Enhanced [Ca2+]i in renal arterial smooth muscle cells of pregnant rats with reduced uterine perfusion pressure

Increased Ca2+-dependent intrinsic tone and arterial stiffness in mesenteric microvessels of hypertensive pregnant rats

Preeclampsia is a pregnancy-related hypertensive disorder (HTN-Preg) with unclear mechanisms. We have shown increased vascular reactivity to extrinsic vasoconstrictors in HTN-Preg rats. Here, we test whether microvascular intrinsic tone and arterial stiffness could contribute to HTN-Preg, and examined the underlying cellular mechanisms. On gestational day 19, BP was recorded in normal pregnant (Preg) rats and Preg rats with reduced uterine perfusion pressure (RUPP), and mesenteric microvessels were mounted on a pressure myograph for measurement of intrinsic tone, simultaneous changes in [Ca2+]i (fura-2 340/380 ratio), and arterial stiffness. Arteries were incubated in Ca2+-containing and 0 Ca2+ (2 mM EGTA) Krebs, pressurized at 10 to 110 mmHg in 10 mmHg increments, and the % change in vessel diameter from initial diameter at 10 mmHg was analyzed for measurement of total (active + passive) intrinsic tone and passive intrinsic response, respectively. The passive response was then subtracted from the total intrinsic tone to determine the active myogenic tone. The strain-stress relationship was also constructed as a measure of arterial stiffness. BP was higher in RUPP vs Preg rats. In Ca2+-containing Krebs, increases in intraluminal pressure caused smaller increases in diameter and greater increases in [Ca2+]i in microvessels of RUPP vs Preg rats, suggesting increased Ca2+-dependent myogenic tone. In 0 Ca2+ Krebs, increases in pressure also caused less increases in diameter in microvessels of RUPP vs Preg rats, but with no changes in [Ca2+]i, suggesting changes in the structure and mechanics of the arterial wall. The total and passive strain-stress relationship was shifted to the left in microvessels of RUPP vs Preg rats, suggesting increased arterial wall stiffness. Histology and immunohistochemistry showed greater vascular wall thickness and collagen-I staining in RUPP vs Preg rats, supporting changes in the wall architecture and structural proteins. The increased active myogenic tone and underlying increases in Ca2+ signaling as well as the increased passive intrinsic response, arterial stiffness and collagen-I in the mesenteric microvessels could play a role in the regulation of blood flow to the splanchnic region and the increased vascular resistance and BP in HTN-Preg.

Oxidative Regulation of Vascular Cav1.2 Channels Triggers Vascular Dysfunction in Hypertension-Related Disorders

Blood pressure is determined by cardiac output and peripheral vascular resistance. The L-type voltage-gated Ca²⁺ (Ca_v1.2) channel in small arteries and arterioles plays an essential role in regulating Ca²⁺ influx, vascular resistance, and blood pressure. Hypertension and preeclampsia are characterized by high blood pressure. In addition, diabetes has a high prevalence of hypertension. The etiology of these disorders remains elusive, involving the complex interplay of environmental and genetic factors. Common to these disorders are oxidative stress and vascular dysfunction. Reactive oxygen species (ROS) derived from NADPH oxidases (NOXs) and mitochondria are primary sources of vascular oxidative stress, whereas dysfunction of the Ca_v1.2 channel confers increased vascular resistance in hypertension. This review will discuss the importance of ROS derived from NOXs and mitochondria in regulating vascular Ca_v1.2 and potential roles of ROS-mediated Ca_v1.2 dysfunction in aberrant vascular function in hypertension, diabetes, and preeclampsia.

Preserved oxytocin-induced myometrium contraction and sensitivity to progesterone inhibition following rat uterus thermal insult. Impact on fertility

Women seeking improved fertility often undergo diagnostic hysteroscopy that could cause uterine thermal injury with unclear impact on uterine contraction, embryo implantation and fertility. We tested whether uterine thermal insult adversely affects myometrium function and contraction related receptors, channels, junctional proteins and remodeling enzymes. Female Sprague-Dawley rats were anesthetized, the left uterine horn was infused with 85 ℃ hot saline (thermal Insult) and the right horn was infused with 25℃ warm saline (control) for 3 min. After 7-days recovery, uterine strips were prepared for tissue histology and measurement of contraction, and mRNA and protein levels of oxytocin receptor, progesterone (P4) receptor A (PR-A), membrane K⁺ channel TREK-1, junctional protein connexin-43 (CX-43) and matrix metalloproteinases MMP-2 and MMP-9. Uterine tissue histology showed cellular swelling and inflammatory cell infiltration immediately following thermal insult, and recovery with no difference from control 7-days later. KCl (96 mM) and oxytocin (10^-13-10^-7 M) caused significant contraction that was not different in thermal insult vs control uterine strips. Pretreatment with P4 (10^-5 M) for 1 h caused marked inhibition of KCl and oxytocin contraction that was insignificantly greater in thermal vs control uterus. RT-PCR showed decreases in oxytocin receptor, PR-A, TREK-1, CX-43, MMP-2 and MMP-9 mRNA in thermal vs control uterus. Western blots showed decreases in oxytocin receptor, no change in TREK-1 and increased PRA, CX-43, MMP-2, and MMP-9 protein levels in thermal vs control uterus. To assess the impact on fertility, female rats were housed with male rats, and on gestational day 19, the litter size, pup weight and crown-rump length, and placenta weight were not different in thermal vs control uterus. Thus, after thermal insult-induced immediate inflammation and reduced heat-sensitive mRNA expression, the uterus undergoes a recovery and adaptation process involving preserved oxytocin-induced contraction, P4 inhibition and TREK-1 channels. The uterus self-healing process appears to require improved PR-A signaling, intercellular communication via CX-43 and tissue remodeling by MMP-2 and MMP-9. The uterine thermal recovery processes could be essential for maintaining fertility and future pregnancy outcome.

Gestational Intermittent Hypoxia Induces Sex-Specific Impairment in Endothelial Mechanisms and Sex Steroid Hormone Levels in Male Rat Offspring

Obstructive sleep apnea (OSA) is highly prevalent during gestation and is linked with adverse fetal outcomes. We examined whether gestational intermittent hypoxia (GIH), the main feature of OSA, leads to sex-specific alterations in cardiovascular function and vascular mechanisms in the offspring. Pregnant rats exposed to intermittent hypoxia or ambient air from gestation days 10 to 21 and their offspring were used for the study. GIH exposure did not affect water and food intake in dams. Compared to controls, the male and female offspring born to GIH dams were smaller in weight by 14% and 12%, respectively, and exhibited catch-up growth. Cardiac function was not affected in either GIH males or females. At 12 weeks of age, blood pressure was increased in GIH males, but not GIH females, compared to their control counterparts. While mesenteric arterial contractile responses to phenylephrine and endothelin were unaffected in GIH males and females, relaxation response to acetylcholine was reduced in GIH males but not GIH females. Relaxation to sodium nitroprusside was unaffected in both GIH males and females. Total eNOS expression was not affected, but phospho(Ser1177)-eNOS levels were decreased in GIH males. eNOS expression and its phosphorylation status were unaffected in GIH females. Serum testosterone and estradiol levels were higher in GIH males but were unaltered in GIH females. Together, these findings suggest that GIH leads to a sex-specific increase in blood pressure in adult male offspring with blunted endothelium-mediated relaxation, decreased eNOS activity, and elevated sex steroid hormone levels.

Characterization of Contractile Machinery of Vascular Smooth Muscles in Hypertension

Hypertension is a key risk factor for cardiovascular disease and it is a growing public health problem worldwide. The pathophysiological mechanisms of vascular smooth muscle (VSM) contraction contribute to the development of hypertension. Calcium (Ca²⁺)-dependent and -independent signaling mechanisms regulate the balance of the myosin light chain kinase and myosin light chain phosphatase to induce myosin phosphorylation, which activates VSM contraction to control blood pressure (BP). Here, we discuss the mechanism of the contractile machinery in VSM, especially RhoA/Rho kinase and PKC/CPI-17 of Ca²⁺ sensitization pathway in hypertension. The two signaling pathways affect BP in physiological and pathophysiological conditions and are highlighted in pulmonary, pregnancy, and salt-sensitive hypertension.

Perfluorooctane sulfonic acid (PFOS) exposure during pregnancy increases blood pressure and impairs vascular relaxation mechanisms in the adult offspring

Perfluorooctanesulfonate (PFOS) is a persistent environmental agent. We examined whether PFOS exposure during pregnancy alters blood pressure in male and female offspring, and if this is related to sex-specific changes in vascular mechanisms. PFOS was administered through drinking water (50 μg/mL) to pregnant Sprague-Dawley rats from gestational day 4 until delivery. PFOS-exposure decreased maternal weight gain but did not significantly alter feed and water intake in dams. The male and female pups born to PFOS mothers were smaller in weight by 29 % and 27 %, respectively. The male PFOS offspring remained smaller through adulthood, but the female PFOS offspring exhibited catch-up growth. The blood pressure at 12 and 16 weeks of age was elevated at similar magnitude in PFOS males and females than controls. Mesenteric arterial relaxation to acetylcholine was reduced in both PFOS males and females, but the extent of decrease was greater in females. Relaxation to sodium-nitroprusside was reduced in PFOS females but unaffected in PFOS males. Vascular eNOS expression was not changed, but phospho(Ser¹¹⁷⁷)-eNOS was decreased in PFOS males. In PFOS females, both total eNOS and phospho(Ser¹¹⁷⁷)-eNOS expression were reduced. In conclusion, PFOS exposure during prenatal life (1) caused low birth weight followed by catch-up growth only in females (2) lead to hypertension of similar magnitude in both males and females; (2) decreased endothelium-dependent vascular relaxation in males but suppressed both endothelium-dependent and -independent relaxation in females. The endothelial dysfunction is associated with reduced activity of eNOS in males and decreased expression and activity of eNOS in females.

Vascular mechanisms and molecular targets in hypertensive pregnancy and preeclampsia

Preeclampsia is a major complication of pregnancy manifested as hypertension and often intrauterine growth restriction, but the underlying pathophysiological mechanisms are unclear. Predisposing genetic and environmental factors cause placental maladaptations leading to defective placentation, apoptosis of invasive cytotrophoblasts, inadequate expansive remodeling of the spiral arteries, reduced uteroplacental perfusion pressure, and placental ischemia. Placental ischemia promotes the release of bioactive factors into the maternal circulation, causing an imbalance between antiangiogenic soluble fms-like tyrosine kinase-1 and soluble endoglin and proangiogenic vascular endothelial growth factor, placental growth factor, and transforming growth factor-β. Placental ischemia also stimulates the release of proinflammatory cytokines, hypoxia-inducible factor, reactive oxygen species, and angiotensin type 1 receptor agonistic autoantibodies. These circulating factors target the vascular endothelium, causing generalized endotheliosis in systemic, renal, cerebral, and hepatic vessels, leading to decreases in endothelium-derived vasodilators such as nitric oxide, prostacyclin, and hyperpolarization factor and increases in vasoconstrictors such as endothelin-1 and thromboxane A₂. The bioactive factors also target vascular smooth muscle and enhance the mechanisms of vascular contraction, including cytosolic Ca²⁺, protein kinase C, and Rho-kinase. The bioactive factors could also target matrix metalloproteinases and the extracellular matrix, causing inadequate vascular remodeling, increased arterial stiffening, and further increases in vascular resistance and hypertension. As therapeutic options are limited, understanding the underlying vascular mechanisms and molecular targets should help design new tools for the detection and management of hypertension in pregnancy and preeclampsia.

Sulodexide promotes arterial relaxation via endothelium-dependent nitric oxide-mediated pathway

Sulodexide (SDX) is a highly purified glycosaminoglycan with antithrombotic and profibrinolytic properties and reported benefits in thrombotic and atherosclerotic vascular disorders. However, the effects of SDX on vascular function are unclear. We tested whether SDX affects vascular relaxation and examined the potential underlying mechanisms. Isolated segments of male rat abdominal aorta and mesenteric artery were suspended in a tissue bath, and the changes in arterial contraction/relaxation were measured. The α-adrenergic receptor agonist phenylephrine (Phe) (10^-9-10^-5 M) caused concentration-dependent aortic and mesenteric artery contraction that was reduced in tissues pretreated with SDX (1 mg/ml). In aortic and mesenteric arterial segments precontracted with submaximal concentration of Phe (3 × 10^-7-6 × 10^-7 M), SDX (0.001-1 mg/ml) caused concentration-dependent relaxation. To test the role of endothelium, SDX-induced relaxation was compared with that of acetylcholine (ACh), a known activator of endothelium-dependent relaxation. In Phe precontracted aorta, ACh relaxation was abolished and SDX relaxation was significantly inhibited by endothelium removal or the nitric oxide synthase (NOS) inhibitor N_ω-nitro-l-arginine methyl ester (L-NAME), suggesting a role of NO. In mesenteric artery, ACh relaxation was abolished by endothelium removal, partially blocked by L-NAME, and completely blocked by a mixture of indomethacin, a cyclooxygenase inhibitor and blocker of the PGI₂-cAMP pathway, and tetraethylammonium, a blocker of K⁺ channels and EDHF-dependent hyperpolarization pathway. In comparison, SDX relaxation of mesenteric artery was almost completely inhibited by endothelium removal or NOS inhibitor L-NAME. SDX enhanced vascular relaxation and increased nitrate/nitrite production in response to all ACh concentrations in the aorta, but only to low ACh concentrations (<10^-7 M) in mesenteric artery. SDX did not affect aortic or mesenteric artery endothelium-independent relaxation to the NO donor sodium nitroprusside. Thus, SDX promotes arterial relaxation via a mechanism involving endothelium-dependent NO production; an effect that could enhance vasodilation and decrease vasoconstriction in vascular disorders.

Placental nitric oxide formation and endothelium-dependent vasodilation underlie pravastatin effects against angiogenic imbalance, hypertension in pregnancy and intrauterine growth restriction

Pre-eclampsia and hypertensive disorders of pregnancy are frequently associated with foeto-placental growth restriction, and that may be triggered by angiogenic imbalance and endothelial dysfunction. Impaired nitric oxide (NO) bioavailability seems to be involved in these pathophysiological changes observed in hypertensive pregnancy. Pravastatin has shown efficacy and to be safe during hypertension in pregnancy. However, NO involvement in pravastatin effects during maternal hypertension and foeto-placental development is unclear. Therefore, we aimed to examine pravastatin effects on placental NO formation, endothelium-dependent vasodilation, systolic blood pressure and foeto-placental development in hypertensive pregnant rats. Biochemical determinants of angiogenesis and oxidative stress were also assessed. Pregnant rats were distributed into four groups: normal pregnancy (Norm-Preg), pregnancy+pravastatin (Preg-Prava), hypertensive pregnancy (HTN-Preg) and hypertensive pregnancy+pravastatin (HTN-Preg+Prava). Our results showed that pravastatin treatment blunts hypertension and foeto-placental growth restriction. Also, increases in placental NO levels were found in the HTN-Preg+Prava group. Pravastatin prevents impaired endothelium-dependent acetylcholine-induced vasodilation, exacerbated contractile response to phenylephrine and increases in oxidative stress in the HTN-Preg+Prava group. Increased soluble fms-like tyrosine kinase-1-to-placental growth factor (sFlt-1/PlGF) ratio is reversed by pravastatin treatment in the HTN-Preg+Prava group. We conclude that NO formation and endothelium-dependent vasodilation underlie pleiotropic effects associated with pravastatin treatment against hypertension in pregnancy, intrauterine growth restriction, vascular dysfunction and angiogenic imbalance.

Molecular determinants of microvascular dysfunction in hypertensive pregnancy and preeclampsia

Preeclampsia is a pregnancy-related disorder characterized by hypertension and often fetal intrauterine growth restriction, but the underlying mechanisms are unclear. Defective placentation and apoptosis of invasive cytotrophoblasts cause inadequate remodeling of spiral arteries, placental ischemia, and reduced uterine perfusion pressure (RUPP). RUPP causes imbalance between the anti-angiogenic factors soluble fms-like tyrosine kinase-1 and soluble endoglin and the pro-angiogenic vascular endothelial growth factor and placental growth factor, and stimulates the release of proinflammatory cytokines, hypoxia-inducible factor, reactive oxygen species, and angiotensin AT1 receptor agonistic autoantibodies. These circulating factors target the vascular endothelium, smooth muscle and various components of the extracellular matrix. Generalized endotheliosis in systemic, renal, cerebral, and hepatic vessels causes decreases in endothelium-derived vasodilators such as nitric oxide, prostacyclin and hyperpolarization factor, and increases in vasoconstrictors such as endothelin-1 and thromboxane A2. Enhanced mechanisms of vascular smooth muscle contraction, such as intracellular Ca2+ , protein kinase C, and Rho-kinase cause further increases in vasoconstriction. Changes in matrix metalloproteinases and extracellular matrix cause inadequate vascular remodeling and increased arterial stiffening, leading to further increases in vascular resistance and hypertension. Therapeutic options are currently limited, but understanding the molecular determinants of microvascular dysfunction could help in the design of new approaches for the prediction and management of preeclampsia.

Smooth muscle cell-driven vascular diseases and molecular mechanisms of VSMC plasticity

Vascular smooth muscle cells (VSMCs) are the major cell type in blood vessels. Unlike many other mature cell types in the adult body, VSMC do not terminally differentiate but retain a remarkable plasticity. Fully differentiated medial VSMCs of mature vessels maintain quiescence and express a range of genes and proteins important for contraction/dilation, which allows them to control systemic and local pressure through the regulation of vascular tone. In response to vascular injury or alterations in local environmental cues, differentiated/contractile VSMCs are capable of switching to a dedifferentiated phenotype characterized by increased proliferation, migration and extracellular matrix synthesis in concert with decreased expression of contractile markers. Imbalanced VSMC plasticity results in maladaptive phenotype alterations that ultimately lead to progression of a variety of VSMC-driven vascular diseases. The nature, extent and consequences of dysregulated VSMC phenotype alterations are diverse, reflecting the numerous environmental cues (e.g. biochemical factors, extracellular matrix components, physical) that prompt VSMC phenotype switching. In spite of decades of efforts to understand cues and processes that normally control VSMC differentiation and their disruption in VSMC-driven disease states, the crucial molecular mechanisms and signalling pathways that shape the VSMC phenotype programme have still not yet been precisely elucidated. In this article we introduce the physiological functions of vascular smooth muscle/VSMCs, outline VSMC-driven cardiovascular diseases and the concept of VSMC phenotype switching, and review molecular mechanisms that play crucial roles in the regulation of VSMC phenotypic plasticity.

Increases in placental nitric oxide, but not nitric oxide-mediated relaxation, underlie the improvement in placental efficiency and antihypertensive effects of hydrogen sulphide donor in hypertensive pregnancy

Dysregulation of hydrogen sulphide (H₂ S) producing enzymes has been related to hypertensive pregnancy, and H₂ S donor, sodium hydrosulphide (NaHS) exerts antihypertensive effects, modulates angiogenic factors production and acts as an antioxidant. Moreover, reduction in nitric oxide (NO) bioavailability is related to hypertensive pregnancy and H₂ S may interact with NO, modulating its production. We aimed to investigate the NaHS effects in hypertension-in-pregnancy and also in feto-placental parameters. Female Wistar rats (200-250 g) were mated and desoxycorticosterone acetate injections followed by replacement of water by 0.9% saline solution were used to induce hypertensive pregnancy. Rats were divided into four groups: normal pregnant (Norm-Preg), pregnant + NaHS (Preg+NaHS), hypertensive pregnant (HTN-Preg) and HTN-Preg+NaHS. Systolic blood pressure was increased in HTN-Preg and this increase was blunted in HTN-Preg+NaHS. Fetal and placental weights were decreased in HTN-Preg animals, while fetal growth restriction was improved in HTN-Preg+NaHS. Placental weight was lower in HTN-Preg+NaHS than in HTN-Preg; however, placental efficiency was re-established in HTN-Preg+NaHS rats. We observed that a partial contribution of placental NO, but not changes in anti-angiogenic factors may mediate the increases in placental efficiency in HTN-Preg+NaHS. HTN-Preg presented thoracic aorta hyperreactivity to phenylephrine while NaHS treatment blunted this hyperreactivity, which seems not to be related to NO-mediated relaxation induced by acetylcholine. Therefore, changes in vascular responsiveness promoted by NaHS treatment may underlie the beneficial effects in systolic blood pressure and feto-placental parameters in our study.

Evolving mechanisms of vascular smooth muscle contraction highlight key targets in vascular disease

Vascular smooth muscle (VSM) plays an important role in the regulation of vascular function. Identifying the mechanisms of VSM contraction has been a major research goal in order to determine the causes of vascular dysfunction and exaggerated vasoconstriction in vascular disease. Major discoveries over several decades have helped to better understand the mechanisms of VSM contraction. Ca2+ has been established as a major regulator of VSM contraction, and its sources, cytosolic levels, homeostatic mechanisms and subcellular distribution have been defined. Biochemical studies have also suggested that stimulation of Gq protein-coupled membrane receptors activates phospholipase C and promotes the hydrolysis of membrane phospholipids into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 stimulates initial Ca2+ release from the sarcoplasmic reticulum, and is buttressed by Ca2+ influx through voltage-dependent, receptor-operated, transient receptor potential and store-operated channels. In order to prevent large increases in cytosolic Ca2+ concentration ([Ca2+]c), Ca2+ removal mechanisms promote Ca2+ extrusion via the plasmalemmal Ca2+ pump and Na+/Ca2+ exchanger, and Ca2+ uptake by the sarcoplasmic reticulum and mitochondria, and the coordinated activities of these Ca2+ handling mechanisms help to create subplasmalemmal Ca2+ domains. Threshold increases in [Ca2+]c form a Ca2+-calmodulin complex, which activates myosin light chain (MLC) kinase, and causes MLC phosphorylation, actin-myosin interaction, and VSM contraction. Dissociations in the relationships between [Ca2+]c, MLC phosphorylation, and force have suggested additional Ca2+ sensitization mechanisms. DAG activates protein kinase C (PKC) isoforms, which directly or indirectly via mitogen-activated protein kinase phosphorylate the actin-binding proteins calponin and caldesmon and thereby enhance the myofilaments force sensitivity to Ca2+. PKC-mediated phosphorylation of PKC-potentiated phosphatase inhibitor protein-17 (CPI-17), and RhoA-mediated activation of Rho-kinase (ROCK) inhibit MLC phosphatase and in turn increase MLC phosphorylation and VSM contraction. Abnormalities in the Ca2+ handling mechanisms and PKC and ROCK activity have been associated with vascular dysfunction in multiple vascular disorders. Modulators of [Ca2+]c, PKC and ROCK activity could be useful in mitigating the increased vasoconstriction associated with vascular disease.

Animal models of preeclampsia: translational failings and why

Preeclampsia affects up to 8% of pregnancies worldwide and is a leading cause of both maternal and fetal morbidity and mortality. Our current understanding of the cause(s) of preeclampsia is far from complete, and the lack of a single reliable animal model that recapitulates all aspects of the disease further confounds our understanding. This is partially due to the heterogeneous nature of the disease, coupled with our evolving understanding of its etiology. Nevertheless, animal models are still highly relevant and useful tools that help us better understand the pathophysiology of specific aspects of preeclampsia. This review summarizes the various types and characteristics of animal models used to study preeclampsia, highlighting particular features of these models relevant to clinical translation. This review points out the strengths and limitations of these models to illustrate the importance of using the appropriate model depending on the research question.

Clinical and Experimental Evidences of Hydrogen Sulfide Involvement in Lead-Induced Hypertension

Lead- (Pb-) induced hypertension has been shown in humans and experimental animals and cardiovascular effects of hydrogen sulfide (H₂S) have been reported previously. However, no studies examined involvement of H₂S in Pb-induced hypertension. We found increases in diastolic blood pressure and mean blood pressure in Pb-intoxicated humans followed by diminished H₂S plasmatic levels. In order to expand our findings, male Wistar rats were divided into four groups: Saline, Pb, NaHS, and Pb + NaHS. Pb-intoxicated animals received intraperitoneally (i.p.) 1st dose of 8 μg/100 g of Pb acetate and subsequent doses of 0.1 μg/100 g for seven days and sodium hydrosulfide- (NaHS-) treated animals received i.p. NaHS injections (50 μmol/kg/twice daily) for seven days. NaHS treatment blunted increases in systolic blood pressure, increased H₂S plasmatic levels, and diminished whole-blood lead levels. Treatment with NaHS in Pb-induced hypertension seems to induce a protective role in rat aorta which is dependent on endothelium and seems to promote non-NO-mediated relaxation. Pb-intoxication increased oxidative stress in rats, while treatment with NaHS blunted increases in plasmatic MDA levels and increased antioxidant status of plasma. Therefore, H₂S pathway may be involved in Pb-induced hypertension and treatment with NaHS exerts antihypertensive effect, promotes non-NO-mediated relaxation, and decreases oxidative stress in rats with Pb-induced hypertension.

Adaptive reduction of human myometrium contractile activity in response to prolonged uterine stretch during term and twin pregnancy. Role of TREK-1 channel

Quiescence of myometrium contractile activity allows uterine expansion to accommodate the growing fetus and prevents preterm labor particularly during excessive uterine stretch in multiple pregnancy. However, the mechanisms regulating uterine response to stretch are unclear. We tested the hypothesis that prolonged uterine stretch is associated with decreased myometrium contractile activity via activation of TWIK-related K⁺ channel (TREK-1). Pregnant women at different gestational age (preterm and term) and uterine stretch (singleton and twin pregnancy) were studied, and uterine strips were isolated for measurement of contractile activity and TREK-1 channel expression/activity. Both oxytocin- and KCl-induced contraction were reduced in term vs preterm pregnancy and in twin vs singleton pregnancy. Oxytocin contraction was reduced in uterine segments exposed to 8 g stretch compared to control tissues under 2 g basal tension. TREK-1 mRNA expression and protein levels were augmented in Singleton-Term vs Singleton-Preterm, and in uterine strips exposed to 8 g stretch. The TREK-1 activator arachidonic acid reduced oxytocin contraction in preterm and term, singleton and twin pregnant uterus. The TREK-1 blocker l-methionine enhanced oxytocin contraction in Singleton-Term and twin pregnant uterus, and reversed the decreases in contraction in uterine strips exposed to prolonged stretch. Carboprost-induced uterine contraction was also reduced by arachidonic acid and enhanced by l-methionine. Thus, myometrium contraction decreases with gestational age and uterine expansion in twin pregnancy. The results suggest that prolonged stretch enhances the expression/activity of TREK-1 channel, leading to decreased myometrium contractile activity and maintained healthy term pregnancy particularly in multiple pregnancy.

Matrix Metalloproteinases in Normal Pregnancy and Preeclampsia

Normal pregnancy is associated with marked hemodynamic and uterine changes that allow adequate uteroplacental blood flow and uterine expansion for the growing fetus. These pregnancy-associated changes involve significant uteroplacental and vascular remodeling. Matrix metalloproteinases (MMPs) are important regulators of vascular and uterine remodeling. Increases in MMP-2 and MMP-9 have been implicated in vasodilation, placentation, and uterine expansion during normal pregnancy. The increases in MMPs could be induced by the increased production of estrogen and progesterone during pregnancy. MMP expression/activity may be altered during complications of pregnancy. Decreased vascular MMP-2 and MMP-9 may lead to decreased vasodilation, increased vasoconstriction, hypertensive pregnancy, and preeclampsia. Abnormal expression of uteroplacental integrins, cytokines, and MMPs may lead to decreased maternal tolerance, apoptosis of invasive trophoblast cells, inadequate remodeling of spiral arteries, and reduced uterine perfusion pressure (RUPP). RUPP may cause imbalance between the antiangiogenic factors soluble fms-like tyrosine kinase-1 and soluble endoglin and the proangiogenic vascular endothelial growth factor and placental growth factor, or stimulate the release of inflammatory cytokines, hypoxia-inducible factor, reactive oxygen species, and angiotensin AT1 receptor agonistic autoantibodies. These circulating factors could target MMPs in the extracellular matrix as well as endothelial and vascular smooth muscle cells, causing generalized vascular dysfunction, increased vasoconstriction and hypertension in pregnancy. MMP activity can also be altered by endogenous tissue inhibitors of metalloproteinases (TIMPs) and changes in the MMP/TIMP ratio. In addition to their vascular effects, decreases in expression/activity of MMP-2 and MMP-9 in the uterus could impede uterine growth and expansion and lead to premature labor. Understanding the role of MMPs in uteroplacental and vascular remodeling and function could help design new approaches for prediction and management of preeclampsia and premature labor.

Mesenteric Vascular Responsiveness in a Rat Model of Pregnancy-Induced Hypertension

Reduced perfusion to the placenta in early pregnancy is believed to be the initiating factor in the development of preeclampsia, triggering local ischemia and systemic vascular hyperresponsiveness. This sequence of events creates a predisposition to the development of altered vascular function and hypertension. This study was designed to determine the influence of placental insufficiency on the responsiveness of mesenteric resistance arteries in an animal model of preeclampsia. Placental insufficiency was induced by reduction in uteroplacental perfusion pressure (RUPP) in experimental Sprague-Dawley rat dams. The uterine branches of the ovarian arteries and the abdominal aortae of pregnant rats were surgically constricted on gestational Day 14. Dams in the control group underwent a sham procedure. Rats were euthanized on gestational Day 20, followed by removal of the small intestine and adjacent mesentery. First-order mesenteric resistance arteries were mounted on a small vessel wire myograph and challenged with incremental concentrations of vasoconstrictors and vasorelaxants. Mesenteric arteries in dams with placental insufficiency demonstrated an increased maximal tension to phenylephrine (7.15 ± 0.15 vs. 5.4 ± 0.27 mN/mm, P < 0.001); potassium chloride at 60 mM (3.43 ± 0.11 vs. 2.77 ± 0.14 mN/mm, P < 0.01) and 120 mM (3.92 ± 0.18 vs. 2.97 ± 0.16 mN/mm, P < 0.01); and angiotensin II (2.59 ± 0.42 vs. 1.51 ± 0.22 mN/mm, P < 0.05). Maximal relaxation to endothelium-dependent relaxants acetylcholine and calcium lonophore (A23187) was not significantly reduced. Data suggest that placental insufficiency leads to hyperresponsiveness to vasoconstrictor stimuli in mesenteric arteries.

Restoring placental growth factor-soluble fms-like tyrosine kinase-1 balance reverses vascular hyper-reactivity and hypertension in pregnancy

Preeclampsia (PE) is a pregnancy-related hypertensive disorder (HTN-Preg) with unclear mechanism. An imbalance between antiangiogenic soluble fms-like tyrosine kinase-1 (sFlt-1) and angiogenic placental growth factor (PlGF) has been observed in PE, but the vascular targets and signaling pathways involved are unclear. We assessed the extent of sFlt-1/PlGF imbalance and vascular dysfunction in a rat model of HTN-Preg produced by reduction of uteroplacental perfusion pressure (RUPP), and tested whether inducing a comparable sFlt-1/PlGF imbalance by infusing sFlt-1 (10 μg·kg(-1)·day(-1)) in day 14 pregnant (Preg) rats cause similar increases in blood pressure (BP) and vascular reactivity. Using these guiding measurements, we then tested whether restoring sFlt-1/PlGF balance by infusing PIGF (20 μg·kg(-1)·day(-1)) in RUPP rats would improve BP and vascular function. On gestational day 19, BP was in Preg+sFlt-1 and RUPP > Preg, and in RUPP+PlGF < RUPP rats. Plasma sFlt-1/PlGF ratio was increased in Preg+sFlt-1, and RUPP and was reduced in RUPP+PlGF rats. In isolated endothelium-intact aorta, carotid, mesenteric, and renal artery, phenylephrine (Phe)- and high KCl-induced contraction was in Preg+sFlt-1 and RUPP > Preg, and in RUPP+PlGF < RUPP. The differences in vascular reactivity to Phe and KCl between groups were less apparent in vessels treated with the nitric oxide synthase (NOS) inhibitor l-NAME or guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) or endothelium-denuded, suggesting changes in endothelial NO-cGMP pathway. In Phe precontracted vessels, ACh-induced relaxation was in Preg+sFlt-1 and RUPP < Preg, and in RUPP+PlGF > RUPP, and was blocked by N(ω)-nitro-l-arginine methyl ester (l-NAME) or ODQ treatment or endothelium removal. Western blots revealed that aortic total endothelial NOS (eNOS) and activated phosphorylated-eNOS were in Preg+sFlt-1 and RUPP < Preg and in RUPP+PlGF > RUPP. ACh-induced vascular nitrate/nitrite production was in Preg+sFlt-1 and RUPP < Preg, and in RUPP+PlGF > RUPP. Vascular relaxation to the exogenous NO donor sodium nitroprusside was not different among groups. Thus, a tilt in the angiogenic balance toward anti-angiogenic sFlt-1 is associated with decreased vascular relaxation and increased vasoconstriction and BP. Restoring the angiogenic/antiangiogenic balance using PlGF enhances endothelial NO-cGMP vascular relaxation and decreases vasoconstriction and BP in HTN-Preg rats and could offer a new approach in the management of PE.

Placental Ischemia and Resultant Phenotype in Animal Models of Preeclampsia

Preeclampsia is new onset (or worsening of preexisting) hypertension that occurs during pregnancy. It is accompanied by chronic inflammation, intrauterine growth restriction, elevated anti-angiogenic factors, and can occur with or without proteinuria. Although the exact etiology is unknown, it is thought that preeclampsia begins early in gestation with reduced uterine spiral artery remodeling leading to decreased vasculogenesis of the placenta as the pregnancy progresses. Soluble factors, stimulated by the ischemic placenta, shower the maternal vascular endothelium and are thought to cause endothelial dysfunction and to contribute to the development of hypertension during pregnancy. Due to the difficulty in studying such soluble factors in pregnant women, various animal models have been designed. Studies from these models have contributed to a better understanding of how factors released in response to placental ischemia may lead to increased blood pressure and reduced fetal weight during pregnancy. This review will highlight various animal models and the major findings indicating the importance of placental ischemia to lead to the pathophysiology observed in preeclamptic patients.

The role of inflammation in the pathology of preeclampsia

Preeclampsia (PE) affects 5-7% of all pregnancies in the United States and is the leading cause of maternal and prenatal morbidity. PE is associated with hypertension after week 20 of gestation, decreased renal function and small-for-gestational-age babies. Women with PE exhibit chronic inflammation and production of autoantibodies. It is hypothesized that during PE, placental ischaemia occurs as a result of shallow trophoblast invasion which is associated with an immune imbalance where pro-inflammatory CD4(+) T-cells are increased and T regulatory cells (Tregs) are decreased. This imbalance leads to chronic inflammation characterized by oxidative stress, pro-inflammatory cytokines and autoantibodies. Studies conducted in our laboratory have demonstrated the importance of this immune imbalance in causing hypertension in response to placental ischaemia in pregnant rats. These studies confirm that increased CD4(+) T-cells and decreased Tregs during pregnancy leads to elevated inflammatory cytokines, endothelin (ET-1), reactive oxygen species (ROS) and agonistic autoantibodies to the angiotensin II (Ang II), type 1 receptor (AT1-AA). All of these factors taken together play an important role in increasing the blood pressure during pregnancy. Specifically, this review focuses on the decrease in Tregs, and their associated regulatory cytokine interleukin (IL)-10, which is seen in response to placental ischaemia during pregnancy. This study will also examine the effect of regulatory immune cell repopulation on the pathophysiology of PE. These studies show that restoring the balance of the immune system through increasing Tregs, either by adoptive transfer or by infusing IL-10, reduces the blood pressure and pathophysiology associated with placental ischaemia in pregnant rats.

Increased risk for the development of preeclampsia in obese pregnancies: weighing in on the mechanisms

Preeclampsia (PE) is a pregnancy-specific disorder typically presenting as new-onset hypertension and proteinuria. While numerous epidemiological studies have demonstrated that obesity increases the risk of PE, the mechanisms have yet to be fully elucidated. Growing evidence from animal and human studies implicate placental ischemia in the etiology of this maternal syndrome. It is thought that placental ischemia is brought about by dysfunctional cytotrophoblast migration and invasion into the uterus and subsequent lack of spiral arteriole widening and placental perfusion. Placental ischemia/hypoxia stimulates the release of soluble placental factors into the maternal circulation where they cause endothelial dysfunction, particularly in the kidney, to elicit the clinical manifestations of PE. The most recognized of these factors are the anti-angiogenic sFlt-1 and pro-inflammatory TNF-α and AT1-AA, which promote endothelial dysfunction by reducing levels of the provasodilator nitric oxide and stimulating production of the potent vasoconstrictor endothelin-1 and reactive oxygen species. We hypothesize that obesity-related metabolic factors increase the risk for developing PE by impacting various stages in the pathogenesis of PE, namely, 1) cytotrophoblast migration and placental ischemia; 2) release of soluble placental factors into the maternal circulation; and 3) maternal endothelial and vascular dysfunction. This review will summarize the current experimental evidence supporting the concept that obesity and metabolic factors like lipids, insulin, glucose, and leptin affect placental function and increase the risk for developing hypertension in pregnancy by reducing placental perfusion; enhancing placental release of soluble factors; and by increasing the sensitivity of the maternal vasculature to placental ischemia-induced soluble factors.

Genetic, immune and vasoactive factors in the vascular dysfunction associated with hypertension in pregnancy

INTRODUCTION

Preeclampsia (PE) is a major complication of pregnancy that could lead to maternal and fetal morbidity and mortality. The pathophysiological mechanisms of PE are not completely understood, but recent research has begun to unravel some of the potential mechanisms.

AREAS COVERED

Genetic polymorphisms and altered maternal immune response may cause impaired remodeling of the spiral arteries; a potential early defect in PE. Inadequate invasion of cytotrophoblasts into the decidua leads to reduced uteroplacental perfusion pressure (RUPP) and placental ischemia/hypoxia. Placental ischemia causes the release of biologically active factors such as anti-angiogenic factors, inflammatory cytokines, reactive oxygen species, hypoxia-inducible factors, and angiotensin II receptor autoantibodies. These vasoactive factors could cause systemic vascular endotheliosis and consequent increase in vascular resistance and blood pressure, glomerular endotheliosis causing proteinuria, cerebrovascular endotheliosis causing cerebral edema, seizures and visual disturbances, and hepatic endotheliosis, which may contribute to the manifestations of HELLP syndrome. PE-associated vascular endotheliosis causes a decrease in vasodilator mediators such as nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor, an increase in vasoconstrictors such as endothelin-1, angiotensin II and thromboxane A2, and enhanced mechanisms of vascular smooth muscle contraction such as intracellular Ca(2+), protein kinase C and Rho-kinase. Changes in matrix metalloproteinase activity and extracellular matrix cause vascular remodeling and further vasoconstriction.

EXPERT OPINION

Some of the genetic, immune and vasoactive factors involved in vascular endotheliosis could be used as biomarkers for early detection, and as potential targets for prevention and treatment of PE.

Bioactive factors in uteroplacental and systemic circulation link placental ischemia to generalized vascular dysfunction in hypertensive pregnancy and preeclampsia

Preeclampsia is a pregnancy-associated disorder characterized by hypertension, and could lead to maternal and fetal morbidity and mortality; however, the pathophysiological mechanisms involved are unclear. Predisposing demographic, genetic and environmental risk factors could cause localized abnormalities in uteroplacental cytoactive factors such as integrins, matrix metalloproteinases, cytokines and major histocompatibility complex molecules leading to decreased vascular remodeling, uteroplacental vasoconstriction, trophoblast cells apoptosis, and abnormal development of the placenta. Defective placentation and decreased trophoblast invasion of the myometrium cause reduction in uteroplacental perfusion pressure (RUPP) and placental ischemia/hypoxia, an important event in preeclampsia. RUPP could stimulate the release of circulating bioactive factors such as the anti-angiogenic factors soluble fms-like tyrosine kinase-1 and soluble endoglin that cause imbalance with the pro-angiogenic factors vascular endothelial growth factor and placental growth factor, or cause the release of inflammatory cytokines, reactive oxygen species, hypoxia-induced factor-1 and AT1 angiotensin receptor agonistic autoantibodies. The circulating bioactive factors target endothelial cells causing generalized endotheliosis, endothelial dysfunction, decreased vasodilators such as nitric oxide and prostacyclin and increased vasoconstrictors such as endothelin-1 and thromboxane A2, leading to increased vasoconstriction. The bioactive factors also stimulate the mechanisms of VSM contraction including Ca(2+), protein kinase C, and Rho-kinase and induce extracellular matrix remodeling leading to further vasoconstriction and hypertension. While therapeutic options are currently limited, understanding the underlying mechanisms could help design new interventions for management of preeclampsia.

A model of preeclampsia in rats: the reduced uterine perfusion pressure (RUPP) model

Preeclampsia is defined as new-onset hypertension with proteinuria after 20 wk gestation and is hypothesized to be due to shallow trophoblast invasion in the spiral arteries thus resulting in progressive placental ischemia as the fetus grows. Many animal models have been developed that mimic changes in maternal circulation or immune function associated with preeclampsia. The model of reduced uterine perfusion pressure in pregnant rats closely mimics the hypertension, immune system abnormalities, systemic and renal vasoconstriction, and oxidative stress in the mother, and intrauterine growth restriction found in the offspring. The model has been successfully used in many species; however, rat and primate are the most consistent in comparison of characteristics with human preeclampsia. The model suffers, however, from lack of the ability to study the mechanisms responsible for abnormal placentation that ultimately leads to placental ischemia. Despite this limitation, the model is excellent for studying the consequences of reduced uterine blood flow as it mimics many of the salient features of preeclampsia during the last weeks of gestation in humans. This review discusses these features.

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.

Vascular and cellular calcium in normal and hypertensive pregnancy

Normal pregnancy is associated with significant hemodynamic changes in the cardiovascular system in order to meet the metabolic demands of mother and fetus. These changes include increased cardiac output, decreased vascular resistance, and vascular remodeling in the uterine and systemic circulation. Preeclampsia (PE) is a major complication of pregnancy characterized by proteinuria and hypertension. Several risk factors have been implicated in the pathogenesis of PE including genetic and dietary factors. Ca2+ is an essential dietary element and an important regulator of many cellular processes including vascular function. The importance of adequate dietary Ca2+ intake during pregnancy is supported by many studies. Pregnancy-associated changes in Ca2+ metabolism and plasma Ca2+ have been observed. During pregnancy, changes in intracellular free Ca2+ concentration ([Ca2+](i)) have been described in red blood cells, platelets and immune cells. Also, during pregnancy, an increase in [Ca2+](i) in endothelial cells (EC) stimulates the production of vasodilator substances such as nitric oxide and prostacyclin. Normal pregnancy is also associated with decreased vascular smooth muscle (VSM) [Ca2+](i) and possibly the Ca2+-sensitization pathways of VSM contraction including protein kinase C, Rho-kinase, and mitogen-activated protein kinase. Ca2+-dependent matrix metalloproteinases could also promote extracellular matrix degradation and vascular remodeling during pregnancy. Disruption in the balance between dietary, plasma and vascular cell Ca2+ may be responsible for some of the manifestation of PE including procoagulation, decreased vasodilation, and increased vasoconstriction and vascular resistance. The potential benefits of Ca2+ supplements during pregnancy, and the use of modulators of vascular Ca2+ to reduce the manifestations of PE in susceptible women remain an important area for experimental and clinical research.

Cellular mediators of renal vascular dysfunction in hypertension

The renal vasculature plays a major role in the regulation of renal blood flow and the ability of the kidney to control the plasma volume and blood pressure. Renal vascular dysfunction is associated with renal vasoconstriction, decreased renal blood flow, and consequent increase in plasma volume and has been demonstrated in several forms of hypertension (HTN), including genetic and salt-sensitive HTN. Several predisposing factors and cellular mediators have been implicated, but the relationship between their actions on the renal vasculature and the consequent effects on renal tubular function in the setting of HTN is not clearly defined. Gene mutations/defects in an ion channel, a membrane ion transporter, and/or a regulatory enzyme in the nephron and renal vasculature may be a primary cause of renal vascular dysfunction. Environmental risk factors, such as high dietary salt intake, vascular inflammation, and oxidative stress further promote renal vascular dysfunction. Renal endothelial cell dysfunction is manifested as a decrease in the release of vasodilatory mediators, such as nitric oxide, prostacyclin, and hyperpolarizing factors, and/or an increase in vasoconstrictive mediators, such as endothelin, angiotensin II, and thromboxane A(2). Also, an increase in the amount/activity of intracellular Ca(2+) concentration, protein kinase C, Rho kinase, and mitogen-activated protein kinase in vascular smooth muscle promotes renal vasoconstriction. Matrix metalloproteinases and their inhibitors could also modify the composition of the extracellular matrix and lead to renal vascular remodeling. Synergistic interactions between the genetic and environmental risk factors on the cellular mediators of renal vascular dysfunction cause persistent renal vasoconstriction, increased renal vascular resistance, and decreased renal blood flow, and, consequently, lead to a disturbance in the renal control mechanisms of water and electrolyte balance, increased plasma volume, and HTN. Targeting the underlying genetic defects, environmental risk factors, and the aberrant renal vascular mediators involved should provide complementary strategies in the management of HTN.

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.

Prolonged increases in vein wall tension increase matrix metalloproteinases and decrease constriction in rat vena cava: Potential implications in varicose veins

BACKGROUND

Increased venous hydrostatic pressure plays a role in the pathogenesis of varicose veins. Increased expression of matrix metalloproteinases (MMPs) has been identified in varicose veins. Also, we have shown that MMP-2 inhibits venous contraction. However, the relation between venous pressure, MMP expression, and venous dysfunction is unclear. The purpose of this study was to test the hypothesis that prolonged increases in venous wall tension cause overexpression of MMPs and decreased contractility, which in turn promote venous dilation.

METHODS

Circular segments of inferior vena cava (IVC) were isolated from male Sprague-Dawley rats and suspended between two wires in Krebs solution. Preliminary vein wall tension-contraction relation showed maximal potassium chloride (KCl) (96 mmol/L) contraction at 0.5 g basal tension, which remained steady with increases in tension up to 2 g. Vein segments were subjected to either control (0.5 g) or high (2 g) basal tension for short (1 hour) or long duration (24 hours). Isometric contraction in response to phenylephrine (Phe, 10(-5) mol/L), angiotensin II (AngII, 10(-6) mol/L), and KCl was measured. The veins were frozen to determine the expression and localization of MMPs using immunoblots and immunohistochemistry.

RESULTS

In IVC segments subjected to 0.5 g tension for 1 hour, Phe and AngII produced significant contraction. At higher 2 g basal tension for 24 hours, both Phe and AngII contractions were significantly reduced. Reduction in KCl contraction was also observed at high 2 g basal tension for 24 hours, suggesting that the reduction in vein contraction is not specific to a particular receptor, and likely involves inhibition of a post-receptor contraction mechanism. In vein segments under 2 g tension for 24 hours and treated with TIMP-1, Phe, AngII, and KCl contractions were partially restored, suggesting the involvement of MMPs. IVC immunoblot analysis demonstrated prominent bands corresponding to MMP-2 and MMP-9 protein. High 2 g wall tension for 24 hours was associated with marked increase in the amount of MMP-2 and -9 relative to the housekeeping protein actin. There was a correlation between MMP expression and decreased vein contraction. Also, significant increases in MMP-2 and -9 immunostaining were observed in IVC segments subjected to high 2 g tension for 24 hours. Both MMP-2 and MMP-9 caused significant inhibition of Phe contraction in IVC segments.

CONCLUSIONS

In rat IVC, increases in magnitude and duration of wall tension is associated with reduced contraction and overexpression of MMP-2 and -9. In light of our findings that MMP-2 and -9 promote IVC relaxation, the data suggest that protracted increases in venous pressure and wall tension increase MMPs expression, which in turn reduce venous contraction and lead to progressive venous dilation.

Involvement of marinobufagenin in a rat model of human preeclampsia

BACKGROUND

Preeclampsia is a potentially devastating disorder of hypertension in pregnancy for which there is currently no definitive treatment short of delivery. The bufadienolide, marinobufagenin (MBG), an inhibitor of Na(+)/K(+) ATPase, has been found to be elevated in extracellular fluid volume-expanded hypertensive patients, a condition similar to preeclampsia. Thus, these studies sought to examine the role of MBG in our rat model of preeclampsia.

METHODS AND RESULTS

Pregnant female rats were injected intraperitoneally with deoxycorticosterone acetate (DOCA) and given 0.9% saline as drinking water for the duration of their pregnancy. Urinary MBG was measured using a DELFIA immunoassay. Blood pressure was measured via the tail-cuff method. Injections of anti-MBG antibody were given intraperitoneally or intravenously to hypertensive pregnant rats. MBG was given intraperitoneally to pregnant rats. Uterine arterioles were dissected free and their diameters were measured before and after perfusion of MBG, ouabain, or digoxin. MBG was found to be elevated in the pregnant + DOCA + saline (PDS) rats compared to normal pregnant animals. In addition, when PDS rats were injected with anti-MBG antibody, there was a subsequent reduction in blood pressure. Administration of MBG in normal pregnant rats caused an elevation in blood pressure equivalent to the PDS model. Also, uterine vessel measurements showed an increased vasoconstrictive reactivity to MBG in the PDS animals vs. the normal pregnant controls; while no changes were observed with perfusion of digoxin or ouabain at the same concentration.

CONCLUSION

These results suggest a relationship between MBG and a syndrome in rats resembling preeclampsia. Armed with these promising results, it would seem logical to further examine the role of MBG in human preeclampsia.

Reduced Uteroplacental Perfusion Alters Uterine Arcuate Artery Function in the Pregnant Sprague-Dawley Rat1

Evidence continues to implicate reduced placental perfusion as the cause of preeclampsia, initiating a sequence of events leading to altered vascular function and hypertension. The present study was designed to determine the influence of reduced uteroplacental perfusion pressure (RUPP) on the responsiveness of uterine arcuate resistance arteries. A condition of RUPP was surgically induced in pregnant Sprague-Dawley rats on Gestational Day 14. On Gestational Day 20, uterine arcuate arteries were mounted on a small-vessel wire myograph and challenged with incremental concentrations of vasoconstrictors and vasorelaxants for measurement of isometric tension. Compared to the sham-operated controls, uterine arteries from the RUPP group demonstrated an increased maximal tension in response to phenylephrine (P < 0.01); potassium chloride at 30 mM (P < 0.05), 60 mM (P < 0.01), and 120 mM (P < 0.01); and angiotensin II (P < 0.05). In arteries from the RUPP and sham-operated control groups, endothelium-dependent relaxation in response to acetylcholine (P < 0.05) and calcium ionophore (A23187; P < 0.05) was significantly reduced in the RUPP group compared to the sham-operated controls. Fetal growth indices, including litter size, fetal weight, and placental weight, were significantly reduced in the RUPP group compared to sham-operated controls, which is consistent with significant growth restriction. Data suggest that RUPP promotes hyperresponsiveness and impaired endothelium-dependent relaxation in uterine arcuate arteries, leading to intrauterine fetal growth restriction.

T-type calcium channels in the regulation of afferent and efferent arterioles in rats

L-type Ca2+ channels predominantly influence preglomerular arterioles, but there is less information regarding the role of T-type Ca2+ channels in regulating the renal microvasculature. We compared the effects of T- and L-type channel blockade on afferent and efferent arterioles using the in vitro blood-perfused juxtamedullary nephron preparation. Single afferent or efferent arterioles of Sprague-Dawley rats were visualized and superfused with solutions containing Ca2+ channel blockers. We confirmed that L-type channel blockade with diltiazem dilates afferent arterioles but has no significant effects on efferent arterioles. In contrast, T-type channel blockade with pimozide (10 micromol/l) or mibefradil (1 micromol/l) dilated both afferent (26.8 +/- 3.4 and 24.6 +/- 1.9%) and efferent (19.2 +/- 2.9 and 19.1 +/- 4.8%) arterioles. Adding diltiazem did not significantly augment the dilation of afferent arterioles elicited by pimozide and mibefradil, and adding pimozide after diltiazem likewise did not elicit further vasodilation. Diltiazem blocked the depolarization-induced afferent arteriolar constriction elicited by 55 mM KCl; however, the constrictor response to KCl remained intact during treatment with 10 microM pimozide. Pimozide also prevented the afferent arterioles from exhibiting autoregulatory-mediated constrictor responses to increases in perfusion pressure. We conclude that T-type channel blockers dilate efferent arterioles as well as afferent arterioles and diminish afferent arteriolar autoregulatory responses to changes in perfusion pressure. To the extent that these agents exert their effects primarily on T-type Ca2+ channels in our experimental setting, these results indicate that T-type channels are functionally expressed in juxtamedullary afferent and efferent arterioles and may act cooperatively with L-type channels to regulate afferent arteriolar resistance. Because L-type channels are not functionally expressed in efferent arterioles, T-type channels may be particularly significant in the regulation of efferent arteriolar function.

Reduced endothelial vascular relaxation in growth-restricted offspring of pregnant rats with reduced uterine perfusion

Low birth weight as the result of placental insufficiency increases the risk of hypertension in young adults; however, the vascular mechanisms involved are unclear. We tested the hypothesis that intrauterine fetal growth restriction caused by placental insufficiency results in low-birth-weight offspring with impaired endothelium-dependent vascular relaxation, enhanced vasoconstriction, and hypertension. The body weight and arterial pressure were measured in young (4 weeks), adolescent (8 weeks), and adult (12 weeks) male offspring of normal pregnant rats and pregnant rats with reduced uteroplacental perfusion (intrauterine growth-restricted, IUGR), and aortic strips were isolated for measurement of isometric contraction. The body weight was lower whereas the arterial pressure was higher in IUGR than normal rats at 4 weeks (113+/-3 versus 98+/-2), 8 weeks (133+/-3 versus 121+/-6), and 12 weeks (144+/-4 versus 131+/-3 mm Hg). Phe (10(-5) mol/L) caused an increase in active stress that was greater in IUGR than in normal rats at 4 weeks (12.4 versus 7.8), 8 weeks (13.3 versus 8.4), and 12 weeks (14.6 versus 9.0x10(4) N/m2). Removal of the endothelium enhanced Phe-induced stress in normal but not IUGR rats. In endothelium-intact strips, acetylcholine (ACh) caused relaxation of Phe contraction and induced nitrite/nitrate production that were smaller in IUGR than normal rats. L-NAME (10(-4) mol/L), which inhibits NO synthase, or ODQ (10(-5) mol/L), which inhibits cGMP production in smooth muscle, inhibited ACh-induced relaxation and enhanced Phe contraction in normal but not IUGR rats. Thus endothelium-dependent NO-mediated vascular relaxation is inhibited in IUGR offspring of pregnant rats with reduced uteroplacental perfusion, and this may explain the increased vascular constriction and arterial pressure in young adults with low birth weight.