Abstract 293: Endothelial Type B Endothelin Receptor is a Critical Microvascular Target in Placental Ischemia and Tumor Necrosis Factor-Mediated Hypertensive Pregnancy

Preeclampsia is a pregnancy-related hypertensive disorder (HTN-Preg) with unclear mechanism, and a role of cytokines and endothelin-1 (ET-1) has been suggested. We have recently shown downregulation of endothelial type B ET-1 receptor (ET B R) in Preg rats with reduced uterine perfusion pressure (RUPP). To test if cytokines are a possible mechanism linking RUPP to downregulation of ET B R, day 14-Preg rats were either nontreated or infused with TNFα (200 ng/kg/day), and RUPP rats were either nontreated or infused with the TNFα decoy receptor etanercept (0.4 mg/kg/day) for 5 days by osmotic minipump. On day 19, BP was recorded and mesenteric microvessels were isolated for simultaneous measurement of diameter and [Ca 2+ ] i (fura-2 340/380 ratio). BP was in TNFα-Preg (127±8) > Preg (97±5mmHg) and in etanercept-RUPP (113±2) < RUPP (124±3mmHg). ET-1 vasoconstriction was in TNFα-Preg (86.1±4.7) > Preg (58.1±5.2%), and in etanercept-RUPP (65.9±5.0) < RUPP (86.2±3.7%). ET-1 caused parallel increases in microvascular [Ca 2+ ] i that were in TNFα-Preg (0.90±0.01) > Preg (0.86±0.01), and in etanercept-RUPP (0.85±0.01) < RUPP (0.92±0.01). Endothelium removal or microvessel treatment with ET B R antagonist BQ-788 enhanced ET-1 vasoconstriction and [Ca 2+ ] i in Preg and etanercept-RUPP, but not in TNFα-Preg or RUPP. ET B R-mediated relaxation with IRL-1620 was in TNFα-Preg (4.11±6.1) < Preg (28.8±4.2%), and in etanercept-RUPP (20.2±4.6) > RUPP (10.17±2.9%). The NOS inhibitor L-NAME partially reduced ACh-induced and ET B R-mediated relaxation in Preg and etanercept-RUPP, but not TNFα-Preg or RUPP, suggesting decreased NO-dependent and ET B R-mediated vasorelaxation in HTN-Preg. Addition of the K + channel blocker teraethylammonium (non specific), or apamin (SK Ca ) plus TRAM-34 (IK Ca ) abolished the remaining ET B R-mediated relaxation in all groups, suggesting equal role of EDHF. Thus similar to RUPP, increasing TNFα in Preg rats increases ET-1 microvascular constriction and decreases ET B R-mediated NO-dependent vasodilation, and counteracting TNFα reduces BP and ET-1 vasoconstriction, and enhances ET B R-mediated vasodilation in RUPP rats. The results support that endothelial ET B R is a major microvascular target in placental ischemia and TNFα-mediated HTN-Preg.

Abstract 244: Increased Expression and Enhanced Vasorelaxation Activity of Specific Estrogen Receptor Subtypes in the Aorta and Mesenteric Vessels during Pregnancy

Pregnancy (Preg) is associated with hormonal and vascular changes, and estrogen (E2) may promote systemic vasodilation during Preg; however, the specific E2 receptor (ER), post-ER signaling mechanisms and vascular bed involved are unclear. To test if Preg is associated with distinct expression/activity of ERs in different blood vessels, BP and plasma E2 were measured in virgin and day-19 Preg rats, and the aorta, carotid, mesenteric and renal artery were isolated for measurement of ERα, ERβ and GPR30 expression, and the responses to E2 and specific ER agonists PPT (ERα), DPN (ERβ) and G1 (GPR30). BP was in Preg (89±6) < virgin (98±4mmHg), and plasma E2 was in Preg (120.5±5.8) > virgin (94.3±7.5pg/ml). Western blots revealed increased ERα and ERβ in aorta and mesenteric artery and GPR30 in aorta of Preg vs virgin. Immunohistochemistry revealed that the increases in ERs were mainly in intima and media. E2 and PPT caused greater relaxation of aorta of Preg (52.8±5.5, 49.3±11.4) than virgin (30.0±3.9, 19.3±3.8%) and of mesenteric artery of Preg (77.9±4.7, 75.4±4.5) than virgin (57.4±5.9, 46.5±9.5%), but similar relaxation in carotid and renal artery of Preg vs virgin. DPN and G1 caused greater relaxation in mesenteric and renal artery (15 to 30%) than aorta and carotid artery (<10%), but only aortic relaxation to G1 was in Preg (26.2±4.4) > virgin (5.3±6.7%). The NOS inhibitor L-NAME ± EDHF blocker tetraethylammonium or endothelium removal reduced PPT relaxation in aorta, suggesting an endothelium-dependent mechanism, but did not affect E2, PPT, DPN or G1-induced relaxation in other vessels, suggesting endothelium-independent mechanisms. PPT caused relaxation of Ca 2+ entry-dependent KCl contraction of mesenteric artery that was in Preg (69.7±5.5) > virgin rats (52.9±8.11%). Thus, during pregnancy, an increased ERα expression in endothelial and smooth muscle layers of aorta and mesenteric artery is associated with increased ERα-mediated relaxation via endothelium-derived vasodilators and direct inhibition of Ca 2+ entry pathways, supporting a role of aortic and mesenteric arterial ERα in pregnancy-associated systemic vasodilation. GPR30 may contribute to aortic dilation while the enhanced ERβ may mediate other genomic vascular effects during pregnancy.

Downregulation of microvascular endothelial type B endothelin receptor is a central vascular mechanism in hypertensive pregnancy

Preeclampsia is a pregnancy-related disorder characterized by hypertension with an unclear mechanism. Studies have shown endothelial dysfunction and increased endothelin-1 (ET-1) levels in hypertensive pregnancy (HTN-Preg). ET-1 activates endothelin receptor type-A in vascular smooth muscle to induce vasoconstriction, but the role of vasodilator endothelial endothelin receptor type-B (ETBR) in the changes in blood pressure (BP) and vascular function in HTN-Preg is unclear. To test whether downregulation of endothelial ETBR expression/activity plays a role in HTN-Preg, BP was measured in normal pregnancy (Norm-Preg) rats and rat model of HTN-Preg produced by reduction of uteroplacental perfusion pressure (RUPP), and mesenteric microvessels were isolated for measuring diameter, [Ca(2+)]i, and endothelin receptor type-A and ETBR levels. BP, ET-1- and potassium chloride-induced vasoconstriction, and [Ca(2+)]i were greater in RUPP than in Norm-Preg rats. Endothelium removal or microvessel treatment with ETBR antagonist BQ-788 enhanced ET-1 vasoconstriction and [Ca(2+)]i in Norm-Preg, but not RUPP, suggesting reduced vasodilator ETBR in HTN-Preg. The ET-1+endothelin receptor type-A antagonist BQ-123 and the ETBR agonists sarafotoxin 6c and IRL-1620 caused less vasorelaxation and nitrate/nitrite production in RUPP than in Norm-Preg. The nitric oxide synthase inhibitor Nω-nitro-L-arginine methyl ester reduced sarafotoxin 6c- and IRL-1620-induced relaxation in Norm-Preg but not in RUPP, supporting that ETBR-mediated nitric oxide pathway is compromised in RUPP. Reverse transcription polymerase chain reaction, Western blots, and immunohistochemistry revealed reduced endothelial ETBR expression in RUPP. Infusion of BQ-788 increased BP in Norm-Preg, and infusion of IRL-1620 reduced BP and ET-1 vasoconstriction and [Ca(2+)]i and enhanced ETBR-mediated vasorelaxation in RUPP. Thus, downregulation of microvascular vasodilator ETBR is a central mechanism in HTN-Preg, and increasing ETBR activity could be a target in managing preeclampsia.

Altered matrix metalloproteinase-2 and -9 expression/activity links placental ischemia and anti-angiogenic sFlt-1 to uteroplacental and vascular remodeling and collagen deposition in hypertensive pregnancy

Preeclampsia is a complication of pregnancy manifested as maternal hypertension and often fetal growth restriction. Placental ischemia could be an initiating event, but the linking mechanisms leading to hypertension and growth restriction are unclear. We have shown an upregulation of matrix metalloproteinases (MMPs) during normal pregnancy (Norm-Preg). To test the role of MMPs in hypertensive-pregnancy (HTN-Preg), maternal and fetal parameters, MMPs expression, activity and distribution, and collagen and elastin content were measured in uterus, placenta and aorta of Norm-Preg rats and in rat model of reduced uteroplacental perfusion pressure (RUPP). Maternal blood pressure was higher, and uterine, placental and aortic weight, and the litter size and pup weight were less in RUPP than Norm-Preg rats. Western blots and gelatin zymography revealed decreases in amount and gelatinase activity of MMP-2 and MMP-9 in uterus, placenta and aorta of RUPP compared with Norm-Preg rats. Immunohistochemistry confirmed reduced MMPs in uterus, placenta and aortic media of RUPP rats. Collagen, but not elastin, was more abundant in uterus, placenta and aorta of RUPP than Norm-Preg rats. The anti-angiogenic factor soluble fms-like tyrosine kinase-1 (sFlt-1) decreased MMPs in uterus, placenta and aorta of Norm-Preg rats, and vascular endothelial growth factor (VEGF) reversed the decreases in MMPs in tissues of RUPP rats. Thus placental ischemia and anti-angiogenic sFlt-1 decrease uterine, placental and vascular MMP-2 and MMP-9, leading to increased uteroplacental and vascular collagen, and growth-restrictive remodeling in HTN-Preg. Angiogenic factors and MMP activators may reverse the decrease in MMPs and enhance growth-permissive remodeling in preeclampsia.

Adaptive regulation of endothelin receptor type-A and type-B in vascular smooth muscle cells during pregnancy in rats

Normal pregnancy is associated with systemic vasodilation and decreased vascular contraction, partly due to increased release of endothelium-derived vasodilator substances. Endothelin-1 (ET-1) is an endothelium-derived vasoconstrictor acting via endothelin receptor type A (ETA R) and possibly type B (ETB R) in vascular smooth muscle cells (VSMCs), with additional vasodilator effects via endothelial ETB R. However, the role of ET-1 receptor subtypes in the regulation of vascular function during pregnancy is unclear. We investigated whether the decreased vascular contraction during pregnancy reflects changes in the expression/activity of ETAR and ETBR. Contraction was measured in single aortic VSMCs isolated from virgin, mid-pregnant (mid-Preg, day 12), and late-Preg (day 19) Sprague-Dawley rats, and the mRNA expression, protein amount, tissue and cellular distribution of ETAR and ETBR were examined using RT-PCR, Western blots, immunohistochemistry, and immunofluorescence. Phenylephrine (Phe, 10(-5)  M), KCl (51 mM), and ET-1 (10(-6)  M) caused VSMC contraction that was in late-Preg < mid-Preg and virgin rats. In VSMCs treated with ETB R antagonist BQ788, ET-1 caused significant contraction that was still in late-Preg < mid-Preg and virgin rats. In VSMCs treated with the ETAR antagonist BQ123, ET-1 caused a small contraction; and the ETBR agonists IRL-1620 and sarafotoxin 6c (S6c) caused similar contraction that was in late-Preg < mid-Preg and virgin rats. RT-PCR revealed similar ETAR, but greater ETBR mRNA expression in pregnant versus virgin rats. Western blots revealed similar ETAR, and greater protein amount of ETBR in endothelium-intact vessels, but reduced ETBR in endothelium-denuded vessels of pregnant versus virgin rats. Immunohistochemistry revealed prominent ETBR staining in the intima, but reduced ETAR and ETBR in the aortic media of pregnant rats. Immunofluorescence signal for ETAR and ETBR was less in VSMCs of pregnant versus virgin rats. The pregnancy-associated decrease in ETAR- and ETBR-mediated VSMC contraction appears to involve downregulation of ETAR and ETBR expression/activity in VSM, and may play a role in the adaptive vasodilation during pregnancy.

Sex hormone replacement therapy and modulation of vascular function in cardiovascular disease

Epidemiological and experimental studies suggest vascular protective effects of estrogen. Cardiovascular disease (CVD) is less common in premenopausal women than in men and postmenopausal women. Cytosolic/nuclear estrogen receptors (ERs) have been shown to mediate genomic effects that stimulate endothelial cell growth but inhibit vascular smooth muscle proliferation. However, the Heart and Estrogen/Progestin Replacement Study (HERS), HERS-II and Women's Health Initiative clinical trials demonstrated that hormone replacement therapy (HRT) may not provide vascular benefits in postmenopausal women and may instead trigger adverse cardiovascular events. HRT may not provide vascular benefits because of the type of hormone used. Oral estrogens are biologically transformed by first-pass metabolism in the liver. By contrast, transdermal preparations avoid first pass metabolism. Also, natural estrogens and phytoestrogens may provide alternatives to synthetic estrogens. Furthermore, specific ER modulators could minimize the adverse effects of HRT, including breast cancer. HRT failure in CVD could also be related to changes in vascular ERs. Genetic polymorphism and postmenopausal decrease in vascular ERs or the downstream signaling mechanisms may reduce the effects of HRT. HRT in the late postmenopausal period may not be as effective as during menopausal transition. Additionally, while HRT may aggravate pre-existing CVD, it may thwart its development if used in a timely fashion. Lastly, the vascular effects of progesterone and testosterone, as well as modulators of their receptors, may modify the effects of estrogen and thereby provide alternative HRT strategies. Thus, the beneficial effects of HRT in postmenopausal CVD can be enhanced by customizing the HRT type, dose, route of administration and timing depending on the subject's age and cardiovascular condition.

Dissociation of hyperglycemia from altered vascular contraction and relaxation mechanisms in caveolin-1 null mice

Hyperglycemia and endothelial dysfunction are associated with hypertension, but the specific causality and genetic underpinning are unclear. Caveolin-1 (cav-1) is a plasmalemmal anchoring protein and modulator of vascular function and glucose homeostasis. Cav-1 gene variants are associated with reduced insulin sensitivity in hypertensive individuals, and cav-1(-/-) mice show endothelial dysfunction, hyperglycemia, and increased blood pressure (BP). On the other hand, insulin-sensitizing therapy with metformin may inadequately control hyperglycemia while affecting the vascular outcome in certain patients with diabetes. To test whether the pressor and vascular changes in cav-1 deficiency states are related to hyperglycemia and to assess the vascular mechanisms of metformin under these conditions, wild-type (WT) and cav-1(-/-) mice were treated with either placebo or metformin (400 mg/kg daily for 21 days). BP and fasting blood glucose were in cav-1(-/-) > WT and did not change with metformin. Phenylephrine (Phe)- and KCl-induced aortic contraction was in cav-1(-/-) < WT; endothelium removal, the nitric-oxide synthase (NOS) blocker L-NAME (N(ω)-nitro-L-arginine methyl ester), or soluble guanylate cyclase (sGC) inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) enhanced Phe contraction, and metformin blunted this effect. Acetylcholine-induced relaxation was in cav-1(-/-) > WT, abolished by endothelium removal, L-NAME or ODQ, and reduced with metformin. Nitric oxide donor sodium nitroprusside was more potent in inducing relaxation in cav-1(-/-) than in WT, and metformin reversed this effect. Aortic eNOS, AMPK, and sGC were in cav-1(-/-) > WT, and metformin decreased total and phosphorylated eNOS and AMPK in cav-1(-/-). Thus, metformin inhibits both vascular contraction and NO-cGMP-dependent relaxation but does not affect BP or blood glucose in cav-1(-/-) mice, suggesting dissociation of hyperglycemia from altered vascular function in cav-1-deficiency states.

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.

Estrogen, vascular estrogen receptor and hormone therapy in postmenopausal vascular disease

Cardiovascular disease (CVD) is less common in premenopausal women than men of the same age or postmenopausal women, suggesting vascular benefits of estrogen. Estrogen activates estrogen receptors ERα, ERβ and GPR30 in endothelium and vascular smooth muscle (VSM), which trigger downstream signaling pathways and lead to genomic and non-genomic vascular effects such as vasodilation, decreased VSM contraction and growth and reduced vascular remodeling. However, randomized clinical trials (RCTs), such as the Women's Health Initiative (WHI) and Heart and Estrogen/progestin Replacement Study (HERS), have shown little vascular benefits and even adverse events with menopausal hormone therapy (MHT), likely due to factors related to the MHT used, ER profile, and RCT design. Some MHT forms, dose, combinations or route of administration may have inadequate vascular effects. Age-related changes in ER amount, distribution, integrity and post-ER signaling could alter the vascular response to MHT. The subject's age, preexisting CVD, and hormone environment could also reduce the effects of MHT. Further evaluation of natural and synthetic estrogens, phytoestrogens, and selective estrogen-receptor modulators (SERMs), and the design of appropriate MHT combinations, dose, route and 'timing' could improve the effectiveness of conventional MHT and provide alternative therapies in the peri-menopausal period. Targeting ER using specific ER agonists, localized MHT delivery, and activation of specific post-ER signaling pathways could counter age-related changes in ER. Examination of the hormone environment and conditions associated with hormone imbalance such as polycystic ovary syndrome may reveal the causes of abnormal hormone-receptor interactions. Consideration of these factors in new RCTs such as the Kronos Early Estrogen Prevention Study (KEEPS) could enhance the vascular benefits of estrogen in postmenopausal CVD.

Abstract 82: Critical Role of Striatin in Vascular Responses to Sodium Intake

Striatin is a scaffolding protein that plays a role in vesicular trafficking in neurons. Striatin binds to regulatory proteins such as caveolin-1, Ca2+-calmodulin, Gαi and phosphatase 2A, thereby activating transduction molecules such as eNOS and mitogen-activated protein kinase. We have shown that striatin colocalizes with the minerlacorticoid receptor (MR), and that MR activation increases striatin levels in vascular cells in vivo and in vitro. To test the hypothesis that striatin is a critical regulator of vascular function, WT mice and heterozygous striatin-deficient mice lacking one allele for striatin (Strn-HET) were randomized in a crossover intervention to liberal salt (HS, 1.6% NaCl) and low salt (LS, 0.03% NaCl) diets for 7 days on each diet. Blood pressure (BP) and plasma aldosterone (ALDO) levels were measured and the aorta was excised to assess vascular function. Δ Systolic BP (BP on HS - BP on LS) was in Strn-HET > WT (16.5±3.5 vs 3.7±6.1 mmHg). Plasma ALDO levels were higher during LS diet, but were similar in WT and Strn-HET mice (152.6±23.9 vs 131.5±47.6 ng/dL on LS; 72.9±7.7 vs 70.9±8.3 ng/dL on HS). Phenylephrine (Phe) caused vascular contraction that was in Strn-HET (max 0.31±0.07g) > WT (0.23±0.07g). Also, high KCl (96 mM)-induced contraction was in Strn-HET (0.44±0.06g) > WT mice (0.33±0.05g) on HS diet, suggesting that the enhanced vascular contraction is not limited to a particular receptor. Endothelium removal, NOS inhibitor L-NAME and guanylate cyclase inhibitor ODQ enhanced contraction and increased sensitivity to Phe in WT mice and to a greater extent in Strn-HET mice on HS but not LS diet. On HS, acetylcholine (ACh) relaxation was in Strn-HET (max 33.16±4.47%) < WT (50.94±10.88%). ACh relaxation was blocked by endothelium removal, L-NAME and ODQ, supporting a role of the NO-cGMP pathway. Vascular relaxation to the exogenous NO donor sodium nitroprusside was not different between groups. Thus striatin deficiency during HS diet is associated with salt sensitivity of BP, enhanced vasoconstriction and decreased vascular relaxation. The results suggest a critical role for striatin, possibly through modulation of endothelium-dependent NO-cGMP pathway, in regulation of vascular function and BP during changes in dietary sodium intake.

Abstract 562: Differential Effects of Renin Inhibitors and Ca2+ Channel Blockers on Blood Pressure and Vascular Function in Caveolin-1 Null Mice

Caveolin-1 (cav-1) is a transmembrane protein identified in plasma membrane caveolae, and a potential modulator of renal and vascular function and insulin sensitivity. We have shown that cav-1 gene variants are associated with insulin resistance (IR) in hypertensive humans, and that cav-1 deficiency in mice leads to increased blood pressure (BP) and IR. To test whether these changes in the cav-1 KO involve renal or vascular abnormalities, we treated WT and cav-1 KO mice for 14 days with placebo, the renin inhibitor aliskiren (50 mg/kg/day), or the Ca 2+ channel blocker amlodipine (6 mg/kg/day) and assessed BP, fasting blood glucose, HOMA-IR, plasma aldosterone (ALDO), and vascular function.

Cav-1 KO mice, as compared with WT, showed increased BP (131±7 vs. 110±2 mm Hg), blood glucose (112±4 vs. 83±4 mg/dl), HOMA-IR (1.9±1.1 vs. 1.1±0.4), lower plasma ALDO (97±10 vs. 131±42 ng/dl), and altered vascular reactivity--reduced Phe-induced vasoconstriction (0.6±0.2 vs. 1.1±0.2g), enhanced acetylcholine (ACh)-induced relaxation (65±11 vs 23±7%), and enhanced relaxation in response to exogenous NO. Endothelium removal, NOS inhibition, or guanylate cyclase inhibition abolished ACh-induced relaxation, suggesting changes in endothelium-dependent NO-cGMP pathway in cav-1 KO mice. In cav-1 KO mice aliskiren significantly reduced BP to 113±4 mm Hg, ALDO levels by 40%, and HOMA-IR to 0.9±0.1, but had no significant effects on blood glucose, Phe-induced vasoconstriction, ACh- or exogenous NO-induced vasorelaxation. In contrast, amlodipine reduced BP to 117±4 mmHg (this effect did not reach significance), had no effect on ALDO levels, and showed a trend for increased IR. Importantly, amlodipine enhanced the sensitivity to Phe in both WT and cav-1 KO, and reduced the ACh-induced relaxation in cav-1 KO mice to 47±11%.

Thus aliskiren treatment in cav-1 KO mice reduced BP possibly through suppression of RAAS and improved insulin sensitivity, but did not affect vascular function. In contrast, amlodipine treatment showed small changes in BP and IR but had adverse effects on vascular reactivity in cav-1 KO mice, raising the concern that it could have similar adverse effects on vascular function in hypertensive individuals that carry the cav-1 minor allele gene variants.

EMMPRIN-mediated induction of uterine and vascular matrix metalloproteinases during pregnancy and in response to estrogen and progesterone

Pregnancy is associated with uteroplacental and vascular remodeling in order to adapt for the growing fetus and the hemodynamic changes in the maternal circulation. We have previously shown upregulation of uterine matrix metalloproteinases (MMPs) during pregnancy. Whether pregnancy-associated changes in MMPs are localized to the uterus or are generalized in feto-placental and maternal circulation is unclear. Also, the mechanisms causing the changes in uteroplacental and vascular MMPs during pregnancy are unclear. MMPs expression, activity and tissue distribution were measured in uterus, placenta and aorta of virgin, mid-pregnant (mid-Preg) and late pregnant (late-Preg) rats. Western blots and gelatin zymography revealed increases in MMP-2 and -9 in uterus and aorta of late-Preg compared with virgin and mid-Preg rats. In contrast, MMP-2 and -9 were decreased in placenta of late-Preg versus mid-Preg rats. Extracellular MMP inducer (EMMPRIN) was increased in uterus and aorta of pregnant rats, but was less in placenta of late-Preg than mid-Preg rats. Prolonged treatment of uterus or aorta of virgin rats with 17β-estradiol and progesterone increased the amount of EMMPRIN, MMP-2 and -9, and the sex hormone-induced increases in MMPs were prevented by EMMPRIN neutralizing antibody. Immunohistochemistry revealed that MMP-2 and -9 and EMMPRIN increased in uterus and aorta of pregnant rats, but decreased in placenta of late-Preg versus mid-Preg rats. Thus pregnancy-associated upregulation of uterine MMPs is paralleled by increased vascular MMPs, and both are mediated by EMMPRIN and induced by estrogen and progesterone, suggesting similar role of MMPs in uterine and vascular tissue remodeling and function during pregnancy. The decreased MMPs and EMMPRIN in placenta of late-Preg rats suggests reduced role of MMPs in feto-placental circulation during late pregnancy.

Matrix metalloproteinases as potential targets in the venous dilation associated with varicose veins

Varicose veins (VVs) are a common venous disease of the lower extremity characterized by incompetent valves, venous reflux, and dilated and tortuous veins. If untreated, VVs could lead to venous thrombosis, thrombophlebitis and chronic venous leg ulcers. Various genetic, hormonal and environmental factors may lead to structural changes in the vein valves and make them incompetent, leading to venous reflux, increased venous pressure and vein wall dilation. Prolonged increases in venous pressure and vein wall tension are thought to increase the expression/activity of matrix metalloproteinases (MMPs). Members of the MMPs family include collagenases, gelatinases, stromelysins, matrilysins, membrane- type MMPs and others. MMPs are known to degrade various components of the extracellular matrix (ECM). MMPs may also affect the endothelium and vascular smooth muscle, causing changes in the vein relaxation and contraction mechanisms. Endothelial cell injury also triggers leukocyte infiltration, activation and inflammation, which lead to further vein wall damage. The vein wall dilation and valve dysfunction, and the MMP activation and superimposed inflammation and fibrosis would lead to progressive venous dilation and VVs formation. Surgical ablation is an effective treatment for VVs, but may be associated with high recurrence rate, and other less invasive approaches that target the cause of the disease are needed. MMP inhibitors including endogenous tissue inhibitors (TIMPs) and pharmacological inhibitors such as zinc chelators, doxycycline, batimastat and marimastat, have been used as diagnostic and therapeutic tools in cancer, autoimmune and cardiovascular disease. However, MMP inhibitors may have side effects especially on the musculoskeletal system. With the advent of new genetic and pharmacological tools, specific MMP inhibitors with fewer undesirable effects could be useful to retard the progression and prevent the recurrence of VVs.

Vascular effects of estrogenic menopausal hormone therapy

Cardiovascular disease (CVD) is more common in men and postmenopausal women (Post-MW) than premenopausal women (Pre-MW). Despite recent advances in preventive measures, the incidence of CVD in women has shown a rise that matched the increase in the Post-MW population. The increased incidence of CVD in Post-MW has been related to the decline in estrogen levels, and hence suggested vascular benefits of endogenous estrogen. Experimental studies have identified estrogen receptor ERα, ERβ and a novel estrogen binding membrane protein GPR30 (GPER) in blood vessels of humans and experimental animals. The interaction of estrogen with vascular ERs mediates both genomic and non-genomic effects. Estrogen promotes endothelium-dependent relaxation by increasing nitric oxide, prostacyclin, and hyperpolarizing factor. Estrogen also inhibits the mechanisms of vascular smooth muscle (VSM) contraction including [Ca2+]i, protein kinase C and Rho-kinase. Additional effects of estrogen on the vascular cytoskeleton, extracellular matrix, lipid profile and the vascular inflammatory response have been reported. In addition to the experimental evidence in animal models and vascular cells, initial observational studies in women using menopausal hormonal therapy (MHT) have suggested that estrogen may protect against CVD. However, randomized clinical trials (RCTs) such as the Heart and Estrogen/ progestin Replacement Study (HERS) and the Women's Health Initiative (WHI), which examined the effects of conjugated equine estrogens (CEE) in older women with established CVD (HERS) or without overt CVD (WHI), failed to demonstrate protective vascular effects of estrogen treatment. Despite the initial set-back from the results of MHT RCTs, growing evidence now supports the 'timing hypothesis', which suggests that MHT could increase the risk of CVD if started late after menopause, but may produce beneficial cardiovascular effects in younger women during the perimenopausal period. The choice of an appropriate MHT dose, route of administration, and estrogen/progestin combination could maximize the vascular benefits of MHT and minimize other adverse effects, especially if given within a reasonably short time after menopause to women that seek MHT for the relief of menopausal symptoms.

Vascular effects of phytoestrogens and alternative menopausal hormone therapy in cardiovascular disease

Phytoestrogens are estrogenic compounds of plant origin classified into different groups including isoflavones, lignans, coumestans and stilbenes. Isoflavones such as genistein and daidzein are the most studied and most potent phytoestrogens, and are found mainly in soy based foods. The effects of phytoestrogens are partly mediated via estrogen receptors (ERs): ERα, ERβ and possibly GPER. The interaction of phytoestrogens with ERs is thought to induce both genomic and non-genomic effects in many tissues including the vasculature. Some phytoestrogens such as genistein have additional non-ER-mediated effects involving signaling pathways such as tyrosine kinase. Experimental studies have shown beneficial effects of phytoestrogens on endothelial cells, vascular smooth muscle, and extracellular matrix. Phytoestrogens may also affect other pathophysiologic vascular processes such as lipid profile, angiogenesis, inflammation, tissue damage by reactive oxygen species, and these effects could delay the progression of atherosclerosis. As recent clinical trials showed no vascular benefits or even increased risk of cardiovascular disease (CVD) and CV events with conventional menopausal hormone therapy (MHT), phytoestrogens are being considered as alternatives to pharmacologic MHT. Epidemiological studies in the Far East population suggest that dietary intake of phytoestrogens may contribute to the decreased incidence of postmenopausal CVD and thromboembolic events. Also, the WHO-CARDIAC study supported that consumption of high soybean diet is associated with lower mortalities from coronary artery disease. However, as with estrogen, there has been some discrepancy between the experimental studies demonstrating the vascular benefits of phytoestrogens and the data from clinical trials. This is likely because the phytoestrogens clinical trials have been limited in many aspects including the number of participants enrolled, the clinical end points investigated, and the lack of long-term follow-up. Further investigation of the cellular mechanisms underlying the vascular effects of phytoestrogens and careful evaluation of the epidemiological evidence and clinical trials of their potential vascular benefits would put forward the use of phytoestrogens as an alternative MHT for the relief of menopausal symptoms and amelioration of postmenopausal CVD.

Abstract 236: Reduced Epigastric Artery Reactivity in a Non-Modulator Phenotype of Human Hypertension

In normal and modulator hypertensive individuals sodium intake modifies plasma levels and target tissue response to ANG II. This sodium-mediated modulation is defective in 25-30% of the hypertensive population, termed non-modulators. Non-modulators have insulin resistance (IR), abnormal renal function, polymorphisms in the renin-angiotensin-aldosterone system (RAAS) genes, increased tissue levels of ANG II particularly during liberal dietary sodium intake, and increased risk of cardiovascular (CV) damage. We hypothesized that the increased risk of CV damage in non-modulators reflects abnormalities in vascular function. Male hypertensive subjects were placed on restricted salt diet 10 mmol/day for 7 days and phenotyped as modulators (PRA 8.7 ng/ml/hr, HOMA-IR 1.0, ALDO 18.85 ng/dl, n=4, age ≈48) and non-modulators (PRA 8.8 ng/ml/hr, HOMA-IR 1.7, ALDO 8.52 ng/dl, n=3, age ≈60). The subjects were then placed on liberal salt diet (HS, 200 mmol/day for 7 days), BP was measured, then underwent subcutaneous surgery to isolate the superficial inferior epigastric artery for ex vivo vascular function studies. Systolic BP was 144.8 in modulators and 142.0 mmHg in non-modulators. Diastolic BP was 88.5 in modulators and 87.3 mmHg in non-modulators. In epigastric arteries, contraction to ANG II, phenylephrine (Phe), and KCl was less in non-modulators (0.24, 0.56, and 0.53) than in modulators (0.8, 1.43, and 1.1 g/mg tissue). Endothelium-dependent relaxation to acetylcholine (ACh) was not different between non-modulators (22.1) and modulators (22.6%). Bradykinin caused larger endothelium-dependent relaxation than ACh, but was still not different in non-modulators (57.8) vs. modulators (46.3%). In contrast, endothelium-independent relaxation to the nitric oxide (NO) donor sodium nitroprusside was reduced in non-modulators (64.2) vs. modulators (92.5%). The reduced vascular responsiveness to ANG II in non-modulators is consistent with increased vascular tissue RAAS activity, and desensitization to ANG II. The reduced vascular reactivity to the vasoconstrictors Phe and KCl and the vasodilator NO donors is consistent with vascular smooth muscle dysfunction and may explain the increased risk of CV damage in non-modulators during HS dietary intake.

Abstract 531: Role of Insulin Resistance in the Altered Vascular Relaxation Mechanisms and Hypertension in Caveolin-1 Deficient Mice

Insulin resistance (IR) and endothelial dysfunction are often associated with hypertension; however, the specific causality and genetic underpinnings of these associations are unclear. Caveolin-1 (cav-1) is a transmembrane anchoring protein and potential modulator of vascular function and insulin sensitivity of the vascular and metabolic pathways. Our recent findings point to a role for cav-1 in IR, endothelial dysfunction and hypertension. In humans, cav-1 gene variants are associated with IR in hypertensive individuals. In mice, cav-1 deficiency leads to changes in endothelial function, IR and blood pressure (BP). To test whether the vascular changes associated with cav-1 deficiency are related to or are independent of IR, we assessed BP, blood glucose and vascular function in WT and cav-1 KO mice treated with placebo or metformin 400 mg/Kg/day for 21 days. BP was greater in cav-1 KO vs WT (140.1±2.1 vs 116.5±1.3 mmHg), and metformin treatment did not change BP in cav-1 KO (140.7±1.4) or WT (112.5±1.6 mmHg). Fasting blood glucose was greater in cav-1 KO vs WT (112±3.9 vs. 83.1±4.4 mg/dl), supporting a link between cav-1 deficiency and IR. Metformin did not change blood glucose levels in cav-1 KO (110.4±4.1) or WT (86.7±8.2 mg/dl). Acetylcholine (ACh)-induced maximal aortic relaxation was greater in cav-1 KO vs WT (85.3±5.7 vs. 17.5±4.4%), and was abolished by endothelium removal or the NOS inhibitor L-NAME, supporting changes in endothelial NO production/signaling. Metformin reduced ACh relaxation in cav-1 KO to 60.7±6.6%, but had no effect in WT. The exogenous NO donor sodium nitroprusside (SNP) produced similar maximal relaxation in cav-1 KO and WT (98.4±1.6 and 98.2±1.1%), but was more potent in cav-1 KO vs WT (pEC50, 8.6 vs 8.1). Metformin reduced SNP relaxation in cav-1 KO (84.9±6.4%) but not in WT, and reversed the enhanced sensitivity to SNP in cav-1 KO mice. The metformin-induced decrease in vascular relaxation and sensitivity to NO in cav-1 KO mice suggests a role for vascular IR in the changes in endothelial function. The lack of effect of metformin on fasting blood glucose in cav-1 KO mice suggests recalcitrant IR of the metabolic pathways. Together, these data support partial independence of vascular function from systemic IR in cav-1 deficiency states.

Sex difference in cardiovascular risk: role of pulse pressure amplification

OBJECTIVES

The study was to explore whether the brachial/carotid pulse pressure (B/C-PP) ratio selectively predicts the sex difference in age-related cardiovascular (CV) death.

BACKGROUND

Hypertension and CV complications are more severe in men and post-menopausal women than in pre-menopausal women. C-PP is lower than B-PP, and the B/C-PP ratio is a physiological marker of PP amplification between B and C arteries that tends toward 1.0 with age.

METHODS

The study involved 72,437 men (ages 41.0 ± 11.1 years) and 52,714 women (39.5 ± 11.6 years). C-PP was calculated for each sex by a multiple regression analysis including B-PP, age, height and risk factors, and a method validated beforehand in a subgroup of 834 subjects. During the 12 years of follow-up, 3,028 men and 969 women died.

RESULTS

In the total population, the adjusted hazard ratios (HR) (95% confidence interval [CI]) of B/C-PP ratio were: 1) for all-cause mortality: men, HR: 1.51 (95% CI: 1.47 to 1.56), women; HR: 2.46 (95% CI: 2.27 to 2.67) (p < 0.0001); and 2) for CV mortality: men, HR 1.81 (95% CI: 1.70 to 1.93); women, HR: 4.46 (95% CI: 3.66 to 5.45) (p < 0.0001). The B/C-PP impact on mortality did not significantly increase from younger men to those ≥ 55 years of age, from: HR: 1.44 (95% CI: 1.31 to 1.58) to HR 1.65 (95% CI: 1.48 to 1.84), but increased significantly with age in women: HR: 3.19 (95% CI: 2.08 to 4.89) versus HR: 5.60 (95% CI: 4.17 to 7.50) (p < 0.01). Thus, the mortality impact of B/C-PP ratio was 3-fold higher in women than in men ≥ 55 years old.

CONCLUSIONS

PP amplification is highly predictive of differences in CV risk between men and women. In post-menopausal women, the attenuation of PP amplification, mainly related to increased aortic stiffness, contributes to the significant increase in CV risk.

Modulators of the vascular endothelin receptor in blood pressure regulation and hypertension

Endothelin (ET) is one of the most investigated molecules in vascular biology. Since its discovery two decades ago, several ET isoforms, receptors, signaling pathways, agonists and antagonists have been identified. ET functions as a potent endothelium-derived vasoconstrictor, but could also play a role in vascular relaxation. In endothelial cells, preproET and big ET are cleaved by ET converting enzymes into ET-1, -2, -3 and -4. These ET isoforms bind with different affinities to ET(A) and ET(B) receptors in vascular smooth muscle (VSM), and in turn increase [Ca(2+)](i), protein kinase C and mitogen-activated protein kinase and other signaling pathways of VSM contraction and cell proliferation. ET also binds to endothelial ET(B) receptors and stimulates the release of nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor. ET, via endothelial ET(B) receptor, could also promote ET re-uptake and clearance. While the effects of ET on vascular reactivity and growth have been thoroughly examined, its role in the regulation of blood pressure and the pathogenesis of hypertension is not clearly established. Elevated plasma and vascular tissue levels of ET have been identified in salt-sensitive hypertension and in moderate to severe hypertension, and ET receptor antagonists have been shown to reduce blood pressure to variable extents in these forms of hypertension. The development of new pharmacological and genetic tools could lead to more effective and specific modulators of the vascular ET system for treatment of hypertension and related cardiovascular disease.

Increased MMPs expression and decreased contraction in the rat myometrium during pregnancy and in response to prolonged stretch and sex hormones

Normal pregnancy is associated with uterine relaxation to accommodate the stretch imposed by the growing fetus; however, the mechanisms underlying the relationship between pregnancy-associated uterine stretch and uterine relaxation are unclear. We hypothesized that increased uterine stretch during pregnancy is associated with upregulation of matrix metalloproteinases (MMPs), which in turn cause inhibition of myometrium contraction and promote uterine relaxation. Uteri from virgin, midpregnant (day 12), and late-pregnant rats (day 19) were isolated, and myometrium strips were prepared for measurement of isometric contraction and MMP expression and activity using RT-PCR, Western blot analysis, and gelatin zymography. Oxytocin caused concentration-dependent contraction of myometrium strips that was reduced in mid- and late-pregnant rats compared with virgin rats. Pretreatment with the MMP inhibitors SB-3CT (MMP-2/MMP-9 Inhibitor IV), BB-94 (batimastat), or Ro-28-2653 (cipemastat) enhanced contraction in myometrium of pregnant rats. RT-PCR, Western blot analysis, and gelatin zymography demonstrated increased mRNA expression, protein amount, and activity of MMP-2 and MMP-9 in myometrium of late-pregnant>midpregnant>virgin rats. Prolonged stretch of myometrium strips of virgin rats under 8 g basal tension for 18 h was associated with reduced contraction and enhanced expression and activity of MMP-2 and MMP-9, which were reversed by MMP inhibitors. Concomitant treatment of stretched myometrium of virgin rats with 17β-estradiol (E2), progesterone (P4), or E2+P4 was associated with further reduction in contraction and increased MMP expression and activity. MMP-2 and MMP-9 caused significant reduction of oxytocin-induced contraction of myometrium of virgin rat. Thus, normal pregnancy is associated with reduced myometrium contraction and increased MMPs expression and activity. The results are consistent with the possibility that myometrium stretch and concomitant increase in sex hormones during pregnancy are associated with increased expression/activity of specific MMPs, which in turn inhibit uterine contraction and promote uterine relaxation.

Molecular mechanisms regulating the vascular prostacyclin pathways and their adaptation during pregnancy and in the newborn

Prostacyclin (PGI(2)) is a member of the prostanoid group of eicosanoids that regulate homeostasis, hemostasis, smooth muscle function and inflammation. Prostanoids are derived from arachidonic acid by the sequential actions of phospholipase A(2), cyclooxygenase (COX), and specific prostaglandin (PG) synthases. There are two major COX enzymes, COX1 and COX2, that differ in structure, tissue distribution, subcellular localization, and function. COX1 is largely constitutively expressed, whereas COX2 is induced at sites of inflammation and vascular injury. PGI(2) is produced by endothelial cells and influences many cardiovascular processes. PGI(2) acts mainly on the prostacyclin (IP) receptor, but because of receptor homology, PGI(2) analogs such as iloprost may act on other prostanoid receptors with variable affinities. PGI(2)/IP interaction stimulates G protein-coupled increase in cAMP and protein kinase A, resulting in decreased [Ca(2+)](i), and could also cause inhibition of Rho kinase, leading to vascular smooth muscle relaxation. In addition, PGI(2) intracrine signaling may target nuclear peroxisome proliferator-activated receptors and regulate gene transcription. PGI(2) counteracts the vasoconstrictor and platelet aggregation effects of thromboxane A(2) (TXA(2)), and both prostanoids create an important balance in cardiovascular homeostasis. The PGI(2)/TXA(2) balance is particularly critical in the regulation of maternal and fetal vascular function during pregnancy and in the newborn. A decrease in PGI(2)/TXA(2) ratio in the maternal, fetal, and neonatal circulation may contribute to preeclampsia, intrauterine growth restriction, and persistent pulmonary hypertension of the newborn (PPHN), respectively. On the other hand, increased PGI(2) activity may contribute to patent ductus arteriosus (PDA) and intraventricular hemorrhage in premature newborns. These observations have raised interest in the use of COX inhibitors and PGI(2) analogs in the management of pregnancy-associated and neonatal vascular disorders. The use of aspirin to decrease TXA(2) synthesis has shown little benefit in preeclampsia, whereas indomethacin and ibuprofen are used effectively to close PDA in the premature newborn. PGI(2) analogs have been used effectively in primary pulmonary hypertension in adults and have shown promise in PPHN. Careful examination of PGI(2) metabolism and the complex interplay with other prostanoids will help design specific modulators of the PGI(2)-dependent pathways for the management of pregnancy-related and neonatal vascular disorders.

Vascular endothelin receptor type B: structure, function and dysregulation in vascular disease

Endothelin-1 (ET-1) is a major regulator of vascular function, acting via both endothelin receptor type A (ET(A)R) and type B (ET(B)R). Although the role of ET(A)R in vascular smooth muscle (VSM) contraction has been studied, little is known about ET(B)R. ET(B)R is a G-protein coupled receptor with a molecular mass of ~50 kDa and 442 amino acids arranged in seven transmembrane domains. Alternative splice variants of ET(B)R and heterodimerization and cross-talk with ET(A)R may affect the receptor function. ET(B)R has been identified in numerous blood vessels with substantial effects in the systemic, renal, pulmonary, coronary and cerebral circulation. ET(B)R in the endothelium mediates the release of relaxing factors such as nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor, and could also play a role in ET-1 clearance. ET(B)R in VSM mediates increases in [Ca(2+)](i), protein kinase C, mitogen-activated protein kinase and other pathways of VSM contraction and cell growth. ET-1/ET(A)R signaling has been associated with salt-sensitive hypertension (HTN) and pulmonary arterial hypertension (PAH), and ET(A)R antagonists have shown some benefits in these conditions. In search for other pathogenetic factors and more effective approaches, the role of alterations in endothelial ET(B)R and VSM ET(B)R in vascular dysfunction, and the potential benefits of modulators of ET(B)R in treatment of HTN and PAH are being examined. Combined ET(A)R/ET(B)R antagonists could be more efficacious in the management of conditions involving upregulation of ET(A)R and ET(B)R in VSM. Combined ET(A)R antagonist with ET(B)R agonist may need to be evaluated in conditions associated with decreased endothelial ET(B)R expression/activity.