpha was metabolized via the well-known pathway into 15-keto-PGF2 alpha and 13,14-dihydro-15-keto-PGF2 alpha, while 13,14-dihydro-PGF2 alpha was tentatively identified in some tissues. The presence of 15-hydroxyprostaglandin dehydrogenase (PGDH) and 13,14-prostaglandin reductase was demonstrated in all tissues from each of the three species studied, but the quantitative intrauterine distribution of these enzymes differed from one species to another. In man, PGDH activities were highest in fetal membranes followed by fetal placenta and then by decidua and myometrium. In sheep, PGDH activities were highest in the maternal placenta followed in decreasing order by myometrium, fetal placenta and membranes. In the guinea pig, PGDH activity was highest in the fetal membranes followed in decreasing order by maternal placenta, fetal placenta and myometrium. Quantitative assay of PGDH showed that PGDH activity in the pregnant uterus is higher in women than in sheep and guinea pig. The results are discussed in relation to the involvement of prostaglandins in parturition.     

Lysyl oxidases: expression in the fetal membranes and placenta

The cross-linking of the connective tissues in the fetal membranes and placenta is important for their tensile strength and elasticity. We have studied the expression of lysyl oxidase (LOX) because it is the classical enzyme responsible for the cross-linking of collagen and elastin. We have also studied the two recently described, genetically distinct lysyl oxidase-like genes and proteins, lysyl oxidase-like (LOXL) and lysyl oxidase-like 2 (LOXL2), of unknown functions.Specific antisera have been used for immunolocalization in fetal membranes and placentae from early pregnancy terminations and after caesarean section at both preterm and term, prior to labour. In addition, the steady state mRNA levels of the three genes has been quantitated in separated amnion, chorion, decidua and placentae collected at term before labour. The immunocytochemistry shows that the spatial expression of the three lysyl oxidases is similar in early pregnancy in both the fetal membranes and placentae. However, by preterm this pattern had diverged and becomes greatest at term. The expression of the genes found at term was similar to the results of protein expression obtained by immunocytochemistry, with the exception of LOXL which had high placental gene expression, but low levels of immunolocalized protein. Thus by term, LOX was expressed predominantly in the amniotic epithelium, with little expression in the placenta, while LOXL showed highest gene expression in the placenta and lowest expression in the amnion. LOXL2 expression was again different and was expressed predominantly in the chorionic cytotrophoblast of the membranes with low expression in both the amnion and placentae. These results suggest that these three members of the lysyl oxidase family may have similar roles in early pregnancy during the development of the placenta and fetal membranes, but their divergence as pregnancy advances to term, may reflect changes in substrate specificity and connective tissue composition.     

Multicystic neonatal encephalopathy after a traffic accident with minor maternal injuries

We report a case of traffic accident at 30 weeks of gestation. The maternal injuries were minor. The fetal heart rate patterns showed tachycardia and decreased modulation. Ultrasound scanning was normal, without abruptio placentae. Ten days after the accident, a cesarean section was done on altered fetal heart rate with a normal infant at birth. This baby died 17 days latter from an ischemic multicystic encephalomalacia. With the view of the literature, we try to explain the pathophysiological mechanism of this severe fetal outcome despite minor maternal injuries. Hypovolemic collapsus, caval syndrome and maternal stress could be the cause of placental hypoperfusion. Abruptio placenta and feto-placental hemorrhage are others explanations. We propose the management for first aid workers and the specialized unit care.     

Ontogeny of expression of insulin-like growth factor (IGF) and IGF binding protein mRNAs in the guinea-pig placenta and uterus.

To determine the temporal and spatial distribution of insulin-like growth factor (IGF) and its family of binding proteins (IGFBPs), guinea-pig yolk sac and chorioallantoic placentae were collected at 15, 20, 25, 29, 44-45, 55 and 65-66 days of gestation. Messenger RNAs for IGF I, IGF II and IGFBP 1-6 were identified in tissue sections by in situ hybridization, using 35S-cRNA probes. Epithelial and mesenchymal cell types were identified by immunohistochemistry for cytokeratin and vimentin, respectively. At 15 days of gestation, IGF-II mRNA was expressed in ectoplacental mesoderm, cytotrophoblasts and syncytiotrophoblast, and IGFBP-5 mRNA was detected in the syncytiotrophoblast. In the mid-gestation placenta, IGFBP-5 mRNA was expressed in the marginal and interlobular syncytium and IGF-II mRNA in the labyrinth. Near term, when expansion of the labyrinth was complete, IGFBP-5 mRNA was coexpressed with IGF-II mRNA in the marginal and interlobular syncytium. These observations suggest that interaction between IGF-II and IGFBP-5 plays a role in the vascularization of the placenta by fetal vessels. IGF-II mRNA was not expressed in the maternal tissues at any gestational age. IGFBP-2, -3 and -5 mRNAs were expressed in the endometrial stroma at 7-12 days of gestation but, following establishment of the placenta, IGFBP mRNAs were more abundant in the myometrium than in the decidua. IGF-II mRNA was detected in trophoblasts invading the walls of maternal vessels, and the endothelium of the preplacental vessels expressed IGFBP-4 mRNA, while IGFBP-2 and IGFBP-5 mRNAs were present in the tunica media of mesometrial arteries that had not been invaded by trophoblast. These findings suggest that IGF-II produced by the trophoblast acts in an autocrine and/or paracrine fashion to promote trophoblast invasion and that this process is modulated by interaction with IGFBPs present in maternal tissues.