Autacoid interactions in the regulation of blood flow in the human placenta

Human Placental Vascular Reactivity in Health and Disease: Implications for the Treatment of Pre-eclampsia

Adequate development of the placenta is essential for optimal pregnancy outcome. Pre-eclampsia (PE) is increasingly recognized to be a consequence of placental dysfunction and can cause serious maternal and fetal complications during pregnancy. Furthermore, PE increases the risk of neonatal problems and has been shown to be a risk factor for cardiovascular disease of the mother later in life. Currently, there is no adequate treatment for PE, mainly because its multifactorial pathophysiology remains incompletely understood. It originates in early pregnancy with abnormal placentation and involves a cascade of dysregulated systems in the placental vasculature. To investigate therapeutic strategies it is essential to understand the regulation of vascular reactivity and remodeling of blood vessels in the placenta. Techniques using human tissue such as the ex vivo placental perfusion model provide insight in the vasoactive profile of the placenta, and are essential to study the effects of drugs on the fetal vasculature. This approach highlights the different pathways that are involved in the vascular regulation of the human placenta, changes that occur during PE and the importance of focusing on restoring these dysfunctional systems when studying treatment strategies for PE.

An emerging role for comprehensive proteome analysis in human pregnancy research

Elucidation of underlying cellular and molecular mechanisms is pivotal to the comprehension of biological systems. The successful progression of processes such as pregnancy and parturition depends on the complex interactions between numerous biological molecules especially within the uterine microenvironment. The tissue- and stage-specific expression of these bio-molecules is intricately linked to and modulated by several endogenous and exogenous factors. Malfunctions may manifest as pregnancy disorders such as preterm labour, pre-eclampsia and fetal growth restriction that are major contributors to maternal and perinatal morbidity and mortality. Despite the immense amount of information available, our understanding of several aspects of these physiological processes remains incomplete. This translates into significant difficulties in the timely diagnosis and effective treatment of pregnancy-related complications. However, the emergence of powerful mass spectrometry-based proteomic techniques capable of identifying and characterizing multiple proteins simultaneously has added a new dimension to the field of biomedical research. Application of these high throughput methodologies with more conventional techniques in pregnancy-related research has begun to provide a novel perspective on the biochemical blueprint of pregnancy and its related disorders. Further, by enabling the identification of proteins specific to a disease process, proteomics is likely to contribute, not only to the comprehension of the underlying pathophysiologies, but also to the clinical diagnosis of multifactorial pregnancy disorders. Although the application of this technology to pregnancy research is in its infancy, characterization of the cellular proteome, unearthing of functional networks and the identification of disease biomarkers can be expected to significantly improve maternal healthcare in the future.

Growth and function of the normal human placenta

The placenta is the highly specialised organ of pregnancy that supports the normal growth and development of the fetus. Growth and function of the placenta are precisely regulated and coordinated to ensure the exchange of nutrients and waste products between the maternal and fetal circulatory systems operates at maximal efficiency. The main functional units of the placenta are the chorionic villi within which fetal blood is separated by only three or four cell layers (placental membrane) from maternal blood in the surrounding intervillous space. After implantation, trophoblast cells proliferate and differentiate along two pathways described as villous and extravillous. Non-migratory, villous cytotrophoblast cells fuse to form the multinucleated syncytiotrophoblast, which forms the outer epithelial layer of the chorionic villi. It is at the terminal branches of the chorionic villi that the majority of fetal/maternal exchange occurs. Extravillous trophoblast cells migrate into the decidua and remodel uterine arteries. This facilitates blood flow to the placenta via dilated, compliant vessels, unresponsive to maternal vasomotor control. The placenta acts to provide oxygen and nutrients to the fetus, whilst removing carbon dioxide and other waste products. It metabolises a number of substances and can release metabolic products into maternal and/or fetal circulations. The placenta can help to protect the fetus against certain xenobiotic molecules, infections and maternal diseases. In addition, it releases hormones into both the maternal and fetal circulations to affect pregnancy, metabolism, fetal growth, parturition and other functions. Many placental functional changes occur that accommodate the increasing metabolic demands of the developing fetus throughout gestation.

Expression of nitric oxide synthase isoforms in the human placenta is not altered by labor

Nitric oxide has various biological activities including smooth muscle relaxation, anti-inflammatory activity, anti-coagulatory activity. As the human placenta is known to express nitric oxide synthases, this study investigated the possible effect of labor on the expression of endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) in human placental tissues at term. Both eNOS and iNOS mRNA expression in placental tissues in labor were significantly higher than those in the amnion, chorion laeve, decidua vera and myometrium. The eNOS mRNA and protein expressions in placental tissues in labor (n = 12) were 1.6023 +/- 0.1652 (eNOS/GAPDH, mean +/- SEM) and 12.8 +/- 1.3 arbitrary units (AU), respectively, which were similar to those not in labor (n = 10), 1.5806 +/- 0.2042 (eNOS/GAPDH) and 11.4 +/- 1.8 AU. The iNOS mRNA and protein expressions in the placental tissues in labor were 1.2831 +/- 0.2436 (iNOS/GAPDH) and 10.7 +/- 2.1 AU respectively, similar to those not in labor, 1.9254 +/- 0.8004 (iNOS/GAPDH) and 13.3 +/- 1.8 AU. The guanosine 3',5'-cyclic monophosphate (cGMP) concentration in the placental tissues in labor was 23.6 +/- 1.4 fmol/g wet tissue, similar to that not in labor, 26.1 +/- 2.0 fmol/g wet tissue. These findings suggest that nitric oxide production in the human placenta is maintained during labor.

Increase of endothelial nitric oxide synthase and endothelin-1 mRNA expression in human placenta during gestation

OBJECTIVE

To investigate the maturation of the paracrine system's endothelial nitric oxide synthase (eNOS), inducible NOS (iNOS), endothelin-1 (ET-1) and adrenomedullin (AM) in human placenta during the 2nd and 3rd trimester of pregnancy.

STUDY DESIGN

Placental tissue from 14 healthy women with normal pregnancy and from 13 patients giving birth to premature infants following premature labor was obtained. Messenger RNA expression was determined using quantitative TaqMan real-time PCR.

RESULTS

Placental eNOS/GAPDH and ET-1/GAPDH mRNA expression significantly increased as a function of gestational age (r=0.63, P<0.001 and r=0.53, P=0.007, respectively). There was no change in gene expression of neither iNOS nor AM mRNA/GAPDH during gestation (r=0.02, P=0.75 and r=0.001, P=0.99, respectively).

CONCLUSION

There is a maturation of eNOS and ET-1 in human placenta with gestation reflecting developmental changes of important paracrine endothelial and trophoblastic regulators. AM and iNOS show no maturation during pregnancy.

Amplification effect and mechanism of action of ET-1 in U-46619-induced vasoconstriction in pig skin

The aim of this study was to investigate if a low concentration of endothelin-1 (ET-1; 8 x 10(-10) M) may amplify the skin vasoconstrictor effect of other vasoactive substances in the pathogenesis of skin vasospasm. Pig skin flaps (6 x 16 cm) were perfused with Krebs buffer equilibrated with 95% O(2) and 5% CO(2) at 37 degrees C and pH 7.4. Skin perfusion pressure measured by a pressure transducer and skin perfusion assessed by the dermofluorometry technique were used for assessment of skin vasoconstriction. We observed that ET-1 (8 x 10(-10) M) significantly amplified the concentration-dependent (10(-7)-10(-5) M) skin vasoconstrictor effect of norepinephrine. More importantly, we observed for the first time that this low concentration of ET-1 also amplified the concentration-dependent (10(-8)-10(-6) M) skin vasoconstrictor effect of the thromboxane A(2) mimetic U-46619, and this amplification effect of ET-1 was completely blocked by the protein kinase C (PKC) inhibitor chelerythrine (5 x 10(-6) M). Conversely, the PKC activator phorbol 12,13-dibutyrate (10(-7) M) amplified the vasoconstrictor effect of U-46619. Furthermore, the sensitivity of the skin vasculature to the vasoconstrictor effect of extracellular Ca(2+) in U-46619-induced skin vasoconstriction was significantly enhanced in the presence of 8 x 10(-10) M ET-1. Finally, the cyclooxygenase inhibitor indomethacin (5 x 10(-6) M) did not affect the amplification effect of ET-1 on U-46619-induced skin vasoconstriction. We conclude that a low concentration of ET-1 can amplify the skin vasoconstrictor effect of U-46619 independent of endogenous cyclooxygenase products, and the mechanism may involve activation of PKC and increase in sensitivity of the contractile apparatus to Ca(2+) in smooth muscle cells.

Effect of ginger tea on the fetal development of Sprague-Dawley rats

This study investigated the effect of ginger, a common morning sickness remedy, on fetal development. Pregnant Sprague-Dawley rats were administered, from gestation day 6 to 15, 20 g/liter or 50 g/liter ginger tea via their drinking water and then sacrificed at day 20. No maternal toxicity was observed, however embryonic loss in the treatment groups was double that of the controls (P<0.05). No gross morphologic malformations were seen in the treated fetuses. Fetuses exposed to ginger tea were found to be significantly heavier than controls, an effect that was greater in female fetuses and was not correlated with increased placental size. Treated fetuses also had more advanced skeletal development as determined by measurement of sternal and metacarpal ossification centers. The results of this study suggest that in utero exposure to ginger tea results in increased early embryo loss with increased growth in surviving fetuses.

Stimulation of endothelin B receptor modulates the inflammatory activation of rat astrocytes

Inside the brain tissue, endothelins play numerous important biological roles. One of the targets, astrocytes, predominantly display endothelin receptor subtype B (ET(B)). On cultured primary rat astroglial cells, we analyzed the effect of IRL1620, a selective ET(B) receptor agonist, on the production of nitric oxide (NO) and the synthesis of interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha. We performed these experiments in the presence or absence of interferon-gamma (IFN-gamma) and/or lipopolysaccharide (LPS). IRL1620 decreases NO production under basal conditions and after IFN-gamma stimulation. However, during LPS-induced NO production, IRL1620 enhances this release. The basal IL-6 secretion and especially the LPS-induced synthesis are enhanced by the IRL1620 stimulation. The LPS-dependent TNF-alpha production is increased by the ET(B) stimulation. The IRL1620-induced decrease of basal NO production is not dependent on Ca2+ entry or on phospholipase C (PLC) activation, as shown by the use of LaCl3 and U73122, respectively. In the presence of LPS, the IRL1620 potentiation of NO production is inhibited by LaCl3 and U73122. The IRL1620-induced increase of IL-6 is dependent on PLC activation. These results suggest that endothelins can have dual effects depending on the costimulatory factors present. Endothelins thus have important immunomodulatory functions in the brain.