Objective-Plasma levels of an endogenous nitric oxide (NO) synthase inhibitor, asymmetric dimethylarginine (ADMA), are elevated in chronic renal failure, hypertension, and chronic heart failure. In patients with renal failure, plasma ADMA levels are an independent correlate of left ventricular ejection fraction. However, the cardiovascular effects of a systemic increase in ADMA in humans are not known. Methods and Results-In a randomized, double-blind, placebo-controlled study in 12 healthy male volunteers, we compared the effects of intravenous low-dose ADMA and placebo on heart rate, blood pressure, cardiac output, and systemic vascular resistance at rest and during exercise. We also tested the hypothesis that ADMA is metabolized in humans in vivo by dimethylarginine dimethylaminohydrolase (DDAH) enzymes. Low-dose ADMA reduced heart rate by 9.2Ϯ1.4% from 58.9Ϯ2.0 bpm (PϽ0.001) and cardiac output by 14.8Ϯ1.2% from 4.4Ϯ0.3 L/min (PϽ0.001).ADMA also increased mean blood pressure by 6.0Ϯ1.2% from 88.6Ϯ3.4 mm Hg (PϽ0.005) and SVR by 23.7Ϯ2.1% from 1639.0Ϯ91.6 dyne · s · cm Ϫ5 (PϽ0.001). Handgrip exercise increased cardiac output in control subjects by 96.8Ϯ23.3%, but in subjects given ADMA, cardiac output increased by only 35.3Ϯ10.6% (PϽ0.05). DDAHs metabolize ADMA to citrulline and dimethylamine. Urinary dimethylamine to creatinine ratios significantly increased from 1.26Ϯ0.32 to 2.73Ϯ0.59 after ADMA injection (PϽ0.01). We estimate that humans generate approximately 300 mol of ADMA per day, of which approximately 250 mol is metabolized by DDAHs. Conclusions-This study defines the cardiovascular effects of a systemic increase in ADMA in humans. These are similar to changes seen in diseases associated with ADMA accumulation. Finally, our data also indicate that ADMA is metabolized by DDAHs extensively in humans in vivo. Key Words: asymmetric methylarginine Ⅲ dimethylarginine dimethylaminohydrolase Ⅲ nitric oxide Ⅲ hypertension Ⅲ cardiac output N itric oxide (NO) plays an important role in the regulation of cardiovascular function, and asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthesis, has been implicated in the impairment of NO generation in a variety of cardiovascular diseases. 1 The finding that plasma ADMA levels are elevated in chronic renal failure led to speculation that ADMA may in part be responsible for increased cardiovascular risk and hypertension in these patients. 2 Subsequent studies have shown strong associations between raised ADMA levels and cardiovascular risk factors, endothelial dysfunction, hypertension, atherosclerosis, and cardiovascular mortality. 3-7 ADMA levels are also significantly raised in patients with chronic heart failure, 8 rats with heart failure induced by coronary artery ligation, 9 and dogs with heart failure induced by rapid pacing. 10 A recent analysis of a large group of patients with end-stage renal failure demonstrated an inverse relationship between ADMA levels and left ventricular (LV) ejection fraction; in a multivariate analysis that included L...

1Dimethylarginine dimethylaminohydrolase (DDAH), an enzyme that metabolizes the endogenous nitric oxide synthase inhibitors N0-monomethyl-L-arginine and NG,NG-dimethy-L-arginine to citrulline, was identified by Western blotting in rat and human tissue homogenates.2 S-2-amino-4(3-methylguanidino)butanoic acid (4124W) inhibited the metabolism of ["4C]-N0-monomethyl-L-arginine to ["4C]-citrulline by rat liver homogenates (IC50 416 + 66 giM; n = 9), human cultured endothelial cells (IC50 250 + 34 gLM; n = 9) and isolated purified dimethylarginine dimethylaminohydrolase. 3 Addition of 4124W to culture medium increased the accumulation of endogenously-generated N',N0-dimethy-L-arginine in the supernatant of human cultured endothelial cells from 3.1 + 0.3 to 5+0.7 ,M (n= 15; P<0.005). 4 4124W (1 uM-1 mM) had no direct effect on endothelial nitric oxide synthase activity but caused endothelium-dependent contraction of rat aortic rings (1 mM 4124W increased tone by 81.5 + 9.6% of that caused by phenylephrine 100 nM). This effect was reversed by L-arginine (100 giM). 4124W reversed endothelium-dependent relaxation of human saphenous vein (19.2 + 6.7% reversal of bradykinin-induced relaxation at 1 mM 4124W). 5 These data suggest that inhibition of dimethylarginine dimethylaminohydrolase increases the intracellular concentration of N',N0-dimethyl-L-arginine sufficiently to inhibit nitric oxide synthesis.Inhibiting the activity of DDAH may provide an alternative mechanism for inhibition of nitric oxide synthases and changes in the activity of DDAH could contribute to pathophysiological alterations in NO generation.

Methylarginines inhibit nitric oxide synthases (NOS). Cellular concentrations of methylarginines are determined in part by the activity of dimethylarginine dimethylaminohydrolase (DDAH; EC 3.5.3. 18). We have cloned human DDAH and identified and expressed a second novel DDAH isoform (DDAH I and II respectively). DDAH I predominates in tissues that express neuronal NOS. DDAH II predominates in tissues expressing endothelial NOS. These results strengthen the hypothesis that methylarginine concentration is actively regulated and identify molecular targets for the tissue and cell-specific regulation of methylarginine concentration.

A number of important changes take place in the maternal uterine vasculature during the first few weeks of pregnancy resulting in increased blood flow to the intervillous space. Vascular endothelial and smooth muscle cells are lost from the spiral arteries and are replaced by fetal trophoblast cells. Failure of the vessels to remodel sufficiently is a common feature of pregnancy pathologies such as early pregnancy loss, intrauterine growth restriction and pre-eclampsia. There is evidence to suggest that some vascular changes occur prior to trophoblast invasion, however, in the absence of trophoblasts remodelling of the spiral arteries is reduced. Until recently our knowledge of these events has been obtained from immunohistochemical studies which, although extremely useful, can give little insight into the mechanisms involved. With the development of more complex in vitro models a picture of events at a cellular and molecular level is beginning to emerge, although some caution is required in extrapolating to the in vivo situation. Trophoblasts synthesise and release a plethora of cytokines and growth factors including members of the tumour necrosis factor family. Studies suggest that these factors may be important in regulating the remodelling process by inducing both endothelial and vascular smooth muscle cell apoptosis. In addition, it is evident from studies in other vascular beds that the structure of the vessel is influenced by factors such as flow, changes in the composition of the extracellular matrix, the phenotype of the vascular cells and the local immune cell environment. It is the aim of this review to present our current knowledge of the mechanisms involved in spiral artery remodelling and explore other possible pathways and cellular interactions that may be involved, informed by studies in the cardiovascular field.

Objective-Invasion of uterine spiral arteries by extravillous trophoblasts in the first trimester of pregnancy results in loss of endothelial and musculoelastic layers. This remodeling is crucial for an adequate blood supply to the fetus with a failure to remodel implicated in the etiology of the hypertensive disorder preeclampsia. The mechanism by which trophoblasts induce this key process is unknown. This study gives the first insights into the potential mechanisms involved. Methods and Results-Spiral arteries were dissected from nonplacental bed biopsies obtained at Caesarean section, and a novel model was used to mimic in vivo events. Arteries were cultured with trophoblasts in the lumen, and apoptotic changes in the endothelial layer were detected after 20 hours, leading to loss of endothelium by 96 hours. In vitro, coculture experiments showed that trophoblasts stimulated apoptosis of primary decidual endothelial cells and an endothelial cell line. This was blocked by caspase inhibition and NOK2, a FasL blocking antibody. NOK2 also abrogated trophoblast-induced endothelial apoptosis in the vessel model. Key Words: apoptosis Ⅲ endothelium Ⅲ trophoblast Ⅲ pregnancy Ⅲ arteries R emodeling of the uterine arteries is a key event in early pregnancy. In the first trimester of pregnancy, a subpopulation of fetal trophoblast cells, the extravillous trophoblast, invade the uterine wall (interstitial invasion) and its blood vessels (endovascular invasion) as far as the myometrial segments. In the uterine spiral arteries, the trophoblasts interdigitate between the endothelial cells (ECs), replacing the endothelial lining and most of the musculoelastic tissue in the vessel walls. This creates a high-flow, low-resistance circulation that increases maternal blood flow to the placental villi at the maternal-fetal interface. Conclusions-ExtravillousData suggest that trophoblasts bind to and migrate along the luminal surfaces of the endothelium and transiently coexist on the walls of partially modified spiral arteries before replacing the endothelium. 1,2 Little is known as to how these processes are regulated in normal pregnancies; however, their pivotal importance in the establishment and maintenance of a successful pregnancy is illustrated when they fail to occur or occur to a significantly reduced extent. Defective remodeling of the spiral arteries is associated with pregnancies complicated by preeclampsia and intrauterine growth restriction (IUGR) 3 and is proposed to lead to an overall state of oxidative stress or fluctuations in oxygen concentrations analogous to hypoxia-reperfusion within the placental environment. 4 Preeclampsia and IUGR are responsible for considerable perinatal mortality and morbidity and carry health implications in adult life, including increased risk of hypertension, heart disease, and diabetes. 5 The importance of interactions between trophoblasts and the vascular cells of the spiral arteries, which may account for these differences in remodeling, have yet to be determined in normal or compli...

No abstract

During human pregnancy, natural killer (NK) cells accumulate in the maternal decidua, but their specific roles remain to be determined. Decidual NK (dNK) cells are present during trophoblast invasion and uterine spiral artery remodelling. These events are crucial for successful placentation and the provision of an adequate blood supply to the developing fetus. Remodelling of spiral arteries is impaired in the dangerous pregnancy complication pre-eclampsia. We studied dNK cells isolated from pregnancies at 9–14 weeks' gestation, screened by uterine artery Doppler ultrasound to determine resistance indices which relate to the extent of spiral artery remodelling. dNK cells were able to promote the invasive behaviour of fetal trophoblast cells, partly through HGF. Cells isolated from pregnancies with higher resistance indices were less able to do this and secreted fewer pro-invasive factors. dNK cells from pregnancies with normal resistance indices could induce apoptotic changes in vascular smooth muscle and endothelial cells in vitro, events of importance in vessel remodelling, partly through Fas signalling. dNK cells isolated from high resistance index pregnancies failed to induce vascular apoptosis and secreted fewer pro-apoptotic factors. We have modelled the cellular interactions at the maternal-fetal interface and provide the first demonstration of a functional role for dNK cells in influencing vascular cells. A potential mechanism contributing to impaired vessel remodelling in pregnancies with a higher uterine artery resistance is presented. These findings may be informative in determining the cellular interactions contributing to the pathology of pregnancy disorders where remodelling is impaired, such as pre-eclampsia.Copyright © 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The success of pregnancy is a result of countless ongoing interactions between the placenta and the maternal immune and cardiovascular systems. Pre-eclampsia is a serious pregnancy complication that arises from multiple potential aberrations in these systems. The pathophysiology of pre-eclampsia is established in the first trimester of pregnancy, when a range of deficiencies in placentation affect the key process of spiral artery remodelling. As pregnancy progresses to the third trimester, inadequate spiral artery remodelling along with multiple haemodynamic, placental and maternal factors converge to activate the maternal immune and cardiovascular systems, events which may in part result from increased shedding of placental debris. As we understand more about the pathophysiology of pre-eclampsia, it is becoming clear that the development of early-and late-onset pre-eclampsia, as well as intrauterine growth restriction (IUGR), does not necessarily arise from the same underlying pathology.