Relaxation Of Veins Research Articles

The effect of temperature on vascular smooth muscle: cooling-induced vasodilation in deep arteries and veins.

Blood vessels in the cardiovascular system include arteries and veins, which are responsible for moving blood to and from tissues around the body. Our previous studies showed that cooling induces relaxation of arteries. The aim of this study is to investigate the effect of cooling on both arteries and veins pairs. Isometric tension was recorded in rat artery ring preparations (aorta, carotid, pulmonary arteries) and their vein pairs (vena cava, jugular, pulmonary veins) in organ baths during stepwise cooling from 37 to 4°C. Cooling responses were tested before and after the addition of various standard agents. The possibility of the presence of a cooling-relaxed substance and the influence of endothelium were also examined. Cooling-induced relaxation of both arteries and veins and the degree of relaxation were inversely proportional to the temperature. The cooling response was highest in arteries than their respective paired veins. The relaxation response was not endothelium dependent or affected with neurogenic mechanism (autonomic blockers or tetrodotoxin). Additionally, it was not changed by alterations of extra- or intra-cellular calcium transfer, and no relaxant substance was released from vascular smooth muscles during cooling. The study showed that cooling induces relaxation of both arteries and veins. Our results suggested that the effect of cooling could be through a thermal receptor in the vascular smooth muscle. Therefore, cold temperature can act as an agonist and increase in cooling temperature behaves as increase in concentration of the agonist. This study contributes to a better understanding of the mechanisms behind cooling-induced relaxation of blood vessels, which may have implications for the treatment of cardiovascular diseases.

Insulin Induces Relaxation and Decreases Hydrogen Peroxide-Induced Vasoconstriction in Human Placental Vascular Bed in a Mechanism Mediated by Calcium-Activated Potassium Channels and L-Arginine/Nitric Oxide Pathways.

HIGHLIGHTS Short-term incubation with insulin increases the L-arginine transport in HUVECs.Short-term incubation with insulin increases the NO synthesis in HUVECs.Insulin induces relaxation in human placental vascular bed.Insulin attenuates the constriction induced by hydrogen peroxide in human placenta.The relaxation induced by insulin is dependent on BKCa channels activity in human placenta. Insulin induces relaxation in umbilical veins, increasing the expression of human amino acid transporter 1 (hCAT-1) and nitric oxide synthesis (NO) in human umbilical vein endothelial cells (HUVECs). Short-term effects of insulin on vasculature have been reported in healthy subjects and cell cultures; however, its mechanisms remain unknown. The aim of this study was to characterize the effect of acute incubation with insulin on the regulation of vascular tone of placental vasculature. HUVECs and chorionic vein rings were isolated from normal pregnancies. The effect of insulin on NO synthesis, L-arginine transport, and hCAT-1 abundance was measured in HUVECs. Isometric tension induced by U46619 (thromboxane A2 analog) or hydrogen peroxide (H2O2) were measured in vessels previously incubated 30 min with insulin and/or the following pharmacological inhibitors: tetraethylammonium (KCa channels), iberiotoxin (BKCa channels), genistein (tyrosine kinases), and wortmannin (phosphatidylinositol 3-kinase). Insulin increases L-arginine transport and NO synthesis in HUVECs. In the placenta, this hormone caused relaxation of the chorionic vein, and reduced perfusion pressure in placental cotyledons. In vessels pre-incubated with insulin, the constriction evoked by H2O2 and U46619 was attenuated and the effect on H2O2-induced constriction was blocked with tetraethylammonium and iberiotoxin, but not with genistein, or wortmannin. Insulin rapidly dilates the placental vasculature through a mechanism involving activity of BKCa channels and L-arginine/NO pathway in endothelial cells. This phenomenon is related to quick increases of hCAT-1 abundance and higher capacity of endothelial cells to take up L-arginine and generate NO.

Cross-sectional and longitudinal lipid determination studies in pregnant women reveal an association between increased maternal LDL cholesterol concentrations and reduced human umbilical vein relaxation

IntroductionMaternal hypercholesterolemia and hypertriglyceridemia during pregnancy is correlated with fetoplacental endothelial dysfunction and atherosclerotic lesions in fetal arteries. Few studies have reported the distribution of the concentrations of maternal total cholesterol (TCh), lipoprotein cholesterol and triglycerides during pregnancy. Therefore, we determined maternal lipid concentration during pregnancy and established the percentiles over which fetoplacental endothelial dysfunction is observed. MethodsA lipoprotein profile was determined for 249 pregnant Chilean women in each trimester of pregnancy in cross-sectional and longitudinal lipid determination studies. Distribution percentiles for TCh, high–, low– and very-low–density lipoprotein (HDL, LDL, and vLDL, respectively) cholesterol and triglycerides were estimated. The reactivity of human umbilical vein rings to the calcitonin gene-related peptide (0.1–1000 nmol/L, 5 min) and sodium nitroprusside (10 μmol/L, 5 min) was measured (wire myography) in KCl-preconstricted vessels. ResultsMaternal lipoproteins and triglyceride concentrations increased over time from preconception to the 3rd trimester of pregnancy. Newborn umbilical blood lipoprotein and triglyceride concentrations were lower than those in maternal circulation. Changes in maternal HDL correlated with newborn HDL concentration; however, no correlation between maternal lipoprotein concentrations and newborn weight was found. Maternal TCh and LDL concentrations were inversely correlated with the maximal dilation, but the >75th percentile of maternal TCh and LDL concentrations (>291 and >169 mg/dL, respectively) correlated with reduced calcitonin gene-related peptide sensitivity of the vein rings. Discussion and conclusionWe identified percentiles for maternal TCh and LDL concentrations over which abnormal endothelium-dependent human fetoplacental vascular response is observed.

Multiresolution analysis of pathological changes in cerebral venous dynamics in newborn mice with intracranial hemorrhage: adrenorelated vasorelaxation

Intracranial hemorrhage (ICH) is the major problem of modern neonatal intensive care. Abnormalities of cerebral venous blood flow (CVBF) can play a crucial role in the development of ICH in infants. The mechanisms underlying these pathological processes remain unclear; however it has been established that the activation of the adrenorelated vasorelaxation can be an important reason. Aiming to reach a better understanding of how the adrenodependent relaxation of cerebral veins contributes to the development of ICH in newborns, we study here the effects of pharmacological stimulation of adrenorelated dilation of the sagittal sinus by isoproterenol on the cerebral venous hemodynamics. Our study is performed in newborn mice at different stages of ICH using the laser speckle contrast imaging and wavelet analysis of the vascular dynamics of CVBF. We show that the dilation of the sagittal sinus with the decreased velocity of blood flow presides to the stress-induced ICH in newborn mice. These morphofunctional vascular changes are accompanied by an increased variance of the wavelet-coefficients in the areas of endothelial and non-endothelial (KATP-channels activity of vascular muscle) sympathetic components of the CVBF variability. Changes in the cerebral venous hemodynamics at the latent stage of ICH are associated with a high responsiveness of the sagittal sinus to isoproterenol quantifying by wavelet-coefficients related to a very slow region of the frequency domain. The obtained results certify that a high activation of the adrenergic-related vasodilatory responses to severe stress in newborn mice can be one of the important mechanisms underlying the development of ICH. Thus, the venous insufficiency with the decreased blood outflow from the brain associated with changes in the endothelial and the sympathetic components of CVBF-variability can be treated as prognostic criteria for the risk of ICH during the first days after birth.

P86 Role of hydrogen sulfide as an oxygen sensor in the human pulmonary vasculature

Introduction Animal studies have shown that H 2 S can act as an oxygen sensor in the vasculature. To date the role of H 2 S as an oxygen sensor has not been investigated in human vascular preparations. The aim of this study was to compare the effects of H 2 S and hypoxia on pulmonary vascular tone in human pulmonary arteries and veins. Methods Human pulmonary arteries and veins were obtained at resection for cancer and mounted in organ baths to measure isometric tension. The effects of H 2 S on resting tension and active tension to ET-1 were determined by cumulative addition of NaHS. In the same vessels the effects of hypoxia on resting and active tension were determined by changing the aerating gas to 95% N 2 : 5% CO 2 . Results NaHS caused a dose dependent (0.1–3 mM) relaxation of human pulmonary arteries ( n = 8) and veins ( n = 8) from resting and active tension. Hypoxia also caused a relaxation of arteries and veins and the magnitude of relaxation to hypoxia was comparable to the maximum relaxation to NaHS. However, the effects of hypoxia and NaHS were not consistent in all vessels. In some vessels hypoxia caused a relaxation whereas NaHS had no effect and in others NaHS caused a relaxation and hypoxia had no effect. Conclusion It has been shown for the first time that H 2 S causes a dose dependent relaxation of human pulmonary vessels. Similarities in the effect of H 2 S and hypoxia suggest a causal relationship, however, some inconsistencies in the results warrant further investigation.

Maternal Hypercholesterolemia in Pregnancy Associates With Umbilical Vein Endothelial Dysfunction

Objective— Human pregnancy that courses with maternal supraphysiological hypercholesterolemia (MSPH) correlates with atherosclerotic lesions in fetal arteries. It is known that hypercholesterolemia associates with endothelial dysfunction in adults, a phenomenon where nitric oxide (NO) and arginase are involved. However, nothing is reported on potential alterations in the fetoplacental endothelial function in MSPH. The aim of this study was to determine whether MSPH alters fetal vascular reactivity via endothelial arginase/urea and l -arginine transport/NO signaling pathways. Approach and Results— Total cholesterol <280 mg/dL was considered as maternal physiological hypercholesterolemia (n=46 women) and ≥280 mg/dL as MSPH (n=28 women). Maternal but not fetal total cholesterol and low-density lipoprotein-cholesterol levels were elevated in MSPH. Umbilical veins were used for vascular reactivity assays (wire myography), and primary cultures of umbilical vein endothelial cells to determine arginase, endothelial NO synthase (eNOS), and human cationic amino acid transporter 1 and human cationic amino acid transporter 2A/B expression and activity. MSPH reduced calcitonine gene–related peptide-umbilical vein relaxation and increased intima/media ratio (histochemistry), as well as reduced eNOS activity ( l -citrulline synthesis from l -arginine, eNOS phosphorylation/dephosphorylation), but increased arginase activity and arginase II protein abundance. Arginase inhibition increased eNOS activity and l -arginine transport capacity without altering human cationic amino acid transporter 1 or human cationic amino acid transporter 2A/B protein abundance in maternal physiological hypercholesterolemia and MSPH. Conclusions— MSPH is a pathophysiological condition altering umbilical vein reactivity because of fetal endothelial dysfunction associated with arginase and eNOS signaling imbalance. We speculate that elevated maternal circulating cholesterol is a factor leading to fetal endothelial dysfunction, which could have serious consequences to the growing fetus.

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.

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.

Portal hypertension and liver cirrhosis in rats: effect of the β3‐adrenoceptor agonist SR58611A

β(3) -Adrenoceptors participate in the regulation of vascular tone in physiological and pathological conditions. We aimed to assess the effect of pharmacological modulation of β(3) -adrenoceptors on portal pressure (PP) and systemic haemodynamics and their expression in the liver and mesenteric vessels of cirrhotic rats. PP, central venous pressure (CVP) and systemic haemodynamics were invasively assessed in control and CCl(4) -treated cirrhotic rats before and during infusion of the selective β(3) -adrenoceptor agonist, SR58611A. Tissue samples were also collected from liver, heart, portal vein and mesenteric artery for immunohistochemistry and molecular biology analysis. The effect of SR58611A on isolated portal vein was assessed. At baseline, cirrhotic rats showed portal hypertension, reduced CVP and hyperdynamic circulation. SR58611A induced a significant, dose-dependent decrease in PP in cirrhotic rats, but not in controls. Although both groups manifested a dose-dependent reduction in mean arterial pressure, this effect was associated with decreased cardiac index (CI) and unchanged indicized peripheral vascular resistance (PVRI) in cirrhotic rats and increased CI and decreased PVRI in control animals. Pretreatment with the selective β(3) -adrenoceptor antagonist SR59230 prevented all SR58611A-induced changes in cirrhotic rats. SR58611A concentration-dependently relaxed portal vein in cirrhotic rats to a significantly greater extent than in healthy rats; pretreatment with SR59230A completely prevented SR58611A-induced cirrhotic portal vein relaxation. Finally, β(3) -adrenoceptors were identified in the liver, heart and portal vein of cirrhotic and control animals; their expression was increased in cirrhotic rats. β(3) -Adrenoceptors are altered in portal hypertension of experimental cirrhosis and may represent a novel therapeutic target.

Characteristics of ACh‐induced hyperpolarization and relaxation in rabbit jugular vein

The roles played by endothelium-derived NO and prostacyclin and by endothelial cell hyperpolarization in ACh-induced relaxation have been well characterized in arteries. However, the mechanisms underlying ACh-induced relaxation in veins remain to be fully clarified. ACh-induced smooth muscle cell (SMC) hyperpolarization and relaxation were measured in endothelium-intact and -denuded preparations of rabbit jugular vein. In endothelium-intact preparations, ACh (≤ 10⁻⁸ M) marginally increased the intracellular concentration of Ca²⁺ ([Ca²⁺](i)) in endothelial cells but did not alter the SMC membrane potential. However, ACh (10⁻¹⁰ -10⁻⁸ M) induced a concentration-dependent relaxation during the contraction induced by PGF(2α) and this relaxation was blocked by the NO synthase inhibitor N(ω) -nitro-l-arginine. ACh (10⁻⁸ -10⁻⁶ M) concentration-dependently increased endothelial [Ca²⁺](i) and induced SMC hyperpolarization and relaxation. These SMC responses were blocked in the combined presence of apamin [blocker of small-conductance Ca²⁺-activated K⁺ (SK(Ca) , K(Ca) 2.3) channel], TRAM 34 [blocker of intermediate-conductance Ca²⁺ -activated K⁺ (IK(Ca) , K(Ca) 3.1) channel] and margatoxin [blocker of subfamily of voltage-gated K⁺ (K(V) ) channel, K(V) 1]. In rabbit jugular vein, NO plays a primary role in endothelium-dependent relaxation at very low concentrations of ACh (10⁻¹⁰ -10⁻⁸ M). At higher concentrations, ACh (10⁻⁸ -3 × 10⁻⁶ M) induces SMC hyperpolarization through activation of endothelial IK(Ca) , K(V) 1 and (possibly) SK(Ca) channels and produces relaxation. These results imply that ACh regulates rabbit jugular vein tonus through activation of two endothelium-dependent regulatory mechanisms.

Endothelium-dependent nitric oxide and hyperpolarization-mediated venous relaxation pathways in rat inferior vena cava

The vascular endothelium plays a major role in the control of arterial tone; however, its role in venous tissues is less clear. The purpose of this study was to determine the role of endothelium in the control of venous function and the relaxation pathways involved. Circular segments of inferior vena cava (IVC) from male Sprague-Dawley rats were suspended between two wires and isometric contraction to phenylephrine (Phe; 10(-5)M) and 96 mM KCl was measured. Acetylcholine (Ach; 10(-10) to 10(-5)M) was added and the percentage of venous relaxation was measured. To determine the role of nitric oxide (NO) and prostacyclin (PGI(2)), vein relaxation was measured in the presence of the nitric oxide synthase inhibitor N(ω)-nitro-L-arginine methyl ester (L-NAME; 3 × 10(-4) M) and the cyclooxygenase inhibitor indomethacin (10(-5) M). To measure the role of hyperpolarization, vein relaxation was measured in the presence of K(+) channel activator cromakalim (10(-11) to 10(-6) M), and the nonselective K(+) channel blocker tetraethylammonium (TEA; 10(-3) M). To test for the contribution of a specific K(+) channel, the effects of K(+) channel blockers: glibenclamide (adenosine triphosphate [ATP]-sensitive K(ATP), 10(-5) M), 4-aminopyridine (4-AP; voltage-dependent K(v), 10(-3) M), apamin (small conductance Ca(2+)-dependent SK(Ca), 10(-7) M), and iberiotoxin (large conductance Ca(2+)-dependent BK(Ca), 10(-8) M) on Ach-induced relaxation were tested. Ach caused concentration-dependent relaxation of Phe contraction (maximum 49.9 ± 4.9%). Removal of endothelium abolished Ach-induced relaxation. IVC treatment with L-NAME partially reduced Ach relaxation (32.8 ± 4.9%). In IVC treated with L-NAME plus indomethacin, significant Ach-induced relaxation (33.6 ± 3.2%) could still be observed, suggesting a role of endothelium-derived hyperpolarizing factor (EDHF). In IVC treated with L-NAME, indomethacin and TEA, Ach relaxation was abolished, supporting a role of EDHF. In veins stimulated with high KCl, Ach caused relaxation (maximum 59.5 ± 3.5%) that was abolished in the presence of L-NAME and indomethacin suggesting that any Ach-induced EDHF is blocked in the presence of high KCl depolarizing solution, which does not favor outward movement of K(+) ion and membrane hyperpolarization. Cromakalim, an activator of K(ATP), caused significant IVC relaxation when applied alone or on top of maximal Ach-induced relaxation, suggesting that the Ach response may not involve K(ATP). Ach-induced relaxation was not inhibited by glibenclamide, 4-AP, or apamin, suggesting little role of K(ATP), K(v) or SK(Ca), respectively. In contrast, iberiotoxin significantly inhibited Ach-induced relaxation, suggesting a role of BK(Ca). Thus, endothelium-dependent venous relaxation plays a major role in the control of venous function. In addition to NO, an EDHF pathway involving BK(Ca) may play a role in endothelium-dependent venous relaxation.

Insulin‐stimulated L‐arginine transport requires SLC7A1 gene expression and is associated with human umbilical vein relaxation

Insulin causes endothelium-derived nitric oxide (NO)-dependent vascular relaxation, and increases L-arginine transport via cationic amino acid transporter 1 (hCAT-1) and endothelial NO synthase (eNOS) expression and activity in human umbilical vein endothelium (HUVEC). We studied insulin effect on SLC7A1 gene (hCAT-1) expression and hCAT-transport activity role in insulin-modulated human fetal vascular reactivity. HUVEC were used for L-arginine transport and L-[(3) H]citrulline formation (NOS activity) assays in absence or presence of N-ethylmaleimide (NEM) or L-lysine (L-arginine transport inhibitors). hCAT-1 protein abundance was estimated by Western blot, mRNA quantification by real time PCR, and SLC7A1 promoter activity by Luciferase activity (-1,606 and -650 bp promoter fragments from ATG). Specific protein 1 (Sp1), and total or phosphorylated eNOS protein was determined by Western blot. Sp1 activity (at four sites between -177 and -105 bp from ATG) was assayed by chromatin immunoprecipitation (ChIP) and vascular reactivity in umbilical vein rings. Insulin increased hCATs-L-arginine transport, maximal transport capacity (V(max) /K(m) ), and hCAT-1 expression. NEM and L-lysine blocked L-arginine transport. In addition, it was trans-stimulated (∼7.8-fold) by L-lysine in absence of insulin, but unaltered (~1.4-fold) in presence of insulin. Sp1 nuclear protein abundance and binding to DNA, and SLC7A1 promoter activity was increased by insulin. Insulin increased NO synthesis and caused endothelium-dependent vessel relaxation and reduced U46619-induced contraction, effects blocked by NEM and L-lysine, and dependent on extracellular L-arginine. We suggest that insulin induces human umbilical vein relaxation by increasing HUVEC L-arginine transport via hCATs (likely hCAT-1) most likely requiring Sp1-activated SLC7A1 expression.

Insulin Restores Gestational Diabetes Mellitus–Reduced Adenosine Transport Involving Differential Expression of Insulin Receptor Isoforms in Human Umbilical Vein Endothelium

OBJECTIVETo determine whether insulin reverses gestational diabetes mellitus (GDM)–reduced expression and activity of human equilibrative nucleoside transporters 1 (hENT1) in human umbilical vein endothelium cells (HUVECs).RESEARCH DESIGN AND METHODSPrimary cultured HUVECs from full-term normal (n = 44) and diet-treated GDM (n = 44) pregnancies were used. Insulin effect was assayed on hENT1 expression (protein, mRNA, SLC29A1 promoter activity) and activity (initial rates of adenosine transport) as well as endothelial nitric oxide (NO) synthase activity (serine1177 phosphorylation, l-citrulline formation). Adenosine concentration in culture medium and umbilical vein blood (high-performance liquid chromatography) as well as insulin receptor A and B expression (quantitative PCR) were determined. Reactivity of umbilical vein rings to adenosine and insulin was assayed by wire myography. Experiments were in the absence or presence of l-NG-nitro-l-arginine methyl ester (l-NAME; NO synthase inhibitor) or ZM-241385 (an A2A-adenosine receptor antagonist).RESULTSUmbilical vein blood adenosine concentration was higher, and the adenosine- and insulin-induced NO/endothelium-dependent umbilical vein relaxation was lower in GDM. Cells from GDM exhibited increased insulin receptor A isoform expression in addition to the reported NO–dependent inhibition of hENT1-adenosine transport and SLC29A1 reporter repression, and increased extracellular concentration of adenosine and NO synthase activity. Insulin reversed all these parameters to values in normal pregnancies, an effect blocked by ZM-241385 and l-NAME.CONCLUSIONSGDM and normal pregnancy HUVEC phenotypes are differentially responsive to insulin, a phenomenon where insulin acts as protecting factor for endothelial dysfunction characteristic of this syndrome. Abnormal adenosine plasma levels, and potentially A2A-adenosine receptors and insulin receptor A, will play crucial roles in this phenomenon in GDM.

A time-invariant visco-elastic windkessel model relating blood flow and blood volume

The difference between the rate of change of cerebral blood volume (CBV) and cerebral blood flow (CBF) following stimulation is thought to be due to circumferential stress relaxation in veins (Mandeville, J.B., Marota, J.J.A., Ayata, C., Zaharchuk, G., Moskowitz, M.A., Rosen, B.R., Weisskoff, R.M., 1999. Evidence of a cerebrovascular postarteriole windkessel with delayed compliance. J. Cereb. Blood Flow Metab. 19, 679–689). In this paper we explore the visco-elastic properties of blood vessels, and present a dynamic model relating changes in CBF to changes in CBV. We refer to this model as the visco-elastic windkessel (VW) model. A novel feature of this model is that the parameter characterising the pressure–volume relationship of blood vessels is treated as a state variable dependent on the rate of change of CBV, producing hysteresis in the pressure–volume space during vessel dilation and contraction. The VW model is nonlinear time-invariant, and is able to predict the observed differences between the time series of CBV and that of CBF measurements following changes in neural activity. Like the windkessel model derived by Mandeville, J.B., Marota, J.J.A., Ayata, C., Zaharchuk, G., Moskowitz, M.A., Rosen, B.R., Weisskoff, R.M., 1999. Evidence of a cerebrovascular postarteriole windkessel with delayed compliance. J. Cereb. Blood Flow Metab. 19, 679–689, the VW model is primarily a model of haemodynamic changes in the venous compartment. The VW model is demonstrated to have the following characteristics typical of visco-elastic materials: (1) hysteresis, (2) creep, and (3) stress relaxation, hence it provides a unified model of the visco-elastic properties of the vasculature. The model will not only contribute to the interpretation of the Blood Oxygen Level Dependent (BOLD) signals from functional Magnetic Resonance Imaging (fMRI) experiments, but also find applications in the study and modelling of the brain vasculature and the haemodynamics of circulatory and cardiovascular systems.

The Mechanisms of the Direct Vascular Effects of Sevoflurane on Saphenous Veins in Vitro

Aim: The purpose of this study was to determine the mechanism of the directs effects of sevoflurane on human veins in vitro. Methods: Dose-response curves were obtained for cumulative doses of sevoflurane (0.5, 1, 1.5 and 2 MAC) on saphenous vein strips precontracted with 5-hydroxytryptamine ( 5-HT 10-6 mol/L) incubated with either Nω-nitroL-arginine-methyl ester (L-NAME) (10-4 mol/L), indomethacine (10-5 mol/L), glibenclamide (10-6 mol/L) or tetraethylammonium (10-4 mol/L) Results: Preincubation of vein strips with tetraethylammonium (TEA, Ca++-activated K+ channel blocker) did not influence the relaxant responses to sevoflurane (p>0.05). L-NAME, indomethacine and glibenclamide reduced the relaxation response to sevoflurane (p<0.05). Conclusion: Our results demonstrated that sevoflurane produces concentration dependent relaxation in human saphenous vein. The relaxant effects of sevoflurane are probably related with activation of nitric oxide synthase, cyclooxygenase and KATP channels pathways.

MMP-2 Induced Vein Relaxation via Inhibition of [Ca 2+] e-Dependent Mechanisms of Venous Smooth Muscle Contraction. Role of RGD Peptides

Matrix metalloproteinases (MMPs) are implicated in the pathogenesis of varicose veins. We have shown that MMP-2 causes relaxation of venous segments and suggested a role of venous smooth muscle (VSM) hyperpolarization; however, the downstream mechanisms are unclear. We tested whether MMP-2 induced venous relaxation involves inhibition of the Ca(2+) mobilization mechanisms of VSM contraction due to generation of Arg-Gly-Asp (RGD)-containing peptides. Circular segments of inferior vena cava (IVC) were isolated from male Sprague-Dawley rats, suspended between two wires in a tissue bath, and isometric contraction was measured. Contraction data in mg/mg tissue were presented as means +/- SEM. In IVC incubated in normal Krebs (2.5 mM Ca(2+)), the alpha-adrenergic agonist phenylephrine (Phe, 10(-5) M) caused initial peak (133.2 +/- 17.5) followed by a maintained contraction (73.4 +/- 11.6), that was inhibited by MMP-2 (1 microg/mL) to 32.4 +/- 12.8 in 30 min. The inhibitory effects of MMP-2 were reversible by washing the tissue with Krebs or in the presence of the MMP inhibitors TIMP-1 (1 microg/mL), Ro 28-2653, and BB-94 (10(-6) M), and were not associated with changes in IVC structure, demonstrating specificity. Angiotensin II (AngII, 10(-6) M) caused a monophasic contraction (114.2 +/- 12.2), that was also inhibited by MMP-2 (66.0 +/- 7.4), suggesting a post-receptor effect on the downstream mechanisms of VSM contraction. To test the role of Ca(2+) release from the sarcoplasmic reticulum, IVC was incubated in Ca(2+)-free 2 mM ethylene glycol-bis(2-aminoethyl ether-N,N,N',N'-tetra-acetic acid (EGTA) Krebs with or without MMP-2. In Ca(2+)-free Krebs, caffeine did not cause contraction, suggesting a limited role of the Ca(2+)-induced Ca(2+)-release mechanism, and Phe and AngII caused a small contraction (7.2 +/- 1.7 and 14.9 +/- 2.8) that was slightly increased by MMP-2 (10.4 +/- 3.0 and 33.8 +/- 10.0), suggesting little effect on IP(3)-induced Ca(2+) release. To test the role of Ca(2+) entry through membrane channels, after eliciting a transient Phe contraction in nominally 0 Ca(2+) Krebs, increasing concentrations of CaCl(2) (0.1, 0.3, 0.6, 1, 2.5 mM) were added and the extracellular Ca(2+) concentration [Ca(2+)](e)-contraction relationship was constructed. The [Ca(2+)](e)-contraction relation was reduced in MMP-2 treated IVC, suggesting inhibition of Ca(2+) entry. In IVC treated with MMP-2, the Ca(2+) channel blocker diltiazem (10(-5)M) did not cause any further inhibition of Phe contraction, suggesting that Ca(2+) entry is already inhibited by MMP-2. To test whether MMP-2 actions involve generation of RGD and modulation of integrin receptors, experiments where repeated in IVC segments saturated with RGD (10(-5) M), or pretreated with the alpha(v)beta(3) integrin blocker cyclo(Ala-Arg-Gly-Asp-3-aminomethylbenzoyl) (cyclo-RGD). RGD-peptide caused only small relaxation of Phe contracted IVC (6.4 +/- 3.4%), and addition of MMP-2 to RGD-treated IVC caused further relaxation (69.7 +/- 3.0%). Pretreatment of IVC with cyclo-RGD did not significantly affect MMP-2 induced relaxation (55.0 +/- 5.0%). In rat IVC, MMP-2 attenuates [Ca(2+)](e)-dependent VSM contraction without affecting Ca(2+) release from intracellular Ca(2+) stores. MMP-2 induced VSM relaxation may not involve RGD generation or activation of alpha(v)beta(3) integrin receptor. MMP-2 induced inhibition of the Ca(2+) entry mechanism of VSM contraction may play a role in the venous dilation associated with varicose vein formation.

Preservation of cGMP-induced relaxation of pulmonary veins of fetal lambs exposed to chronic high altitude hypoxia: role of PKG and Rho kinase

The roles of Rho kinase (ROCK) and cGMP-dependent protein kinase (PKG) in cGMP-mediated relaxation of fetal pulmonary veins exposed to chronic hypoxia (CH) were investigated. Fourth generation pulmonary veins were dissected from near-term fetuses ( approximately 140 days of gestation) delivered from ewes exposed to chronic high altitude hypoxia for approximately 110 days (CH) and from control ewes. After constriction with endothelin-1, 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP) caused a similar relaxation of both control and CH vessels. Rp-8-Br-PET-cGMPS (a PKG inhibitor) inhibited whereas Y-27632 (a ROCK inhibitor) augmented relaxation of control veins to 8-Br-cGMP. These effects were significantly diminished in CH veins. PKG protein expression and activity were greater whereas ROCK protein expression and activity were less in CH vessels compared with controls. Phosphorylation of threonine 696 (ROCK substrate) and serine 695 (PKG substrate) of the regulatory myosin phosphatase targeting subunit MYPT1 of myosin light chain (MLC) phosphatase was stimulated to a lesser extent in CH than in control veins by endothelin-1 (ROCK stimulant) and 8-Br-cGMP (PKG stimulant), respectively. The phosphorylation and dephosphorylation of MLC caused by endothelin-1 and 8-Br-cGMP, respectively, were less in CH veins than in controls. These results suggest that CH in utero upregulates PKG activity but attenuates PKG action in fetal pulmonary veins. These effects are offset by the diminished ROCK action on MYPT1 and MLC and thus lead to an unaltered response to cGMP.

Endogenous antimicrobial peptide LL-37 induces human vasodilatation

BackgroundSeptic shock includes blood vessel dilatation and activation of innate immunity, which in turn causes release of antimicrobial peptides such as LL-37. It has been shown that LL-37 can attract leucocytes via the lipoxin A4 receptor (ALX, FPRL1). ALX is also present in vascular endothelial cells. To explore possible ways of pharmacological intervention in septic shock, we investigated if LL-37 can affect vascular tone. MethodsHuman omental arteries and veins were obtained during abdominal surgery, and circular smooth muscle activity was studied in organ baths. Gene expression was studied using reverse transcriptase–polymerase chain reaction. ResultsLL-37, at micromolar concentrations, induced a concentration- and endothelium-dependent relaxation in vein but not in artery segments precontracted by endothelin-1. The relaxation was profoundly reduced by potassium chloride (30 mM) to inhibit endothelium-derived hyperpolarizing factor (EDHF), whereas it was less affected by the NOS inhibitor, l-NG-nitroarginine methyl ester, and not at all by indomethacin. The ALX agonist, WKYMVm, also induced a relaxation and both the relaxations induced by LL-37 and WKYMVm were inhibited by the ALX antagonist, WRWWWW. ALX was expressed in the vein endothelium. ConclusionsWe demonstrate, for the first time, that the human antimicrobial peptide, LL-37, induces endothelium-dependent relaxation in human omental veins mediated via an effect on endothelial ALX. The relaxation involves the release of nitric oxide and EDHF but not prostanoids. LL-37 released from white blood cells could contribute to blood vessel dilatation during sepsis and treatment with ALX antagonists might be successful.

Human saphenous vein relaxation in response to sodium nitroprusside correlates with systolic blood pressure and phosphorylated heat shock protein 27

Stress has been shown to cause hypertension and increase heat shock protein 27 (HSP27) expression and phosphorylation in animal models. Impaired relaxation of vascular smooth muscle occurs during hypertension and may be associated with HSP27 expression and/or phosphorylation. Human saphenous vein (HSV) was used as a model system to examine impaired relaxation and HSP27 expression and phosphorylation in a hypertensive patient population. Relaxation of HSV samples was determined by measurements of tension produced in a muscle bath in response to submaximal norepinephrine dose followed by a sodium nitroprusside dose curve. Relaxation was found to be significantly inversely correlated with systolic blood pressure at patient admission (R2=0.6175, n=10, p&lt;0.05). Western blotting for HSP27 and phosphorylated HSP27 revealed a significant inverse correlation between relaxation and the amount of phosphoryated HSP27 present in the HSV samples (R2=0.8699, n=5, p&lt;0.05). Hence this study provides a link between hypertension, HSP27 phosphorylation, and impaired relaxation in human vascular tissue. The mechanism for this impaired relaxation may involve the expression and/or phosphorylation of HSP27 since phosphoHSP27 also appears to be associated with impaired relaxation. Support: NIH RO1 70715

Protein kinase G regulates the basal tension and plays a major role in nitrovasodilator‐induced relaxation of porcine coronary veins

Coronary venous activity is modulated by endogenous and exogenous nitrovasodilators. The present study was to determine the role of protein kinase G (PKG) in the regulation of the basal tension and nitrovasodilator-induced relaxation of coronary veins. Effects of a PKG inhibitor on the basal tension and responses induced by nitroglycerin, DETA NONOate, and 8-Br-cGMP in isolated porcine coronary veins were determined. Cyclic cGMP was measured with radioimmunoassay. PKG activity was determined by measuring the incorporation of 32P from gamma-32P-ATP into the specific substrate BPDEtide. Rp-8-Br-PET-cGMPS, a specific PKG inhibitor, increased the basal tension of porcine coronary veins and decreased PKG activity. The increase in tension was 38% of that caused by nitro-L-arginine. Relaxation of the veins induced by nitroglycerin and DETA NONOate was accompanied with increases in cGMP content and PKG activity. These effects were largely eliminated by inhibiting soluble guanylyl cyclase with ODQ. The increase in PKG activity induced by the nitrovasodilators was abolished by Rp-8-Br-PET-cGMPS. The relaxation caused by these dilators and by 8-Br-cGMP at their EC50 was attenuated by the PKG inhibitor by 51-66%. These results suggest that PKG is critically involved in nitric oxide-mediated regulation of the basal tension in porcine coronary veins and that it plays a primary role in relaxation induced by nitrovasodilators. Since nitric oxide plays a key role in modulating coronary venous activity, augmentation of PKG may be a therapeutic target for improving coronary blood flow.