Placental transport of chromium.

Since trivalent chromium (Cr+3) transport into certain tissues is rapid, the placental transport of injected high specific activity 51Cr+3 was studied in pregnant rats at days 17-20 of gestation. Three days after the intravenous injection of 51Cr+3, body retention of 51Cr was similar in pregnant and nonpregnant rats, but in the pregnant rats placentofetal uptake of 51Cr accounted for 25-30% of the 51Cr retention. The mean 51Cr content per placentofetal unit was 0.89 +/? 0.03% injected dose. Serum and tissue 51Cr contents per milliliter or gram in the pregnant rats were decreased by 50-80% except in uterus, which was unchanged. Tissue/serum 51Cr ratios were increased by 70-300% in the pregnant rats compared to the nonpregnant controls. These results indicate that the placentofetal unit is capable of extracting large amounts of Cr from the mother, and support the suggestion that maternal Cr is depleted during pregnancy. The data also suggest that body tissues may defend their Cr stores against Cr depletion by adaptive cellular Cr transport mechanisms.     

Placental transport function

Placental transport provides a means of supplying nutrients to and removing metabolites from the fetus. Transport is based on substrate exchange and net flux from mother to fetus or vice versa and can be a result of a concentration difference or of unidirectional carrier-mediated transport. Blood flow regulates delivery to and removal from the area of placental exchange, and rapidly crossing compounds are dependent on blood flow for their rate of passage. There are substantial species differences in terms of flow rates normalized for fetal weight and also in terms of vascular arrangement. The barrier can be overcome via paracellular water-filled channels or via a transcellular route. Hydrophilic molecules that are not actively transported diffuse through paracellular channels, and the placentae of rodents and primates are much more permeable than the placenta of the sheep. Many different substrates such as glucose, amino acids, electrolytes and vitamins are transported by carrier systems. Transport proteins are located in the microvillous and basal membranes of the trophoblast. Asymmetry in the kinetics of binding results in differences in influx and efflux at the interface with maternal and fetal blood, allowing directional net flux across the placenta. Immunoglobulins are believed to cross by receptor-mediated endocytosis.     

Placental transport of immunoglobulin G

Maternal antibodies transported across the placenta protect the newborn. Maternal immunoglobulin G (IgG) concentrations in fetal blood increase from early in the second trimester through term, most antibodies being acquired during the third trimester. IgG1 is the most efficiently transported subclass and IgG2 the least. Transfer across the syncytiotrophoblast of the chorionic villi is mediated by the neonatal Fc receptor, FcRn. Immune complexes are absorbed in the stroma of the villi, probably by FcgammaRI, FcgammaRII, and FcgammaRIII on placental macrophages. The mechanism of IgG transport across the endothelium of fetal capillaries is not understood. Endothelial cells in terminal villi express FcgammaRIIb. However, it is not known whether this receptor transports IgG or prevents transport of immune complexes to the fetus.     

Placental transport: a function of permeability and perfusion

Studies in ovine fetus and placenta have pointed to an interaction between the fetal liver and the placenta. The supply of amino acids and carbohydrates depends on this interaction. These studies have led to clinical studies in normal and high-risk pregnancies. The objective of the present review was to compare changes in fetal circulation, in terms of both velocimetry and actual blood flow measurements, and to couple such data with data on the placental transport of amino acids. Flow studies were carried out on the umbilical vein with measurements of time-averaged velocity and venous diameter. A similar approach was used for measurements of ductus venosus flow. Stable-isotope-labeled amino acids were used to study placental transport by the non-steady state approach. The studies of flow showed a marked reduction in umbilical blood flow even when expressed per kilogram fetal body weight in fetal-growth-restricted pregnancies. This may be coupled with an increased ductus venosus shunt, the combination leading to a marked reduction in fetal hepatic blood flow. The placental transport of some amino acids is reduced in fetal-growth-restricted pregnancies. Furthermore, nonglucose carbohydrates and polyols are found in fetal blood, some in concentrations higher than maternal concentrations. There is significant uptake of several polyols and of mannose across the umbilical circulation in normal pregnancies. In conclusion, both perfusion and permeability can now be studied in both normal and high-risk pregnancies.     

Placental transport of retinol in ewes fed high intakes of vitamin A

Twelve ewes were fed retinyl propionate equivalent to 12,000 micrograms retinol/kg body weight per day for the last two trimesters of pregnancy (group fed high vitamin A). Four ewes received a control level of 120 micrograms/kg body weight per day. Indwelling catheters were implanted surgically in fetal jugular veins and carotid arteries. Ewes or fetal lambs received [3H]retinol intravenously, and blood was sampled until parturition. The ewes fed large amounts of vitamin A maintained viable fetal lambs for 6 d less than did controls. Plasma retinyl ester concentrations were elevated in the ewes fed a high level of vitamin A but not in their fetal lambs. Rates of plasma retinol transport and clearance increased with vitamin A intake in ewes and their fetal lambs. Efficiency of placental retinol transport in the group fed high levels of vitamin A was less than one-quarter that for controls. However, placental transport rate was approximately 100 micrograms/d greater than that of controls with an equivalent amount retained by the fetoplacental unit in the group fed high vitamin A. These data indicate that placental transport of retinol is partially regulated. High maternal vitamin A intake results in high retinol transport to the fetus.     

Placental biopsy

There is increasing patient demand for placental biopsy, principally for karyotyping because it enables termination of pregnancy in the first trimester if an abnormality is detected. Precise risks in terms of fetal loss rates due to the procedure have not been clearly established. Over 41,000 biopsies have been performed worldwide, with an average fetal loss rate of 3.54%.     

凶险型前置胎盘中胎盘主体附着位置对母体预后的影响

目的 探讨凶险型前置胎盘中胎盘主体附着位置对母体预后的影响.方法 选取2011年9月至2012年8月于成都市妇女儿童中心医院行剖宫产时诊断为凶险型前置胎盘的13例患者的临床病历资料为研究对象.按照胎盘主体附着位置的不同,将其分为前壁组（n=9,胎盘主体附着于子宫前壁）和后壁组（n=4,胎盘主体附着于子宫侧壁及后壁）.13例受试者的年龄为20-42岁,孕龄为34＋1-37＋6孕周,距前次剖宫产时间为3-14年.两组患者的年龄、孕龄等一般资料比较,差异无统计学意义（P〉0.05）（本研究遵循的程序符合成都市妇女儿童中心医院人体试验委员会制定的伦理学标准,得到该委员会批准,分组征得受试对象的知情同意,并与之签署临床研究知情同意书）.两组患者术前均经彩色多普勒超声、MRI提示为瘢痕子宫、完全性前置胎盘伴不同程度胎盘植入,并于剖宫产分娩时确诊.对两组患者剖宫产术中出血量、子宫切除率及术后并发症发生率的情况进行统计学分析.结果 前壁组术中出血量（850-7 055 mL）较后壁组多（350-1 200 mL）,且差异有统计学意义（P〈0.01）.前壁组患者中,全子宫切除率为55.56%（5/9）,后壁组为25.00%（1/4）;后壁组中术后无一例发生并发症.结论 胎盘主体附着于子宫前壁（跨越前次手术瘢痕处）的中央型前置胎盘,若术前经彩色多普勒超声及MRI提示胎盘主体位于子宫前壁,完全覆盖宫颈内口,并伴有前壁下段及瘢痕处植入者,为实际意义上的凶险型前置胎盘,可导致严重产后出血的发生.     

PEDF对胎盘位置附着异常中异常胎盘微血管床形成的研究

目的探讨色素上皮衍生因子(PEDF)对胎盘位置附着异常中胎盘微血管床形成的影响。方法选择2014年6月至2015年8月我院剖宫产分娩的孕妇48例,其中胎盘植入(PA组)16例,前置胎盘(PP组)16例,对照组16例。胎盘进行病理学检查,免疫组化检测三组胎盘组织的MVD;RT-PCR及Western Blot检测胎盘组织中PEDF和VEGF的m RNA和蛋白质表达。结果①三组胎盘组织中PEDF及VEGF蛋白含量、PEDF及VEGF m RNA含量及MVD比较,差异均有统计学意义(P<0.05)。②胎盘中PEDF与VEGF、MVD均呈负相关关系(r=-0.778,P=0.000;r=-0.827,P=0.000)。③胎盘血管情况:PA组绒毛血管数量丰富,管径粗大,侵及肌壁间血管;PP组绒毛间血管增生程度有所减轻,未侵及肌层;对照组则无上述变化。结论①胎盘位置异常组中胎盘的PEDF表达过低是导致VEGF负性调节不足以及胎盘病理性血管形成的原因,参与了胎盘位置异常的发生。②三组胎盘中PEDF含量均有显著差异,提示PEDF含量可以反映异常胎盘血管的侵袭程度。     

胎盘灌流模型及其在胎盘物质转运研究中的应用

妊娠期妇女接受药物治疗的广泛性,使得妊娠期用药安全性问题成为学者们关注的焦点。妊娠期用药对妊娠结局的影响,除可导致流产外,药物还可透过胎盘屏障造成胎儿宫内暴露,影响胎儿,导致胎儿畸形甚至死亡。而胎儿风险评估中一个关键性的因素是胎儿的药物暴露量,即药物经胎盘转运的程度,因此,胎盘物质转运研究对于指导妊娠期安全用药具有重要意义。胎盘灌流模型在理论上被认为是最好的模拟胎盘物质转运的模型,其不仅避免了种属差异,也不存在伦理学问题,已成为国际上公认的研究胎盘物质转运的经典方法。详细介绍胎盘灌流模型的起源和发展、建立与鉴定,以及该模型在常用药物和纳米材料胎盘物质转运研究中的应用。然而,由于胎盘灌流模型制备过程比较复杂且存在一些缺陷和不足,因此,还需探索新的研究胎盘物质转运的体外模型,更好地指导妊娠期安全用药。     

Estriol and Placental Function

Providing a guide to placental adequacy and fetal weight, measurements of urinary estriol excretion in the last trimester can be of great assistance to the physician who must decide whether to interrupt a complicated pregnancy or permit it to continue with the goal of achieving greater fetal maturity. A plea is made for the more widespread use of this valuable tool in a variety of situations.     

胎盘血管瘤临床分析

目的:探讨胎盘血管瘤的临床特点和处理方法。方法:对我院收治的7例胎盘血管瘤患者的临床资料进行回顾性分析。结果:在7例胎盘血管瘤患者中,6例临床诊断为胎盘血管瘤,1例误诊为胎盘早剥血肿;7例患者中,2例发生早产,1例合并羊水过多,1例新生儿轻度窒息;胎盘病理大体观检查,肿瘤大小2cm×2cm×1cm至5cm×5cm×4cm;7例患者肿瘤均为单个;6例肿瘤颜色为暗红色,1例部分暗红色、部分灰白色。7例患者中,3例阴道分娩,4例剖宫产。结论:胎盘血管瘤可引起早产、羊水过多、新生儿窒息等并发症;胎盘血管瘤在产前不易确诊,彩色多普勒超声是产前诊断胎盘血管瘤的唯一辅助手段。孕期和产程中发现胎心异常时应想到脐带和胎盘的病变,给予及时处理,适时终止妊娠。     

Placental characteristics and birthweight

Standard gross placental measures capture dimensions relevant to specific placental functions. Our objective was to determine their accountability independent of placental weight for variance in birthweight, an important proxy for intrauterine 'adequacy' in fetal origins studies. The sample consisted of 24 152 singleton liveborn children of the Collaborative Perinatal Project delivered from 34 to 42 completed weeks gestation, with complete data for six placental measures (placental disc shape, umbilical cord length, distance from cord insertion to nearest margin, large diameter, small diameter, placental thickness) and placental weight. Associations between birthweight and placental measures were examined using multiple linear regression. Placental weight alone accounted for 36.6% of birthweight variation; the six other placental measures accounted for 28.1%. Combined, all placental measures accounted for 39.1% of birthweight variation. Seven maternal characteristics (age, height, weight, parity, socio-economic status, cigarette use, and race) were investigated to determine whether their known associations with birthweight were mediated by placental markers. Analysis suggested that the impact of all maternal characteristics except smoking was consistent with mediation by placental characteristics.