Characterization of human placental explants: morphological, biochemical and physiological studies using first and third trimester placenta

Management of other complications specific to monochorionic twin pregnancies

Monochorionic (MC) twins have a 3-10-fold higher perinatal mortality and morbidity than dichorionic twins. This is largely attributable to their common vascular architecture and the high rate of discordant fetal growth, growth restriction and congenital abnormalities. In the event of a single intrauterine death (IUD), intertwin agonal transfusion results in up to a 38% risk of death and a 46% risk of neurological injury to the co-twin. This chapter addresses the management of complications unique to MC twins. The primary aim of management is to prevent single IUD or, if inevitable, prevent agonal transfusion occurring by vascular occlusive selective feticide. Older fetoscopic techniques have been replaced by the simpler ultrasound-guided techniques of interstitial laser and bipolar cord occlusion. Their application in twin reversed-arterial perfusion sequence has been associated with a 50% reduction of perinatal mortality in the pump twin. Moreover, prophylactic interstitial laser therapy in early pregnancy might obviate the technical and clinical difficulties in the presence of fetal decompensation in later pregnancy. Recent strategies to reduce the high perinatal mortality due to cord entanglement in antenatally diagnosed monoamniotic twins including medical amnioreduction and elective caesarean delivery at 32 weeks, are also discussed.

Nitric oxide and superoxide impair human placental amino acid uptake and increase Na+ permeability: implications for fetal growth

Based on evidence that thiol and tyrosine reagents inhibit some amino acid transporters, we tested the hypothesis that NO- and O2- -derived free radicals would impair nutrient uptake by the human placenta. Syncytiotrophoblast microvillous plasma membrane vesicles (MVM) and placental villous fragments were exposed to the drug SIN-1 in the presence or absence of superoxide dismutase (SOD) and hemoglobin (Hb). The uptake of [3H]arginine, [3H]taurine, and [3H]leucine; [14C]MeAIB; and 22Na was studied in MVM, whereas the uptake of [3H]taurine was examined in villous fragments. Nitrotyrosine formation was assessed by Western blotting and quantified by ELISA. In MVM, SIN-1 caused an inhibition of [3H]arginine, [3H]taurine, and [14C]MeAIB uptake but had no significant effect on equilibrium [3H]leucine uptake. These effects were prevented by SOD or Hb, implying that both NO and O2- radicals were essential. In contrast, 22Na+ uptake was significantly increased, and this effect was prevented by SOD. In villous fragments, SIN-1 impaired Na+-dependent [3H]taurine uptake, with no effect on Na+-independent uptake. Increased nitrotyrosine formation was observed in MVM after SIN-1 treatment. Endogenous NO- and O2- -derived free radicals may alter human placental nutrient transfer in vivo, with implications for fetal growth.

Leptin stimulates the activity of the system A amino acid transporter in human placental villous fragments

The activity and expression of placental nutrient transporters are primary determinants for the supply of nutrients to the fetus, and these nutrients in turn regulate fetal growth. We developed an experimental system to assess amino acid uptake in single primary villous fragments to study hormonal regulation of the amino acid transporter system A in term human placenta. Validation of the method, using electron microscopy and studies of hormone production, indicated that fragments maintained ultrastructural and functional integrity for at least 3 h. The activity of system A was measured as the Na(+)-dependent uptake of methylaminoisobutyric acid (MeAIB), and the effect of 1 h incubation in various hormones was investigated. Uptake of MeAIB into villous fragments in the presence of Na(+) was linear up to at least 30 min. Insulin (300 ng/ml, n = 14) increased system A activity by 56% (P < 0.05). This effect was also present at insulin concentrations in the physiological range (+47% at 0.6 ng/ml, n = 10, P < 0.05). Leptin (500 ng/ml, n = 14) increased Na(+)-dependent MeAIB uptake by 37% (P < 0.05). System A activity increased in a concentration-dependent fashion in response to leptin (n = 10). However, neither epidermal GF (600 ng/ml), cortisol (340 ng/ml), nor GH (500 ng/ml) altered system A activity significantly (n = 14). We conclude that primary single isolated villous fragments can be used in studies of hormonal regulation of nutrient uptake into the syncytiotrophoblast. These data suggest that leptin regulates system A, a key amino acid transporter.

Secretion of interleukin-1beta and interleukin-6 by fragments of term human placental villi: signalling pathways and effects of tumour necrosis factor alpha and mode of delivery

The regulation of cytokine secretion has not been extensively investigated in placental tissue. Fragments of term human placenta were incubated in Tyrode's medium for 3h and cytokine concentrations were measured in the supernatant. IL-1beta secretion after vaginal delivery (VD) was (mean +/- SEM fmol/mg wet weight/3h) 0.193 +/- 0.005 (basal) and 0.549 +/- 0.18 (+1n M TNFalpha) and was more sensitive to TNFalpha dose after elective Caesarean section in the absence of clinical labour (CS) than VD. Secretion of IL-6 after VD was 2.3 +/- 0.47 (basal) and 3.01 +/- 0.34 (+1n M TNFalpha), was correlated with the secretion of IL-1beta and was more sensitive to TNFalpha dose after VD than CS. The inhibitors SB203580, PD98059, SN50, cycloheximide and D-ribofuranosylbenzimidazole each reduced the basal and TNFalpha-stimulated secretion of IL-1beta and also reduced IL-6 secretion with the exception of SN50. There were no interactions between effects of inhibitors and mode of delivery or TNFalpha. In summary we found that term placenta spontaneously secretes IL-1beta and IL-6 in vitro. Delivery after labour alters placental sensitivity to TNFalpha. Exposure to agents known to inhibit MAPK pathways, NF-kappaB, or synthesis of protein and mRNA reduces placental cytokine secretion.

The functional regeneration of syncytiotrophoblast in cultured explants of term placenta

We have investigated the functional characteristics of term human placental villous explants kept in long-term (7-11 days) culture. Fragments of placental villous tissue (approximately 5-10 mg wet wt) were cultured in supplemented CMRL-1066 culture medium for up to 11 days. After the first day of culture, the syncytiotrophoblast appeared vacuolated and eventually degenerated. However, a new syncytiotrophoblast developed by day 4, being indistinguishable from that of a fresh placenta by 11 days. Release of human chorionic gonadotrophin increased and activity of lactate dehydrogenase in culture medium decreased with culture time. Transport variables were measured over the first 7 days of culture. Basal (86)Rb efflux was reduced with time in culture and was inhibited by Ba2+, suggesting the efflux was mediated by K+ channels. At all stages of culture, (86)Rb efflux was stimulated by ATP, hyposmotic medium, and ANG II. A complex pattern of efflux changes with culture time and type of stimulator was observed, suggesting that several compartments of the tissue contributed to stimulated efflux. This culture system provides opportunities for studies of chronic regulation of placental function.