Cadmium exposure on day 12 of gestation in the Wistar rat: distribution, uteroplacental blood flow, and fetal viability

The effects of cadmium exposure (40 mumole CdCl2/kg, s.c.) on day 12 of gestation were evaluated in the Wistar rat. At 16-18 hours following such cadmium exposure, blood flow (as determined by radiolabeled microspheres) to the chorioallantoic placenta (CAP) was significantly reduced by 35%; at 24-26 hours, blood flow to the CAP had returned to control levels and was still unaffected at 38-43 hours. Uterine blood flow was not significantly altered at any of these timepoints. Between 16-18 and 24-26 hours after cadmium exposure, the concentration of cadmium in the placenta decreased significantly, while total cadmium content did not change. By 38-43 hours after cadmium exposure, total cadmium content of the placenta had increased significantly, although cadmium concentration was unchanged. There were no adverse effects on fetal viability or growth, as determined on day 20 of gestation. In sharp contrast, near-term (day 18) exposure to 40 or 50 mumole CdCl2/kg (s.c.) resulted in 53% and 82% mean incidences of fetolethality, respectively, within 24 hours. Administration of 50 mumole CdCl2/kg (sc) on day 12 also had no effect on fetal growth but resulted in increased fetolethality (12%). Thus midgestational cadmium exposure and its accompanying alterations in placental blood flow do not compromise fetal viability or growth. The differential response to cadmium at mid- and late gestation, in terms of fetolethality, is not due to maternal cadmium dose.     

Metabolism of glucose by fetus and placenta of sheep. The effects of normal fluctuations in uterine blood flow

The metabolism by the fetus and placenta of [2-3H, U-14C]glucose infused into fetal sheep has been studied. Uptake of glucose from the fetus by the placenta and transfer to the ewe, as well as placental metabolism of glucose to fructose and lactate have been quantified. About two-thirds of the glucose removed from the fetal circulation was taken up by placenta. Less than 15% of this passed back into the maternal circulation, the remainder was converted, at roughly equivalent rates, into lactate and fructose, most of which was transferred back to the fetus. It seems likely that little of this glucose is oxidised by the placenta. This data indicates that there are substrate cycles between the placenta and fetus, one possible function of which is to limit fetal glucose loss back to the mother; lactate and fructose have limited placental permeability. At uterine blood flow rates in the middle of the normal range net glucose uptake by the placenta from the maternal circulation was about 7-fold higher than that from the fetus. About 20% of this was transported to the fetus, 50% was oxidised and much of the remainder converted to lactate and transferred back to the ewe. Labelling patterns in fructose and lactate make it unlikely that this placental pool of glucose mixes freely with that derived from uptake from the fetus. Net movement of glucose across the placenta is markedly influenced by fluctuations in uterine blood flow over the normal range of 500-3000 ml/min. At low flow rates there is net output of glucose from the fetus to the placenta, and in some instances from the placenta to the ewe, i.e. there is evidence of net utero-placental production of glucose to the ewe separate from output by the fetus. There is a close linear relationship between uterine glucose supply (maternal arterial concentration x uterine blood flow) and net balance across the placenta. As uterine supply of glucose falls there is increased uptake by the placenta of glucose from the fetal circulation and corresponding enhanced recycling of fructose and lactate to the fetus. This production of fructose and lactate by the placenta may function to reduce glucose loss from the fetus to the ewe. Hence at high rates of placental uptake of glucose from the fetus placental production of lactate and particularly fructose may approach saturation and allow significant backflow of glucose from the fetus to the ewe. Under these conditions glucose uptake may in part sustain placental oxygen consumption.     

The effect of elevation of maternal plasma catecholamines on the fetus and placenta of the pregnant sheep

To study the effects of reduced uterine blood flow on fetal and placental metabolism, adrenaline has been infused at physiological doses (0.5 microgram/min per kg) into the circulation of the pregnant sheep. This gives a reduction of about one third of uterine blood flow at days 120-143 of pregnancy, but causes no significant change in umbilical blood flow. In contrast to the effects of constricting the uterine artery to reduce blood flow to a similar degree, placental oxygen consumption was reduced and that, together with a large increase in lactate production, indicated the placenta became hypoxic. The fetal blood gas status and hence oxygen consumption was not affected significantly. A consistent arterio-venous difference for glucose across the umbilical or uterine circulations was not detected unless the uterine blood flow was comparatively high. Glucose balance across the uterus showed a close linear relationship with uterine blood flow and more particularly with the supply of glucose to the uterus. There was clear evidence for glucose uptake by the placenta and fetus and also glucose output by both. The latter was more common when uterine blood flow was comparatively low or reduced by adrenaline infusion. The results are consistent with the concept that glucose supply has to be maintained to the placenta even at the expense of fetal stores, although lactate can substitute if there is enhanced output because of fetal hypoxia. They indicate that placental mobilisation of glycogen can lead to a net output of glucose to the mother. The manner of communicating to the fetus changes in placental state that occur during maternal adrenaline infusion is not clear. However towards the end of the 60 min infusion, elevation of fetal plasma adrenaline, probably resulting from a breakdown of the placental permeability barrier, may be an important signal.     

Low iron diet and parenteral cadmium exposure in pregnant rats: the effects on trace elements and fetal viability

The effects of latent iron deficiency combined with parenteral subchronic or acute cadmium exposure during pregnancy on maternal and fetal tissue distribution of cadmium, iron and zinc, and on fetal viability were evaluated. Timed-pregnant Sprague-Dawley rats were fed on semisynthetic test diets with either high iron (240 mg kg) or low iron (10 mg kg), and concomitantly exposed to 0, 3 or 5 mg cadmium (as anhydrous CdCl₂) per kilogram body weight. Animals were exposed to cadmium from gestation day 1 through 19 by subcutaneously implanted mini pumps (Subchronic exposure) or on gestation day 15 by a single subcutaneous injection (Acute exposure). All rats were killed on gestation day 19. Blood samples, selected organs and fetuses were removed and prepared for element analyses by atomic absorption spectrometry. Low iron diet caused decreases in maternal body weight, maternal and fetal liver weights, placental weights and tissue iron concentrations. By cadmium exposure, both subchronic and acute, tissue cadmium concentrations were increased and the increase was dose-related, maternal liver and kidney zinc concentrations were increased, and fetal zinc concentration was decreased. Cadmium concentration in maternal liver was additionally increased by low iron diet. Acute cadmium exposure caused lower maternal body and organ weights, high fetal mortality, and decreased fetal weights of survivors. In conclusion, parenteral cadmium exposure during pregnancy causes perturbations in essential elements in maternal and fetal compartments. Acute cadmium exposure in the last trimester of gestation poses a risk for fetal viability especially when combined with low iron in maternal diet.     

Placental compliance during fetal extracorporeal circulation.

The fetus requires large amounts of volume when weaning from cardiac bypass. This suggests that placental vasculature can act as a large capacitor in the fetal circulation. To assess placental compliance of fetal lambs, seven isolated in situ lamb placentas were placed on extracorporeal circulation. Umbilical artery blood flow was varied from 0 to 350 ml. min(-1). kg fetal wt(-1). Because the extracorporeal circuit is a closed system, volume changes in the placenta induced by umbilical artery pressure changes were measured from reciprocal volume changes in the reservoir. There was a wide range of change in absolute volume of blood within the fetal placental compartment (216.4 +/- 29.3 ml). Placental compliance was linear over the entire range of pressure changes exerted on the placental vasculature (r(2) = 0.83, P = 0.0001). This indicates that the placenta is a unique and sensitive capacitor in the fetal circulation. This information is important clinically because it establishes that aggressive resuscitation of the fetus using volume may be necessary when weaning the fetus from cardiac bypass.     

Uterine blood flow, oxygen and glucose uptakes at mid-gestation in the sheep

In early ovine fetal development, the placenta grows more rapidly than the fetus so that at mid-gestation the aggregate weight of placental cotyledons exceeds fetal weight. The purpose of this study was to compare two separate methods of measuring uterine blood flow and glucose and oxygen uptakes in seven mid-gestation ewes, each carrying a single fetus. Uterine blood flow to both uterine horns was measured by microsphere and by tritiated water steady-state diffusion methodology. Calculations of tritiated water blood flows and oxygen and glucose uptakes were based on measurements of arteriovenous concentration differences across each uterine horn. The distribution of blood flow and oxygen uptake between the two uterine horns was strongly correlated with placental mass distribution. The two methods gave comparable results for uterine blood flow (457 +/- 35 vs 476 +/- 35 ml/min), oxygen uptake (457 +/- 35 vs 476 +/- 35 mumol/min), and glucose uptake (63 +/- 8 vs 64 +/- 6 mumol/min). Uterine blood flow was approximately 38% of the late gestation value and 56.1 +/- 1 times higher than umbilical blood flow. Uteroplacental oxygen consumption was about 58% of late gestation measurements and 3.9 +/- 0.5 times higher than fetal oxygen uptake. We confirm that the large placental mass of mid-gestation is associated with high levels of maternal placental blood flow and placental oxidative metabolism.     

Time-dependent physiological regulation of ovine placental GLUT-3 glucose transporter protein

We immunolocalized the GLUT-3 glucose transporter isoform versus GLUT-1 in the late-gestation epitheliochorial ovine placenta, and we examined the effect of chronic maternal hyperglycemia and hypoglycemia on placental GLUT-3 concentrations. GLUT-3 was limited to the apical surface of the trophoectoderm, whereas GLUT-1 was on the basolateral and apical surfaces of this cell layer and in the epithelial cells lining the placental uterine glands. GLUT-3 concentrations declined at 17-20 days of chronic hyperglycemia (P < 0.05), associated with increased uterine and uteroplacental net glucose uptake rate, but a normal fetal glucose uptake rate was observed. Chronic hypoglycemia did not change GLUT-3 concentrations, although uterine, uteroplacental, and fetal net glucose uptake rates were decreased. Thus maternal hyperglycemia causes a time-dependent decline in the entire placental glucose transporter pool (GLUT-1 and GLUT-3). In contrast, maternal hypoglycemia decreases GLUT-1 but not GLUT-3, resulting in a relatively increased GLUT-3 contribution to the placental glucose transporter pool, which could maintain glucose delivery to the placenta relative to the fetus when maternal glucose is low.     

Regional blood flow distribution in fetal sheep with intrauterine growth retardation produced by decreased umbilical placental perfusion

To determine the capacity of the fetus to adapt to chronic O2 deficiency produced by decreased placental perfusion in the early development of growth retardation, we embolized the umbilical placental vascular bed of fetal sheep for a period of 9 days. Fetal umbilical placental embolization decreased arterial O2 content by 39%, decreased total placental blood flow by 33%, and produced a 20% reduction in mean fetal body weight. Neither the combined ventricular output nor the regional blood flow distribution was significantly different between the 8 growth-retarded and 7 normally grown fetuses despite the 39% decrease in fetal arterial O2 content. Thus a 33% reduction in total placental blood flow restricts normal fetal growth, but does not exceed the placental circulatory reserve capacity necessary to maintain normal basal metabolic oxygenation. Because the proportion of combined ventricular output to the placenta at rest is decreased in late IUGR fetuses but not in early IUGR fetuses, despite chronic oxygen deficiency, we conclude that the growth retarded fetus maintains a normal regional blood flow distribution until the placental circulatory reserve capacity is depleted.     

Cadmium-induced mRNA expression of Hsp32 is augmented in metallothionein-I and -II knock-out mice

Cadmium is toxic and carcinogenic to humans and animals. The testis and lung are the target organs for cadmium carcinogenesis. Heat shock proteins (HSPs) as well as metallothionein (MT) and glutathione (GSH) play an important role in protection against its toxicity. HSP32, also known as heme oxygenase-1, is a 32-kDa protein induced by heme, heavy metals, oxidative stresses, and heat. We investigated expression of the Hsp32 gene of various organs (the liver, lung, heart, stomach, kidney, and testis) in transgenic mice deficient in the MT-I and -II genes (MT-KO) and in control mice (MT-W) after an injection of cadmium chloride (CdCl2). Survival of MT-W mice after a subcutaneously injection of CdCl2 was higher than that of MT-KO mice, while no significant difference was observed in the level of GSH in each organ between MT-W and MT-KO mice. Northern blot analysis showed that the MT-I mRNA was more extensively induced in the liver, kidney, and heart than other organs 6 h after an injection of CdCl2 (30 micromol/kg body wt, sc). There was little increase of the MT-I mRNA in the testis when induced by CdCl2. Expression of the Hsp32 gene in the liver and kidney in response to CdCl2 was more extensively augmented in MT-KO mice than in MT-W mice. In the lung and testis, there was little induction and no augmentation in expression of the Hsp32 gene induced by CdCl2 in both MT-W and MT-KO mice. In the stomach, there was little induction of the Hsp32 mRNA in MT-W mice, but was increased in MT-KO mice. Immunohistochemical staining revealed that the HSP32 protein was strongly expressed in the kidney and liver of MT-W mice 24 h after an injection of CdCl2 (20 micromol/kg body wt, sc), while the expression of HSP32 protein was not increased in the testis. In metabolically active organs such as the liver and kidney, expression of the Hsp32 gene as well as the MT-I gene was extensively induced by cadmium in MT-W mice, and more eminently induced in MT-KO mice. We suggest that organs of low stress response to cadmium such as the testis and lung may be vulnerable target sites for cadmium toxicity and carcinogenesis.     

A theoretical analysis of the effect of placental metabolism on fetal oxygenation under conditions of limited oxygen availability.

The purpose of this theoretical paper is to examine the effects of placental metabolism on fetal oxygenation under conditions of limited oxygen availability. Features of the mathematical model used here include: (1) ordinary non-linear differential equations defining the oxygen partial pressure profiles in the maternal and fetal streams for a concurrent flow pattern; (2) the presence of maternal and fetal blood flow shunts; (3) consumption of oxygen by a metabolically active placenta; and (4) modification of the fetal input to the placenta by changing the rate of fetal oxygen consumption in response to changes in the rate of oxygen delivered to the fetus via the umbilical vein. Model parameters were chosen to be well within the range of values cited in the literature. Based on these calculations, we conclude that: (1) under normal conditions, approximately one-half of the fetal uterine-umbilical venous oxygen partial pressure difference can be attributed to placental oxygen consumption; (2) utilization of fetal oxygen to help maintain the metabolic activities of the placenta does not significantly impair fetal oxygenation under normal conditions; (3) consumption of oxygen by the placenta will have a significant detrimental effect on the rate of oxygen delivered to the fetus if oxygen availability is compromised; and (4) for the same rate of maternal oxygen delivered to the placenta, maternal hypoxemia has a significantly greater adverse effect on fetal oxygenation than does maternal anemia.     

The effect of zinc levels in fetal circulation on zinc clearance across the in situ perfused guinea pig placenta

Although zinc is essential for normal fetal growth and development, little is known about factors that influence its transfer across the placenta. The in situ perfused guinea pig placenta model was used to study the influence of the zinc concentration of fetal circulation on maternofetal placental zinc transfer. A placenta of the anaesthetized sow was perfused (on the fetal side) with a physiological perfusate via the umbilical vessels, with the fetus excluded. The sow was infused intravenously with 65zinc as a tracer of placental Zn clearance, and with antipyrine as an indirect indicator of maternal placental blood flow. Maternal plasma and placental effluent samples collected at intervals were counted for 65zinc by gamma counter, and the absorbance of nitrosated antipyrine was measured at 350 nm. Varying the mean zinc concentration in the perfusate from 0.176 to 1.87 mg/L had no effect on relative zinc clearance calculated as zinc clearance/antipyrine clearance (mean +/- SEM; 0.085 +/- 0.010 vs. 0.114 +/- 0.018; n = 6; p greater than 0.05). The results suggest that short-term changes in fetal zinc status do not influence placental zinc transfer.     

Fetal metabolism and placental transfer of vasoactive intestinal peptide in sheep

Vasoactive Intestinal Peptide (VIP) is a 28-amino-acid putative neurotransmitter that may have a role in the regulation of myometrial blood flow and uterine contractility. The chronically cannulated fetal sheep preparation was used to examine the fetal clearance and placental transfer of VIP. Metabolic Clearance Rate (MCR) and placental transfer of VIP were measured by alternate steady-state infusion of VIP into the mother and fetus. Plasma concentrations of VIP were measured by radioimmunoassay. MCR was similar in the pregnant (45 +/- 10 ml/kg/min) and nonpregnant ewes (35 +/- 5 ml/kg/min). However, compared to both pregnant and nonpregnant ewes, fetal MCR was significantly increased at 77 +/- 15 ml/kg/min, indicating highly developed clearance mechanisms in the fetus. VIP did not cross the placenta in either direction. Both the placenta and fetal liver metabolized VIP and contributed to the elevated fetal clearance of VIP. The results show that VIP in fetal tissue is unlikely to influence maternal uterine activity with any VIP-mediated effects emanating from maternal and/or placental sources.     

Drugs of abuse and human placenta

Drugs of abuse such as cocaine and amphetamines, when used by pregnant women, exert deleterious effects on the fetus. These drugs produce their effects through inhibition of the serotonin transporter, norepinephrine transporter, and dopamine transporter. The inhibition can occur in the pregnant mother as well as in the fetus. These events contribute to the detrimental effects of these drugs on the fetus. However, the role of placenta, which serves as the link between the pregnant mother and the fetus, in the process remains understudied. It has been assumed that the placenta did not play any direct role in the process except that it allowed the passage of these drugs from maternal circulation into fetal circulation. This was before the discovery that the placenta expresses two of the three monoamine transporters. The serotonin transporter and the norepinephrine transporter are expressed on the maternal-facing side of the syncytiotrophoblast, thus exposed to the inhibitory actions of cocaine and amphetamines if present in maternal blood. Inhibition of these transporters in the placenta could lead to elevation of serotonin and norepinephrine in the intervillous space that may cause uterine contraction and vasoconstriction, resulting in premature delivery, decreased placental blood flow, and intrauterine growth retardation. Thus, the placenta is actually a direct target for these abusable drugs. Since the placental serotonin transporter and norepinephrine transporter are also inhibited by many antidepressants, therapeutic use of these drugs in pregnant women may have similar detrimental effects on placental function and fetal growth and development.     

Transfer of antibodies directed to paternal major histocompatibility class I antigens from pregnant mice to the developing fetus

The placental transmission of antibodies directed toward paternal MHC Class I antigens to the developing fetus was studied to assess their effect on the expression of MHC antigens during fetal development and on the development of immune function. 125I-monoclonal anti-paternal MHC antibodies injected i.v. into pregnant mice on day 15 of gestation were efficiently transferred to the fetus within 24 hr in a dose-dependent manner. Biochemical studies on the transferred radioactivity showed that intact antibodies accumulated in the fetus for up to 3 days after antibody injection. During the same period, antibodies were eliminated from the maternal system. The transfer and accumulation of anti-MHC antibodies were independent of the MHC haplotype of the fetus. The pathway of antibody transfer and the localization of transmitted antibodies in the fetus were studied by autoradiographic analysis of the entire fetoplacental unit 24 hr after the injection of anti-paternal MHC antibodies. Our results indicate that antibodies are transferred by way of the placenta and yolk sac, and reach the fetus predominantly via the circulation. Within the embryo proper, the highest levels of antibody were found in the order of blood greater than thymus greater than fetal liver. Most other fetal organs, with the exception of brain and cartilage, showed antibody accumulation, but to a lesser extent. This pattern of antibody distribution over different tissues was similar for allogeneic and syngeneic fetuses. These findings demonstrate that various fetal tissues, including developing lymphoid cells can be directly exposed to the maternally transmitted anti-MHC antibodies, with possible functional consequences on the development of the fetal immune system.     

The fetal phenotype of the 18p-syndrome. Report of a male fetus at twenty-one weeks

Morphological and cytogenetic findings in a male fetus at 21 weeks gestation after prenatally detected monosomy 18p are reported. The fetus displayed dysmorphic features resembling the 18p-syndrome, such as decreased head circumference, slightly receding forehead, hypertelorism, epicanthus, horizontal palpebral fissures, depressed nasal bridge, long philtrum, carp mouth, irregular crenated maxillar alveolar ridge, retrognathia, lowset dysplastic ears with posterior rotation, edema of neck, hands and feet respectively, fingers with drop-shaped tips, short first toes with dysplastic nails, hypoplastic male external genitalia. After termination of the pregnancy, biopsies from different fetal organs as well as from the placenta were taken and set up for long term cell cultures. The metaphases of fetal organs all showed the karyotype 46,XY,18p-. A fetal blood culture failed to grow. Unexpectedly, the metaphases of the placenta showed the mosaic karyotype 46,XY/46,XY,18p-/46,XY,18p+.     

Restriction of placental growth in sheep enhances placental metabolism of fetal beta-endorphin-like immunoreactivity

The opioid polypeptide beta-endorphin is present in fetal blood but it is not clear whether its source is the fetus or the placenta. We therefore measured beta-endorphin in extracts of fetal femoral arterial and umbilical venous blood plasma in sheep by radioimmunoassay to determine whether the fetus or the placenta is the major source of beta-endorphin in the fetal circulation. Chromatographic analysis of extracts of fetal arterial plasma showed that beta-lipotropin and other precursors of beta-endorphin made only a minor contribution to the immunoreactivity detected. Concentrations of immunoreactive beta-endorphin were higher in the femoral artery than in the umbilical vein in fetal sheep between 113 and 128 days of pregnancy. Therefore the placenta removes beta-endorphin or a closely related polypeptide of fetal origin from the umbilical circulation in sheep at this stage of gestation. Acute hypoxaemia and hypoglycaemia increase the concentrations of immunoassayable beta-endorphin in blood plasma of adult and fetal sheep, but little is known about the effects of chronic hypoxaemia or hypoglycaemia on the circulating levels of beta-endorphin and related polypeptides in the fetus. Therefore we also measured immunoreactive beta-endorphin in blood plasma from fetal sheep in which growth retardation in association with restricted placental growth was produced by removal of endometrial caruncles before mating. Intra-uterine growth retardation was accompanied by chronic hypoglycaemia and chronic hypoxaemia in the fetuses. This was not associated with higher concentrations of beta-endorphin-like immunoreactivity in fetal arterial or umbilical venous plasma, but was accompanied by significantly increased placental extraction of fetal immunoreactive beta-endorphin from the umbilical circulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Computer model of fetal-maternal heat exchange in sheep

We constructed and used a mathematical model of maternal-fetal heat exchange in the sheep to explore the effects of changes in certain parameters on steady-state fetal temperatures and to determine whether the fetus in the model has any potential to control its own temperature. The model took into account both fetal and placental heat production and exchange of heat in the placenta, across the fetal skin, via amniotic fluid, and through the uterine wall. The maternal ewe was assumed to be a constant temperature heat sink. Changes in placental or fetal heat production were calculated to change the ratio of heat exiting across the placenta or fetal skin significantly but to have little effect on fetal core temperature, e.g., a rise of only 0.8 degrees C was predicted after a twofold increase in fetal heat production. Fetal placental blood flow was calculated to affect fetal temperature the most of any flow, a reduction to zero causing fetal temperature to rise 5.0 degrees C. Changes in heat conductances between fetal skin and amniotic fluid, or between amniotic fluid and uterine wall, had minimal effect on fetal temperature. From the model calculations here and because heat exchange within the sheep placenta has previously been calculated to be extremely efficient, we conclude that the fetal sheep has little ability to control its temperature by changes in heat dissipated through extraplacental pathways. Thus the model predicts an effective heat clamp that closely links fetal to maternal temperature.     

Interaction of cadmium and zinc during prenatal development in the rat

Cadmium chloride, zinc chloride, or a mixture of the two, labeled with 115m-Cd or 65-Zn was administered intraperitoneally to Wistar rats on day 9 of gestation. On day 20 fetuses of Cd-treated rats exhibited malformations, but those of rats given zinc or zinc plus cadmium did not. No radioactive cadmium was recovered in the fetuses or fetal membranes, although some was found in the placentas. Simultaneous administration of zinc did not alter the distribution of cadmium, but cadmium significantly increased the amount of zinc in the fetus and placenta. In a second experiment, cadmium or cadmium plus zinc was administered on day 9 of gestation and embryonic units were removed on days 10, 11, and 12. On day 10 cadmium was found in the embryonic unit and maternal uterus, and cadmium in both was significantly reduced by simultaneous administration of zinc. The cadmium concentration in uterus and embryonic units decreased sharply on day 11 and 12 and by day 12 did not differ in animals treated with cadmium or with cadmium plus zinc. It is concluded that cadmium reaches the placenta or embryo at an organogenetically sensitive time, and that zinc may protect the embryo by decreasing the exposure to cadmium this time.     

The effects of prostacyclin and thromboxane analogue (U46619) on the fetal circulation and umbilical flow velocity waveforms

In placental insufficiency and pre-eclampsia the relative production rates of prostacyclin and thromboxane by the placenta and umbilical vessels are altered and the Doppler umbilical flow velocity waveform shows a high resistance pattern. To investigate the control of umbilical placental blood flow by those eicosanoids either prostacyclin (10 micrograms/min), or the thromboxane analogue U46619 (10 ng/min) was infused into the distal aorta of 12 chronically catheterized fetal lambs at day 125. Thromboxane produced a rise in mean arterial pressure and a rise in the systolic diastolic ratio of the umbilical artery flow waveform (2.6 to 3.1; P less than 0.05). Umbilical blood flow did not change and there was no evidence of altered flow to other organs. Prostacyclin caused a fall in fetal mean arterial pressure and a decrease in the umbilical artery systolic diastolic ratio (2.9 to 2.4; P less than 0.05). Prostacyclin produced a three-fold increase in lung perfusion (and the onset of fetal breathing movements) and this was associated with a 90% reduction in muscle blood flow (hindlimb muscle flow reduced from 12.5 to 1.1 ml.min-1 100g-1; P less than 0.01). We conclude that the local release of thromboxane in the fetal placental vascular bed could account for the rise in systolic diastolic ratio seen in umbilical placental insufficiency.     

In situ hybridization for the detection of human parvovirus B19 nucleic acid sequences in paraffin-embedded specimens

Parvovirus infection of pregnant women leading to a transplacentar infection of the fetus may result in hydrops fetalis, and ultimately in intrauterine death of the fetus. In situ hybridization with a biotinylated as well as with a 35S-labeled probe for human parvovirus B19 was performed on formalin-fixed paraffin-embedded (FFPE) tissue from a fetus suffering from non-immunologic hydrops fetalis. Histology was suggestive of viral infection probably with human parvovirus. Parvovirus DNA could be detected and precisely localized mainly in the nuclei of erythroid precursors cells within fetal blood vessels of all organs examined. There was no detection of B19 nucleic acid in parenchymal cells of the placenta or the fetal organs, nor within maternal blood cells. These findings are in agreement with the well-known properties of animal parvoviruses to replicate exclusively in proliferating cells. Taking into consideration the problems in diagnosing human parvovirus infection by light microscopy, we conclude that in situ hybridization with an appropriate non-radioactive probe is a valuable, rapid and safe complementary detection method for the diagnosis and study of human parvovirus infections. The 35S-labeled probe is more sensitive than the biotinylated probe, but has the disadvantages of lower resolution of the signal, longer duration of the assay, the hazard of radioactivity and the shorter shelf-life of the probe.