Prostacyclin producing activity of human umbilical, placental and uterine vessels

Prostacyclin-like material producing activity of umbilical, placental and uterine vessels was studied.Umbilical arteries and veins were separated at sites 10–15 cm and 1–2 cm from insertion of the umbilical cord to the placenta. Placental arteries and veins were prepared from the first, second and third branches on the chorionic plate. Uterine vessels were obtained at abdominal hysterectomy.After incubation of each specimen in Tris buffer 1 ml (pH8.5, 0.5M) for 30 min at room temperature, the inhibitory effect of the medium on ADP induced platelet aggregation was measured and the prostacyclin-like material was quantified. These procedures were repeated consecutively four times in total for each specimen. Prostacyclin-like material production rate and its total production were calculated.In total prostacyclin-like material production, umbilical arteries and veins were much higher than placental arteries and veins respectively (p<0.001), but there was no significant difference between placental and uterine vessels.These results showed that prostacyclin-like material producing activity of blood vessels declined remarkably at the transitive region from umbilical to placental vessels. It seems that this distribution of vascular prostacyclin-like material producibility in the fetoplacental vascular system correlates with that of vascular reactivity to prostacyclin.     

Prostacyclin and human foetal circulation

Tissues from human umbilical cord arteries and placental veins generated much greater prostacyclin activity than vessels from normal adults. High prostacyclin generation could contribute to maintaining the low peripheral vascular resistance typical of foetal circulation in which blood pressure is low despite very high cardiac output.     

Prostacyclin and human foetal circulation.

Tissues from human umbilical cord arteries and placental veins generated much greater prostacyclin activity than vessels from normal adults. High prostacyclin generation could contribute to maintaining the low peripheral vascular resistance typical of foetal circulation in which blood pressure is low despite very high cardiac output.     

Study of "prostacyclin-like" activity in the rat blood vessel: changes in prostacyclin production related to body weight

The prostacyclin-producing capacity of various blood vessels was studied using platelet aggregation bioassay in rats of different ages. Results showed that --the PGI2 producing capacity of arteries was five to tenfold of the respective veins; --in the arteries the PGI2 production calculated for unit vascular mass declined from the centre to the periphery, despite the relative increase of endothelial surface area. This points to the importance of other vascular elements in the control of PGI2 production; --the PGI2 forming activity of some blood vessels increased with the age up to a limit (300-400 g body weight), decreasing thereafter. Based on these results we conclude that major part of PGI2 in systemic blood originates from the large arteries, whereas the low PGI2 production of the veins might play a role, among others, in the more frequent occurrence of venous thrombosis.     

Prostacyclin producing activity of human umbilical blood vessels in adrenergic innervated and non-innervated portions

The present experiment was performed in order to clarify the significance of prostacyclin (PGI2) in the regulation of human umbilical blood flow. Distribution of adrenergic nerve fibers in umbilical cord was examined by means of a modification of the glyoxylic acid fluorescence histochemical technique. PGI2 producing activity in various portions of umbilical blood vessels was measured by platelet bioassay. Adrenergic nerve fibers were observed only in the region surrounding umbilical arteries at the fetal end of the cord. PGI2 producing activity of umbilical arteries was significantly lower in the innervated region than in the non-innervated region. There were no significant regional differences in umbilical vein which has no adrenergic innervation. The relationship between vascular PGI2 producing activity and adrenergic innervation, and the significance of PGI2 in the regulation of human umbilical blood flow are discussed.     

Reactivity of human placental chorionic plate vessels from pregnancies complicated by intrauterine growth restriction (IUGR)

A successful pregnancy is dependent on liberal placental perfusion via the maternal and fetal circulations. Doppler waveform analyses of umbilical arteries suggest increased resistance to flow in the fetoplacental circulation of pregnancies complicated by intrauterine growth restriction (IUGR). Neither the site nor the mediators responsible for this altered vascular reactivity are known, to date. In placentas in normal pregnancy, reduced oxygenation promotes contraction of the in vitro-perfused placental cotyledon and modulates agonist-induced contraction of chorionic plate arteries and veins. Placental oxygenation has also been suggested to be reduced in IUGR. We tested the hypothesis that oxygen tension could directly modify placental chorionic plate vessel vasoreactivity in IUGR. Small arteries and veins from the chorionic plate were dissected from biopsies from placentas of pregnancies complicated by IUGR and were studied using parallel wire myography. Vasoconstriction at 20%, 7%, and 2% oxygen was assessed utilizing the thromboxane mimetic U46619. Experiments were also performed in the presence of 4-aminopyridine (4AP), a blocker of voltage-gated potassium channels. Increased oxygenation reduced venous vasoconstriction but did not modify arterial vasoconstriction. 4AP increased basal tone in arteries and veins. We suggest that venoconstriction in response to hypoxia may provide a mechanism for increased fetoplacental vascular resistance associated with IUGR.     

Production of prostacyclin, 6-keto-PGF1 alpha and thromboxane B2 by incubated samples of umbilical vessels: a comparison of methods for expressing the results on dry weight, wet weight, protein or DNA bases

The production of PGI2 (determined by bioassay), and of 6-keto-PGF1 alpha and TXB2 (determined by radioimmunoassay) by samples of human umbilical vessels have been measured. The results have been calculated on four bases: dry weight, wet weight, protein and DNA. There was a higher production of PGI2 and 6-keto-PGF1 alpha by umbilical veins than by umbilical arteries; no significant difference in TXB2 production was observed between umbilical veins and arteries. The ratio of 6-keto-PGF1 alpha: TXB2 production was about 100 for the samples of veins and about 40 for the samples of arteries. The best methods of expressing the results were on the bases of protein and DNA, the latter basis being marginally the best. The least satisfactory method for expressing the results was that based on dry weight. The physiological and practical implications of the results are discussed.     

Concentrations of progesterone in arterial and venous plasma of fetal pigs and their dams in late gestation

Blood samples were drawn from uterine arteries and veins of pregnant gilts and from the umbilical artery and vein of each of their fetuses during laparotomy at Day 80. Concentrations of progesterone (P) were greater in fetal than maternal plasma. Uptake of P from the placenta by the fetal blood was evident but was not equivalent to the maternal uterine arterial-venous difference in P concentration. No correlation between plasma P and fetal weight was noted. Concentrations of P in both umbilical vessels of female fetuses were higher than in male fetuses. These data indicate that fetal sex affects the rate of transport and/or synthesis of P in the utero/placental compartment and/or the rate of metabolism of P in the fetus. The relative importance of de novo synthesis and transplacental transport of P in establishing concentrations of P in fetal blood remains to be elucidated.     

Maternal cigarette smoking increases F2-isoprostanes and reduces prostacyclin and nitric oxide in umbilical vessels.

The objective of this study was to evaluate the influence of smoking on F2-isoprostanes, prostacylin and nitric oxide in human umbilical vessels. Umbilical cords from 13 babies of smoking mothers and from 28 babies of non-smoking mothers were examined for levels of F2-isoprostanes, prostacyclin, L-arginine, and L-citrulline. Forty-one umbilical arteries and eleven umbilical veins were analyzed. Statistical analysis of data was done using modified t-test. Cigarette smoking increased F2-isoprostane levels and reduced the generation of prostacyclin, L-arginine and L-citrulline comparably in umbilical arteries and veins. Notably, in umbilical cords of babies of non-smoking mothers the F2-isoprostane level was significantly higher in arteries. Cigarette smoking correlates with a direct vasoconstrictive effect. We suggest that smoking might enhance the vasoconstrictory capacity in umbilical arteries by increased F2-isoprostanes and by a simultaneous decrease in the production of the vasodilatory compounds, prostacyclin, and nitric oxide.     

Vascular endothelial expression of indoleamine 2,3-dioxygenase 1 forms a positive gradient towards the feto-maternal interface

We describe the distribution of indoleamine 2,3-dioxygenase 1 (IDO1) in vascular endothelium of human first-trimester and term placenta. Expression of IDO1 protein on the fetal side of the interface extended from almost exclusively sub-trophoblastic capillaries in first-trimester placenta to a nearly general presence on villous vascular endothelia at term, including also most bigger vessels such as villous arteries and veins of stem villi and vessels of the chorionic plate. Umbilical cord vessels were generally negative for IDO1 protein. In the fetal part of the placenta positivity for IDO1 was restricted to vascular endothelium, which did not co-express HLA-DR. This finding paralleled detectability of IDO1 mRNA in first trimester and term tissue and a high increase in the kynurenine to tryptophan ratio in chorionic villous tissue from first trimester to term placenta. Endothelial cells isolated from the chorionic plate of term placenta expressed IDO1 mRNA in contrast to endothelial cells originating from human umbilical vein, iliac vein or aorta. In first trimester decidua we found endothelium of arteries rather than veins expressing IDO1, which was complementory to expression of HLA-DR. An estimation of IDO activity on the basis of the ratio of kynurenine and tryptophan in blood taken from vessels of the chorionic plate of term placenta indicated far higher values than those found in the peripheral blood of adults. Thus, a gradient of vascular endothelial IDO1 expression is present at both sides of the feto-maternal interface.     

Heterogeneous histochemical reaction pattern of the lectin Bandeiraea (Griffonia) simplicifolia with blood vessels of human full-term placenta

Bandeiraea simplicifolia lectin (BS-I) stains vascular endothelium in various species. In humans, less than 10% of the specimens studied exhibit a reaction with BS-I. In the present histochemical study, the reactivity of BS-I with placental blood vessels and its correlation with the blood group from mother and newborn child was investigated. Acetone-fixed cryosections of representative tissue segments of human full-term placenta and umbilical cord were stained with BS-I. The staining pattern of tissues from patients with different blood groups was identical, although the reaction of BS-I in the placenta was heterogeneous. BS-I did not react with the umbilical cord. Vascular smooth muscle cells at the insertion site of the umbilical cord into the chorionic plate, and endothelium deeper in the chorionic plate, became progressively stained. The endothelial cells and tunica muscularis of smaller arteries and veins in stem villi lost their reactivity in parallel with decreasing vessel size. Arterioles and venules reacted heterogeneously. Capillaries, trophoblastic basement membranes, especially epithelial plates, and sometimes the syncytiotrophoblast were labelled in several terminal villi. The data indicate that 1) the placenta binds BS-I to fetal endothelium independent of the blood group, 2) cell-surface antigens on placental endothelial cells are expressed heterogeneously and 3) cell-surface glycans are constituted in an organ-specific manner on human endothelial cells.     

Alterations in relaxation to lactate and H(2)O(2) in human placental vessels from gestational diabetic pregnancies

We determined whether alterations in the mechanism of relaxation to H(2)O(2) potentially contribute to the enhanced prostaglandin-mediated contractile response to H(2)O(2) and posthypoxic reoxygenation seen in human placental vessels of pregnancies with gestational diabetes mellitus (GDM). Isolated placental arteries and veins from GDM and uncomplicated full-term pregnancies were precontracted with prostaglandin F(2alpha) (PO(2) 35-38 Torr) and then exposed to lactate (1-10 mM), arachidonic acid (0.01-10 microM), nitroglycerin (1 nM-1 microM), forskolin (0.01-10 microM), or H(2)O(2) (1 microM-1 mM + 10 microM indomethacin). The rates of tissue H(2)O(2) metabolism by catalase and nitrite production were measured. The relaxation to lactate was reduced in GDM placental arteries and veins by 54-85 and 66-80%, and the relaxation to H(2)O(2) was inhibited by 80-94% in GDM placental veins compared with vessels from uncomplicated full-term pregnancies. H(2)O(2) caused only minimal relaxation of placental arteries. Responses to other relaxing agents were not altered in the GDM placental vessels. Diabetic vessels showed rates of nitrite production that were increased by 113-195% and rates of H(2)O(2) metabolism by catalase that were decreased by 44-61%. The loss of relaxation to H(2)O(2) and lactate (mediated via H(2)O(2)), perhaps as a result of the inhibition of catalase by nitric oxide, may explain the previously reported enhancement of prostaglandin-mediated contractile responses to H(2)O(2) and posthypoxic reoxygenation seen in GDM placental vessels.     

Element content of human umbilical artery and vein in umbilical cord

To elucidate the element content of newborn blood vessels, umbilical arteries and veins in human umbilical cords, which had the advantage of easy sampling, were examined by ICP-AES. Umbilical cords were removed after birth. Mothers’ ages ranged from 26 to 35 yr. It was found that the content of sulfur was the highest in both umbilical arteries and veins, being higher than the content of calcium and phosphorus. With respect of the content of sulfur, calcium, and magnesium, there were significant differences between the arteries and veins.     

Production of prostacyclin, 6-keto-PGF1α and thromboxane B2 by incubated samples of umbilical vessels: A comparison of methods for expressing the reults on dry weight, wet weight, protein or DNA bases

The production of PG12 (determined by abioassay), and of 6-keto-PGF1α and TXB2 (determined by radioummunoassay) by samples of human umbilical vessels have been measured. The results have been calculated on four bases: dry weigt, wet weight, protein and DNA.There was a higher production of PG12 and 6-keto-PGF1α by umbilical veins than by umbilical arteries; no significant difference in TXB2 production was observed between umbilical veins and arteries. The ratio of 6-keto-PGF1α: TXB2 production was about 100 for the samples of veins and about a40 for the samples of arteries.The best methods of expressing the results were on the bases of protein and DNA, the latter basis being marginally the best. The least satisfactory method for expressing the results was that based on dry weight.The physiological and practical implications of the results are discussed.     

Prostacyclin formation by myometrial & decidual fractions of the pregnant rat uterus

Chopped samples of myometrium, decidua and extrinsic blood vessels from the pregnant rat uterus when incubated at room temperature generated a prostacyclin-like substance. Activity in the incubation mixtures was compared against authentic prostacyclin in two assay systems: relaxation of strips of bovine coronary artery and inhibition of ADP-induced aggregation of rabbit platelet-rich plasma. Results estimated from inhibition of platelet aggregation showed that activity generated by all samples was low on day 12 of pregnancy (less than 0.25 ng/mg). However at the time of delivery (day 22) myometrial synthesis had increased 18.5 fold to over 3 ng/mg of prostacyclin whereas decidual production had only increased 5 times. As there was no increase in synthesis by the extrinsic uterine blood vessels over this period it is proposed that the myometrial muscle cells are the probable source of the prostacyclin-like material.     

Prostacyclin formation by myometrial & decidual fractions of the pregnant rat uterus.

Chopped samples of myometrium, decidua and extrinsic blood vessels from the pregnant rat uterus when incubated at room temperature generated a prostacyclin-like substance. Activity in the incubation mixtures was compared against authentic prostacyclin in two assay systems: relaxation of strips of bovine coronary artery and inhibition of ADP-induced aggregation of rabbit platelet-rich plasma. Results estimated from inhibition of platelet aggregation showed that activity generated by all samples was low on day 12 of pregnancy (less than 0.25 ng/mg). However at the time of delivery (day 22) myometrial synthesis had increased 18.5 fold to over 3 ng/mg of prostacyclin whereas decidual production had only increased 5 times. As there was no increase in synthesis by the extrinsic uterine blood vessels over this period it is proposed that the myometrial muscle cells are the probable source of the prostacyclin-like material.     

Regulation of maternal and fetal hemodynamics by heme oxygenase in mice

Heme oxygenase (HMOX) regulates vascular tone and blood pressure through the production of carbon monoxide (CO), a vasodilator derived from the heme degradation pathway. During pregnancy, the maternal circulation undergoes significant adaptations to accommodate the hemodynamic demands of the developing fetus. Our objective was to investigate the role of HMOX on maternal and fetal hemodynamics during pregnancy in a mouse model. We measured and compared maternal tissue and placental HMOX activity and endogenous CO production, represented by excreted CO and carboxyhemoglobin levels, during pregnancy (Embryonic Days 12.5-15.5) to nonpregnant controls. Micro-ultrasound was used to monitor maternal abdominal aorta diameters as well as blood flow velocities and diameters of fetal umbilical arteries. Tin mesoporphyrin, a potent HMOX inhibitor, was used to inhibit HMOX activity. Changes in maternal vascular tone were monitored by tail cuff blood pressure measurements. Effects of HMOX inhibition on placental structures were assessed by histology. We showed that maternal tissue and placental HMOX activity and CO production were significantly elevated during pregnancy. When HMOX in the placenta was inhibited, maternal and fetal hemodynamics underwent significant changes, with maternal blood pressures increasing. We concluded that increases in maternal tissue and placental HMOX activity contribute to the regulation of peripheral vascular resistance and therefore are important for the maintenance of normal maternal vascular tone and fetal hemodynamic functions during pregnancy.     

Characterization of the in vivo wall shear stress environment of human fetus umbilical arteries and veins

The endothelial cells of the umbilical vessels are frequently used in mechanobiology experiments. They are known to respond to wall shear stress (WSS) of blood flow, which influences vascular growth and remodeling. The in vivo environment of umbilical vascular WSS, however, is not well characterized. In this study, we performed detailed characterization of the umbilical vascular WSS environments using clinical ultrasound scans combined with computational simulations. Doppler ultrasound scans of 28 normal human fetuses from 32nd to 33rd gestational weeks were investigated. Vascular cross-sectional areas were quantified through 3D reconstruction of the vascular geometry from 3D B-mode ultrasound images, and flow velocities were quantified through pulse wave Doppler. WSS in umbilical vein was computed with Poiseuille’s equation, whereas WSS in umbilical artery was obtained via computational fluid dynamics simulations of the helical arterial geometry. Results showed that blood flow velocity for umbilical artery and vein did not correlate with vascular sizes, suggesting that velocity had a very weak trend with or remained constant over vascular sizes. Average WSS for umbilical arteries and vein was 2.81 and 0.52 Pa, respectively. Umbilical vein WSS showed a significant negative correlation with the vessel diameter, but umbilical artery did not show any correlation. We hypothesize that this may be due to differential regulation of vascular sizes based on WSS sensing. Due to the helical geometry of umbilical arteries, bending of the umbilical cord did not significantly alter the vascular resistance or WSS, unlike that in the umbilical veins. We hypothesize that the helical shape of umbilical arteries may be an adaptation feature to render a higher constancy of WSS and flow in the arteries despite umbilical cord bending.