Umbilical and placental vessels: modifications of their mechanical properties in preeclampsia

Methodological challenges in using human umbilical artery as a model for in vitro studies

NEW FINDINGS

What is the central question of this study? What are the biggest challenges in performing in vitro studies on isolated human umbilical arteries? What is the main finding and its importance? The protocols presented in this study indicate some potential outcomes important for interpretation of the vascular responsivities of human umbilical arteries and could be useful for planning future in vitro studies with human umbilical arteries.

ABSTRACT

Human umbilical artery (HUA) preparations are of particular importance for in vitro studies on isolated blood vessels because their sampling is not risky for the patient, and they can provide the closest possible impression of changes related to the uteroplacental circulation during pre-eclampsia. Using organ bath techniques, useful experimental protocols are provided for measuring some pathophysiological phenomena in the vascular responses of HUAs. Several vasoconstrictors (serotonin, prostaglandin F and phenylephrine) and vasodilators (acetylcholine and minoxidil) were seleted for determination of their vasoactivity in HUAs. The role of L-type voltage-operated calcium channels and different types of potassium channels (KATP , BKCa and KV ) were assessed, as was the impact of homocysteine. Serotonin was confirmed to be the most potent vasoconstrictor, while acetylcholine and phenylephrine caused variability in the relaxation and contraction response of HUA, respectively. The observed increase in serotonin-induced contraction and a decrease in minoxidil-induced relaxation in the presence of homocysteine suggested its procontractile effect on HUA preparations. Using selective blockers, it was determined that KATP and KV channels participate in the minoxidil-induced relaxation, while L-type voltage-dependent Ca2+  channels play an important role in the serotonin-induced contraction. The presented protocols reveal some of the methodological challenges related to HUA preparations and indicate potential outcomes in interpreting the vascular effects of the investigated substances, both in physiological conditions and in the homocysteine-induced pre-eclampsia model.

The preeclampsia condition alters external potassium-evoked contraction of human umbilical vessels

INTRODUCTION

Pre-eclampsia (PE) is a disease of high incidence in parturients, that adversely affects both mother and fetus. Although PE prevalence is high, there are few studies on literature describing its etiology or its mechanism of action. Thus, the aim of this study was to elucidate PE-induced alterations of contractile reactivity in umbilical vessels.

METHOD

Segments of human umbilical artery (HUA) and human umbilical vein (HUV) from neonates of normotensive or PE parturients were obtained and contractile responses measured with a myograph. The segments were allowed to stabilize (2 h) under 1.0, 2.0 and 3.0 g force (gf) at pre-stimulation and, then, were stimulated with high isotonic K⁺ concentrations ([K⁺]_o; 10-120 mM).

RESULTS

All preparations responded to increases in isotonic K⁺ concentrations. In HUA and HUV of neonates of normotensive parturients, and in HUV of neonates of PE parturients, the contraction saturated at nearly 50 mM [K⁺]_o, while in HUA of neonates of PE parturients, saturation occurred at 30 mM [K⁺]_o. Additionally, several differences between contractile responses of HUA and HUV from neonates of normotensive parturients and those from neonates of parturients with PE were observed. PE alters the contractile response of the HUA and HUV to increased [K⁺]_o, and its contractile modulation by the pre-stimulus basal tension. Moreover, in HUA of PE, reactivity is decreased for 2.0 and 3.0 gf basal tensions and increased for 1.0 gf; in the HUV of PE condition, it is increased for all basal tensions.

DISCUSSION

In conclusion, PE promotes several alterations in HUA and HUV contractile reactivity, vessels in which important circulatory alterations are known to occur.

Relaxant Effect of Monoterpene (-)-Carveol on Isolated Human Umbilical Cord Arteries and the Involvement of Ion Channels

Carveol is a monoterpene present in the structure of many plant products. It has a variety of biological activities: antioxidant, anticancer and vasorelaxation. However, studies investigating the effect of monoterpenoids on human vessels have not yet been described. Thus, the present study aimed to characterize the effect of (−)-carveol on human umbilical arteries (HUAs). HUA ring preparations were isolated and subjected to isometric tension recordings of umbilical artery smooth muscle contractions. (−)-Carveol exhibited a significant vasorelaxant effect on KCl and 5-HT-induced contractions, obtaining EC₅₀ values of 344.25 ± 8.4 and 175.82 ± 4.05 µM, respectively. The participation of calcium channels in the relaxation produced by (−)-carveol was analyzed using vessels pre-incubated with (−)-carveol (2000 µM) in a calcium-free medium, where the induction of contractions was abolished. The vasorelaxant effect of (−)-carveol on HUAs was reduced by tetraethylammonium (TEA), which increased the (−)-carveol EC₅₀ to 484.87 ± 6.55 µM. The present study revealed that (−)-carveol possesses a vasorelaxant activity in HUAs, which was dependent on the opening of calcium and potassium channels. These results pave the way for further studies involving the use of monoterpenoids for the vasodilatation of HUAs. These molecules have the potential to treat diseases such as pre-eclampsia, which is characterized by resistance in umbilical arteries.

Time-dependent and force-dependent vasoreactivity of isolated human umbilical arteries

Background/Aim: There have been different experimental conditions for in vitro studies on human umbilical arteries (HUA) in tissue bath system. This diversity was mainly reflected in variables such as stretching tension, incubation period and initial constriction challenging with potassium (KCl). The aim of the study was to establish optimal experimental conditions which will provide better responsiveness of HUA preparations, as well as to examine the impact of 24 h cold storage on viability and responsiveness of HUA to KCl and serotonin. Methods: The KCl-induced constrictions at different stretching tensions (0.5 g, 1.0 g, 2.0 g, 4.0 g), incubation times (30 min, 60 min, 120 min), and after multiple initial constriction challenging were compared. Dose response curves for serotonin were obtained under different conditions (1.0 g and 60 min vs. 2.0 g and 120 min). The influence of 24 h cold storage on KCland serotonininduced vasoconstriction of HUA preparations was examined as well. Results: The strongest constrictions induced by serotonin or KCl were obtained when preparations were adjusted at 2.0 g and incubated for 120 min. The KCl-induced constrictions observed after 120 min were statistically higher (p < 0.05) when preparations were challenged three times (30 min, 60 min, 120 min), compared to those challenged only once. The preparations that were stored at 4 ⁰C for 24 h showed significantly stronger serotonin-induced constrictions (p < 0.01). The cold storage had no influence on KCl-induced constriction. Conclusion: For performing in vitro studies on HUA preparations in tissue bath, we propose stretching tension of 2.0 g, incubation period of 120 min and multiple initial constriction challenging with KCl as optimal experimental condition. We also showed that HUA preparations retained functional viability even after 24 h of cold storage.

Determination of hyperelastic properties for umbilical artery in preeclampsia from uniaxial extension tests

OBJECTIVE

Preeclampsia often results in altered hemodynamics and structurally remodeled umbilical arteries in the fetus--alterations that may be associated with arterial stiffening. We therefore hypothesized that the mechanical function of preeclamptic (PE) umbilical arteries had increased stiffness compared to control.

STUDY DESIGN

Umbilical arteries were collected from control (n=9) and PE (n=6) pregnancies without any other complications. Samples were tested uniaxially in axial and circumferential directions for the passive mechanics. The umbilical artery was modeled as a fiber reinforced hyperelastic material in both control and PE conditions.

RESULTS

The PE arteries were stiffer than control arteries at stresses of 20-160 mmHg in the axial direction and 65-200 mmHg in the circumferential direction (P<0.05). The PE umbilical arteries exhibited a 58% and 48% increase in circumferential moduli at the systolic and diastolic blood pressure respectively compared to the controls (P<0.05). A hyperelastic model showed a substantial increase in both isotropic and anisotropic contribution in the mechanical behavior. Collectively, the changes observed correlated to a higher collagen fiber density in the PE group with increased hyperelastic material parameters (P<0.05).

CONCLUSION

PE umbilical arteries demonstrated stiffer biomechanics compared to the controls due to the change in collagen fiber content. These altered biomechanical and structural changes provide a potential snapshot into systemic vasculature remodeling occurring in the newborn.

Enhanced angiogenic capacity of human umbilical vein endothelial cells from women with preeclampsia

Maternal and placental angiogenic abnormalities are a common feature of preeclampsia. The aim of this study was to determine if endothelial cells from women with preeclampsia exhibit different angiogenic responses compared to healthy cells. Using the endothelial tube formation assay, we have shown that primary human umbilical vein endothelial cells (HUVECs) isolated from women with preeclampsia display greater levels of in vitro angiogenic branching compared to cells from healthy women. A comparable increase in tube formation was observed in healthy cells cultured at 0.5% O(2). Vascular endothelial growth factor (VEGF) receptor inhibition resulted in a decrease in angiogenesis in both healthy hypoxic cells and cells from women with preeclampsia. These findings demonstrate that HUVECs from women with preeclampsia exhibit inherent differences in their angiogenic capacity which are apparent in the absence of placental or maternal factors.

Acute and chronic modulation of placental chorionic plate artery reactivity by reactive oxygen species

Control of vascular resistance and blood flow in the fetoplacental circulation is incompletely understood. Reactive oxygen species (ROS), physiological and pathophysiological regulators of vascular tone, are elevated in preeclampsia (PE), a disease of pregnancy characterized by increased fetoplacental vascular resistance. We tested the hypothesis that ROS modulate vascular reactivity in placental chorionic plate arteries. Wire myography was used to examine (1) the effects of acute exposure to ROS on arterial function in normal pregnancy and (2) the effects of maternal antioxidant supplementation on arterial reactivity in women at high risk for PE participating in the Vitamins in Pre-eclampsia (VIP) trial. ROS generated by xanthine plus xanthine oxidase enhanced basal tension, vasoconstriction in response to the thromboxane mimetic U46619, and relaxation in response to sodium nitroprusside. Hydrogen peroxide and peroxynitrite increased basal tone and relaxed preconstricted arteries (U44619), respectively. In women at risk for PE, chorionic plate artery constriction in response to U46619 was greater in the women receiving placebo compared to the women supplemented with the antioxidant vitamins C and E. ROS may regulate fetoplacental vascular resistance and blood flow in the short term, and chronic exposure to raised ROS could contribute to elevated fetoplacental vascular resistance in PE and fetal growth restriction (FGR).

Bioengineering aspects of the umbilical cord

The umbilical cord and its constituent tissues: an outer layer of amnion, porous Wharton's jelly, two umbilical arteries, and one umbilical vein, are designed to protect blood flow to the fetus during a term pregnancy. The outer amnion layer may regulate fluid pressure within the umbilical cord. The porous, fluid filled Wharton's jelly likely acts to prevent compression of the vessels. Blood flow is regulated by smooth muscle surrounding the arteries that is intermingled with a collagen based extracellular matrix (ECM). Doppler ultrasound measurements of blood flow within the umbilical cord, and at specific sites within the developing fetus, provide evidence of impaired blood flow in conditions such as preeclampsia. Mechanosensory communication between cells and the extracellular matrix (ECM) may likely result in cords possessing abnormal physical dimensions, impaired hemodynamics, and altered composition within the umbilical cord tissues. Few studies have explored the biomechanics of the intact umbilical cord, with its constituent tissues, from normal pregnancies or abnormal pregnancies, maternal or fetal complications. Here, alterations in the umbilical cord are reviewed concerning anatomical abnormalities, disease, or chromosomal alterations using sonography, Doppler ultrasound, histology, and biomolecular and biochemical analyses. This paper considers how current knowledge of the umbilical cord and its constituent tissues can be used to infer biomechanical function. In addition, the mechanical consequences of structural abnormalities and altered tissue structure or composition are discussed with a specific focus on preeclampsia.

Control of the fetoplacental circulation

This year marks the 250th anniversary of the discovery by William Hunter of the existence of two distinct circulations within the human placenta. Until relatively recently the placenta has been viewed with “respect” – a passive structure which occasionally elicited fear and anxiety if implanted either too low or too deep. More recently our understanding of perinatal physiology, blood flow regulation and epidemiological data linking prenatal events with adult disease has created renewed interest in the placenta. This review will focus on the regulation of fetal blood flow in the placenta, the possible mechanisms whereby it may be deranged and why this might be relevant to adult disease.

Vasoreactivity of chorionic plate arteries in response to vasoconstrictors produced by preeclamptic placentas

Inadequate blood flow and increased vasoconstriction of the placenta contribute to pregnancy associated disorders such as preeclampsia (PE). Because placental vessels lack autonomic innervation, humoral effects of the placenta must play critical roles in regulation of fetal-placental vascular contractility. In this study, we examined the nature of humoral factors produced by PE trophoblasts on placental vessel contractility using an organ bath perfusion model. Vasomotor responses were studied in vitro using placental chorionic plate arteries. Vessel rings from third branch chorionic plate arteries were dissected from human placentas following normal or PE delivery. The arterial rings were equilibrated in Krebs Henseleit buffer and exposed to placental conditioned medium, which was prepared by culture of villous tissue from PE placentas. Receptor antagonists for angiotensin II (ANG II), thromboxane (TX), and endothelin (ET) were used to determine which humoral factor produced by placental tissue (trophoblasts) was more effective in promoting vasoconstriction. The role of angiotensin converting enzyme (ACE) and non-ACE ANG II generating enzymes in regulation of placental vasomotor tone were also investigated. A total of 80 arterial rings from 48 placentas were studied. Our results showed: 1) enhanced vasomotor tone in arteries from PE placentas compared to those from normal placentas; 2) PE-CM induced vaso-constrictive activity could be partially attenuated by receptor antagonists for TX, ANG II and ET, respectively; and 3) chymostatin (a chymase inhibitor) produced a stronger inhibitory effect than captopril (ACE inhibitor) on PE conditioned medium induced vasoconstriction. Our data demonstrate increased vasocontractility in PE placentas and suggest that the non-ACE pathway is probably a major source of ANG II produced in the human placenta.

Efficacy of different vasodilators on human umbilical arterial smooth muscle under normal and reduced oxygen conditions

The ability of the smooth muscle of the human umbilical artery to relax may vary under physiological and pathological conditions. We investigated the responsiveness of that preparation to relaxation, as well as the influence of reduced oxygen condition on these responses. Rings of human umbilical arteries from full-term Caesarian deliveries were suspended in modified Krebs-Henseleit solutions bubbled with a gas mixture of 95% O2:5% CO2 (normal oxygen condition) or 2.5% O2:8% CO2 balanced with N2 (reduced oxygen condition). These rings were contracted with potassium chloride, serotonin or the thromboxane A2 mimetic U46619, before being exposed to either the nitrovasodilator sodium nitroprusside, the potassium channel opener levcromakalim or the calcium channel antagonist amlodipine. While sodium nitroprusside elicited relaxation in this blood vessel, the maximal relaxation to the nitric oxide donor was significantly smaller than that induced by levcromakalim and amlodipine. The nature of the constrictor agent used, or changes of oxygen conditions did not significantly affect the relaxation profile of this human blood vessel. These data suggest that the smooth muscle of the human umbilical artery may be less responsive to vasodilators that act via the nitric oxide pathway. Moreover, vascular responses of umbilical arterial smooth muscle to relaxing agents do not alter under hypoxic or different vasoconstricting conditions.

Stimulation of the ADRB3 adrenergic receptor induces relaxation of human placental arteries: influence of preeclampsia

Preeclampsia, which complicates 3-8% of pregnancies, is one of the leading causes of neonatal morbidity and mortality. Its pathophysiology remains unclear. The aim of the present study was to investigate the presence and the role of beta2- and beta2-adrenergic receptors (ADRB2 and ADRB3, respectively) in human placental arteries and to assess the influence of preeclampsia on ADRB responsiveness. SR 59119A, salbutamol, and isoproterenol (ADRB3, ADRB2, and nonselective ADRB agonists, respectively) induced a concentration-dependent relaxation of placental artery rings obtained from women with uncomplicated or preeclamptic pregnancies. SR 59119A-induced relaxation was unaffected by the blockade of ADRB1 and ADRB2 by 0.1 microM propranolol but was significantly decreased by the blockade of ADRB1, ADRB2, and ADRB3 by 10 microM propranolol. Both SR 59119A and salbutamol were associated with a significant increase in cAMP production that was significantly inhibited by pretreatment with 0.1 microM propranolol only for salbutamol. SR 59119A-induced relaxation (E(max) = 28% +/- 5% vs. 45% +/- 4%, respectively) and cAMP production (2.7 +/- 0.5 vs. 4.9 +/- 0.4 pmol/mg of protein, respectively; P < 0.01) were decreased in arteries obtained from preeclamptic compared to normotensive women. Both ADRB2 and ADRB3 transcripts were expressed at the same level between arteries from normotensive and preeclamptic women. Western blot analysis, however, revealed a decreased expression of the ADRB3 immunoreactive protein in arteries from preeclamptic compared to normotensive women. We suggest the presence of functional ADRB2 and ADRB3 in human placental arteries. Even if preeclampsia is associated with an impairment of the ADRB3 responsiveness, ADRB3 agonists may have future pharmaceutical implications in the management of pregnancy-related disorders.

The effects of preeclampsia and oxygen environment on endothelial release of matrix metalloproteinase-2

BACKGROUND

There is evidence of altered vascular endothelial function in women with preeclampsia as well as in the endothelial cells from umbilical vessels of preeclamptic pregnancies. Matrix metalloproteinase (MMP)-2 is elevated in the plasma of preeclamptic women and is a mediator of vascular reactivity; however, whether MMP-2 release is altered in preeclamptic endothelial cells is unknown. We hypothesize that MMP-2 release is enhanced in endothelial cells from preeclamptic compared with uncomplicated pregnancies and that this phenomenon may be mediated by an oxygen-dependent mechanism. Our specific hypothesis is that cells from normal pregnancies will demonstrate enhanced MMP-2 release at low oxygen (< 0.5%, 2%) compared to high oxygen (20%), thus mimicking the behavior of preeclamptic cells.

METHODS

Human umbilical vein endothelial cells (HUVECs) from preeclamptic pregnancies (n = 4) and normal pregnancies (n = 4) were incubated for 12 hr in standard culture conditions (20% oxygen). In a separate series of experiments, HUVECs from normal pregnancies (n = 6) were incubated for 12 hr at < 0.5%, 2%, and 20% oxygen. Supernatants were analyzed for MMP-2 and tissue inhibitors of metalloproteinases (TIMP)-1 and -2.

RESULTS

The HUVECs from women with preeclampsia demonstrated significantly enhanced release of MMP-2 (p < 0.05), TIMP-1 (p < 0.001), and TIMP-2 (p = 0.01) compared to normal cells. MMP-2 release from HUVECs from uncomplicated pregnancies was significantly elevated at 2% oxygen compared to < 0.5% and 20% oxygen (p < 0.05). TIMP-1 and -2 secretion was not altered with varying oxygen.

CONCLUSIONS

Preeclamptic endothelial cells demonstrate significantly enhanced MMP-2, TIMP-1 and TIMP-2 release compared to normal cells. Our data show that there are significant effects of oxygen tension on MMP-2 release from normal cells; however, the magnitude of the enhanced release is small when compared to the differences in MMP-2 release in cells from preeclamptic and normal pregnancies. Furthermore, TIMP-1 and -2 release is not affected by changes in oxygen. It is unlikely that oxygen is a key mediator of the enhanced MMP-2, TIMP-1 and TIMP-2 release observed in preeclamptic cells.

Vasoconstrictor effects of 8-iso-prostaglandin E2 and 8-iso-prostaglandin F2α on human umbilical vein

The present study was undertaken to determine whether 8-iso-prostaglandin E2 and 8-iso-prostaglandin F(2alpha) posses contractile action on human umbilical vein and to evaluate the possible involvement of prostanoid TP receptors in this effect. Human umbilical vein rings were mounted in organ baths and concentration-response curves to 8-iso-prostaglandin E2 or 8-iso-prostaglandin F(2alpha) were constructed. Both isoprostanes evoked concentration-dependent contraction. 8-iso-prostaglandin E2 (pEC50=6.90+/-0.03) was significantly more potent than 8-iso-prostaglandin F(2alpha) (pEC50=6.10+/-0.04). However, both isoprostanes were equieffective. The prostanoid TP receptor antagonists, ICI-192,605 (4-(Z)-6-(2-o-Chlorophenyl-4-o-hydroxyphenyl-1,3-dioxan-cis-5-yl)hexenoic acid) and SQ-29548 (7-[3-[[2-[(phenylamino)carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-[1S(1alpha,2alpha(Z),3alpha,4alpha)]-5-Heptenoic acid) produced a competitive rightward shift of 8-iso-prostaglandin E2 concentration-response curves with pKB values of 8.91+/-0.04 and 8.07+/-0.07, respectively. When ICI-192,605 (1 nM) and SQ-29548 (10 nM) were evaluated against 8-iso-prostaglandin F(2alpha) they produced a parallel rightward displacement of 8-iso-prostaglandin F(2alpha) concentration-response curves without affecting the maximum responses giving pA2 values of 9.02+/-0.12 and 8.26+/-0.13, respectively. In conclusion, the present study describes for the first time the vasoconstrictor action of 8-iso-prostaglandin E2 and 8-iso-prostaglandin F(2alpha) in human umbilical vein. Furthermore, the affinity values obtained with ICI-192,605 and SQ-29548 provide strong pharmacological evidence of prostanoid TP receptors involvement in this effect.

Fetoplacental vascular tone is modified by magnesium sulfate in the preeclamptic ex vivo human placental cotyledon

OBJECTIVE

The purpose of this study was to evaluate fetoplacental vascular tone and response to a vasoconstrictor in placentas of preeclamptic and normotensive pregnancies with and without the presence of magnesium sulfate.

STUDY DESIGN

Two cotyledons from each placenta were selected from preeclamptic (n=8) and normotensive (n=7) pregnancies. In one cotyledon from each pair, the maternal circuit was perfused with magnesium sulfate. The fetal arteries were injected sequentially with angiotensin II (10(-10)mol and 10(-11.5) mol). Perfusion pressures and response to angiotensin II were compared, with regard to preeclampsia and exposure to magnesium sulfate.

RESULTS

Perfusion pressure was higher in preeclamptic placentas, compared with normotensive placentas (30.4 mm Hg vs 24.4 mm Hg, P=.02). There was a decrease in perfusion pressure with exposure to magnesium sulfate in preeclamptic placentas (22.5 mm Hg, P<.01), but not in normotensive placentas. Fetoplacental vascular response to angiotensin II was not affected by preeclampsia or magnesium sulfate.

CONCLUSION

In placentas from preeclamptic pregnancies there is increased fetoplacental perfusion pressure, which decreases with exposure to sulfate.

TGF-beta 3 expression during umbilical cord development and its alteration in pre-eclampsia

Members of the TGF-beta family have been shown to play an important role in numerous tissues during development. In the present study we have investigated the spatial and temporal expression of TGF-beta 3, in human umbilical cord development. Total TGF-beta 3 protein content, assessed by immunoblotting, increased with advancing gestation as did immunostaining and mRNA in Wharton's jelly fibroblasts. Immunohistochemical analysis revealed that TGF-beta 3 was present in all cell types. Temporal changes in TGF-beta 3 expression were observed in the vascular smooth muscle cells, such that with advancing gestation TGF-beta 3 protein expression and became mostly restricted to the extracellular compartment of the vascular media. This was associated with a decrease in TGF-beta 3 mRNA expression in umbilical vascular smooth muscle cells. Of clinical significance, umbilical cords from pregnancies complicated by pre-eclampsia, showed a significant reduction in total TGF-beta 3 protein expression when compared to those of age-matched patients. Both TGF-beta 3 mRNA and protein expression were downregulated in the endothelium and smooth muscle layers of the umbilical arteries, as well as in the Wharton jelly fibroblasts. Our data demonstrate that during umbilical cord development TGF-beta 3 expression is spatially and temporally regulated and that TGF-beta 3 expression is altered in umbilical cords of pregnancies complicated by pre-eclampsia. We speculate that the downregulation of TGF-beta 3 expression found in pre-eclamptic umbilical cord may contribute to the abnormal structure and mechanical properties seen in these pathological umbilical cords.

Reactivities to serotonin and histamine in umbilical and placental vessels during the third trimester after normotensive pregnancies and pregnancies complicated by preeclampsia

OBJECTIVE

The aim of the study was to evaluate responses of umbilical and placental arteries and veins to serotonin and histamine after normotensive pregnancies and pregnancies complicated by preeclampsia.

STUDY DESIGN

Each pair of placentas from a normotensive woman and a woman with preeclampsia was matched for gestational age. Rings of these vessels were prepared and mounted in tissue baths under their respective optimal passive tension. Cumulative concentration-response curves to serotonin and histamine were measured.

RESULTS

Responses to serotonin were decreased in umbilical vessels from the preeclampsia group with respect to the normotensive group. This is reflected by reduced maximum responses and sensitivity (negative logarithm of the 50% effective concentration) to serotonin. Maximum response to serotonin was significantly decreased in placental vein rings from the preeclampsia group. We recorded a decreased maximal response to histamine in placental vein rings from pregnancies complicated by preeclampsia with respect to those from normal pregnancies. Among normotensive women there was a significant positive linear relationship between neonatal weight and sensitivity to serotonin in umbilical and placental veins. This relationship was totally absent in preeclampsia. Sensitivity to histamine was linearly related to neonatal weight in umbilical vessels of the pooled results of both experimental groups.

CONCLUSION

The vasoconstrictive effects of serotonin, but not those of histamine, are decreased in umbilical and placental vessels after preeclampsia. Sensitivities to serotonin and histamine change in umbilicoplacental vessels during the third trimester. Altered reactivity to serotonin may play a significant role in the reduction of umbilicoplacental blood flow in preeclampsia.

Isolated human chorionic vascular reactivity: technical considerations for fresh preparations

1. Sixty chorionic vascular rings from normal term placentas were immersed in an organ bath for isometric tension recording to study (A) the contractile response to 120 mM of potassium chloride (KCl) after adjustment and equilibration to 1-5 g of passive tension; and (B) the concentration-response curve to KCl after adjustment and equilibration to the optimal passive tension. 2. Adjustment to 4 g of passive tension elicited the maximal (P < 0.007) and the latest (P < 0.006) KCl-induced contraction among arterial rings. Venous rings showed the greatest contraction when adjusted to 3 g, but the differences were not significant except when compared to 1 g of passive tension (P < 0.03). 3. The EC50 for chorionic arteries and veins was 14.2 and 25.7 mM, respectively (P < 0.003). The maximal contraction was already obtained with 40 mM of KCl. 4. Our results suggest that (A) the optimal passive tension for fresh human chorionic arteries is 4 g; (B) chorionic venous reactivity is less influenced by the initial tension; and (C) the optimal concentration of KCl to be used as a contracting agent of these tissues is 40 mM.

Computerized microscope morphometry of umbilical vessels from pregnancies with intrauterine growth retardation and abnormal umbilical artery Doppler

Computerized microscope morphometry was used to study cross sections from the vessels of the umbilical cord in placentas of patients with intrauterine growth retardation (IUGR) that displayed either normal or abnormal umbilical arteries (UA) Doppler flow velocity waveforms (FVW). Cords from 63 eutrophic fetuses with normal Doppler (controls), 47 IUGR fetuses with normal Doppler and 32 IUGR fetuses with abnormal Doppler underwent morphometric analysis using a highly optimized microscope environment (HOME) and "CordHOME" software. IUGR with an accompanying normal Doppler versus control showed a reduction of Wharton jelly and both the total and lumen vein areas. IUGR with an accompanying pathological Doppler showed a comparable reduction in wall thickness and areas of every vessel. These findings indicate that the hypoplastic umbilical vessels are associated with an increase in placental vascular resistance that may be the consequence of underdevelopment in response to a chronic reduction in placental blood flow.

Evidence of endothelial activation and endothelial activators in cord blood of infants of preeclamptic women

OBJECTIVE

In preeclampsia markers of endothelial activation (e.g., increased cellular fibronectin and activities that alter in vitro endothelial function (e.g., stimulation of nitric oxide and prostacyclin generation) are increased in the maternal circulation. We tested preeclamptic infant blood for these markers and activities and correlated these findings with fetal growth.

STUDY DESIGN

Plasma was obtained from 17 term nulliparcus preeclamptic and normal pregnant women and their infants and from 8 additional preeclamptic mother-baby pairs from earlier gestations. Plasma cellular fibronectin and production of nitric oxide and prostacyclin by cultured endothelial cells exposed to 2% plasma were measured.

RESULTS

Cellular fibronectin was higher in maternal plasma of preeclamptic than nonpregnant women (6.1 +/- 0.29 vs 4.2 +/- 0.27 microgram/ml, p < 0.01), as were stimulated endothelial nitric oxide and prostacyclin production (nitric oxide 42.5 +/- 3.9 vs 26.9 +/- 2.3 nmol nitrite/microgram protein/24 hours, p < 0.05; prostacyclin 261.7 +/- 31.2 vs 151.9 +/- 18.7 pg prostaglandin F1 alpha/microgram protein/24 hours, p < 0.05). In the preeclamptic infants cellular fibronectin was also greater (3.3 +/- 0.15 vs 2.6 +/- 0.14 microgram/ml, p < 0.01), as was endothelial nitric oxide production in response to the plasma (24.4 +/- 1.1 vs 21.4 +/- 0.09 mumol/L nmol nitrite/microgram protein/24 hours, p < 0.05). Prostacyclin production was not significantly different. In preeclamptic infants across a wide gestational age there was no correlation of endothelial activation and fetal growth.

CONCLUSIONS

Infants of women with preeclampsia may be affected by endothelial dysfunction, as well as reduced uteroplacental perfusion.