Pregnancy-associated reduction in vascular protein kinase C activity rebounds during inhibition of NO synthesis

Increased uterine arterial tone, stiffness and remodeling with augmented matrix metalloproteinase-1 and -7 in uteroplacental ischemia-induced hypertensive pregnancy

Preeclampsia is a pregnancy-related disorder manifested as hypertensive pregnancy (HTN-Preg) and often fetal growth restriction (FGR), but the mechanisms involved are unclear. We have reported enhanced reactivity of systemic vessels in HTN-Preg rats, but the critical changes in the uterine circulation are less clear. We tested whether HTN-Preg involves localized aberrations in uterine arterial tone, stiffness and remodeling by matrix metalloproteinases (MMPs). Blood pressure (BP) and litter size were recorded in normal pregnant (Preg) rats and Preg rats with reduced uteroplacental perfusion pressure (RUPP). Isolated uterine arteries were placed in a pressure myograph for measuring intrinsic and extrinsic tone and arterial stiffness. Arteries were bathed in normal Krebs solution (2.5 mM Ca2+), Ca2+-free (2 mM EGTA) Krebs, treated with sodium nitroprusside (SNP), or endothelium denuded, then pressurized at 10 mmHg steps from 10 to 110 mmHg, and the % change in diameter was analyzed to measure total (active + passive), active Ca2+-dependent myogenic, passive, and endothelium-dependent tone, respectively. BP was higher and the litter size and pup weight were reduced in RUPP vs Preg rats. In normal Krebs, increasing intraluminal pressure caused smaller increments in diameter in arteries of RUPP vs Preg rats, suggesting greater total vascular tone. Arterial incubation in Ca2+-free Krebs, treatment with SNP or endothelium-removal abolished the differences in vascular tone, and subtraction of each of these components from total vascular tone revealed significant active Ca2+-dependent myogenic, passive, and endothelium-dependent tone, respectively, in RUPP vs Preg rats. The total and passive strain-stress curves were shifted leftward in arteries of RUPP vs Preg rats, indicating increased uterine arterial stiffness. Arterial sections showed decreased lumen/total and increased wall/total area, and immunohistochemistry revealed greater MMP-1 and MMP-7 staining particularly in the media, suggesting uterine arterial remodeling by MMPs in RUPP vs Preg rats. The increased uterine arterial active myogenic, passive, and endothelium-dependent tone, arterial stiffness and remodeling by MMPs would further reduce uterine blood flow and exacerbate uteroplacental ischemia, FGR and HTN-Preg.

Regulation of vascular angiotensin II type 1 and type 2 receptor and angiotensin-(1-7)/MasR signaling in normal and hypertensive pregnancy

Normal pregnancy (Norm-Preg) is associated with a slight reduction in blood pressure (BP) and decreased BP response to vasoconstrictor stimuli such as angiotensin II (Ang II), although the renin-angiotensin-aldosterone system (RAAS) is upregulated. Preeclampsia (PE) is a complication of pregnancy manifested as hypertension-in-pregnancy (HTN-Preg), and dysregulation of angiotensin biosynthesis and signaling have been implicated. Ang II activates vascular Ang II type-1 receptor (AT1R) and Ang II type-2 receptor (AT2R), while angiotensin-(1-7) promotes Ang-(1-7)/MasR signaling. The role of AT1R in vasoconstriction and the activated cellular mechanisms are well-characterized. The sensitivity of vascular AT1R to Ang II and consequent activation of vasoconstrictor mechanisms decrease during Norm-Preg, but dramatically increase in HTN-Preg. Placental ischemia in late pregnancy could also initiate the release of AT1R agonistic autoantibodies (AT1AA) with significant impact on endothelial dysfunction and activation of contraction pathways in vascular smooth muscle including [Ca2+]c and protein kinase C. On the other hand, the role of AT2R and Ang-(1-7)/MasR in vascular relaxation, particularly during Norm-Preg and PE, is less clear. During Norm-Preg, increases in the expression/activity of vascular AT2R and Ang-(1-7)/MasR promote the production of endothelium-derived relaxing factors such as nitric oxide (NO), prostacyclin and endothelium-derived hyperpolarizing factor leading to generalized vasodilation. Aortic segments of Preg rats show prominent endothelial AT2R staining and increased relaxation and NO production in response to AT2R agonist CGP42112A, and treatment with AT2R antagonist PD123319 enhances phenylephrine-induced contraction. Decreased vascular AT2R and Ang-(1-7)/MasR expression and receptor-mediated mechanisms of vascular relaxation have been suggested in HTN-Preg animal models, but their role in human PE needs further testing. Changes in angiotensin-converting enzyme-2 (ACE2) have been observed in COVID-19 patients, and whether ACE2 influences the course of COVID-19 viral infection/immunity in Norm-Preg and PE is an intriguing area for research.

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.

Uteroplacental Circulation in Normal Pregnancy and Preeclampsia: Functional Adaptation and Maladaptation

Uteroplacental blood flow increases as pregnancy advances. Adequate supply of nutrients and oxygen carried by uteroplacental blood flow is essential for the well-being of the mother and growth/development of the fetus. The uteroplacental hemodynamic change is accomplished primarily through uterine vascular adaptation, involving hormonal regulation of myogenic tone, vasoreactivity, release of vasoactive factors and others, in addition to the remodeling of spiral arteries. In preeclampsia, hormonal and angiogenic imbalance, proinflammatory cytokines and autoantibodies cause dysfunction of both endothelium and vascular smooth muscle cells of the uteroplacental vasculature. Consequently, the vascular dysfunction leads to increased vascular resistance and reduced blood flow in the uteroplacental circulation. In this article, the (mal)adaptation of uteroplacental vascular function in normal pregnancy and preeclampsia and underlying mechanisms are reviewed.

Collagen I Induces Preeclampsia-Like Symptoms by Suppressing Proliferation and Invasion of Trophoblasts

Preeclampsia is a common obstetric disorder affecting 2-8% of pregnancy worldwide. Fibrosis is an important histological change occurring in preeclamptic placenta, and might depend on the excess deposition of collagen I. However, the role of fibrotic placenta and collagen I in the pathogenesis of preeclampsia remains unclear. Therefore, we analyzed the collagen deposition and the expression of Collagen I in human placenta by Masson staining, Sirius red staining and western blotting. Further, the role of collagen I in preeclampsia pathogenesis was studied in C57BL/6 mice. HTR-8/SVneo cells were used to investigate the mechanisms underlying the effects of collagen I in trophoblasts by transcriptome sequencing and pharmacological agonists. Human preeclamptic placenta exhibited a significantly higher degree of fibrosis in stem villi and terminal villi than normal placenta, and was characterized by collagen I deposition. In vivo, a single injection of collagen I on gestational day 0.5 led to an increase in systolic pressure of pregnant mice from gestational days 4.5-17.5, to a decrease in weight and number of embryos, and to enhanced placental collagen I expression and degree of fibrosis compared with control mice. In vitro, collagen I attenuated the proliferation and invasion of HTR-8SV/neo cells. This effect could be reversed by treatment with agonists of ERK and β-catenin. Moreover, transcriptome sequencing demonstrated that signaling pathways related to cell proliferation and invasion were significantly downregulated in HTR-8SV/neo cells. Thus, we propose that collagen I induced preeclampsia-like symptoms by suppressing the proliferation and invasion of trophoblasts through inhibition of the ERK phosphorylation and WNT/β-catenin signaling pathways. Our findings could pave the way to the discovery of small-molecule inhibitors for preeclampsia treatment and future studies with larger sample size are required.

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.

The effects of estradiol on inflammatory and endothelial dysfunction in rats with preeclampsia

Preeclampsia (PE), a hypertensive disorder during pregnancy, has adverse effects to both the mother and the fetus. Maternal inflammatory and vascular endothelial dysfunction are important factors in the pathogenesis of PE. The present study aimed to investigate the effects of estradiol (E2) on inflammatory and endothelial dysfunction in an N (omega)-nitro-L-arginine methyl ester (L-NAME)-induced rat model of PE. Adult pregnant female Sprague-Dawley rats were divided into four equal groups between days 7 and 11 of gestation and treated as follows: i) Pregnant rats receiving daily intraperitoneal (i.p.) injections of equal volume of 0.9% normal saline (NS) (Control group, n=12); ii) pregnant rats receiving daily i.p. injections of L-NAME at 50 mg/kg (L-NAME group, n=12); iii) pregnant rats receiving a daily i.p. injection of 50 mg/kg L-NAME and NS from day 11 (L-NAME + NS group, n=12); and iv) pregnant rats receiving daily i.p. injections of 50 mg/kg L-NAME and 100 µg/kg/day E2 from day 11 (L-NAME + E2 group, n=12). On day 21, blood pressure (BP) and the level of 24-h urine protein in the maternal rats, fetal weight and percentage of stillbirths following a cesarean section were recorded. The activities of nitric oxide (NO) and inducible NO synthase (iNOS), the levels of inflammatory cytokines [interleukin (IL)-1β, IL-6, interferon-γ and monocyte chemoattractant protein-1], adherence factors (CD49d, intracellular adhesion molecule 1 and lymphocyte function-associated antigen-1) and uterine angiogenic status (Fms-like tyrosine kinase-1, vascular cell adhesion molecule and matrix metalloproteinase 2/9) were also assessed. In addition, the histopathology of the placenta, the expression of estrogen receptor α 36 (ERα36), ERα, ERβ and G protein-coupled ER, as well as the activation of the toll-like receptor 4 (TLR4) signaling pathway (TLR4, myeloid differentiation primary response 88, IL-1 receptor-associated kinase 4 and tumor necrosis factor receptor-associated factor 6) were evaluated by H&E staining, immunofluorescence and western blot assays. Treatment with L-NAME increased the BP, urine protein and rate of stillbirths and suppressed fetal weight compared with those in the control group. The L-NAME-induced effects were attenuated by the administration of E2. In addition, the administration of E2 decreased inflammation and NO levels and altered the uterine angiogenic status. The histological analysis of PE rat placenta in the E2-treated group confirmed the effects on biochemical parameters. Of note, E2 treatment significantly suppressed the TLR4 signaling pathway. In the rat model of PE, adverse outcomes including BP, fetal rat weight and proteinuria, high neonatal death rate, inflammatory response, oxidative stress and endothelial dysfunction were attenuated by exogenous E2 administration, which may present a novel approach for the clinical treatment of PE.

Mechanotransduction and Uterine Blood Flow in Preeclampsia: The Role of Mechanosensing Piezo 1 Ion Channels

There is a large increase in uterine arterial blood flow during normal pregnancy. Structural and cellular adjustments occur in the uterine vasculature during pregnancy to accommodate this increased blood flow through a complex adaptive process that is dependent on multiple coordinated and interactive influences and this process is known as "vascular remodeling." The etiology of preeclampsia involves aberrant placentation and vascular remodeling leading to reduced uteroplacental perfusion. The placental ischemia leads to development of hypertension and proteinuria in the mother, intrauterine growth restriction, and perinatal death in the fetus. However, the underlying source of the deficient vascular remodeling and the subsequent development of preeclampsia remain to be fully understood. Mechanoreceptors in the vascular system convert mechanical force (shear stress) to biochemical signals and feedback mechanisms. This review focuses on the Piezo 1 channel, a mechanosensitive channel that is sensitive to shear stress in the endothelium; it induces Ca2+ entry which is linked to endothelial nitric oxide synthase (eNOS) activation as the mechanoreceptor responsible for uterine vascular dilatation during pregnancy. Here we describe the downstream signaling pathways involved in this process and the possibility of a deficiency in expression of Piezo 1 in preeclampsia leading to the abnormal vascular dysfunction responsible for the pathophysiology of the disease. The Piezo 1 ion channel is expressed in the endothelium and vascular smooth muscle cells (VSMCs) of small-diameter arteries. It plays a role in the structural remodeling of arteries and is involved in mechanotransduction of hemodynamic shear stress by endothelial cells (ECs).

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.

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.

Decreased homodimerization and increased TIMP-1 complexation of uteroplacental and uterine arterial matrix metalloproteinase-9 during hypertension-in-pregnancy

Preeclampsia is a complication of pregnancy manifested as hypertension-in-pregnancy (HTN-Preg) and often intrauterine growth restriction (IUGR). Placental ischemia could be an initiating event, but the molecular mechanisms are unclear. To test the hypothesis that dimerization of matrix metalloproteinases (MMPs) plays a role in HTN-Preg and IUGR, the levels/activity of MMP-9, tissue inhibitor of metalloproteinase (TIMP-1), and their dimerization forms were measured in the placenta, uterus, and uterine artery of normal pregnant (Preg) rats and a rat model of reduced uteroplacental perfusion pressure (RUPP). Consistent with our previous report, blood pressure (BP) was higher, pup weight was lower, and gelatin zymography showed different gelatinolytic activity for pro-MMP-9, MMP-9, pro-MMP-2 and MMP-2 in RUPP vs Preg rats. Careful examination of the zymograms showed additional bands at 200 and 135kDa. Western blots with MMP-9 antibody suggested that the 200kDa band was a MMP-9 homodimer. Western blots with TIMP-1 antibody as well as reverse zymography suggested that the 135kDa band was a MMP-9/TIMP-1 complex. The protein levels and gelatinase activity of MMP-9 homodimer were decreased while MMP-9/TIMP-1 complex was increased in placenta, uterus and uterine artery of RUPP vs Preg rats. The epidermal growth factor (EGF) receptor blocker erlotinib and protein kinase C (PKC) inhibitor bisindolylmaleimide decreased MMP-9 homodimer and increased MMP-9/TIMP-1 complex in placenta, uterus and uterine artery of Preg rats. EGF and the PKC activator phorbol-12,13-dibutyrate (PDBu) reversed the decreases in MMP-9 homodimer and the increases in MMP-9/TIMP-1 complex in tissues of RUPP rats. Thus, the increased BP and decreased pup weight in placental ischemia model of HTN-Preg are associated with a decrease in MMP-9 homodimer and an increase in MMP-9/TIMP-1 complex in placenta, uterus, and uterine artery, which together would cause a net decrease in MMP-9 activity and reduce uteroplacental and vascular remodeling in the setting of HTN-Preg and IUGR. Enhancing EGFR/PKC signaling may reverse the MMP-9 unfavorable dimerization patterns and thereby promote uteroplacental and vascular remodeling in preeclampsia.

Protein Kinase C as Regulator of Vascular Smooth Muscle Function and Potential Target in Vascular Disorders

Vascular smooth muscle (VSM) plays an important role in maintaining vascular tone. In addition to Ca2+-dependent myosin light chain (MLC) phosphorylation, protein kinase C (PKC) is a major regulator of VSM function. PKC is a family of conventional Ca2+-dependent α, β, and γ, novel Ca2+-independent δ, ɛ, θ, and η, and atypical ξ, and ι/λ isoforms. Inactive PKC is mainly cytosolic, and upon activation it undergoes phosphorylation, maturation, and translocation to the surface membrane, the nucleus, endoplasmic reticulum, and other cell organelles; a process facilitated by scaffold proteins such as RACKs. Activated PKC phosphorylates different substrates including ion channels, pumps, and nuclear proteins. PKC also phosphorylates CPI-17 leading to inhibition of MLC phosphatase, increased MLC phosphorylation, and enhanced VSM contraction. PKC could also initiate a cascade of protein kinases leading to phosphorylation of the actin-binding proteins calponin and caldesmon, increased actin-myosin interaction, and VSM contraction. Increased PKC activity has been associated with vascular disorders including ischemia-reperfusion injury, coronary artery disease, hypertension, and diabetic vasculopathy. PKC inhibitors could test the role of PKC in different systems and could reduce PKC hyperactivity in vascular disorders. First-generation PKC inhibitors such as staurosporine and chelerythrine are not very specific. Isoform-specific PKC inhibitors such as ruboxistaurin have been tested in clinical trials. Target delivery of PKC pseudosubstrate inhibitory peptides and PKC siRNA may be useful in localized vascular disease. Further studies of PKC and its role in VSM should help design isoform-specific PKC modulators that are experimentally potent and clinically safe to target PKC in vascular disease.

Pregnancy-associated adaptations in [Ca2+]i-dependent and Ca2+ sensitization mechanisms of venous contraction: implications in pregnancy-related venous disorders

Pregnancy is associated with significant adaptations in the maternal hemodynamics and arterial circulation, but the changes in the venous mechanisms during pregnancy are less clear. We hypothesized that pregnancy is associated with alterations in venous function, intracellular free Ca(2+) concentration ([Ca(2+)]i), and Ca(2+)-dependent mechanisms of venous contraction. Circular segments of inferior vena cava (IVC) from virgin and late pregnant (Preg, day 19) Sprague-Dawley rats were suspended between two hooks, labeled with fura-2, and placed in a cuvet inside a spectrofluorometer for simultaneous measurement of contraction and [Ca(2+)]i (fura-2 340/380 ratio). KCl (96 mM), which stimulates Ca(2+) influx, caused less contraction (35.6 ± 6.3 vs. 92.6 ± 19.9 mg/mg tissue) and smaller increases in [Ca(2+)]i (1.67 ± 0.12 vs. 2.19 ± 0.11) in Preg vs. virgin rat IVC. The α-adrenergic receptor agonist phenylephrine (Phe; 10(-5) M) caused less contraction (23.8 ± 3.4 vs. 70.9 ± 12.9 mg/mg tissue) and comparable increases in [Ca(2+)]i (1.76 ± 0.10 vs. 1.89 ± 0.08) in Preg vs. virgin rat IVC. At increasing extracellular Ca(2+) concentrations ([Ca(2+)]e) (0.1, 0.3, 0.6, 1, and 2.5 mM), KCl and Phe induced [Ca(2+)]e-contraction and [Ca(2+)]e-[Ca(2+)]i curves that were reduced in Preg vs. virgin IVC, supporting reduced Ca(2+) entry mechanisms. The [Ca(2+)]e-contraction and [Ca(2+)]e-[Ca(2+)]i curves were used to construct the [Ca(2+)]i-contraction relationship. Despite reduced contraction and [Ca(2+)]i in Preg IVC, the Phe-induced [Ca(2+)]i-contraction relationship was greater than that of KCl and was enhanced in Preg vs. virgin IVC, suggesting parallel activation of Ca(2+)-sensitization pathways. The Ca(2+) channel blocker diltiazem, protein kinase C (PKC) inhibitor GF-109203X, and Rho-kinase (ROCK) inhibitor Y27632 inhibited KCl- and Phe-induced contraction and abolished the shift in the Phe [Ca(2+)]i-contraction relationship in Preg IVC, suggesting an interplay between the decrease in Ca(2+) influx and possible compensatory activation of PKC- and ROCK-mediated Ca(2+)-sensitization pathways. The reduced [Ca(2+)]i and [Ca(2+)]i-dependent contraction in Preg rat IVC, despite the parallel rescue activation of Ca(2+)-sensitization pathways, suggests that the observed reduction in [Ca(2+)]i-dependent contraction mechanisms is likely underestimated, and that the veins without the rescue Ca(2+)-sensitization pathways could be even more prone to dilation during pregnancy. These pregnancy-associated reductions in Ca(2+) entry-dependent mechanisms of venous contraction, if occurring in human lower extremity veins and if not adequately compensated by Ca(2+)-sensitization pathways, may play a role in pregnancy-related venous disorders.

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.

Impaired proliferation of pancreatic beta cells, by reduced placental growth factor in pre-eclampsia, as a cause for gestational diabetes mellitus

OBJECTIVES

Reduced increase in serum placental growth factor (PLGF) levels frequently occurs in patients with pre-eclampsia (PE) and thus has been used as a predictive factor for developing PE. However, it has remained elusive how shortage of PLGF could affect pancreatic endocrine homoeostasis and function in pregnancy to lead to development of gestational diabetes mellitus (GDM).

MATERIALS AND METHODS

We used l-NAME injection in mice, as a model of human PE, in which PLGF levels were significantly reduced.

RESULTS

We not only confirmed reduced serum PLGF levels in patients with PE but also detected strong correlation of serum PLGF levels and presence of GDM. We found that growth of beta cell mass during pregnancy was significantly impaired by l-NAME injection, as a result of reduced beta cell proliferation. This may explain the higher risk of developing GDM in patients with PE. Moreover, provision of exogenous PLGF in l-NAME-treated pregnant mice significantly rescued beta cell proliferation, with subsequent increase in beta cell mass, suggesting that shortage in PLGF may be responsible for impaired beta cell growth and higher occurrence of GDM in patients with PE.

CONCLUSIONS

Our study highlighted a pivotal role for PLGF in prevention and treatment of GDM in patients with PE.

Protein Kinase C Inhibitors as Modulators of Vascular Function and their Application in Vascular Disease

Blood pressure (BP) is regulated by multiple neuronal, hormonal, renal and vascular control mechanisms. Changes in signaling mechanisms in the endothelium, vascular smooth muscle (VSM) and extracellular matrix cause alterations in vascular tone and blood vessel remodeling and may lead to persistent increases in vascular resistance and hypertension (HTN). In VSM, activation of surface receptors by vasoconstrictor stimuli causes an increase in intracellular free Ca(2+) concentration ([Ca(2+)]i), which forms a complex with calmodulin, activates myosin light chain (MLC) kinase and leads to MLC phosphorylation, actin-myosin interaction and VSM contraction. Vasoconstrictor agonists could also increase the production of diacylglycerol which activates protein kinase C (PKC). PKC is a family of Ca(2+)-dependent and Ca(2+)-independent isozymes that have different distributions in various blood vessels, and undergo translocation from the cytosol to the plasma membrane, cytoskeleton or the nucleus during cell activation. In VSM, PKC translocation to the cell surface may trigger a cascade of biochemical events leading to activation of mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK), a pathway that ultimately increases the myofilament force sensitivity to [Ca(2+)]i, and enhances actin-myosin interaction and VSM contraction. PKC translocation to the nucleus may induce transactivation of various genes and promote VSM growth and proliferation. PKC could also affect endothelium-derived relaxing and contracting factors as well as matrix metalloproteinase (MMPs) in the extracellular matrix further affecting vascular reactivity and remodeling. In addition to vasoactive factors, reactive oxygen species, inflammatory cytokines and other metabolic factors could affect PKC activity. Increased PKC expression and activity have been observed in vascular disease and in certain forms of experimental and human HTN. Targeting of vascular PKC using PKC inhibitors may function in concert with antioxidants, MMP inhibitors and cytokine antagonists to reduce VSM hyperactivity in certain forms of HTN that do not respond to Ca(2+) channel blockers.

Chronic hypoxia differentially up-regulates protein kinase C-mediated ovine uterine arterial contraction via actin polymerization signaling in pregnancy

Chronic hypoxia (CH) during pregnancy is associated with increased uterine vascular tone. The present study tested the hypothesis that CH up-regulates protein kinase C (PKC)-mediated actin polymerization, resulting in enhanced uterine vascular contraction in pregnancy. Uterine arteries were isolated from nonpregnant (NPUA) and near-term (∼140 days of gestation) pregnant (PUA) sheep that had been maintained at sea level (∼300 m) or exposed to high altitude (3801 m) hypoxia for 110 days. In normoxic animals, the induced contractions by the PKC activator phorbol 12,13-dibutyrate (PDBu) were greater in NPUA than in PUA, which was abrogated by an actin polymerization inhibitor cytochalasin B (Cyto B). In hypoxic animals, PDBu-induced contractions were significantly increased in PUA but not in NPUA, which was inhibited by Cyto B. In contrast, neither pregnancy nor hypoxia affected Cyto B-mediated inhibition of norepinephrine (NE)-induced contractions. Prolonged ex vivo treatment of NPUA with 17beta-estradiol and progesterone significantly attenuated PDBu-induced actin polymerization and contractions, and the hormonal treatment did not alter the inhibitory effect of Cyto B on PDBu- or NE-induced contractions in either normoxic or hypoxic animals. 2-(2-Amino-3-methoxyphenyl)-4H-1-benzopyran-4-one potentiated PDBu-mediated actin polymerization and enhanced PDBu-induced contractions of PUA in normoxic but not hypoxic animals, which was abrogated by Cyto B. The results suggest that chronic hypoxia during pregnancy causes attenuation of steroid hormone-mediated ERK1/2 signaling and results in increased actin polymerization and uterine vascular tone, linking gestational hypoxia to aberrant uteroplacental circulation.

Pregnancy reduces RhoA/Rho kinase and protein kinase C signaling pathways downstream of thromboxane receptor activation in the rat uterine artery

During pregnancy, reduced vascular responses to constrictors contribute to decreased uterine and total vascular resistance. Thromboxane A(2) (TxA(2)) is a potent vasoconstrictor that exerts its actions via diverse signaling pathways, and its biosynthesis increases in preeclampsia. In this study, we hypothesized that maternal vascular responses to TxA(2) will be attenuated via Rho kinase, PKC, p38 MAPK, and ERK1/2 signaling pathways. Isolated ring segments of uterine and small mesenteric arteries from late pregnant (19-21 days) and virgin rats were suspended in a myograph, and isometric force was measured. Pregnancy did not affect uterine and mesenteric artery responses to the TxA(2) analog U-46619 (10(-9)-10(-5) M), but transduction signals associated with these contractions were different between pregnant and nonpregnant rats. Inhibition of Rho kinase (10(-6) M Y-27632) reduced sensitivity to U-46619 in virgin uterine vessels but did not inhibit these contractions in pregnant uterine arteries and had no effect on mesenteric vessels. Treatment of arterial segments with a PKC inhibitor (10(-6) M bisindolylmaleimide I) reduced U-46619-induced contractions in virgin uterine and mesenteric arteries and in pregnant mesenteric arteries. Pregnant uterine arteries, however, were unresponsive to PKC inhibition. Inhibition of ERK1/2 (10(-5) M PD-98059) and p38 MAPK (10(-5) M SB-203580) reduced U46619-induced contractions in nonpregnant vessels and in pregnant uterine and mesenteric vessels. These data suggest that normal pregnancy does not affect uterine and mesenteric contractile responses to TxA(2) but reduces the contribution of Rho kinase and PKC signaling pathways to these contractions in the uterine vasculature. In contrast, the role of ERK1/2 and p38 MAPK in U-46619-induced uterine contractions remains unchanged with pregnancy. TxA(2)-associated transduction signals and its regulators might present potential targets for the development of new treatments for preeclampsia and other pregnancy-associated vascular diseases.

Pregnancy upregulates large-conductance Ca(2+)-activated K(+) channel activity and attenuates myogenic tone in uterine arteries

Uterine vascular tone significantly decreases whereas uterine blood flow dramatically increases during pregnancy. However, the complete molecular mechanisms remain elusive. We hypothesized that increased Ca(2+)-activated K(+) (BK(Ca)) channel activity contributes to the decreased myogenic tone of uterine arteries in pregnancy. Resistance-sized uterine arteries were isolated from nonpregnant and near-term pregnant sheep. Electrophysiological studies revealed a greater whole-cell K(+) current density in pregnant compared with nonpregnant uterine arteries. Tetraethylammonium and iberiotoxin inhibited K(+) currents to the same extent in uterine arterial myocytes. The BK(Ca) channel current density was significantly increased in pregnant uterine arteries. In accordance, tetraethylammonium significantly increased pressure-induced myogenic tone in pregnant uterine arteries and abolished the difference in myogenic responses between pregnant and nonpregnant uterine arteries. Activation of protein kinase C produced a similar effect to tetraethylammonium by inhibiting BK(Ca) channel activity and increasing myogenic tone in pregnant uterine arteries. Chronic treatment of nonpregnant uterine arteries with physiologically relevant concentrations of 17β-estradiol and progesterone caused a significant increase in the BK(Ca) channel current density. Western blot analyses demonstrated a significant increase of the β1, but not α, subunit of BK(Ca) channels in pregnant uterine arteries. In accordance, steroid treatment of nonpregnant uterine arteries resulted in an upregulation of the β1, but not α, subunit expression. The results indicate that the steroid hormone-mediated upregulation of the β1 subunit and BK(Ca) channel activity may play a key role in attenuating myogenic tone of the uterine artery in pregnancy.

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.

Role of KATP and L-type Ca2+ channel activities in regulation of ovine uterine vascular contractility: effect of pregnancy and chronic hypoxia

OBJECTIVE

Our objective was to determine whether the pregnancy and high altitude long-term hypoxia-mediated changes in uterine artery contractility were regulated by K(ATP) and L-type Ca(2+) channel activities.

STUDY DESIGN

Uterine arteries were isolated from nonpregnant and near-term pregnant ewes that had been maintained at sea level (∼300 m) or exposed to high altitude (3801 m) for 110 days. Isometric tension was measured in a tissue bath.

RESULTS

Pregnancy increased diazoxide, but not verapamil-induced relaxations. Long-term hypoxia attenuated diazoxide-induced relaxations in near-term pregnant uterine arteries, but enhanced verapamil-induced relaxations in nonpregnant uterine arteries. Diazoxide decreased the maximal response (E(max)) of phenylephrine-induced contractions in near-term pregnant uterin arteries but not nonpregnant uterine arteries in normoxic sheep. In contrast, diazoxide had no effect on phenylephrine-induced E(max) in near-term pregnant uterine arteries but decreased it in nonpregnant uterine arteries in long-term hypoxia animals. Verapamil decreased the E(max) and pD(2) (-logEC(50)) of phenylephrine-induced contractions in both nonpregnant uterine arteries and near-term pregnant uterine arteries in normoxic and long-term hypoxia animals, except nonpregnant uterine arteries of normoxic animals in which verapamil showed no effect on the pD(2).

CONCLUSION

The results suggest that pregnancy selectively increases K(ATP), but not L-type Ca(2+) channel activity. Long-term hypoxia decreases the K(ATP) channel activity, which may contribute to the enhanced uterine vascular myogenic tone observed in pregnant sheep at high altitude hypoxia.

PKC regulates alpha(1)-adrenoceptor-mediated contractions and baseline Ca(2+) sensitivity in the uterine arteries of nonpregnant and pregnant sheep acclimatized to high altitude hypoxia

Chronic hypoxia has a profound effect on uterine artery adaptation to pregnancy. The present studies tested the hypothesis that pregnant kinase C (PKC) differentially regulates alpha(1)-adrenoceptor-mediated contractions and Ca(2+) sensitivity in the uterine arteries of nonpregnant and pregnant sheep acclimatized to high altitude hypoxia. Uterine arteries were isolated from nonpregnant (NPUA) and near-term pregnant (PUA) ewes maintained at high altitude (3801 m, Pao(2) approximately 60 torr) for 110 days. Phorbol 12,13-dibutyrate (PDBu) decreased phenylephrine-induced contractions in PUA but not in NPUA, which was partly inhibited by the PKC inhibitor GF109203X. Additionally, GF109203X shifted the concentration-response curve of phenylephrine-induced contractions to the right in PUA. In beta-escin-permeabilized arteries, Ca(2+)-induced increases in 20-kDa myosin light chain phosphorylation (MLC(20)-P) were similar in NPUA and PUA. However, Ca(2+) produced a concentration-dependent increase in the ratio of tension to MLC(20)-P in PUA, as compared with NPUA. PKC inhibition decreased Ca(2+)-induced contractions in both NPUA and PUA. PDBu induced contractions of PUA in the absence of changes in MLC(20)-P, which was not affected by PD098059. There was a significant increase in the basal activity of PKCvarepsilon in PUA, but not in NPUA, in hypoxic sheep, as compared with normoxic animals. The results demonstrate that the inhibitory effect of PKC on alpha(1)-adrenoceptor-mediated contractions of uterine arteries is preserved in pregnant sheep at high altitude. However, the PKC-mediated thin-filament regulatory pathway is upregulated, resulting in increased baseline Ca(2+) sensitivity in the uterine artery during pregnancy at high altitude.

Chronic hypoxia inhibits sex steroid hormone-mediated attenuation of ovine uterine arterial myogenic tone in pregnancy

Previous studies in ovine uterine arteries have demonstrated that sex steroid hormones upregulate extracellular signal-regulated kinase 1/2 expression and downregulate the protein kinase C signaling pathway, resulting in the attenuated myogenic tone in pregnancy. The present study tested the hypothesis that chronic hypoxia during gestation inhibits the sex steroid-mediated adaptation of extracellular signal-regulated kinase 1/2 and protein kinase C signaling pathways and increases the myogenic tone of uterine arteries. Uterine arteries were isolated from nonpregnant and near-term pregnant sheep that had been maintained at sea level (≈300 m) or exposed to high-altitude (3801 m) hypoxia for 110 days. In contrast to the previous findings in normoxic animals, 17β-estradiol and progesterone failed to suppress protein kinase C-induced contractions and the pressure-induced myogenic tone in uterine arteries from hypoxic animals. Western analyses showed that the sex steroids lost their effects on extracellular signal-regulated kinase 1/2 expression and phospho- extracellular signal-regulated kinase 1/2 levels, as well as the activation of protein kinase C isozymes in uterine arteries of hypoxic ewes. In normoxic animals, pregnancy and the sex steroid treatments significantly increased uterine artery estrogen receptor-α and progesterone receptor B expression. Chronic hypoxia selectively downregulated estrogen receptor-α expression in uterine arteries of pregnant animals and eliminated the upregulation of estrogen receptor-α in pregnancy or by the steroid treatments observed in normoxic animals. The results demonstrate that, in the ovine uterine artery, chronic hypoxia in pregnancy inhibits the sex steroid hormone-mediated adaptation of decreased myogenic tone by downregulating estrogen receptor-α expression, providing a mechanism linking hypoxia and maladaptation of uteroplacental circulation and an increased risk of preeclampsia in pregnancy.

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.

Increased alpha-1 adrenoceptor expression in pregnant rats with subrenal aortic coarctation

The progression of pregnancy is associated with attenuation in vasopressor response to adrenergic agonists. In pregnancy-induced hypertension this attenuation is reverted. It is not known if this reversion involves alpha-1 adrenoceptor expression.

OBJECTIVE

In this work we propose that in pregnant rats with subrenal aortic coarctation there are changes in the expression of alpha-1 adrenergic receptors in the thoracic and abdominal aorta during pregnancy.

METHODS

We used non-pregnant, normal pregnant and pregnant with subrenal aortic coarctation female Wistar rats. Pregnancy-induced hypertension indicators, systolic blood pressure, 24 hours proteinuria, pup weight and maternal weight were measured. Dose response curves to phenylephrine were carried out to determine vascular reactivity along pregnancy. Alpha 1-adrenoceptors were detected from thoracic and abdominal aorta using immunoblot.

RESULTS

Results show significant increases in arterial pressure and proteinuria in pregnant rats with SRAC at the end of the third week. Pregnancy reduces alpha-(1-A, -B) and (-D) adrenoceptor expression and this event is reverted by subrenal aortic coarctation. This phenomenon is more apparent in the abdominal segment of the aorta.

CONCLUSIONS

These findings suggest that subrenal aortic coarctation is a good animal model of pregnancy-induced hypertension and that alpha1-adrenoceptors participate in its physiopathology increasing their expression in a segment-dependent manner.

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.

Direct chronic effect of steroid hormones in attenuating uterine arterial myogenic tone: role of protein kinase c/extracellular signal-regulated kinase 1/2

Pregnancy is associated with a significant decrease in uterine vascular tone and an increase in uterine blood flow. The present study tested the hypothesis that estrogen and progesterone differentially regulate the extracellular signal-regulated kinase (ERK)1/2 and protein kinase C (PKC) signaling pathways in vascular smooth muscle, resulting in a decrease in uterine vascular myogenic tone in pregnancy. Uterine arteries were isolated from nonpregnant and near-term pregnant sheep. Chronic treatment (48 hours) of nonpregnant uterine arteries with 17beta-estradiol and progesterone caused a significant decrease in PKC-mediated contractions and pressure-induced myogenic tone. In accordance, treatment of near-term pregnant uterine arteries for 48 hours with ICI 182780 and RU 486 significantly increased PKC-induced contractions and myogenic tone. In contrast, acute treatment for 30 minutes had no effect on uterine artery contractility. An ERK1/2 inhibitor, PD098059, restored the chronic effect of steroids on PKC-mediated contractions in nonpregnant sheep. ERK1/2 protein and mRNA levels were greater in near-term pregnant as compared with nonpregnant uterine arteries. 17beta-Estradiol and progesterone increased ERK1/2 protein in nonpregnant sheep. In agreement, ICI 182780 and RU 486 caused significant decreases in ERK1/2 protein in near-term pregnant sheep. Western blot showed 6 PKC isozymes, alpha, beta(I), beta(II), delta, epsilon, and zeta, in the uterine arteries. 17beta-Estradiol and progesterone decreased the particulate:cytosolic ratios of PKCalpha, epsilon, and zeta, respectively, in nonpregnant sheep. ICI 182780 and RU 486 increased the ratios in near-term pregnant sheep. The results indicate a direct chronic effect of the steroid hormones in the upregulation of ERK1/2 expression and downregulation of the PKC signaling pathway, resulting in attenuated myogenic tone of the uterine artery in pregnancy.

Chronic hypoxia increases pressure-dependent myogenic tone of the uterine artery in pregnant sheep: role of ERK/PKC pathway

Chronic hypoxia during pregnancy has profound effects on uterine artery (UA) contractility and attenuates uterine blood flow. The present study tested the hypothesis that chronic hypoxia inhibits the pregnancy-induced reduction in pressure-dependent myogenic tone of resistance-sized UAs. UAs were isolated from nonpregnant ewes (NPUAs) and near-term pregnant ewes (PUAs) that had been maintained at sea level (approximately 300 m) or at high altitude (3,801 m) for 110 days. In normoxic animals, the pressure-dependent myogenic response was significantly attenuated in PUAs compared with NPUAs. Hypoxia significantly increased myogenic tone in PUAs and abolished its difference between PUAs and NPUAs. Consistently, there was a significant increase in PKC-mediated baseline Ca(2+) sensitivity of PUAs in hypoxic animals. Hypoxia significantly increased phorbol 12,13-dibutyrate (PDBu)-induced contractions in PUAs but not in NPUAs. Whereas the inhibition of ERK1/2 by PD-98059 potentiated PDBu-mediated contractions of PUAs in normoxic animals, it failed to do so in hypoxic animals. Hypoxia decreased ERK1/2 expression in PUAs. PDBu induced membrane translocation of PKC-alpha and PKC-epsilon. Whereas there were no significant differences in PKC-alpha translocation among all groups, the translocation of PKC-epsilon was significantly enhanced in NPUAs compared with PUAs in normoxic animals, and hypoxia significantly increased PKC-epsilon translocation in PUAs. In the presence of PD-98059, there were no significant differences in PDBu-induced PKC-epsilon translocation among all groups. Treatment of PUAs isolated from normoxic animals with 10.5% O(2) for 48 h ex vivo significantly increased PDBu-induced contractions and eliminated its difference between PUAs and NPUAs. The results suggest that hypoxia upregulates pressure-dependent myogenic tone through its direct effect in suppressing ERK1/2 activity and increasing the PKC signal pathway, leading to an increase in the Ca(2+) sensitivity of the myogenic mechanism in the UA during pregnancy.

Inhibition of nitric oxide synthases abrogates pregnancy-induced uterine vascular expansive remodeling

BACKGROUND/AIMS

It was the aim of this study to test the hypothesis that hypertension and/or inhibition of nitric oxide (NO) synthases alters uterine vascular remodeling during pregnancy.

METHODS

Using a model of hypertension (NO synthase inhibition with L-NAME) in nonpregnant and pregnant rats, comparisons were made with age-matched controls, as well as with animals receiving hydralazine along with L-NAME to maintain normotension in the presence of NO synthase inhibition. Circumferential and axial remodeling of large (main uterine, MUA) and small (premyometrial radial) arteries were quantified and compared.

RESULTS

L-NAME treatment prevented expansive circumferential remodeling of the MUA; cotreatment with hydralazine was without effect. Circumferential remodeling of smaller premyometrial radial arteries was also significantly attenuated in hypertensive pregnant animals, while premyometrial radial arteries from rats receiving hydralazine with L-NAME were of intermediate diameter. Neither hypertension nor NO synthase inhibition had any effect on the substantial (200-300%) axial growth of MUA or premyometrial radial arteries.

CONCLUSION

NO plays a major role in facilitating pregnancy-induced expansive remodeling in the uterine circulation, particularly in larger arteries. Some beneficial effects of hydralazine on expansive circumferential remodeling were noted in smaller radial vessels, and these may be linked to its prevention of systemic hypertension and/or to local effects on the arterial wall. Neither NO synthase inhibition nor hypertension had any effect on arterial longitudinal growth.

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.

Review article: steroid hormones and uterine vascular adaptation to pregnancy

Pregnancy is a physiological state that involves a significant decrease in uterine vascular tone and an increase in uterine blood flow, which is mediated in part by steroid hormones, including estrogen, progesterone, and cortisol. Previous studies have demonstrated the involvement of these hormones in the regulation of uterine artery contractility through signaling pathways specific to the endothelium and the vascular smooth muscle. Alterations in endothelial nitric oxide synthase expression and activity, nitric oxide production, and expression of enzymes involved in PGI(2) production contribute to the uterine artery endothelium-specific responses. Steroid hormones also have an effect on calcium-activated potassium channel activity, PKC signaling pathway and myogenic tone, and alterations in pharmacomechanical coupling in the uterine artery smooth muscle. This review addresses current understanding of the molecular mechanisms by which steroid hormones including estrogen, progesterone, and cortisol modulate uterine artery contractility to alter uterine blood flow during pregnancy with an emphasis on the pregnant ewe model.

Regulation of baseline Ca2+ sensitivity in permeabilized uterine arteries: effect of pregnancy

The adaptation of contractile mechanisms of the uterine artery to pregnancy is not fully understood. The present study examined the effect of pregnancy on the uterine artery baseline Ca2+ sensitivity. In beta-escin-permeabilized arterial preparations, Ca2+ -induced concentration-dependent contractions were significantly decreased in uterine arteries from pregnant animals compared with those of nonpregnant animals. Time-course studies showed that Ca2+ increased phosphorylation of 20-kDa myosin light chain (MLC20), which preceded the tension development in vessels from both pregnant and nonpregnant animals. When compared with vessels from nonpregnant animals, there was a significant increase in the protein level of MLC20 and an accordance increase in the level of Ca2+ -induced phosphorylated MLC20 (MLC20-P) in uterine arteries during pregnancy. Simultaneous measurements of MCL20-P levels and contractions stimulated with Ca2+ in the same tissues demonstrated a significant attenuation in the tension-to-MLC20-P ratio in uterine arteries during pregnancy. Activation of PKC with phorbol 12,13-dibutyrate (PDBu) potentiated Ca2+ -induced contractions in uterine arteries from nonpregnant but not pregnant animals. Accordingly, inhibition of PKC attenuated Ca2+ -induced contractions in uterine arteries from nonpregnant but not pregnant animals. PDBu produced contractions in the presence or absence of Ca2+ in the beta-escin-permeabilized arteries, which were significantly decreased in uterine arteries from pregnant compared with nonpregnant animals. The results suggest that pregnancy upregulates the thick-filament regulatory pathway by increasing MLC20 phosphorylation but downregulates the thin-filament regulatory pathway by decreasing the contractile sensitivity of MLC20-P, resulting in attenuated baseline Ca2+ sensitivity in the uterine artery. In addition, PKC plays an important role in the regulation of basal Ca2+ sensitivity, which is downregulated during pregnancy.

Mechanism of enhanced calcium sensitivity and alpha 2-AR vasoreactivity in chronic NOS inhibition hypertension

PKC augments calcium sensitivity in spontaneously hypertensive rats and contributes to alpha(2)-adrenergic receptor (AR) contraction in rabbit saphenous vein. We showed previously that denuded aortic rings from N(omega)-nitro-l-arginine-treated hypertensive rats (LHR) contract more to CaCl(2) and to the alpha(2)-AR agonist UK-14304 than do rings from normotensive rats (NR). We hypothesized that enhanced PKC activity or a change in PKC isoform contributes to augmented calcium sensitivity and enhanced alpha(2)-AR contraction in LHR aorta. Current studies demonstrate that non-isoform-specific PKC inhibitors reduced UK-14304 contraction in both NR and LHR aorta. However, the calcium-dependent PKC inhibitor Gö-6976 only attenuated contraction in LHR aorta. Additionally, UK-14304 translocated PKC-delta to the membrane in NR aorta, whereas PKC-alpha was translocated to the membrane in LHR aorta. Finally, in ionomycin-permeabilized aorta Gö-6976 eliminated enhanced basal and augmented alpha(2)-AR-stimulated calcium sensitivity in LHR aorta but did not affect NR contraction. Together, these data suggest that PKC-alpha contributes to augmented calcium sensitivity and alpha(2)-AR reactivity after chronic nitric oxide synthase inhibition hypertension.

Acute and chronic NOS inhibition enhances alpha(2)- adrenoreceptor-stimulated RhoA and Rho kinase in rat aorta

We demonstrated that arteries from rats made hypertensive with chronic nitric oxide (NO) synthase (NOS) inhibition (N(omega)-nitro-L-arginine in drinking water, LHR) have enhanced contractile sensitivity to alpha(2)-adrenergic receptors (alpha(2)-AR) agonist UK-14304 compared with arteries from normotensive rats (NR). NO may regulate vascular tone in part through suppression of RhoA and Rho kinase (ROK). We hypothesized that enhanced RhoA and ROK activity augments alpha(2)-AR contraction in LHR aortic rings. Y-27632 eliminated UK-14304 contraction in LHR and NR aortic rings. The order of increasing sensitivity to Y-27632 was the following: endothelium-intact NR, LHR, and endothelium-denuded NR. UK-14304 stimulated RhoA translocation to the membrane fraction in LHR and denuded NR but not in intact NR aorta. Basally, more RhoA was present in the membrane fraction in denuded NR than in intact NR or LHR aorta. Relaxation to S-nitroso-N-acetyl-penicillamine and Y-27632 in denuded ionomycin-permeabilized rings was greater in NR than in LHR. Together these studies indicate alpha(2)-AR contraction depends on ROK activity more in NR than LHR aorta. Additionally, endogenous NO may regulate RhoA activation, whereas chronic NOS inhibition appears to cause RhoA desensitization.

Vascular mechanisms of increased arterial pressure in preeclampsia: lessons from animal models

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

Estrogen has opposing effects on vascular reactivity in obese, insulin-resistant male Zucker rats

We hypothesized that estradiol treatment would improve vascular dysfunction commonly associated with obesity, hyperlipidemia, and insulin resistance. A sham operation or 17beta-estradiol pellet implantation was performed in male lean and obese Zucker rats. Maximal vasoconstriction (VC) to phenylephrine (PE) and potassium chloride was exaggerated in control obese rats compared with lean rats, but estradiol significantly attenuated VC in the obese rats. Estradiol reduced the PE EC50 in all groups. This effect was cyclooxygenase independent, because preincubation with indomethacin reduced VC response to PE similarly in a subset of control and estrogen-treated lean rats. Endothelium-independent vasodilation (VD) to sodium nitroprusside was similar among groups, but endothelium-dependent VD to ACh was significantly impaired in obese compared with lean rats. Estradiol improved VD in lean and obese rats by decreasing EC50 but impaired function by decreasing maximal VD. The shift in EC50 corresponded to an upregulation in nitric oxide synthase III protein expression in the aorta of the estrogen-treated obese rats. In summary, estrogen treatment improves vascular function in male insulin-resistant, obese rats, partially via an upregulation of nitric oxide synthase III protein expression. These effects are counteracted by adverse factors, such as hyperlipidemia and, potentially, a release of an endothelium-derived contractile agent.

ERK MAP kinases regulate smooth muscle contraction in ovine uterine artery: effect of pregnancy

The present study investigated the potential role of extracellular signal-regulated kinase (ERK) in uterine artery contraction and tested the hypothesis that pregnancy upregulated ERK-mediated function in the uterine artery. Isometric tension in response to phenylephrine (PE), serotonin (5-HT), phorbol 12,13-dibutyrate (PDBu), and KCl was measured in the ring preparation of uterine arteries obtained from nonpregnant and near-term (140 days gestation) pregnant sheep. Inhibiting ERK activation with PD-98059 did not change the KCl-evoked contraction but significantly inhibited the contraction to 5-HT in both nonpregnant and pregnant uterine arteries. PD-98059 did not affect PE-induced contraction in the uterine arteries of nonpregnant sheep but significantly decreased it in the uterine arteries of pregnant sheep. In accordance, PE stimulated activation of ERK in uterine arteries of pregnant sheep, which was blocked by PD-98059. PD-98059-mediated inhibition of the PE-induced contraction was associated with a decrease in both intracellular Ca(2+) concentration and Ca(2+) sensitivity of contractile proteins in the uterine arteries of pregnant sheep. PDBu-mediated contraction was significantly less in pregnant than in nonpregnant uterine arteries. PD-98059 had no effect on PDBu-induced contraction in nonpregnant but significantly increased it in pregnant uterine arteries. In addition, PD-98059 significantly enhanced PDBu-stimulated protein kinase C activity. The results indicate that ERK plays an important role in the regulation of uterine artery contractility, and its effect is agonist dependent. More importantly, pregnancy selectively enhances the role of ERK in alpha(1)-adrenoceptor-mediated contractions and its effect in suppressing protein kinase C-mediated contraction in the uterine artery.

Gender-related distinctions in protein kinase C activity in rat vascular smooth muscle

Gender differences in vascular reactivity have been suggested; however, the cellular mechanisms involved are unclear. We tested the hypothesis that the gender differences in vascular reactivity reflect gender-related, possibly estrogen-mediated, distinctions in the expression and activity of specific protein kinase C (PKC) isoforms in vascular smooth muscle. Aortic strips were isolated from intact and gonadectomized male and female Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). Isometric contraction was measured in endothelium-denuded aortic strips. PKC activity was measured in the cytosolic and particulate fractions, and the amount of PKC was measured using Western blots and isoform-specific anti-PKC antibodies. In intact male WKY rats, phenylephrine (Phe, 10(-5) M) and phorbol 12,13-dibutyrate (PDBu, 10(-6) M) stimulated contraction to 0.37 +/- 0.02 and 0.42 +/- 0.02 g/mg tissue wt, respectively. The basal particulate/cytosolic PKC activity ratio was 0.86 +/- 0.06, and Western blots revealed alpha-, delta-, and zeta-PKC isoforms. Phe and PDBu increased PKC activity and caused significant translocation of alpha- and delta-PKC from the cytosolic to particulate fraction. In intact female WKY rats, basal PKC activity, the amount of alpha-, delta-, and zeta-PKC, the Phe- and PDBu-induced contraction, and PKC activity and translocation of alpha- and delta-PKC were significantly reduced compared with intact male WKY rats. The basal PKC activity, the amount of alpha-, delta-, and zeta-PKC, the Phe and PDBu contraction, and PKC activity and alpha- and delta-PKC translocation were greater in SHR than WKY rats. The reduction in Phe and PDBu contraction and PKC activity in intact females compared with intact males was greater in SHR ( approximately 30%) than WKY rats ( approximately 20%). Phe and PDBu contraction and PKC activity were not significantly different between castrated males and intact males but were greater in ovariectomized (OVX) females than intact females. Treatment of OVX females or castrated males with 17 beta-estradiol, but not 17 alpha-estradiol, subcutaneous implants caused significant reduction in Phe and PDBu contraction and PKC activity that was greater in SHR than WKY rats. Phe and PDBu contraction and PKC activity in OVX females or castrated males treated with 17 beta-estradiol plus the estrogen receptor antagonist ICI-182,780 were not significantly different from untreated OVX females or castrated males. Thus a gender-related reduction in vascular smooth muscle contraction in female WKY rats with intact gonads compared with males is associated with reduction in the expression and activity of vascular alpha-, delta-, and zeta-PKC. The gender differences in vascular smooth muscle contraction and PKC activity are augmented in the SHR and are possibly mediated by estrogen.

Nitric oxide is a downstream mediator of agrin-induced acetylcholine receptor aggregation

The synaptic basal lamina protein, agrin, is required for the formation of the neuromuscular junction. Agrin signals through a muscle-specific receptor tyrosine kinase (MuSK) initiating a cascade of events that lead to the aggregation of acetylcholine receptors (AChR) at the postsynaptic site. Another important synaptic signalling molecule is nitric oxide (NO), which is produced by the enzyme, nitric oxide synthase (NOS). We investigated the interaction between the agrin signalling cascade and the NO signalling cascade by treating cultured myotubes with agrin, NOS inhibitors, and NO donors. NOS inhibitors prevented agrin induced AChR aggregation and phosphorylation of the AChR beta subunit. Furthermore, NO donors induced AChR aggregation in the absence of agrin, as well as phosphorylation of the AChR beta subunit. These results demonstrate a role for NO as a downstream mediator of agrin induced AChR aggregation and AChR beta subunit phosphorylation at the neuromuscular junction.