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Query: UMLS:C0022116 (ischemia)
 91,303 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Normal pregnancy is associated with reductions in total vascular resistance and arterial pressure possibly due to enhanced endothelium-dependent vascular relaxation and decreased vascular reactivity to vasoconstrictor agonists. These beneficial hemodynamic and vascular changes do not occur in women who develop preeclampsia; instead, severe increases in vascular resistance and arterial pressure are observed. Although preeclampsia represents a major cause of maternal and fetal morbidity and mortality, the vascular and cellular mechanisms underlying this disorder have not been clearly identified. Studies in hypertensive pregnant women and experimental animal models suggested that reduction in uteroplacental perfusion pressure and the ensuing placental ischemia/hypoxia during late pregnancy may trigger the release of placental factors that initiate a cascade of cellular and molecular events leading to endothelial and vascular smooth muscle cell dysfunction and thereby increased vascular resistance and arterial pressure. The reduction in uterine perfusion pressure and the ensuing placental ischemia are possibly caused by inadequate cytotrophoblast invasion of the uterine spiral arteries. Placental ischemia may promote the release of a variety of biologically active factors, including cytokines such as tumor necrosis factor-alpha and reactive oxygen species. Threshold increases in the plasma levels of placental factors may lead to endothelial cell dysfunction, alterations in the release of vasodilator substances such as nitric oxide (NO), prostacyclin (PGI(2)), and endothelium-derived hyperpolarizing factor, and thereby reductions of the NO-cGMP, PGI(2)-cAMP, and hyperpolarizing factor vascular relaxation pathways. The placental factors may also increase the release of or the vascular reactivity to endothelium-derived contracting factors such as endothelin, thromboxane, and ANG II. These contracting factors could increase intracellular Ca(2+) concentrations ([Ca(2+)](i)) and stimulate Ca(2+)-dependent contraction pathways in vascular smooth muscle. The contracting factors could also increase the activity of vascular protein kinases such as protein kinase C, leading to increased myofilament force sensitivity to [Ca(2+)](i) and enhancement of smooth muscle contraction. The decreased endothelium-dependent mechanisms of vascular relaxation and the enhanced mechanisms of vascular smooth muscle contraction represent plausible causes of the increased vascular resistance and arterial pressure associated with preeclampsia.
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PMID:Vascular mechanisms of increased arterial pressure in preeclampsia: lessons from animal models. 1206 28

Studies during the past decade have provided a better understanding of the potential mechanisms responsible for the pathogenesis of preeclampsia. The initiating event in preeclampsia has been postulated to be reduced uteroplacental perfusion as a result of abnormal cytotrophoblast invasion of spiral arterioles. Placental ischemia/hypoxia is thought to lead to widespread activation/dysfunction of the maternal vascular endothelium which results in enhanced formation of endothelin, thromboxane, and superoxide, increased vascular sensitivity to angiotensin II, and decreased formation of vasodilators such as nitric oxide and prostacyclin. These endothelial abnormalities, in turn, cause hypertension by impairing renal function and increasing total peripheral resistance. While recent studies support a role for cytokines and other factors such as lipid peroxides and reactive oxygen intermediates as potential mediators of endothelial dysfunction, finding the link between placental ischemia/hypoxia and maternal endothelial and vascular abnormalities remains an important area of investigation. The quantitative importance of the various endothelial and humoral factors in mediating the vasoconstriction and elevation in arterial pressure during preeclampsia has also not been completely elucidated.
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PMID:Pathophysiology of preeclampsia: linking placental ischemia/hypoxia with microvascular dysfunction. 1208 Apr 13

Preeclampsia is a severe disorder of human pregnancy characterized by generalized activation of maternal endothelial cells. Oxidative stress of the placenta is considered a key intermediary step, precipitating deportation of apoptotic fragments into the maternal circulation, but the cause remains unknown. We hypothesize that intermittent placental perfusion, secondary to deficient trophoblast invasion of the endometrial arteries, leads to an ischemia-reperfusion-type insult. We therefore tested whether hypoxia-reoxygenation (H/R) in vitro stimulates apoptosis in human placental tissues compared with controls kept hypoxic or normoxic throughout. After H/R, release of cytochrome c from mitochondria was significantly increased and was associated with intense immunolabeling for active caspase 3 in the syncytiotrophoblast and fetal endothelial cells. There was also increased labeling of syncytiotrophoblastic nuclei for cleaved poly (ADP-ribose) polymerase (PARP), and higher cytosolic concentrations of cleaved PARP fragment were detected by Western blot. Syncytiotrophoblastic nuclei displayed increased chromatin condensation, and a significantly greater percentage was TUNEL positive. These changes were accompanied by increased lactate dehydrogenase release into the medium. Preadministration of the free radical scavenger, desferrioxamine, reduced cytochrome c release and the TUNEL-positive index, suggesting generation of hydroxyl radicals mediates these processes. By contrast, hypoxia alone caused a smaller increase in the TUNEL-positive index, and the majority of syncytiotrophoblastic nuclei displayed karyolysis, whereas normoxic controls remained euchromatic. We conclude that H/R stimulates apoptotic changes within the syncytiotrophoblast, whereas hypoxia principally induces necrosis. The quality of placental perfusion may therefore be a more important factor in the pathophysiology of preeclampsia than the absolute quantity.
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PMID:Hypoxia-reoxygenation: a potent inducer of apoptotic changes in the human placenta and possible etiological factor in preeclampsia. 1208 65

A genetic predisposition (theory 1) to preeclampsia in a woman with or without risk factors, may lead to an immune maladaptation to pregnancy (theory 2) (Th1 type of immune response predominance over Th2). In turn, they may contribute to an early defective 'switch' (quantitatively or out of timing) with a predominant decidual production of 16-kDa PRL over that of a 23-kDa PRL (our hypothesis), which induces an antiangiogenic process with a shallow invasion of the spiral arteries by the endovascular cytotrophoblast. Afterwards, a high-resistance arteriolar system and placental ischemia or hypoxia ensue, leading to endothelial cell dysfunction (theory 3) and an increased oxidative stress (theory 4). We are not proposing any strict chronological sequence of events, but the early occurrence (first 10 weeks) during pregnancy of the predominant decidual secretion of a 16-kDa PRL over that of 23-kDa PRL inducing a defective angiogenic process. No other specific mechanism(s) to explain the 'shallow' invasion of the spiral arteries has been previously proposed. Furthermore, it seems to happen early enough in pregnancy, as a 'very early change which may give a clue to the etiology,' as first suggested 25 years ago by Horrobin.
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PMID:The possible role of prolactin in preeclampsia: 2001, a hypothesis revisited a quarter of century later. 1220 75

Preeclampsia is an obstetric disease of unknown cause that affects approximately 5% of pregnant women. The visual system may be affected with variable intensity, being the retinal detachment a rare complication. The retinal detachment in preeclampsia is usually bilateral and serous, and its pathogenesis is related to the choroidal ischemia secondary to an intense arteriolar vasospasm. The majority of patients have complete recovery of vision with clinical management, and surgery is unnecessary. This is a case report of a 27 year old patient who developed the severe form of preeclampsia on her first pregnancy. She had progressive blurred vision, until she could see only shadows. Ophthalmic examination diagnosed spread and bilateral retinal detachment. With blood pressure control at postpartum, the patient had her retina reattached, and recovery of vision.
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PMID:Retinal detachment in preeclampsia. 1221 93

Preeclampsia, a syndrome affecting 5% of pregnancies, causes substantial maternal and fetal morbidity and mortality. The pathophysiology of preeclampsia remains largely unknown. It has been hypothesized that placental ischemia is an early event, leading to placental production of a soluble factor or factors that cause maternal endothelial dysfunction, resulting in the clinical findings of hypertension, proteinuria, and edema. Here, we confirm that placental soluble fms-like tyrosine kinase 1 (sFlt1), an antagonist of VEGF and placental growth factor (PlGF), is upregulated in preeclampsia, leading to increased systemic levels of sFlt1 that fall after delivery. We demonstrate that increased circulating sFlt1 in patients with preeclampsia is associated with decreased circulating levels of free VEGF and PlGF, resulting in endothelial dysfunction in vitro that can be rescued by exogenous VEGF and PlGF. Additionally, VEGF and PlGF cause microvascular relaxation of rat renal arterioles in vitro that is blocked by sFlt1. Finally, administration of sFlt1 to pregnant rats induces hypertension, proteinuria, and glomerular endotheliosis, the classic lesion of preeclampsia. These observations suggest that excess circulating sFlt1 contributes to the pathogenesis of preeclampsia.
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PMID:Excess placental soluble fms-like tyrosine kinase 1 (sFlt1) may contribute to endothelial dysfunction, hypertension, and proteinuria in preeclampsia. 1261 13

Endothelial dysfunction underlies the pathogenesis of preeclampsia, but its mechanism has not yet been completely understood. Elevated oxygen free radicals may partially explain the endothelial cell damage. In this study, we have aimed to measure homocysteine (Hcy) and nitric oxide (NO) levels as endothelial dysfunction markers in preeclamptic women. Nineteen preeclamptic (33.9 +/- 1.4 weeks) and 15 gestational-age-matched normal pregnant women (35.5 +/- 0.7 weeks) were included in the study. Mean NO level was significantly lower (p < 0.001) and mean Hcy level was significantly higher (p < 0.001) in the preeclamptic group. Elevated Hcy and oxygen free radical levels could decrease NO levels due to the reaction with each other and reduced NO may increase blood pressure and ischemia in preeclamptic patients. We have concluded that increased Hcy and oxygen free radical levels, and decreased NO levels are closely associated with preeclampsia-related endothelial dysfunction.
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PMID:Endothelial dysfunction in preeclampsia. Increased homocysteine and decreased nitric oxide levels. 1461 53

The vascular placental pathology (VPP) is associated with many etiologies. Some are the consequence of a maternal genetic or acquired predisposition. Others are associated with a chronic maternal disease (hypertension, lupus, obesity, diabetes, ...). Finally, some others are associated with placental implantation leading to fetal ischemia (multiple pregnancy, chorioangioma, primiparity, feto-placental hydrops) or to environmental (altitude) or nutritional factors (famine and specific alimentary depressions). We classify these factors into three categories according to the risk level (moderate, significant and elevated). While any of these factors can increase the risk of VPP, no one is sufficiently sensitive or specific in predict inevitable onset of VPP. In most cases VPP results from a combination of two (or more) risk factors. The risk factors of VPP classified as moderate include age (> or = 35 years), increased blood pressure during the second trimester of pregnancy, a new paternity, dietetic factors or environmental factors, smoking and controlled diabetes (class B, C), or inactive systemic diseases. Risk is significantly elevated among obese (BMI > or = 25), primiparous women, women with a past familial history (first degree) of preeclampsia or eclampsia, cocaine use or association of tobacco and caffeine use, increased placental mass (associated with twin pregnancy, fetal hydrops or molar pregnancy), uncontrolled diabetes, lupus, active scleroderma. Risk is considered to be high among patients with chronic hypertension, women with a past history of preeclampsia, diabetes (class D, F, R), patients with active systemic disease or with antiphospholipid antibodies or women with lupus or renal lesions and/or proteinuria as well as chronic kidney disease resulting in proteinuria, hypertension and renal insufficiency. Finally, the risk of VPP is considered to be increased in the presence of acquired thrombophilia. It remains moderate in the presence of isolated genetic thrombophilia, except in forms presenting with multiple genetic mutations or associated with an hyperhomocysteinemia. A "high-risk group" is defined among women with past history of deep venous thromboembolic events outside pregnancy, or with a past history of placental vascular pathology (intra-uterine death, placental abruptio, severe and precocious placental, intra-uterine growth retardation, early and repetitive fetal loss) and who, in addition, present with acquired thrombophilia (antiphospholipid antibodies, thrombocytemia), unique homozygous genetic thrombophilia, amultiple genetic thrombophilia or unique heterozygous genetic thrombophilia associated with hyperhomocysteinemia. Prophylactic treatment of acquired thrombophilia and of the multiple genetic forms or associated with hypercysteinemia is a logical rationale, particularly among women with a past history of placental vascular pathology, or with a past history of venous thromboembolic events. On the contrary, prophylaxis using low-molecular-weight heparin in the event of asymptomatic genetic thrombophilic mutations and for women without a past history of deep venous thromboembolism or vascular placental pathology remains controversial.
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PMID:[Vascular placental pathology in high-risk groups: definition and synopsis]. 1502 87

Placental vascular diseases consist of obstetrical pathologies assumed to be linked to placental ischemia. Preeclampsia, defined as the association of hypertension, proteinuria and edema, occur in 3% of deliveries, in a non-selected population. Eclampsia, defined as the occurrence of convulsions in preeclamptic women, occur in 5 per 10,000 deliveries. Risk factors for preeclampsia are: preeclampsia in the previous pregnancy, maternal age <20 years, multiple pregnancies, and nulliparity. Placenta abruption, defined as premature separation of the placenta before delivery, occur in 5 to 15 per 1,000 deliveries. Risk factors are smoking, infertility, and preeclampsia or placental abruption in the previous pregnancy. Stillbirth, defined as fetal death between 24 weeks of gestation and delivery, occur in 1.5 per 1,000 deliveries, with a higher frequency in case of placental abruption, intrauterine growth restriction or preeclampsia.
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PMID:[Epidemiology of vascular placental disease]. 1502 84

Elevated plasma VEGF concentrations in preeclampsia are associated with local placental ischemia and endothelial dysfunction. We investigated the urinary VEGF excretion in women with severe preeclampsia (n=37) and its relation with proteinuria compared to that in healthy pregnant (n=32) and non-pregnant women (n=30). In women with severe preeclampsia VEGF levels were 54.0 (19.9-192.4) ng/mmol creatinine, significantly (p<0.0001) higher than levels in pregnant controls (28.2 (6.7-63.0) ng/mmol creatinine) and non-pregnant controls (29.5 (10.1-59.1) ng/mmol creatinine). Proteinuria was not significantly correlated with urinary VEGF levels. In conclusion, high urinary VEGF concentrations in severe preeclampsia might reflect increased renal production of VEGF rather than elevated VEGF levels in the systemic circulation.
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PMID:High levels of urinary vascular endothelial growth factor in women with severe preeclampsia. 1507 30


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