Human Chorionic Plate Arteries Research Articles

The expression and function of KCNQ potassium channels in human chorionic plate arteries from women with normal pregnancies and pre-eclampsia.

Pre-eclampsia is associated with altered maternal and placental vascular reactivity. Kv7 channels (encoded by KCNQ 1–5 genes) are a potential contributor to the regulation of vascular tone in CPAs (chorionic plate arteries) during normal pregnancy. The aim of this study is to establish the expression profile of KCNQ subunits in CPAs taken from women with preeclampsia or normotensive women and to examine the functional relevance of the Kv7 channels on an altered expression profile of KCNQ subunits. The effects of Kv7 channel modulators on CPAs were investigated by tension measurement. Quantitative PCR experiments were used to analyze the expression of KCNQ genes. Western blotting and immunofluorescence were both used to analyze the protein expression of Kv7 channels. Finally, in CPAs from normotensive women, the Kv7 channel blocker XE991 increased arterial basal tone and U46619-induced contraction, and pre-contracted CPAs (10−7 M U46619) exhibited significant relaxation following treatment with Retigabine(Kv7.2–7.5 activator) and BMS-204352(Kv7.2–7.5 activator). However, ICA-27243(selective KCNQ2 and KCNQ3 activator) and ML277(selective KV7.1 activator) had no significant effect on tension in the pre-contracted CPAs. Conversely, compared with CPAs from normotensive women, the effects of XE991 on basal tone and agonist (U46619)-induced contractions in CPAs from women with preeclampsia were markedly attenuated. Moreover, the relaxation effects of Retigabine and BMS-204352 on pre-contracted CPA vessels from women with pre-eclampsia were also markedly down-regulated. Interestingly, the relaxation ability of ICA-27243 in pre-contracted CPA vessels in women with pre-eclampsia was enhanced. The mRNA of KCNQ3 was specifically up-regulated, whereas those for KCNQ4 and KCNQ5 were down-regulated in CPAs from women with pre-eclampsia compared with those in normotensive women. Similar observations were found in a subsequent analysis of protein expression of KCNQ genes 3–5. Thus, down-regulated Kv7 channel function in tension regulation of CPAs in women with pre-eclampsia could be associated with considerably altered expression profiles of Kv7 subunits.

Impairment of BKca channels in human placental chorionic plate arteries is potentially relevant to the development of preeclampsia.

Preeclampsia has known associations with insufficient placental perfusion. The large-conductance Ca2+-activated K+ (BKca) channels that have recently been found to play important roles in cellular growth and vasodilatation could potentially participate in the development of preeclampsia. However, the mechanisms by which downregulated BKca channels are involved in the development of preeclampsia remain unknown. In this study, we investigated the mechanism(s) underlying the impairment of vascular tone regulation by BKca channels in human placental chorionic plate arteries (CPAs) in preeclampsia. The levels of BKca channel α and β1 subunits were compared using immunohistochemistry, western blotting, and RT-PCR in CPAs of normal and preeclamptic pregnant women. To explore the role of BKca channels in the regulation of proliferation and apoptosis in human placental CPA smooth muscle cells (SMCs), a specific BKca opener, NS1619, was used to investigate proliferative reduction and apoptotic induction in human placental chorionic plate arterie smooth muscle cells (CPASMCs) collected from normal pregnancies. The vasodilator effects of BKca channels and their response to SNP (an NO donor) in both groups were also evaluated by wire myography. We found that BKca channel β1 subunits were less expressed in preeclamptic CPAs. After pretreatment with NS1619, cellular proliferation was significantly suppressed, and cellular apoptosis was dramatically promoted in cultured CPASMCs, demonstrating a relationship between increased Bax expression and decreased Bcl-2 expression in CPASMCs. Downregulated BKca is also associated with decreased vasodilatation and reduced susceptibility to NO donors. In conclusion, the decreased expression or activation of BKca channels may induce pathologic remodeling of human CPAs, weaken the vasodilation response, and decrease vascular sensitivity to vasoactive substances, thereby reducing fetal-placental blood flow and leading to the future development of preeclampsia.

Activation of KV7 channels stimulates vasodilatation of human placental chorionic plate arteries

IntroductionPotassium (K+) channels are key regulators of vascular smooth muscle cell (VSMC) excitability. In systemic small arteries, Kv7 channel expression/activity has been noted and a role in vascular tone regulation demonstrated. We aimed to demonstrate functional Kv7 channels in human fetoplacental small arteries. MethodsHuman placental chorionic plate arteries (CPAs) were obtained at term. CPA responses to Kv7 channel modulators was determined by wire myography. Presence of Kv7 channel mRNA (encoded by KCNQ1-5) and protein expression were assessed by RT-PCR and immunohistochemistry/immunofluorescence, respectively. ResultsKv7 channel blockade with linopirdine increased CPA basal tone and AVP-induced contraction. Pre-contracted CPAs (AVP; 80 mM K+ depolarization solution) exhibited significant relaxation to flupirtine, retigabine, the acrylamide (S)-1, and (S) BMS-204352, differential activators of Kv7.1 – Kv7.5 channels. All CPAs assessed expressed KCNQ1 and KCNQ3-5 mRNA; KCNQ2 was expressed only in a subset of CPAs. Kv7 protein expression was confirmed in intact CPAs and isolated VSMCs. DiscussionKv7 channels are present and active in fetoplacental vessels, contributing to vascular tone regulation in normal pregnancy. Targeting these channels may represent a therapeutic intervention in pregnancies complicated by increased vascular resistance.

Effects of oxygenation and luminal flow on human placenta chorionic plate blood vessel function

The human fetoplacental vasculature has been suggested to be a low resistance/high flow system, but the mechanisms by which this state is achieved are unclear. This study assessed the effects of intraluminal flow and local oxygenation on isolated human placental chorionic plate arteries and veins at term using pressure myography. Chorionic plate arteries and veins exhibit myogenic tone. A small but significant arterial vasodilatation was observed following exposure to hypoxia; chorionic plate veins contracted to a similar hypoxic stimulus. Under physiological conditions of pressure and oxygenation, increased luminal flow induced contraction in both chorionic plate arteries and veins. [Correction added after online publication 15th November 2011: 'induced vasodilatation' has been changed to 'induced contraction'] Human fetoplacental vascular tone can be manipulated by local physical factors.

Effects and mechanisms of action of sildenafil citrate in human chorionic arteries

ObjectivesSildenafil citrate, a specific phosphodiesterase-5 inhibitor, is increasingly used for pulmonary hypertension in pregnancy. Sildenafil is also emerging as a potential candidate for the treatment of intra-uterine growth retardation and for premature labor. Its effects in the feto-placental circulation are not known. Our objectives were to determine whether phosphodiesterase-5 is present in the human feto-placental circulation, and to characterize the effects and mechanisms of action of sildenafil citrate in this circulation.Study DesignEx vivo human chorionic plate arterial rings were used in all experiments. The presence of phosphodiesterase-5 in the feto-placental circulation was determined by western blotting and immunohistochemical staining. In a subsequent series of pharmacologic studies, the effects of sildenafil citrate in pre-constricted chorionic plate arterial rings were determined. Additional studies examined the role of cGMP and nitric oxide in mediating the effects of sildenafil.ResultsPhosphodiesterase-5 mRNA and protein was demonstrated in human chorionic plate arteries. Immunohistochemistry demonstrated phosphodiesterase-5 within the arterial muscle layer. Sildenafil citrate produced dose dependent vasodilatation at concentrations at and greater than 10 nM. Both the direct cGMP inhibitor methylene blue and the cGMP-dependent protein kinase inhibitor Rp-8-Br-PET-cGMPS significantly attenuated the vasodilation produced by sildenafil citrate. Inhibition of NO production with L-NAME did not attenuate the vasodilator effects of sildenafil. In contrast, sildenafil citrate significantly enhanced the vasodilation produced by the NO donor sodium nitroprusside.ConclusionPhosphodiesterase-5 is present in the feto-placental circulation. Sildenafil citrate vasodilates the feto-placental circulation via a cGMP dependent mechanism involving increased responsiveness to NO.

Histamine-Induced Contraction and Relaxation of Placental Chorionic Plate Arteries

Studies of the human placental vasculature suggest a low resistance circulation. Using wire myography, endothelial-dependent relaxation of human chorionic plate arteries has been difficult to demonstrate with any consistency. However, histamine has been suggested to relax placental vessels in the perfused organ in vitro. Here we aimed to demonstrate endothelial-dependent relaxation to histamine under physiological conditions of stretch and oxygenation. Histamine administration to pre-contracted arteries induced a triphasic response; an initial contraction followed by a dilatation which stabilized to a significant relaxation compared to time control arteries. Relaxation was partially inhibited by blockers of endothelial-dependent relaxation pathways. The initial contraction was abolished by H 1-receptor blockade with mepyramine. The relaxation was significantly reduced by H 2-receptor blockade with famotidine but only abolished in the presence of both H 1- and H 2-receptor antagonists. In conclusion, histamine induced contraction and relaxation of human chorionic plate arteries. Our data suggest that contraction is mediated by activation of H 1-receptors. Relaxation occurs directly, via activation of H 2-receptors on vascular smooth muscle cells, and indirectly via H 1-receptor stimulation of endothelial-dependent relaxation.

Inhibitory effect of erythropoietin on contractility of human chorionic plate vessels

Placenta is a major source of erythropoietin production in the fetus; hypoxia is associated with elevated erythropoietin levels in the fetal circulation. We investigated fetoplacental vascular reactivity after exposure to erythropoietin in vitro. Third-order chorionic plate arteries from human term placentae were incubated in culture medium with or without erythropoietin (3 U/mL) for 24 hours. Vessels were mounted in a myograph for isometric tension recording, and their responses to vasopressors and vasorelaxants were studied. Contractile responses to endothelin-1 and the thromboxane analogue U46619 were decreased in erythropoietin-exposed vessels compared with controls. Relaxant responses to the nitric oxide donor sodium nitroprusside and the phosphodiesterase inhibitor papaverine were not influenced by erythropoietin. Exposure to elevated levels of erythropoietin has an inhibitory effect on contractile responses in human placental chorionic plate arteries. We speculate that this may improve fetoplacental perfusion in hypoxic fetuses with elevated erythropoietin production.

Effects of Oxygen Tension and Normalization Pressure on Endothelin-Induced Constriction of Human Placental Chorionic Plate Arteries

Fetoplacental blood vessels constrict in response to endothelin (ET-1) or reduced oxygen tension in the placental cotyledon perfused in vitro. In nonplacental resistance arteries, hypoxia and ET-1 induce constriction by promoting Ca2+ influx into smooth muscle through membrane ion channels, which include voltage-gated Ca2+ channels (VGCCs). We hypothesized that VGCCs are involved in ET-1-induced constriction of fetoplacental resistance vessels and that their contribution to constriction is enhanced at low oxygen tension. Chorionic plate small arteries from term placentas were studied using parallel wire myography. Arteries were normalized at 0.9 of L(5.1 kPa) ("low stretch" approximately 25 mm Hg; approximating physiologic vascular pressure) or 0.9 of L(13.3 kPa) ("high stretch" approximately 42 mm Hg) and experiments performed at oxygen tensions of 156, 38, and 15 mm Hg. When chorionic plate arteries were normalized at low stretch, oxygen tension did not affect constriction to ET-1. Nifedipine (10(-4) M), a blocker of L-type VGCCs, inhibited ET-1 (EC80)-induced constriction to a similar extent at each oxygen tension (52% to 64% inhibition). In contrast, when arteries were normalized at high stretch, constriction to ET-1 was greater at 38 than at 156 or 15 mm Hg oxygen and nifedipine inhibition of ET-1-induced constriction was greater at 38 and 15 mm Hg than at 156 mm Hg oxygen. VGCCs and nifedipine-insensitive processes underlie the contractile response of chorionic plate arteries to ET-1 and their relative contribution to vasoconstriction is modulated by oxygen tension when vessels are normalized at high stretch. However, contrary to our hypothesis, the response of chorionic plate arteries to ET-1 is not modulated by oxygen when vessels are normalized at physiologic pressure.

Ultrastructural Features of Smooth Muscle and Endothelial Cells of Isolated Isobaric Human Placental and Maternal Arteries

The ability of a blood vessel to develop tone is dependent upon morphological parameters of the smooth muscle cells (SMC), including density, relationship with the endothelium and subcellular distribution of myofilaments and intracellular organelles. Consequently, wall ultrastructure of isolated human placental chorionic plate arteries (n=12), fixed when pressurised to mimic their in vivo geometry, was examined qualitatively using electron microscopy, and compared with maternal arteries (omental, n=10, myometrial, n=6). Arteries from women with uncomplicated pregnancy were tested for contractile viability before fixing, with some vessels post-fixed in osmium-ferricyanide for sarcoplasmic reticulum (SR) identification. In contrast to maternal arteries, placental arteries had no internal elastic lamina but exhibited considerable extracellular matrix separating circularly orientated SMC. Human SMC contained tightly packed arrays of myofilaments running parallel to the plasma membrane, enveloping cellular organelles. Synthetic SMC, with few myofilaments and much rough SR, were observed in placental arteries only. SR in SMC from maternal arteries was located centrally, often encircling mitochondria, and also near the plasma membrane associated with caveolae. Positive SR staining was rarely observed in SMC of placental arteries. This study highlights ultrastructural differences between placental and maternal arteries that may underlie specialised mechanisms of regulating vascular tone in the placenta.

Effects of Nitrovasodilators on the Human Fetal–Placental Circulation In Vitro

This study examines the vasorelaxation of isolated human placental chorionic plate arteries and the perfused fetal-placental vasculature, in vitro, to a variety of nitrovasodilator compounds including glyceryl trinitrate (GTN) sodium nitroprusside (SNP), S-nitroso-N-acetylpenicillamine (SNAP), S-nitroso-N-glutathione (SNG) and NaNO2. The effects of these compounds were also examined under conditions of high (>450mmHg) and low oxygen (<50mmHg) tension. In a separate series of experiments the effects of GTN and NaNO2were further investigated with addition of the antioxidants cysteine (100μm), glutathione (100μm) or superoxide dismutase (SOD) (30I.U./ml). The order of nitrovasodilator potency, when added directly to isolated fetal vessels was GTN=SNP>SNAP=SNG>NaNO2. The order under low oxygen tension was similar, GTN=SNP>SNG= SNAP≥NaNO2. SNG (∼fourfold) and NaNO2(∼50-fold) were significantly more potent under low oxygen conditions. Cysteine, glutathione and SOD were without effect on GTN induced vasodilatation. However, all three agents significantly enhanced (six- to ninefold) the effects of NaNO2under similar conditions. When infused directly into the fetal–placental circulation during in vitro perfusion experiments the order of potency was GTN>SNP≥SNG≥SNAP≥NaNO2. When the nitrovasodilators were infused indirectly via the maternal intervillous space the order of potency was GTN≥SNP≥NaNO2≥SNAP=SNG. Our observations suggest that there are important differences in the action of different classes of nitrovasodilator compounds on the fetal–placental circulation. The changes observed with SNG and NaNO2may be influenced by levels of tissue oxygenation.

Endothelium-derived relaxing factor and cyclic GMP-dependent vasorelaxation in human chorionic plate arteries

Endothelium derived relaxing factor (EDRF), now widely believed to be nitric oxide (NO), may play an important part in the control of fetoplacental vascular tone. To further explore this role we have determined the relaxation responses to exogenous NO and examined the temporal relationship between intracellular concentrations of cyclic GMP and vascular tone in isolated ring segments of human chorionic plate arteries. We have also determined the dose relations for the contractile agonists serotonin and the throm☐ane analog U46619. Lastly, we have explored the relaxation responses to a wide range of agents known to elicit EDRF release in other vascular beds. Chorionic plate arteries relaxed significantly to exogenous NO with concomitant increases in cyclic guanosine monophosphate over basal values. ED 50s for serotonin and U46619 were 1.48 × 10 −6 m and 3.39 × 10 −8 m respectively. The ED 50 for NO derived from S-nitroso-N-acetyl-penicillamine was 1.28 × 10 −6 m. Endothelium-intact segments of chorionic plate arteries pre-contracted with either serotonin or U46619 failed to relax significantly to acetylcholine, adenosine diphosphate, A23187, bradykinin, and histamine and only minimally to substance P. We suggest that EDRF is likely to be important in the control of placental vascular tone, but that it is not possible to demonstrate its action in an unperfused experimental system.

NO is more important than PGI2 in maintaining low vascular tone in feto-placental vessels.

The endothelial cells of the human umbilical artery and vein release the vasodilators prostacyclin [prostaglandin (PG) I2] and nitric oxide (NO). However, the role of these two substances in the maintenance of vasodilator tone in the feto-placental circulation is not known. Studies were therefore undertaken to compare the relative release of PGI2 and NO from perfused segments (10 cm) of endothelium-intact human umbilical artery (HUA) and vein (HUV) utilizing the cascade bioassay. The endothelium-denuded bovine pulmonary arterial strip was used as the detector tissue because this tissue relaxes equally to various concentrations of PGI2 and S-nitroso-N-acetylpenicillimine (SNAP), which acts by releasing NO. The basal release of NO from the HUA was approximately five times greater than that of PGI2. After stimulation with A-23187, the release of NO from HUV was five to six times greater, and from the HUA, the release was three times greater compared with the PGI2. SNAP was significantly more potent compared with PGI2 in relaxing endothelium-denuded rings of human umbilical and chorionic plate arteries in vitro. These studies suggest that NO is more important than PGI2 for maintenance of low vascular tone in feto-placental vessels, because there is a greater release of NO from the HUA and HUV, and NO is more potent in relaxing endothelium-denuded feto-placental vessels in vitro relative to PGI2.

Cyclooxygenase products do not modulate angiotensin II—induced contractions of human chorionic plate arteries

This study sought to determine whether cyclooxygenase products modulate angiotensin II-induced contractions of human placental arteries. Ring segments of chorionic plate arteries (3 to 5 mm inner diameter) were obtained after normal vaginal deliveries. Active force in response to 10(-6) mol/L angiotensin II or 10(-4) mol/L arachidonic acid was measured in the presence or absence of 10(-6) mol/L indomethacin to inhibit cyclooxygenase. The response of K+ contracted arteries to the stable prostacyclin analog iloprost was also tested to determine whether prostacyclin relaxes these vessels. Statistical differences were assessed by analysis of variance, Wilcoxon sign rank test, or Student t test with Bonferroni correction for multiple comparisons. Successive applications of angiotensin II produced significantly less contraction than the original dose (angiotensin II tachyphylaxis). Angiotensin II tachyphylaxis was unaffected by indomethacin. Arachidonic acid caused an indomethacin-sensitive contraction and iloprost failed to relax the arteries. These results suggest that cyclooxygenase products do not mediate angiotensin II tachyphylaxis in these vessels.

Characterization and actions of human umbilical endothelium derived relaxing factor

1. A bioassay cascade superfusion technique was utilized to study the properties of endothelium derived relaxing factor (EDRF) from human umbilical vein (HUV) and compare its actions on umbilical, chorionic plate and bovine pulmonary arterial strips. 2. Histamine (1 microM), bradykinin (1 microM) and A-23187 (0.3 microM, 1 microM) but not acetylcholine (1 microM) released EDRF. 3. The non-innervated human foetoplacental vessels, i.e., umbilical and chorionic plate arteries, do relax to EDRF by a guanosine 3':5'-cyclic monophosphate (cyclic GMP)-mediated mechanism. 4. The sensitivity of the human umbilical arterial strips to EDRF was less than that of the chronic plate arterial strips. Bovine pulmonary arterial strips were the most sensitive to the relaxant actions of human umbilical EDRF.

Human Chorionic Plate Arteries Lack an Endothelium-Dependent Relaxation Response

This study was designed to demonstrate that human chorionic plate arteries exhibit endothelium-dependent relaxation. Vessel ring segments (2mm long) were studied in a wire myograph system in which force and vessel dimensions were measured. The calcium ionophore A23187 (n = 10), or histamine (n = 2) was added to precontracted arteries in concentrations known to stimulate release of endothelium-derived relaxing factor(s) in umbilical vessels (10−8 M-10−6 M). A23187 did not cause relaxation of these arteries, while 10−5 M histamine enhanced contraction. The vessels exhibited concentration-dependent relaxation in response to the addition of nitric oxide (n = 3), and relaxed completely upon addition of 10−6 M sodium nitroprusside (n = 8), indicating a functional guanylate cyclase in the smooth muscle.

Human α- and β-calcitonin gene-related peptides are vasodilators in human chorionic plate vasculature

Calcitonin gene-related peptide receptors are known to be present in the placenta. We studied the effect of alpha- or beta-calcitonin gene-related peptide or carrier on human chorionic plate arteries preconstricted with angiotensin II. Both forms of calcitonin gene-related peptides evoked dose-dependent relaxation, the magnitude of which was proportional to the initial response to angiotensin II.

The effect of a calcium antagonist, nitrendipine, on the responses of isolated strips of human, chorionic plate artery to prostaglandins E2 and E1.

Six point concentration-response curves were established for the contractile effect of prostaglandin E2 (PGE2) on helically-cut strips of human chorionic plate arteries. Tissues were then allocated to one of four treatment groups: a control group and 3 groups exposed to the calcium channel blocker nitrendipine at 10(-9), 10(-7) or 10(-5) M. The concentration-response curves were then repeated. The addition of nitrendipine was associated with a significant depression of the induced contraction. The contractile response to the lower doses of PGE2 was replaced by a small relaxation in 63% of the treated tissues. It is suggested that in these tissues PGE2 exerts its constrictor effect via the receptor-operated channels and that nitrendipine is blocking this effect. Similar experiments performed with PGE1 showed great variability in the initial response. Nitrendipine 10(-5) M failed to exert any detectable effect on this response. Pregnancy-induced hypertension is associated with vasoconstriction in both the maternal and placental circulations. There also appears to be a relative excess of vasoconstrictor eicosanoid production. Nitrendipine may be of use in the treatment of this condition.

The effects of mode of delivery and type of anesthesia on the response of human chorionic plate arteries to prostaglandin E2

In our case presentation there was no evidence of a molar pregnancy or chorioadenoma destruens, the two apparent prerequisites for deportation of chorionic villi. Moreover, the diagnosis of an ectopic pregnancy is usually histologic and is not ruled out by negative findings of uterine curettings. Therefore, although it seems likely that this case represents a vaginal ectopic pregnancy, deportation cannot be ruled out. It is of interest that this patient was delivered of a normal male infant weighing 9 pounds, 12 ounces on March 19, 1983. We wish to thank Dr. Vincent Tricomi, Chairman of the Department of Obstetrics and Gynecology, The Brooklyn Hospital-Caledonian Hospital, and Dr. Robert E. Scully, pathologist, Massachusetts General Hospital, for the review of our article and constructive criticisms. We also wish to thank Dr. Richard H. Schwarz, Chairman of the Department of Obstetrics and Gynecology, State University of New York, Downstate Medical Center, for his advice.

Effects and interactions of prostaglandins E1 and E2 on human chorionic plate arteries

Helically cut strips of human chorionic plate arteries were maintained in a physiologic salt solution in vitro while isotonic measurements of contraction were made. The arterial strips were exposed to two prostaglandins, PGE1 and PGE2, added cumulatively to the tissue baths. The effects and interactions of these two prostaglandins were examined. PGE1 had a dose-dependent relaxatory effect on the strips at low concentrations, but contracted them at higher concentrations. PGE2, on the other hand, only induced contraction. The addition of a low concentration of PGE2 inhibited the relaxatory response to PGE1 in approximately half the tissue strips. The contractile response was enhanced in all strips. Conversely, a low concentration of PGE1, without intrinsic effect on the strips, significantly reduced the contractile response to PGE2. The suggestion is made that, in the human term placenta, PGE1 and PGE2 may act in concert as part of the regulatory mechanism for fetoplacental blood flow.