PHosphate metabolism and foetal growth in the rat. I. Net transfer of 31P and 32P phosphate from the maternal plasma to the normal placenta

Net transfer of 31P and 32P inorganic phosphate form the maternal plasma to the rat chorio-allantoic placenta has been studied after intraperitoneal injection of [32P] ortho-phosphate in primigravid females at the 12th day or late stages of gestation. The concentration and label uptake per unit weight of placenta of the inorganic phosphate (Pi), organic-bound acid-soluble phosphate (POAS) and organic-bound acid-insoluble phosphate (POAIS) fractions are negatively correlated with increasing placental weight, whereas their specific activities are independent of placental weight. The amount and label uptake per whole placenta of the Pi, POAS and POAIS fractions are positively correlated with increasing placental weight. The placental concentrations of inorganic phosphate and calcium are positively related without, however, any marked accumulation of calcium. The growing placenta is thus shown to reduce progressively, on a unit weight basis, both the inorganic phosphate uptake from the maternal plasma and its further incorporation into organic-bound fractions. There is no evidence of a control by the foetal weight, acting per se, on these placental activities.     

Mercury in human maternal and cord blood, placenta, and milk.

Total mercury concentration was measured by atomic absorption spectrophotometry in 100 maternal-umbilical cord blood pairs, 39 placentae, and 32 breast milk samples, all from patients at the University of Iowa Hospitals. The mean maternal and cord blood levels were 1.01 and 1.24 parts per billion (ppb), respectively. Though the difference between maternal and cord values was not statistically significant, the two were significantly correlated with each other, and maternal blood level increased significantly with maternal age. Mean placental and milk concentrations were 2.28 and 0.93 ppb, respectively. The mercury levels in this study were lower than those reported from elsewhere, probably reflecting a combination of methodological refinement and relatively low mercury exposure in a rural population whose diet is low in fish consumption. These low levels suggest that the risk of perinatal mercury damage is small in such a population.     

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.     

Phosphate metabolism and foetal growth in the rat. III. Net transfer of 31P and 32P inorganic phosphate from the maternal plasma to the placenta after foetectomy

In primigravid rat females at the 12th day or later stages of gestation one foetus is surgically removed and the amniotic sac allowed to retract freely around the remaining placenta in situ. One hour to 10 days after foetectomy [32P]ortho-phosphate is injected intraperitoneally. The post-foetectomy placenta and matched normal placenta and foetus in the contralateral horn are taken after labelling periods of one or three hours and analysed for calcium, inorganic phosphate, organic-bound acid-soluble and organic-bound acid-insoluble phosphates in their [31P] and [32P] forms. The acutely foetectomized placenta--up to 24 hours after surgery--may serve as an appropriate model of the physiologically functioning syncytiotrophoblast: it is indeed noteworthy that organic-bound phosphate placental concentrations and labelling are little affected in the early post-foetectomy stages. On the other hand the placental inorganic phosphate concentration and labelling are profoundly affected by foetectomy. A surplus radioactive incorporation in the Pi fraction is observed which is strongly related to the weight of the control foetus and may represent up to twelve times the label incorporation in the control placenta; it decreases as the time interval since foetectomy lengthens. A cumulative increase in Pi concentration is observed which is strongly related to calcium concentration and may reach twenty-five times the maternal plasma Pi concentration. The presence of two independent pools of Pi is suggested: one geared to the metabolic needs of the placenta itself, the other representing the Pi normally transported to the foetus under metabolic control by the latter. The possibility of an electroneutral PO4(2-)/Ca2+ co-transport is evoked.     

Distribution of PCDDs/PCDFs and Co-PCBs in human maternal blood, cord blood, placenta, milk, and adipose tissue: dioxins showing high toxic equivalency factor accumulate in the placenta

To assess levels of dioxin background contamination and transfer of dioxins from mothers to unborn children and infants, concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and coplanar-polychlorinated biphenyls (Co-PCBs) were measured in human samples from expectant and nursing mothers living in Nara, Japan. The average toxic equivalency quantities (TEQs) of PCDDs/PCDFs and Co-PCBs from circulating maternal blood, cord blood, placenta, milk taken 3-10 d after delivery, milk taken one month after delivery, and adipose tissue were 26 and 9.3, 15 and 2.3, 31 and 1.2, 16 and 5.4, 18 and 8.8, and 16 and 7.7 pg-TEQ/g-fat, respectively. Among the various PCDD/PCDF congeners, 1,2,3,7,8-PeCDD and 2,3,4,7,8-PeCDF contributed most heavily to the TEQs of all maternal samples. Among the various Co-PCB congeners, 3,3',4,4',5-PeCB (#126), 2,3,3',4,4',5-HxCB (#156), and 2,3',4,4',5-PeCB (#118) contributed most heavily to the TEQs of all maternal samples. But, the concentrations and relative percentages of congeners differed among the various samples, suggesting that congeners showing high toxic equivalency factor accumulate in the placenta.     

Phosphate metabolism and foetal growth in the rat. II. Net transfer of 31P and 32P inorganic phosphate from the maternal plasma to the normal foetus

Net transfer of 31P and 32P inorganic phosphate from the maternal plasma to the rat foetus has been studied after intraperitoneal injection of [32P] ortho-phosphate in primigravid females at the 12th day or later stages of gestation. The concentration per unit weight of foetus of the inorganic phosphate (P1) fraction increases markedly with increasing foetal weight; labelling data [inverse relationship between P1 concentration and specific activity, absence of precursor/product relationship between P1 and acid-soluble organic-bound phosphates (POAS)] show this increase to result in part from the formation of a relatively inert metabolic pool, presumably in mineralized tissue. The foetal concentrations of calcium and inorganic phosphate show a strong positive correlation, both increasing markedly with foetal weight. The progressive accumulation of calcium does not, however, account entirely for the rising concentration of inorganic phosphate. The concentration per unit weight of foetus of the POAS fraction remains stable for foetuses smaller than 2 000 mg. In heavier foetuses (greater than 2 000 mg) the POAS concentrations are, with an abrupt transition, distinctly lower, rising however slightly with increasing foetal weight. The concentration per unit weight of foetus of the acid-insoluble organic-bound phosphate (POAIS) fraction decreases slightly with increasing foetal weight. The label uptake per unit weight of foetus of both POAS and POAIS fractions is negatively correlated with increasing foetal weight. The amount and label uptake per whole foetus of the P1, POAS and POAIS fractions are positively correlated with increasing foetal weight. Phosphate transfer to the foetus increases continuously, being maximal at or near birth.