Adrenomedullin in perinatal medicine

Adrenomedullin has a pivotal role in trophoblast differentiation: A promising nanotechnology-based therapeutic target for early-onset preeclampsia

Early-onset preeclampsia (EOPE) is a severe pregnancy complication associated with defective trophoblast differentiation and functions at implantation, but manifestation of its phenotypes is in late pregnancy. There is no reliable method for early prediction and treatment of EOPE. Adrenomedullin (ADM) is an abundant placental peptide in early pregnancy. Integrated single-cell sequencing and spatial transcriptomics confirm a high ADM expression in the human villous cytotrophoblast and syncytiotrophoblast. The levels of ADM in chorionic villi and serum were lower in first-trimester pregnant women who later developed EOPE than those with normotensive pregnancy. ADM stimulates differentiation of trophoblast stem cells and trophoblast organoids in vitro. In pregnant mice, placenta-specific ADM suppression led to EOPE-like phenotypes. The EOPE-like phenotypes in a mouse PE model were reduced by a placenta-specific nanoparticle-based forced expression of ADM. Our study reveals the roles of trophoblastic ADM in placental development, EOPE pathogenesis, and its potential clinical uses.

Animal models of the placenta accreta spectrum: current status and further perspectives

Placenta accreta spectrum disorder (PAS) is a kind of disease of placentation defined as abnormal trophoblast invasion of part or all of the placenta into the myometrium, even penetrating the uterus. Decidual deficiency, abnormal vascular remodeling in the maternal-fetal interface, and excessive invasion by extravillous trophoblast (EVT) cells contribute to its onset. However, the mechanisms and signaling pathways underlying such phenotypes are not fully understood, partly due to the lack of suitable experimental animal models. Appropriate animal models will facilitate the comprehensive and systematic elucidation of the pathogenesis of PAS. Due to the remarkably similar functional placental villous units and hemochorial placentation to humans, the current animal models of PAS are based on mice. There are various mouse models induced by uterine surgery to simulate different phenotypes of PAS, such as excessive invasion of EVT or immune disturbance at the maternal-fetal interface, which could define the pathological mechanism of PAS from the perspective of the "soil." Additionally, genetically modified mouse models could be used to study PAS, which is helpful to exploring the pathogenesis of PAS from the perspectives of both "soil" and "seed," respectively. This review details early placental development in mice, with a focus on the approaches of PAS modeling. Additionally, the strengths, limitations and the applicability of each strategy and further perspectives are summarized to provide the theoretical foundation for researchers to select appropriate animal models for various research purposes. This will help better determine the pathogenesis of PAS and even promote possible therapy.

Understanding the Placental Biology of Tobacco Smoke, Nicotine, and Marijuana (THC) Exposures During Pregnancy

Widespread public health campaigns have reduces the prevalence of tobacco and nicotine exposures during pregnancy in the United States. However, tobacco and nicotine exposures during pregnancy persist as a common modifiable perinatal risk exposure. Furthermore, declines in tobacco use have been accompanied by parallel rises in both the prevalence and incidence of marijuana use in pregnancy. This is worrisome, as the macromolecules which comprise tobacco and marijuana smoke affect placental function. In this chapter we summarize the decades of evidence contributing to our understanding of the placental molecular pathophysiology accompanying these chemical exposures, thereby rendering risk of adverse perinatal outcomes.

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.

Cigarette smoke-induced placental adrenomedullin expression and trophoblast cell invasion

Smoking in pregnancy reduces preeclampsia risk, but the mechanism of this effect is unknown. Prior studies have demonstrated that women with preeclampsia have lower placental adrenomedullin (AM) expression, and cigarette smoke extract (CSE) treatment of placental trophoblast cells in culture increases AM cellular production. We hypothesized that CSE alters trophoblast invasion through an AM-mediated mechanism, and that placental AM expression is greater among smokers. HTR-8/SVneo trophoblast cells were incubated for 24 hours in Matrigel-invasion chambers with 6 treatment groups: nonstimulated (NS), AM, AM inhibitor (AM22-52), 1% CSE, AM + AM22-52, and 1% CSE + AM22-52. Cells that penetrated the lower surface of the chambers were quantified, invasion indices were calculated, and compared using a 1-way analysis of variance with Bonferroni corrections for multiple comparisons. Trophoblast cells treated with both AM and 1% CSE demonstrated increased cellular invasion compared to NS controls (1.5-fold [P < .01] and 1.45-fold [P < .01], respectively). Cotreatment with the AM inhibitor significantly attenuated the increased invasion seen with both AM and CSE alone. Next, the placental tissue was obtained from 11 smokers and 11 nonsmokers at term and processed for immunohistochemistry (IHC) and real-time quantitative polymerase chain reaction (PCR) for AM. Placentas from smokers demonstrated more intense AM staining and increased AM gene (ADM) expression compared to placentas from nonsmokers (P = .004 for IHC, P = .022 for PCR). The CSE increases trophoblast cell invasion through an AM-mediated process, and placental AM expression is increased among term smokers compared to nonsmokers. These findings provide evidence that the AM pathway may play a role in the protection from preeclampsia seen in smokers.

GPCRs as potential therapeutic targets in preeclampsia

Preeclampsia is an important obstetric complication that arises in 5% of women after the 20(th) week of gestation, for which there is no specific therapy and no cure. Although much of the recent investigation in this field has focused on soluble forms of the angiogenic membrane receptor tyrosine kinase Flt1 and the transforming growth factor β co-receptor Endoglin, there is significant clinical potential for several GPCR targets and their agonists or antagonists in preeclampsia. In this review, we discuss several of the most promising candidates in this category, including calcitonin receptor-like receptor / receptor activity modifying protein 1 complexes, the angiotensin AT1, 2 and Mas receptors, and the relaxin receptor RXFP1. We also address some of the controversies surrounding the roles and therapeutic potential of these GPCRs and their (ant)agonists in preeclampsia.

Low calcitonin receptor like receptor expression in endometrial vessels from women with unexplained infertility

Adrenomedullin (AM) and its receptor subunit, calcitonin receptor-like receptor (CLR) are known to be important for endothelial function. The genotypes and phenotypes of AM and CLR in the endometrium were studied in relation to unexplained infertility. Endometrial biopsies from 12 fertile and 11 infertile women and blood samples from 156 fertile and 106 infertile women were collected. Protein and mRNA expression of AM and CLR was determined using immunohistochemistry and real time PCR. Allele and genotype frequencies in the AM (rs4399321 and rs7944706) and CLR genes (rs696574, rs1528233 and rs3771073) were performed using Taqman genotyping assays. Unexplained infertility was characterised by lower number of vessels stained with CLR in endometrium compared to fertile controls. There was no difference in AM expression. This could not be explained by SNP analysis in the AM or CLR genes. Imbalance in the AM/CLR system might alter endothelial function in women with unexplained infertility.

Regulation by hypoxia of adrenomedullin output and expression in human trophoblast cells

OBJECTIVES

Plasma adrenomedullin concentrations are increased in the fetal circulation in acute and chronic hypoxic conditions. The effect of hypoxia in regulating adrenomedullin synthesis and secretion was investigated in human placental trophoblast cells.

STUDY DESIGN

Human trophoblast cells obtained from term placentas (n = 7) were cultured in hypoxic condition (3% oxygen). Cytotrophoblast cells were cultured for up to 48 h and syncytiotrophoblasts for 2, 8 and 24 h. Changes in adrenomedullin output compared to normoxic conditions were measured by radioimmunoassay. Protein expression was evaluated with Western blot and immunocytochemistry.

RESULTS

Hypoxia induced a time-dependent increase in adrenomedullin output and protein expression by placental trophoblast cells.

CONCLUSIONS

Hypoxia regulates adrenomedullin secretion and expression by human placenta, thereby promoting increased adrenomedullin concentration in the fetal circulation in clinical circumstances characterized by reduced oxygen levels.

Intrafollicular concentration of adrenomedullin is associated with IVF outcome

OBJECTIVE

To test the hypothesis that serum or intrafollicular concentrations of adrenomedullin (AM) would correlate with reproductive outcomes in in vitro fertilisation (IVF) cycles.

DESIGN

Serum and follicular fluid samples were collected during transvaginal oocyte retrieval. The follicular fluid was individually aspirated, and the presence of oocyte was recorded. AM concentrations were measured using an enzyme-linked immunosorbent assay.

SETTING

Department of Gynaecology, Perinatology and Child Health, 'Sapienza' University of Rome, Italy.

PATIENTS

Eighty women undergoing IVF for primary infertility aged 18-45 years.

MAIN OUTCOME MEASURES

AM concentrations in plasma and follicular fluid were correlated to follicular fluid volume, presence of oocyte, oocyte maturation, embryo grading, fertilisation and pregnancy rates, live-birth rate and plasma estrogen concentration.

RESULTS

Monofollicular fluid AM concentrations did not differ between follicles containing oocyte and those without oocyte; however, AM concentrations were lower in follicles that resulted in pregnancy than in those that failed. Serum but not follicular fluid AM concentrations correlated with serum estrogen levels. Follicular fluid AM correlated with plasma AM levels.

CONCLUSION

We conclude that higher level of AM in the follicular fluid appears to be associated with a negative outcome in IVF treatment.

Effect of corticosteroids and progesterone on adrenomedullin output and expression in human fetal membranes and placenta trophoblasts

OBJECTIVE

Plasma adrenomedullin (AM) concentrations are increased in fetal and maternal circulation in response to exogenous glucocorticoids administration. The role of corticosteroids and progesterone in regulating AM synthesis and secretion was investigated in amnion and chorion trophoblast cells of the fetal membranes and in placental trophoblast cells.

STUDY DESIGN

Cells were treated with betamethasone, hydrocortisone, and progesterone. Changes in AM output were measured with radioimmunoassay. Protein expression was evaluated with Western blot and immunohistochemistry.

RESULTS

Betamethasone stimulated AM secretion and protein expression in placental trophoblast cells and in amnion cells of the fetal membranes. Hydrocortisone and progesterone did not induce any effect either on secretion or protein expression in placenta and fetal membranes cells.

CONCLUSION

Glucocorticoids regulate AM secretion and expression by human placenta thereby promoting increased AM concentration in maternal and fetal circulation in circumstances characterized by increased cortisol levels.

Haploinsufficiency for adrenomedullin reduces pinopodes and diminishes uterine receptivity in mice

Adrenomedullin (AM) is a multifunctional peptide vasodilator that signals through a G-protein-coupled receptor when the receptor, called calcitonin receptor-like receptor (CL), is associated with a receptor activity-modifying protein 2 (RAMP2). We demonstrated previously that haploinsufficieny for each of these genes led to reduced maternal fertility, and that even a modest genetic reduction of AM peptide caused maternal defects in implantation, placentation, and fetal growth. Here, we further demonstrate that Adm(+/-) female mice displayed reduced pregnancy success rates that were not caused by defects in folliculogenesis, ovulation, or fertilization. The poor fertility of Adm(+/-) female mice could not be rescued by transfer of wild-type blastocysts, which suggested an underlying defect in uterine receptivity. In fact, we found that Adm, Calcrl, and Ramp2 gene expressions are tightly and spatiotemporally regulated in the luminal epithelial cells of the uterus during the estrus cycle and the peri-implantation period. RAMP3, which also generates an AM receptor when associated with CL, had a diametrically opposite expression pattern than that of Adm, Calcrl, and Ramp2 and was most robustly induced in the stroma of the uterus. Finally, we discovered that Adm(+/-) female mice have a substantially reduced number of pinopodes on the uterine luminal epithelial surface, which is indicative and possibly causative of the poor uterine receptivity. Taken together, our studies identify a new class of pharmacologically tractable proteins that are involved in establishing uterine receptivity through the regulation of pinopode formation.

Maternal and umbilical venous adrenomedullin and nitric oxide levels in intrauterine growth restriction

OBJECTIVE

To verify whether adrenomedullin (AM) and nitric oxide (NO) concentrations are changed in the maternal and fetal circulation in pregnancies complicated by intrauterine growth restriction (IUGR) compared to normal pregnancies, and to determine any relationship between them.

METHODS

Forty-six small for gestational age (SGA) and 34 appropriate for gestational age (AGA) infants were included in the study. Umbilical and maternal venous AM and NO concentrations were determined.

RESULTS

Umbilical NO concentrations in SGA infants (mean +/- SD; 176.2 +/- 75.8 micromol/L) were significantly greater than in AGA infants (143.4 +/- 39.2 micromol/L) (p = 0.015). However, umbilical AM concentrations were similar in SGA and AGA infants with 14.2 +/- 4.4 pmol/mL and 14.5 +/- 6.2 pmol/mL, respectively (p > 0.05). There was no relationship between NO and AM levels in umbilical blood (r = 0.09, p = 0.40). No difference was found between either AM or NO levels in the maternal plasma of the two groups.

CONCLUSIONS

We suggest that NO is increased in the fetoplacental circulation in SGA infants probably as a response to decreased blood flow, whereas AM is not. Additionally, increased NO in the fetoplacental circulation was found to be independent from AM secretion.

Receptor activity-modifying proteins: RAMPing up adrenomedullin signaling

Adrenomedullin (AM) is a 52-amino-acid multifunctional peptide that circulates in the plasma in the low picomolar range and can exert a multitude of biological effects through an autocrine/paracrine mode of action. The mechanism by which AM transduces its signal represents a novel and pharmacologically tractable paradigm in G protein-coupled receptor signaling. Since its discovery in 1993, the study of AM has emerged into a new field of research with nearly 1800 publications that rivals the renown of other common factors like angiopoetin (1015 publications) and ghrelin (1550 publications). Despite the tremendous strides made in recent years toward unveiling the biochemical and cellular functions of AM, we are still lagging in our understanding of the essential roles of AM in normal and disease physiology. As discussed in this current review, a concerted effort to combine information from clinical, genomic, biochemical, and genetic mouse model sources can provide a focused view to help define the physiological functions of AM. Specifically, we find that certain conditions, such as pregnancy, cardiovascular disease, and sepsis, are associated with robust and dynamic changes in the expression of AM and AM receptor proteins, which together represent an elegant mechanism for altering the physiological responsiveness or function of AM. Thus, the modulation of AM signaling may be further exploited for therapeutic strategies in the management and treatment of human disease.

Reduced maternal expression of adrenomedullin disrupts fertility, placentation, and fetal growth in mice

Adrenomedullin (AM) is a multifunctional peptide vasodilator that is essential for life. Plasma AM expression dramatically increases during pregnancy, and alterations in its levels are associated with complications of pregnancy including fetal growth restriction (FGR) and preeclampsia. Using AM+/- female mice with genetically reduced AM expression, we demonstrate that fetal growth and placental development are seriously compromised by this modest decrease in expression. AM+/- female mice had reduced fertility characterized by FGR. The incidence of FGR was also influenced by the genotype of the embryo, since AM-/- embryos were more often affected than either AM+/- or AM+/+ embryos. We demonstrate that fetal trophoblast cells and the maternal uterine wall have coordinated and localized increases in AM gene expression at the time of implantation. Placentas from growth-restricted embryos showed defects in trophoblast cell invasion, similar to defects that underlie human preeclampsia and placenta accreta. Our data provide a genetic in vivo model to implicate both maternal and, to a lesser extent, embryonic levels of AM in the processes of implantation, placentation, and subsequent fetal growth. This study provides the first genetic evidence to our knowledge to suggest that a modest reduction in human AM expression during pregnancy may have an unfavorable impact on reproduction.

Effect of betamethasone in vivo on placental adrenomedullin in human pregnancy

OBJECTIVE

The aim of the current study was to determine the effects of in vivo administration of prenatal betamethasone in patients at risk for preterm delivery on adrenomedullin (AM) concentrations in maternal and fetal plasma and on AM localization in placenta and fetal membranes.

METHODS

A total of 62 pregnant women between 25 and 35 weeks' gestation were studied. Forty-seven pregnant women received betamethasone (2 x 12 mg intramuscularly given 24 hours apart) for stimulation of fetal lung maturity. Blood samples were collected before betamethasone administration and at different time points after the first and the second dose. Further samples were collected at delivery and, in women who did not deliver, after 1 week and 30 days from betamethasone administration. At delivery, placenta and membranes were collected. Fifteen patients who delivered at the same gestational age not receiving betamethasone represented the control group. AM concentration was determined by radioimmunoassay. Localization of AM in placental tissues was assessed by immunohistochemistry.

RESULTS

Betamethasone caused approximately 50% increase in maternal plasma AM at 1 week after administration, whereas in fetal plasma AM levels increased by about 90% at 48 hours after betamethasone administration. There was increased immunohistochemical staining for AM in fetoplacental tissues collected after betamethasone administration.

CONCLUSION

These results provide the first evidence for in vivo stimulation of AM, likely of placental origin, by glucocorticoids in the third trimester human 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.

Circulating mature adrenomedullin is related to blood volume in full-term pregnancy

Plasma adrenomedullin concentration increases during pregnancy. We measured blood volume and mature adrenomedullin concentration in plasma and cerebrospinal fluid and examined whether mature adrenomedullin in plasma and cerebrospinal fluid was associated with increasing blood volume during pregnancy. We enrolled 47 women undergoing surgery with spinal anesthesia in this study. We first measured mature adrenomedullin concentration in plasma and cerebrospinal fluid of nonpregnant women undergoing orthopedic surgery, pregnant women between 15 and 18 wk of gestation undergoing gynecological surgery, and pregnant women at full-term undergoing cesarean delivery. The second study included 20 healthy and full-term parturients scheduled for cesarean delivery. We measured arterial blood pressure and blood volume by noninvasive pulse spectrophotometry using indocyanine green. Plasma-mature adrenomedullin concentration was 1.24 +/- 0.98, 2.79 +/- 1.23, 4.79 +/- 2.61 fmol/mL (mean +/- sd) in the nonpregnant, the early gestation, and the full-term groups, respectively. But in cerebrospinal fluid, mature adrenomedullin did not significantly increase. Furthermore, mature adrenomedullin in plasma, but not cerebrospinal fluid, had a significant correlation with blood volume per unit body weight (r2= 0.46; P = 0.0009). These findings demonstrate that plasma-mature adrenomedullin concentration increased and that increased plasma-mature adrenomedullin is associated with increased blood volume during pregnancy.

The functional genomic distribution of protein divergence in two animal phyla: coevolution, genomic conflict, and constraint

We compare the functional spectrum of protein evolution in two separate animal lineages with respect to two hypotheses: (1) rates of divergence are distributed similarly among functional classes within both lineages, indicating that selective pressure on the proteome is largely independent of organismic-level biological requirements; and (2) rates of divergence are distributed differently among functional classes within each lineage, indicating species-specific selective regimes impact genome-wide substitutional patterns. Integrating comparative genome sequence with data from tissue-specific expressed-sequence-tag (EST) libraries and detailed database annotations, we find a functional genomic signature of rapid evolution and selective constraint shared between mammalian and nematode lineages despite their extensive morphological and ecological differences and distant common ancestry. In both phyla, we find evidence of accelerated evolution among components of molecular systems involved in coevolutionary change. In mammals, lineage-specific fast evolving genes include those involved in reproduction, immunity, and possibly, maternal-fetal conflict. Likelihood ratio tests provide evidence for positive selection in these rapidly evolving functional categories in mammals. In contrast, slowly evolving genes, in terms of amino acid or insertion/deletion (indel) change, in both phyla are involved in core molecular processes such as transcription, translation, and protein transport. Thus, strong purifying selection appears to act on the same core cellular processes in both mammalian and nematode lineages, whereas positive and/or relaxed selection acts on different biological processes in each lineage.

Adrenomedullin antagonist treatment during early gestation in rats causes fetoplacental growth restriction through apoptosis

Adrenomedullin (AM), a potent vasorelaxant peptide, has been shown to function as an angiogenic and growth factor. The present study investigated whether antagonism of endogenous AM in rats during early gestation results in diminished placental and fetal growth and whether this occurs through induction of apoptosis. Rats on Gestational Day 8 were implanted s.c. with osmotic minipumps delivering 125 and 250 microg rat(-1) day(-1) of AM(22-52) and were killed on Gestational Day 15. In AM(22-52)-treated rats, both placental and fetal weights were dose-dependently inhibited, with 50% reduction in the group receiving 250 microg rat(-1) day(-1). In these animals, fetal resorption sites were also increased. Apoptosis was demonstrated in placenta and uterus by the TUNEL method. Apoptotic changes were more apparent in trophoblast cells in the labyrinth zone of placenta and uterine decidua of AM(22-52)-treated rats when compared with vehicle-control rats. Immunoreactivity to active caspase-3 protein was abundant in the placenta and uterus of the AM(22-52)-treated group. Western blot analysis demonstrated that in homogenates of both the placenta and uterus of AM(22-52)-treated rats, levels of active caspase-9 and -3 as well as of Poly ADP ribose polymerase were significantly increased, whereas levels of Bcl-2 protein decreased, compared with controls. However, no significant treatment-associated changes were observed in Bid, Fas, Fas ligand, p53, and caspase-8 and -10 proteins in either placenta or uterus. Bad protein was undetectable in either tissue. In mitochondrial fractions from both placenta and uterus, the levels of Bax increased with decreases in cytochrome c on AM(22-52) treatment. Conversely, in the cytosol, Bax levels decreased with increases in cytochrome c, demonstrating translocation of Bax from cytosol to mitochondria and release of cytochrome c from mitochondria with AM(22-52) treatment. In conclusion, these findings show that antagonism of AM in rats during early pregnancy caused fetoplacental growth restriction through the activation of mitochondrial apoptotic pathways.

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.