Effect of adrenomedullin on placental arteries in normal and preeclamptic pregnancies

Expression of the Calcitonin Receptor-like Receptor (CALCRL) in Normal and Neoplastic Tissues

Little information is available concerning protein expression of the calcitonin receptor-like receptor (CALCRL) at the protein level. Here, we developed a rabbit monoclonal antibody, 8H9L8, which is directed against human CALCRL but cross-reacts with the rat and mouse forms of the receptor. We confirmed antibody specificity via Western blot analyses and immunocytochemistry using the CALCRL-expressing neuroendocrine tumour cell line BON-1 and a CALCRL-specific small interfering RNA (siRNA). We then used the antibody for immunohistochemical analyses of various formalin-fixed, paraffin-embedded specimens of normal and neoplastic tissues. In nearly all tissue specimens examined, CALCRL expression was detected in the capillary endothelium, smooth muscles of the arterioles and arteries, and immune cells. Analyses of normal human, rat, and mouse tissues revealed that CALCRL was primarily present in distinct cell populations in the cerebral cortex; pituitary; dorsal root ganglia; epithelia, muscles, and glands of the larger bronchi; intestinal mucosa (particularly in enteroendocrine cells); intestinal ganglia; exocrine and endocrine pancreas; arteries, capillaries, and glomerular capillary loops in the kidneys; the adrenals; Leydig cells in the testicles; and syncytiotrophoblasts in the placenta. In the neoplastic tissues, CALCRL was predominantly expressed in thyroid carcinomas, parathyroid adenomas, small-cell lung cancers, large-cell neuroendocrine carcinomas of the lung, pancreatic neuroendocrine neoplasms, renal clear-cell carcinomas, pheochromocytomas, lymphomas, and melanomas. In these tumours with strong expression of CALCRL, the receptor may represent a useful target structure for future therapies.

Pharmacological profile of vascular activity of human stem villous arteries

INTRODUCTION

The function of the placental vasculature differs considerably from other systemic vascular beds of the human body. A detailed understanding of the normal placental vascular physiology is the foundation to understand perturbed conditions potentially leading to placental dysfunction.

METHODS

Behaviour of human stem villous arteries isolated from placentae at term pregnancy was assessed using wire myography. Effects of a selection of known vasoconstrictors and vasodilators of the systemic vasculature were assessed. The morphology of stem villous arteries was examined using IHC and TEM.

RESULTS

Contractile effects in stem villous arteries were caused by U46619, 5-HT, angiotensin II and endothelin-1 (p ≤ 0.05), whereas noradrenaline and AVP failed to result in a contraction. Dilating effects were seen for histamine, riluzole, nifedipine, papaverine, SNP and SQ29548 (p ≤ 0.05) but not for acetylcholine, bradykinin and substance P.

DISCUSSION

Stem villous arteries behave differently to vessels of the systemic vasculature and results indicate that the placenta is cut off from the systemic maternal vascular regulation. Particularly, endothelium-dependent processes were attenuated in the placental vasculature, creating a need to determine the role of the endothelium in the placenta in future studies.

Maternal supraphysiological hypercholesterolemia associates with endothelial dysfunction of the placental microvasculature

Maternal physiological or supraphysiological hypercholesterolemia (MPH, MSPH) occurs during pregnancy. MSPH is associated with foetal endothelial dysfunction and atherosclerosis. However, the potential effects of MSPH on placental microvasculature are unknown. The aim of this study was to determine whether MSPH alters endothelial function in the placental microvasculature both ex vivo in venules and arterioles from the placental villi and in vitro in primary cultures of placental microvascular endothelial cells (hPMEC). Total cholesterol < 280 mg/dL indicated MPH, and total cholesterol ≥280 mg/dL indicated MSPH. The maximal relaxation to histamine, calcitonin gene-related peptide and adenosine was reduced in MSPH venule and arteriole rings. In hPMEC from MSPH placentas, nitric oxide synthase (NOS) activity and L-arginine transport were reduced without changes in arginase activity or the protein levels of endothelial NOS (eNOS), human cationic amino acid 1 (hCAT-1), hCAT-2A/B or arginase II compared with hPMEC from MPH placentas. In addition, it was shown that adenosine acts as a vasodilator of the placental microvasculature and that NOS is active in hPMEC. We conclude that MSPH alters placental microvascular endothelial function via a NOS/L-arginine imbalance. This work also reinforces the concept that placental endothelial cells from the macro- and microvasculature respond differentially to the same pathological condition.

Calcitonin gene related family peptides: importance in normal placental and fetal development

Synchronized molecular and cellular events occur between the uterus and the implanting embryo to facilitate successful pregnancy outcome. Nevertheless, the molecular signaling network that coordinates strategies for successful decidualization, placentation and fetal growth are not well understood. The discovery of calcitonin/calcitonin gene-related peptides (CT/CGRP) highlighted new signaling mediators in various physiological processes, including reproduction. It is known that CGRP family peptides including CGRP, adrenomedulin and intermedin play regulatory functions during implantation, trophoblast proliferation and invasion, and fetal organogenesis. In addition, all the CGRP family peptides and their receptor components are found to be expressed in decidual, placental and fetal tissues. Additionally, plasma levels of peptides of the CGRP family were found to fluctuate during normal gestation and to induce placental cellular differentiation, proliferation, and critical hormone signaling. Moreover, aberrant signaling of these CGRP family peptides during gestation has been associated with pregnancy disorders. It indicates the existence of a possible regulatory role for these molecules during decidualization and placentation processes, which are known to be particularly vulnerable. In this review, the influence of the CGRP family peptides in these critical processes is explored and discussed.

Adrenomedullin and pregnancy: perspectives from animal models to humans

A healthy pregnancy requires strict coordination of genetic, physiologic and environmental factors. The relatively common incidence of infertility and pregnancy complications has resulted in increased interest in understanding the mechanisms that underlie normal versus abnormal pregnancy. The peptide hormone adrenomedullin (AM) has recently been the focus of some exciting breakthroughs in the pregnancy field. Supported by mechanistic studies in genetic animal models, there continues to be a growing body of evidence demonstrating the importance of AM protein levels in a variety of human pregnancy complications. With more extensive mechanistic studies and improved consistency in clinical measurements of AM, there is great potential for the development of AM as a clinically-relevant biomarker in pregnancy and pregnancy complications.

Plasma midregional proadrenomedullin in newborn infants: impact of prematurity and perinatal infection

INTRODUCTION

Adrenomedullin (ADM) is one of the strongest endogenous vasodilating hormones. Its stable by-product midregional-proADM (MR-proADM) is an established indicator of systemic infection and cardiovascular compromise in adult patients.

METHODS

A prospective cross-sectional study was performed to investigate the perinatal factors affecting MR-proADM plasma concentrations in 328 newborn infants with a gestational age (GA) between 24 and 41 wk.

RESULTS

Blood samples were obtained in 270 infants from umbilical veins (with additional 108 paired samples from umbilical arteries), and at 2-3 d of life in 183 infants. Paired venous and arterial umbilical cord MR-proADM concentrations were closely related (Spearman's rank order correlation coefficient (R(s)) = 0.825, P < 0.001). MR-proADM concentrations at birth and at 2-3 d were inversely related to GA (R(s) = -0.403 and R(s) = -0.541, respectively) and birth weight (BW; R(s) = -0.421 and R(s) = -0.530, respectively; all P < 0.001). On stepwise regression analysis, clinical chorioamnionitis and umbilical arterial blood base excess retained a significant impact on MR-proADM cord venous blood concentrations. At 2-3 d of life, histologic chorioamnionitis and GA at delivery were significantly associated with MR-proADM levels.

DISCUSSION

As compared with adults, MR-proADM concentrations are elevated in neonates, especially those born very preterm. Immaturity and infection, which both feature low systemic vascular resistance, are related to increased MR-proADM concentrations.

Adrenomedullin Function in Vascular Endothelial Cells: Insights from Genetic Mouse Models

Adrenomedullin is a highly conserved peptide implicated in a variety of physiological processes ranging from pregnancy and embryonic development to tumor progression. This review highlights past and present studies that have contributed to our current appreciation of the important roles adrenomedullin plays in both normal and disease conditions. We provide a particular emphasis on the functions of adrenomedullin in vascular endothelial cells and how experimental approaches in genetic mouse models have helped to drive the field forward.

The changes of plasma malondialdehyde, nitric oxide, and adrenomedullin levels in patients with preeclampsia

OBJECTIVE

The aim of the study was to investigate the role of malondialdehyde, nitric oxide and adrenomedullin in the etiopathogenesis of preeclampsia.

MATERIAL AND METHODS

Forty-two pregnant women with preeclampsia and 30 healthy pregnant women were involved. The plasma concentrations of malondialdehyde, nitric oxide, and adrenomedullin were compared between the study group and the control group.

RESULTS

In women with preeclampsia the plasma concentrations of malondialdehyde was higher while nitric oxide and adrenomedullin concentrations were lower compared to control subjects.

CONCLUSION

We concluded that the plasma levels of ADM and NO are decreased while MDA levels are increased in subjects with preeclampsia and that might contribute to the pathophysiology of preeclampsia through the lack of a paracrine vasodilatory effect on uteroplacental blood flow.

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).

Evaluation of adrenomedullin and endothelin-1: are they factors in the adaptation of maternal vascular system in normotensive pregnancy

INTRODUCTION

The aim of our study was to analyse the role of adrenomedullin (AM) and endothelin-1 (ET-1) in the adaptation of the maternal vascular system in normotensive pregnancy.

METHODS

Twenty-eight pregnant women, who were normotensive throughout the duration of their pregnancy, were recruited into the study. Plasma levels of AM and ET-1 at each trimester were measured and the AM/ET-1 ratio was calculated.

RESULTS

Our experiment showed a significant decrease in plasma concentrations of AM in the first trimester for the study group (n=28) compared with the non-pregnant control group (n=16). There was also a significant decrease in plasma concentrations of ET-1 in all three trimesters (P<0.05) and a significant increase in the AM/ET-1 ratio in all three trimesters (P<0.05) for the study group compared with the control group.

CONCLUSION

An alteration in vascular equilibrium between AM and ET-1, favouring AM, may be a reason why the physiological adaptation of the maternal vascular system to pregnancy occurs during normotensive pregnancy.

Increased adrenomedullin protein content and mRNA expression in human fetal membranes but not placental tissue in pre-eclampsia

The relationship between Pre-eclampsia (PE) and placental production of Adrenomedullin (AdM) is not completely understood. This study measured placental and fetal membrane AdM protein concentrations by specific radioimmunoassay and mRNA expression by Northern blot analysis in samples obtained at either term or preterm gestation from women either in labour or not in labour. Samples were obtained from women with normotensive and pre-eclamptic pregnancies. There were significant increases in immunoreactive AdM protein concentration (pg/mg DNA) in choriodecidua and amnion of women with PE compared to normal pregnancy for the preterm not-in-labour group (choriodecidua: control 124 +/- 16, n = 10, PE 361 +/- 35, n = 10; amnion: control 94 +/- 12, n = 10, PE 153 +/- 19, n = 10) and for the term not-in-labour (choriodecidua: control 128 +/- 17, n = 14, PE 459 +/- 51, n = 8; amnion: control 112 +/- 15, n = 14, PE 253 +/- 57, n = 8) and in-labour (choriodecidua: control 531 +/- 74, n = 14, PE 881 +/- 188, n = 8; amnion: control 545 +/- 84, n = 14, PE 1008 +/- 230, n = 8) groups. AdM mRNA relative abundance was greater in preterm, not-in-labour choriodecidual samples in PE, but not in amnion. In addition, this study observed labour-associated increases in choriodecidual and amniotic irAdM in term pre-eclamptic and control patients. However, there were no significant changes in AdM protein or mRNA expressions between any of the groups for placental tissue. These results suggest that fetal membranes, but not placental, production of AdM is increased at the post-translational level during PE in preterm and term tissues and at the pre-translational level during PE in preterm tissues. Fetal membranes, AdM may play an important role in the regulation of feto-placental hemodynamics and fetal physiology during pre-eclampsia.

Vascular expression of adrenomedullin is increased in Wistar rats during early pregnancy

OBJECTIVE

Circulating levels of adrenomedullin (ADM)--a vasodilator peptide with long-lasting effects--increase in the course of pregnancy. Neither the site nor the concomitant rate of ADM synthesis in pregnancy is known. The aim of this study was to test the hypothesis that the rise in plasma levels of ADM during pregnancy is paralleled by increased gene expression and protein levels in the vascular bed.

STUDY DESIGN

We determined in cardiovascular and reproductive tissues of non-pregnant (n=10) and 10-days pregnant (n=10) Wistar rats ADM gene expression by semi-quantitative RT-PCR (normalized to GAPDH). As a support for the mRNA data, protein concentrations were measured by both ELISA and Western blot analysis. Finally, ADM in these tissues was localized by immunohistochemical staining. Statistical analysis was carried out by applying Mann-Whitney U-test.

RESULTS

ADM mRNA levels in the abdominal aorta, renal artery and the kidney were increased during pregnancy. In addition, immunohistochemical staining in the kidney, uterus, abdominal aorta, renal, uterine and superior mesenteric artery was more intense as compared to non-pregnant rats. However, we observed lower concentrations of tissue ADM protein in pregnant rats, indicating an increased release of the hormone by the producing cells.

CONCLUSION

Vascular ADM gene expression is increased in the first half of rat pregnancy. This coincides and may be functionally related to the institution of a high flow/low resistance circulation in pregnancy.

Confocal laser scanning microscope study of terminal villi vessels in normal term and pre-eclamptic placentas

The aim of this study was to compare immunocytochemical confocal scanning laser microscopy measures of villus capillarization in control placentas with pre-eclamptic ones. Accordingly, placentas from normal term pregnancies (n=3) and cases of late-onset pre-eclampsia without intrauterine growth retardation (IUGR) featuring normal uterine artery Doppler (n=3) were analyzed by confocal scanning laser microscopy (CSLM), which is a powerful technique for obtaining three-dimensional reconstructions of any kind of blood vessels (arteries, veins, capillaries). A laser light beam is used in order to detect CD34 antibody-related immunofluorescence, which is a marker of endothelial cells. Villus capillarization was assessed by estimating the following parameters: number of pixels, mean, maximum and minimum immunofluorescence amplitude. Our results show a significant hyper-ramification of the capillary loop in pre-eclamptic placentas, featuring irregular profile and narrow lumina. Such findings support the hypothesis that several agents causing angiogenesis and vasoconstriction affect villus vessels in pre-eclamptic placentas, thus promoting a lasting condition of fetal hypoxia by decreasing endothelial surface and materno-fetal exchanges.

Adrenomedullin expression during hypoxia in fetal sheep

AIM

We asked how adrenomedullin (AM), a vasodilator peptide, was distributed in fetal sheep organs and whether expression of AM would be upregulated in response to moderate acute fetal hypoxia in vivo.

METHODS

In four sheep at day 126-130 of gestation, nitrogen was added to the inspired air by tracheal infusion to reduce fetal arterial oxygen content for a period of 4 h. Control fetuses were from four ewes given a tracheal infusion of room air. Fetal and maternal blood samples were taken prior to and during hypoxia/sham hypoxia. Fetal tissue samples were frozen for RNA analysis and fixed for immunohistochemistry.

RESULTS

In hypoxic fetuses, arterial oxygen content was significantly reduced to 50% compared with sham fetuses with no change in arterial pH in either group. Plasma ACTH levels rose significantly at 2 and 4 h in hypoxic fetuses only. Initial plasma concentrations of AM in control and hypoxic fetuses were 457 +/- 20 and 430 +/- 35 pg mL(-1) and did not change during the experiment. The relative abundance of AM mRNA was placental cotyledons >> lung > cerebral cortex approximately equal to renal cortex > left ventricle approximately equal to right ventricle > adrenal gland > renal medulla > aorta approximately equal to liver. Immunohistochemical staining for AM confirmed distinct labelling in organs with significant expression. AM mRNA level increased significantly in cerebral cortex of hypoxic fetuses.

CONCLUSION

Our results show expression of AM in placenta and in several fetal organs in late gestation sheep. AM may participate in the cerebral vasodilatation that is an integral part of the fetal response to hypoxia.

Vascular Actions of Calcitonin Gene-Related Peptide and Adrenomedullin

This review summarizes the receptor-mediated vascular activities of calcitonin gene-related peptide (CGRP) and the structurally related peptide adrenomedullin (AM). CGRP is a 37-amino acid neuropeptide, primarily released from sensory nerves, whilst AM is produced by stimulated vascular cells, and amylin is secreted from the pancreas. They share vasodilator activity, albeit to varying extents depending on species and tissue. In particular, CGRP has potent activity in the cerebral circulation, which is possibly relevant to the pathology of migraine, whilst vascular sources of AM contribute to dysfunction in cardiovascular disease. Both peptides exhibit potent activity in microvascular beds. All three peptides can act on a family of CGRP receptors that consist of calcitonin receptor-like receptor (CL) linked to one of three receptor activity-modifying proteins (RAMPs) that are essential for functional activity. The association of CL with RAMP1 produces a CGRP receptor, with RAMP2 an AM receptor and with RAMP3 a CGRP/AM receptor. Evidence for the selective activity of the first nonpeptide CGRP antagonist BIBN4096BS for the CGRP receptor is presented. The cardiovascular activity of these peptides in a range of species and in human clinical conditions is detailed, and potential therapeutic applications based on use of antagonists and gene targeting of agonists are discussed.

Neurokinin B causes concentration-dependent relaxation of isolated human placental resistance vessels

Placental neurokinin B (NKB) was recently identified as the causative agent in preeclampsia, a condition characterized by increased maternal and feto-placental vascular resistance. We hypothesized that NKB should constrict placental resistance vessels. Placentas were obtained from normotensive pregnancies. Immediately after delivery, stem villous arteries (300 microm diameter, 1.2 mm long) were dissected from macroscopically normal tissue in cold HEPES-physiological salt solution (PSS), mounted on a wire myograph system, and bathed in HEPES-PSS at 37 degrees C. After determination of the passive-tension internal circumference characteristics, the arteries were set to 90% of the internal circumference they would have under a normal physiological transmural pressure. Cumulative concentration-response curves were constructed for NKB (1 x 10(-12) to 1 x 10(-5) mol/l). Since there was no constrictive response to NKB, cumulative constrictive concentration-response curves were constructed to the thromboxane A(2) mimetic U46619 (1 x 10(-9) to 1 x 10(-5) mol/l). The vessels were then pre-constricted to 80% of maximal response and exposed to cumulative concentrations of NKB (1 x 10(-12) to 1 x 10(-6) mol/l). NKB caused a concentration-dependent relaxation (Maximal response NKB, 51+/-5%, n=5; time control, 12+/-6%, n=4; P<0.05). Removal of the endothelium did not alter the vasodilatory response to NKB. We conclude that, contrary to our hypothesis, NKB causes an endothelium-independent relaxation of the placental resistance vessels. We propose that NKB plays a role in the maintenance of high placental blood flow in normal pregnancy.

Adrenomedullin: Multiple functions in human pregnancy

Adrenomedullin is a 52 amino acid peptide originally isolated from human phaeochromocytoma in 1993. It was initially demonstrated to have profound effects on the vasculature including vasodilatation and subsequently promotion of angiogenesis. Since then it has become apparent that it has a wide range of other biological actions including regulation of cell growth and differentiation. Successful pregnancy outcome relies on establishing and maintaining throughout gestation an efficient blood supply to the fetus. This allows the exchange of nutrients, oxygenation of fetal blood and removal of cytotoxins from the fetus, such as carbon dioxide. One of the most important local adaptations to pregnancy is the change in maternal blood flow to the implantation site. Evidence now points towards a vital role for adrenomedullin in the regulation of placentation. It appears that adrenomedullin may play important roles in the regulation of fetal perfusion both in normal and in compromised pregnancies. However, most studies have focused on measuring adrenomedullin levels and studying its expression as well as that of its receptors. More functional studies are now required to elucidate the underlying mechanisms involved.

Cell and molecular biology of the multifunctional peptide, adrenomedullin

Adrenomedullin (AM) is a recently discovered regulatory peptide involved in many functions including vasodilatation, electrolyte balance, neurotransmission, growth, and hormone secretion regulation, among others. This 52-amino acid peptide is expressed by specific cell types in many organs throughout the body. A complex receptor system has been described for AM; it requires at least the presence of a seven-transmembrane-domain G-protein-coupled receptor, a single-transmembrane-domain receptor activity modifying protein, and a receptor component protein needed to establish the connection with the downstream signal transduction pathway, which usually involves cyclicAMP. In addition, a serum-binding protein regulates the biological actions of AM, frequently by increasing AM functional attributes. Changes in levels of circulating AM correlate with several critical diseases, including cardiovascular and renal disorders, sepsis, cancer, and diabetes. Whether AM is a causal agent, a protective reaction, or just a marker for these diseases is currently under investigation. New technologies seeking to elevate and/or reduce AM levels are being investigated as potential therapeutic avenues.

Adrenomedullin in perinatal medicine

This review will consider whether adrenomedullin (AM) plays a role in the different aspects of perinatal medicine: contributing to maternal systemic vasodilatation during pregnancy, regulating uterine and placental blood flow, being involved in the process of implantation and participating in uterine quiescence prior to parturition. In addition, this will also consider whether a modification of AM secretion contributes to some pathological conditions in pregnancy such as preeclampsia and impairment of fetal growth. The biosynthesis of AM increases in gravid rats and in pregnant women, and the placenta represents an important site of AM production during pregnancy. Both the peptide and its receptors have been found in the uterus, placenta, fetal membranes and cord vessels, and fetal membranes and placental tissues in culture secrete AM. AM contributes to maternal systemic vasodilatation, the placental vessels are relaxed by AM in a dose-dependent manner and AM is expressed in the fetoplacental and umbilical vascular endothelium where basal production of AM contributes to low fetoplacental vascular resistances. Controversy exists over the status of circulating and placental AM in preeclampsia and of the relative contribution of AM to impaired fetoplacental circulation and fetal growth. Moreover, the uterus expresses AM mRNA and exogenous AM relaxes the myometrium in a dose-dependent manner; however, clinical studies have shown that AM does not decrease before the onset of parturition. Rather, AM secretion increases during spontaneous labor and in preterm delivery.

Role of placenta in preeclampsia

Preeclampsia, which manifests itself as hypertension, proteinuria, and edema in pregnancy, requires the presence of trophoblast tissue but not a fetus. It is characterized by abnormal trophoblast invasion of the spiral arteries of the decidua and myometrium leading to a failure to establish an adequate uteroplacental blood flow and, therefore, is thought to give rise to relatively hypoxic trophoblast tissue. This, in turn, may promote an exaggerated state of oxidative stress in the placenta. This hypoxia/oxidative stress may then further attenuate trophoblast invasion but also alters placental villous angiogenesis leading to a poorly developed fetoplacental vasculature with abnormal reactivity. Oxidative stress per se may also affect vascular reactivity, blood flow, and oxygen and nutrient delivery to the fetus, which ultimately may be compromised. The synthetic and transport functions of the syncytiotrophoblast may also be altered, and there is an increased rate of trophoblast apoptosis. The linkage among abnormal trophoblast invasion, trophoblast dysfunction, and the maternal disease remains unidentified. The presumptive humoral factor that is released by the preeclamptic placenta to cause maternal disease remains elusive. Current therapies to prevent preeclampsia aim toward preventing the maternal syndrome, not preventing the primary pathophysiology.

Preeclampsia. Part 2: experimental and genetic considerations

Preeclampsia-eclampsia is still one of the leading causes of maternal and fetal morbidity and mortality. Despite active research for many years, the etiology of this disorder exclusive to human pregnancy is an enigma. Recent evidence suggests there may be several underlying causes or predispositions leading to the signs of hypertension, proteinuria, and edema, findings that allow us to make the diagnosis of the "syndrome" of preeclampsia. Despite improved prenatal care, severe preeclampsia and eclampsia still occur. Although understanding of the pathophysiology of these disorders has improved, treatment has not changed significantly in over 50 years. Although postponement of delivery in selected women with severe preeclampsia improves fetal outcome to a degree, this is not done without risk to the mother. In the United States, magnesium sulfate and hydralazine are the most commonly used medications for seizure prophylaxis and hypertension in the intrapartum period. The search for the underlying cause of this disorder and for a clinical marker to predict those women who will develop preeclampsia-eclampsia is ongoing, with its prevention the ultimate goal. This review began with the clinical and pathophysiologic aspects of preeclampsia-eclampsia (Part 1). Now, in Part 2, the experimental observations, the search for predictive factors, and the genetics of this disorder are reviewed.

Adrenomedullin in mammalian embryogenesis

Here are summarized data supporting that adrenomedullin (AM) is a multifunctional factor involved in the complex regulatory mechanisms of mammalian development. During rodent embryogenesis, AM is first expressed in the heart, followed by a broader but also defined spatio-temporal pattern of expression in vascular, neural, and skeletal-forming tissues as well as in the main embryonic internal organs. AM pattern of expression is suggestive of its involvement in the control of embryonic invasion, proliferation, and differentiation processes, probably through autocrine or paracrine modes of action. AM levels in fetoplacental tissues, uterus, maternal and umbilical plasma are highly increased during normal gestation. These findings in addition to other physiological and gene targeting studies support the importance of AM as a vasorelaxant factor implicated in the regulation of maternal vascular adaptation to pregnancy, as well as of fetal and fetoplacental circulations. AM is also present in amniotic fluid and milk, which is suggestive of additional functions in the maturation and immunological protection of the fetus. Altered expression of AM has been found in some gestational pathologies, although it is not yet clear whether this corresponds to causative or compensatory mechanisms. Future studies in regard to the distribution and expression levels of the molecules known to function as AM receptors, together with data on the action of complement factor H (an AM binding protein), may help to better define the roles of AM during embryonic development.