Systemic hemodynamic and regional blood flow changes in response to chronic reductions in uterine perfusion pressure in pregnant rats

Changes in cardiac structure in hypertension produced by placental ischemia in pregnant rats: effect of tumor necrosis factor blockade

OBJECTIVES

Chronic reduction of uteroplacental perfusion pressure (RUPP) in pregnant rats leads to placental ischemia, maternal endothelial cell dysfunction, hypertension and elevated levels of tumor necrosis factor-alpha (TNF-α). In this study we investigated the hypothesis that placental ischemia in pregnant rat, a model of preeclampsia, stimulates cardiac hypertrophy and fibrosis via a TNF-α-dependent mechanism.

METHODS

Normal pregnant Sprague-Dawley rats and RUPP rats were evaluated on day 19 of gestation. To test the role of TNF-α in mediating change in the RUPP rat heart, a TNF-α inhibitor, etanercept, was administered on day 18 of gestation at a dose of 0.8 mg/kg, s.c.

RESULTS

In comparison to normal pregnant rats, RUPP animals display enlarged cardiomyocytes, microvascular rarefaction, fibrosis, apoptosis as well as increased expression of markers of heart hypertrophy and fibrosis. Etanercept (E) treatment prevented enlargement of cardiomyocytes, fibrosis and apoptosis and this was accompanied by significantly lowered blood pressure in RUPP rats. Etanercept treatment lowered expression of mRNA for brain natriuretic peptide, a marker of cardiac hypertrophy. It also heightened expression of endothelial nitric oxide synthase and its phosphorylation as well as oxytocin receptor identified in cardiac microvessels. TNF-α inhibition prevented microvascular rarefaction in the heart as indicated by augmented CD31, a marker of angiogenesis.

CONCLUSIONS

These results suggest that RUPP leads to microvascular rarefaction in the heart, exaggerated cardiomyocyte size, apoptosis, fibrosis, and the alteration of cardiac gene expression that are modulated by the inflammatory cytokine TNFα.

Endothelin type A receptor antagonist attenuates placental ischemia-induced hypertension and uterine vascular resistance

OBJECTIVE

We sought to determine the effect of an endothelin type A receptor antagonist (ETA) on uterine artery resistive index (UARI) and mean arterial pressure (MAP) in a placental ischemia rat model of preeclampsia produced by reduction in uterine perfusion pressure (RUPP).

STUDY DESIGN

UARI was assessed by Doppler velocimetry in RUPP and normal pregnant controls (NP) on gestational days (GD) 12, 15, and 18. UARI was also determined on GD 18 in NP and RUPP pregnant dams after pretreatment with ETA. MAP was recorded on GD 19.

RESULTS

The RUPP group had a higher MAP and UARI on GD 15 and 18 than the NP group. Pretreatment with ETA attenuated both the MAP and GD-18 UARI in the RUPP group without affecting these parameters in the NP group.

CONCLUSION

The improvement in UARI could be one potential mechanism for the reduction in MAP in response to ETA in pregnant dams with ischemic placentas.

Molecular and vascular targets in the pathogenesis and management of the hypertension associated with preeclampsia

Normal pregnancy is associated with significant hemodynamic changes and vasodilation of the uterine and systemic circulation in order to meet the metabolic demands of the mother and developing fetus. Preeclampsia (PE) is one of the foremost complications of pregnancy and a major cause of maternal and fetal mortality. The pathophysiological mechanisms of PE have been elusive, but some parts of the puzzle have begun to unravel. Genetic factors such as leptin gene polymorphism, environmental and dietary factors such as Ca(2+) and vitamin D deficiency, and co-morbidities such as obesity and diabetes may increase the susceptibility of pregnant women to develop PE. An altered maternal immune response may also play a role in the development of PE. Although the pathophysiology of PE is unclear, most studies have implicated inadequate invasion of cytotrophoblasts into the uterine artery, leading to reduced uteroplacental perfusion pressure (RUPP) and placental ischemia/hypoxia. Placental ischemia induces the release of biologically active factors such as growth factor inhibitors, anti-angiogenic factors, inflammatory cytokines, reactive oxygen species, hypoxia-inducible factors, and antibodies to vascular angiotensin II (AngII) receptor. These bioactive factors could cause vascular endotheliosis and consequent increase in vascular resistance and blood pressure, as well as glomerular endotheliosis with consequent proteinuria. The PE-associated vascular endotheliosis could be manifested as decreased vasodilator mediators such as nitric oxide, prostacyclin and hyperpolarizing factor and increased vasoconstrictor mediators such as endothelin-1, AngII and thromboxane A₂. PE could also involve enhanced mechanisms of vascular smooth muscle contraction including intracellular Ca(2+), and Ca(2+) sensitization pathways such as protein kinase C and Rho-kinase. PE-associated changes in the extracellular matrix composition and matrix metalloproteinases activity also promote vascular remodeling and further vasoconstriction in the uterine and systemic circulation. Some of these biologically active factors and vascular mediators have been proposed as biomarkers for early prediction or diagnosis of PE, and as potential targets for prevention or treatment of the disease.

Risk factors and mediators of the vascular dysfunction associated with hypertension in pregnancy

Normal pregnancy is associated with significant hemodynamic changes and vasodilation in the uterine and systemic circulation in order to meet the metabolic demands of the mother and developing fetus. Hypertension in pregnancy (HTN-Preg) and preeclampsia (PE) are major complications and life-threatening conditions to both the mother and fetus. PE is precipitated by various genetic, dietary and environmental factors. Although the initiating events of PE are unclear, inadequate invasion of cytotrophoblasts into the uterine artery is thought to reduce uteroplacental perfusion pressure and lead to placental ischemia/hypoxia. Placental hypoxia induces the release of biologically active factors such as growth factor inhibitors, anti-angiogenic proteins, inflammatory cytokines, reactive oxygen species, hypoxia-inducible factors, and antibodies to vascular angiotensin II receptor. These bioactive factors affect the production/activity of various vascular mediators in the endothelium, smooth muscle and extracellular matrix, leading to severe vasoconstriction and HTN. As an endothelial cell disorder, PE is associated with decreased vasodilator mediators such as nitric oxide, prostacyclin and hyperpolarizing factor and increased vasoconstrictor mediators such as endothelin, angiotensin II and thromboxane A(2). PE also involves enhanced mechanisms of vascular smooth muscle contraction including intracellular free Ca(2+) concentration ([Ca(2+)](i)), and [Ca(2+)](i) sensitization pathways such as protein kinase C, Rho-kinase and mitogen-activated protein kinase. Changes in extracellular matrix composition and matrix metalloproteases activity also promote vascular remodeling and further vasoconstriction in the uterine and systemic circulation. Characterization of the predisposing risk factors, the biologically active factors, and the vascular mediators associated with PE holds the promise for early detection, and should help design specific genetic and pharmacological tools for the management of the vascular dysfunction associated with HTN-Preg.

Circulating and Vascular Bioactive Factors during Hypertension in Pregnancy

Normal pregnancy is associated with significant vascular remodeling in the uterine and systemic circulation in order to meet the metabolic demands of the mother and developing fetus. The pregnancy-associated vascular changes are largely due to alterations in the amount/activity of vascular mediators released from the endothelium, vascular smooth muscle and extracellular matrix. The endothelium releases vasodilator substances such as nitric oxide, prostacyclin and hyperpolarizing factor as well as vasoconstrictor factors such as endothelin, angiotensin II and thromboxane A(2). Vascular smooth muscle contraction is mediated by intracellular free Ca(2+) concentration ([Ca(2+)](i)), and [Ca(2+)](i) sensitization pathways such as protein kinase C, Rho-kinase and mitogen-activated protein kinase. Extracellular matrix and vascular remodeling are regulated by matrix metalloproteases. Hypertension in pregnancy and preeclampsia are major complications and life threatening conditions to both the mother and fetus, precipitated by various genetic, dietary and environmental factors. The initiating mechanism of preeclampsia and hypertension in pregnancy is unclear; however, most studies have implicated inadequate invasion of cytotrophoblasts into the uterine artery, leading to reduction in the uteroplacental perfusion pressure and placental ischemia/hypoxia. This placental hypoxic state is thought to induce the release of several circulating bioactive factors such as growth factor inhibitors, anti-angiogenic proteins, inflammatory cytokines, reactive oxygen species, hypoxia-inducible factors, and vascular receptor antibodies. Increases in the plasma levels and vascular content of these factors during pregnancy could cause an imbalance in the vascular mediators released from the endothelium, smooth muscle and extracellular matrix, and lead to severe vasoconstriction and hypertension. This review will discuss the interactions between the various circulating bioactive factors and the vascular mediators released during hypertension in pregnancy, and provide an insight into the current and future approaches in the management of preeclampsia.

Impaired vascular function in mice with an active cytomegalovirus infection

Human cytomegalovirus (CMV) is implicated in vascular complications through endothelial dysfunction. However, the effect of in vivo infections on vascular function in isolated arteries has not been examined. In pregnancy, systemic and uterine vascular adaptations accommodate increased blood volume through several mechanisms, including decreased sensitivity to vasoconstrictors and increased production of endothelial-dependent vasodilators. We hypothesized that an active in vivo CMV infection would reduce vasodilation of isolated arteries to the endothelial-dependent vasodilator methacholine and increase vasoconstriction to the α1-adrenergic receptor agonist phenylephrine and that these CMV-induced changes would be accentuated in late pregnancy. A mouse CMV infection model was used to study vascular responses in isolated mesenteric and uterine arteries from nonpregnant and late pregnant mice. In the mouse, CMV is not transmitted to the fetus. Accordingly, there was no evidence of active infection in any fetus examined, even though an active infection was found in salivary glands, uterine and mesenteric arteries, and placentas. Contrary to our hypothesis, increased endothelial-dependent vasodilation was found in mesenteric arteries from infected compared with uninfected nonpregnant and pregnant mice These data implicate active CMV infections in hypotensive disorders. Similarly, increased vasodilation was found in uterine arteries from infected vs. uninfected nonpregnant mice. However, this was completely reversed in infected compared with uninfected late pregnant mice in which vasodilation in uterine arteries was significantly reduced. Uterine arteries from infected pregnant mice also showed increased vasoconstriction to phenylephrine. Maternal infection led to decreased placental weights but had no effect on fetal weights in late pregnancy. These novel data demonstrate abnormal systemic and uterine vascular responses during an active CMV infection in both nonpregnant and late pregnant mice. Importantly, despite reduced placental weights, fetal weights were maintained, suggesting effective intrauterine compensation in the mouse model.

Hypertension produced by placental ischemia in pregnant rats is associated with increased soluble endoglin expression

Recent clinical studies indicate that an excess of angiostatic factors, such as soluble endoglin (sEng), is related to the occurrence of preeclampsia. Although recent clinical studies report that sEng is increased in preeclamptic women, the mechanisms underlying its overexpression remain unclear. Evidence suggests that hypoxia and induction of heme oxygenase-1 have opposing effects on sEng expression, the former stimulatory and the latter inhibitory. Hence, we hypothesized that placental ischemia because of reduced uterine perfusion pressure (RUPP) in the pregnant rat would increase sEng expression and decrease heme oxygenase-1. Mean arterial pressure was obtained via arterial catheter, and serum and placental proteins were measured by Western blot. Mean arterial pressure was increased (132+/-3 mm Hg versus 102+/-2 mm Hg; P<0.001), and fetal (2.35+/-0.05 g versus 1.76+/-0.08 g; P<0.001) and placental weight were decreased (0.47+/-0.04 g versus 0.58+/-0.03 g; P<0.01) in the RUPP compared with normal pregnant controls. Serum sEng (0.10+/-0.02 arbitrary pixel units [apu] versus 0.05+/-0.01 apu; P<0.05) and placental endoglin (4.7+/-2.3 apu versus 1.45+/-0.42 apu; P<0.05) were increased along with placental hypoxia inducible factor-1 alpha (1.42+/-0.25 apu versus 0.68+/-0.09 apu; P<0.05) expression in the RUPP versus the normal pregnant dams. Placental HO-1 (1.4+/-0.3 apu versus 2.5+/-0.1 apu; P<0.05) expression decreased in the RUPP compared with normal pregnant dams. The present findings support our hypothesis that placental ischemia because of RUPP increases the expression of sEng and shifts the balance of angiogenic factors in the maternal circulation toward an angiostatic state. The present study provides further evidence that placental ischemia is a strong in vivo stimulus of angiostatic factors during pregnancy.

Placental ischemia and cardiovascular dysfunction in preeclampsia and beyond: making the connections

Hypertensive disorders of pregnancy continue to be a significant source of maternal and fetal morbidity and mortality, and recent evidence suggests that the incidence of preeclampsia (PE) is increasing. Recent epidemiological studies indicate that the effects of PE may persist long after pregnancy, in both the mother and the offspring, as increased incidence of cardiovascular disease. The last decade has produced new insights into the pathogenesis of PE. The initiating event in PE appears to be impaired placental perfusion and subsequent placental ischemia, which results in the elaboration of numerous factors. Factors such as soluble fms-like tyrosine kinase-1, soluble endoglin and the angiotensin II type-1 receptor autoantibodies contribute to maternal endothelial and cardiovascular dysfunction, marked by increased reactive oxygen species and decreased bioavailable VEGF, nitric oxide and prostacyclin. However, the importance of the various endothelial and humoral factors that mediate these changes during PE remain to be elucidated.

Differential [Ca2+]i signaling of vasoconstriction in mesenteric microvessels of normal and reduced uterine perfusion pregnant rats

Vascular resistance and blood pressure (BP) are reduced during late normal pregnancy (Norm-Preg). In contrast, studies in human preeclampsia and in animal models of hypertension in pregnancy (HTN-Preg) have suggested that localized reduction in uterine perfusion pressure (RUPP) in late pregnancy is associated with increased systemic vascular resistance and BP; however, the vascular mechanisms involved are unclear. Because Ca2+ is a major determinant of vascular contraction, we hypothesized that the intracellular free calcium concentration ([Ca2+]i) signaling of vasoconstriction is differentially regulated in systemic microvessels during normal and RUPP in late pregnancy. Pressurized mesenteric microvessels from Norm-Preg and RUPP rats were loaded with fura 2 in preparation for simultaneous measurement of diameter and [Ca2+]i (presented as fura 2 340/380 ratio). Basal [Ca2+]i was lower in RUPP (0.73 +/- 0.03) compared with Norm-Preg rats (0.82 +/- 0.03). Membrane depolarization by 96 mM KCl, phenylephrine (Phe, 10(-5) M), angiotensin II (ANG II, 10(-7) M), or endothelin-1 (ET-1, 10(-7) M) caused an initial peak followed by maintained vasoconstriction and [Ca2+]i. KCl caused similar peak vasoconstriction and [Ca2+]i in Norm-Preg (45.5 +/- 3.3 and 0.89 +/- 0.02%) and RUPP rats (46.3 +/- 2.1 and 0.87 +/- 0.01%). Maximum vasoconstriction to Phe, ANG II, and ET-1 was not significantly different between Norm-Preg (28.6 +/- 4.8, 32.5 +/- 6.3, and 40 +/- 4.6%, respectively) and RUPP rats (27.8 +/- 5.9, 34.4 +/- 4.3, and 38.8 +/- 4.1%, respectively). In contrast, the initial Phe-, ANG II-, and ET-1-induced 340/380 ratio ([Ca2+]i) was reduced in RUPP (0.83 +/- 0.02, 0.82 +/- 0.02, and 0.83 +/- 0.03, respectively) compared with Norm-Preg rats (0.95 +/- 0.04, 0.93 +/- 0.01, and 0.92 +/- 0.02, respectively). Also, the [Ca2+]i-vasoconstriction relationship was similar in KCl-treated but shifted to the left in Phe-, ANG II-, and ET-1-treated microvessels of RUPP compared with Norm-Preg rats. The lower agonist-induced [Ca2+]i signal of vasoconstriction and the leftward shift in the [Ca2+]i-vasoconstriction relationship in microvessels of RUPP compared with Norm-Preg rats suggest activation of [Ca2+]i sensitization pathway(s). The similarity in vasoconstriction in RUPP and Norm-Preg rats suggests that such a [Ca2+]i sensitization pathway(s) may also provide a feedback effect on Ca2+ mobilization/homeostatic mechanisms to protect against excessive vasoconstriction in systemic microvessels during RUPP in late pregnancy.

Role of reactive oxygen species in hypertension produced by reduced uterine perfusion in pregnant rats

BACKGROUND

Although recent studies indicate preeclampsia (PE) is associated with increased oxidative stress, the role of reactive oxygen species in the hypertension associated with PE remains unclear. We sought to test the hypothesis that placental ischemia increases oxidative stress which in turn, contributes to hypertension.

METHODS

Reduction in uterine perfusion pressure (RUPP) was induced by placing silver clips on the abdominal aorta and the ovarian arteries on day 14 of pregnancy. On day 20 of pregnancy, mean arterial pressure (MAP) was measured and oxidative stress was assessed in renal and placental tissues whereas systemic administration of tempol, a superoxide dismutase (SOD) mimetic, was used to evaluate the contribution of reactive oxygen species on RUPP-induced hypertension.

RESULTS

MAP (120 +/- 2 mm Hg vs.106 +/- 3 mm Hg), placental levels of 8-isoprostane (1.9 +/- 0.4 ng/g tissue vs. 0.8 +/- 0.1 ng/g tissue), and malondialdehyde (MDA) (6.9 +/- 0.6 micromol/g tissue vs. 3.9 +/- 0.4 micromol/g tissue) were increased, whereas renal cortical SOD activity was decreased in RUPP rats (1.2 +/- 0.1 units/mg protein vs. 1.6 +/- 0.1 units/mg protein) at day 20 of gestation (20 dG) compared to controls. Chronic treatment with tempol attenuated the hypertension (RUPP + tempol 112 +/- 2 mm Hg vs. RUPP, 120 +/- 2 mm Hg) associated with RUPP, whereas tempol had no effect on MAP (NP, 106 +/- 3 vs. NP + tempol, 108 +/- 2) in control rats.

CONCLUSION

The results of this study indicate that placental ischemia decreases innate antioxidant activity resulting in elevated oxidative stress which appears to play a role in mediating hypertension associated with chronic RUPP in pregnant rats.

Pathophysiology of hypertension during preeclampsia: linking placental ischemia with endothelial dysfunction

Studies over the last decade have provided exciting new insights into potential mechanisms underlying the pathogenesis of preeclampsia. The initiating event in preeclampsia is generally regarded to be placental ischemia/hypoxia, which in turn results in the elaboration of a variety of factors from the placenta that generates profound effects on the cardiovascular system. This host of molecules includes factors such as soluble fms-like tyrosine kinase-1, the angiotensin II type 1 receptor autoantibody, and cytokines such as tumor necrosis factor-alpha, which generate widespread dysfunction of the maternal vascular endothelium. This dysfunction manifests as enhanced formation of factors such as endothelin, reactive oxygen species, and augmented vascular sensitivity to angiotensin II. Alternatively, the preeclampsia syndrome may also be evidenced as decreased formation of vasodilators such as nitric oxide and prostacyclin. Taken together, these alterations cause hypertension by impairing renal pressure natriuresis and increasing total peripheral resistance. Moreover, the quantitative importance of the various endothelial and humoral factors that mediate vasoconstriction and elevation of arterial pressure during preeclampsia remains to be elucidated. Thus identifying the connection between placental ischemia/hypoxia and maternal cardiovascular abnormalities in hopes of revealing potential therapeutic regimens remains an important area of investigation and will be the focus of this review.

Hypertension produced by reduced uterine perfusion in pregnant rats is associated with increased soluble fms-like tyrosine kinase-1 expression

The balance between proangiogenic and antiangiogenic factors, such as vascular endothelial growth factor, placental growth factor, and soluble fms-like tyrosine kinase-1 (sFlt-1), is altered in preeclampsia, and this dysregulation of angiogenic factors may be important in the pathogenesis of preeclampsia. Although sFlt-1 is elevated in preeclampsia, the mechanisms responsible for increasing this antiangiogenic factor remain unclear. We hypothesized that the hypertension produced by reduced uterine perfusion pressure (RUPP) is associated with increased sFlt-1 expression and decreased plasma vascular endothelial growth factor and placental growth factor concentrations in the pregnant rat. Arterial pressure was increased (130+/-3 versus 100+/-2 mm Hg; P<0.01) in the RUPP rats compared with the normal pregnant control rats. Plasma sFlt-1 concentration (660+/-270 versus 82+/-26 pg/mL; P<0.05) was increased, whereas plasma free placental growth factor (0.28+/-0.05 versus 1.7+/-0.5 pg/mL; P<0.01) and vascular endothelial growth factor (594+/-34 versus 830+/-33 pg/mL; P<0.01) concentrations were decreased in the RUPP rats compared with normal pregnant rats. Plasma sFlt-1:placental growth factor (37.2+/-7.8 versus 8.9+/-1.6; P<0.02) and sFlt-1:vascular endothelial growth factor (0.86+/-0.22 versus 0.28+/-0.06; P<0.05) ratios were increased in the RUPP rats compared with normal pregnant rats. Immunoreactive placental sFlt-1 was increased (1.1+/-0.1 versus 0.3+/-0.1; P<0.01) in RUPP rats contrasted with the normal pregnant rats. These findings support our hypothesis that RUPP increases the expression of sFlt-1 and alters the balance of angiogenic factors in the maternal circulation. These data also indicate that the RUPP model of pregnancy-induced hypertension may provide an invaluable model for mechanistic studies into the role of sFlt-1 in the pathogenesis preeclampsia.