Prostacyclin Release Research Articles

Nitrates do not affect prostacyclin formation by rat arteries: this is unrelated to increased vascular prostacyclin formation with age.

The question of whether vasodilator nitrates act by releasing prostacyclin is controversial. Since the ability of blood vessels to form prostacyclin changes with age, we have investigated whether this may explain the discrepancies in the literature. It does not, since isosorbide dinitrate or glyceryl trinitrate incubated with rat aorta or vena cava from male Wistar rats had little or no effect on the release of prostacyclin, measured as 6-keto-PGF1 alpha. We confirm that the aorta produces substantially more prostacyclin than the vena cava. The arterial production of prostacyclin was greater in rats weighing 350-400 g than in those weighing 116-152 g, but the production by the veins was similar in both groups.

Acute and long‐term effects of aldosterone on vascular remodeling

We have previously demonstrated that aldosterone‐induced upregulation of cyclooxygenase (COX) expression in the kidney is blocked by eplerenone. The objective of this study was to determine whether ALDO causes biochemical and molecular remodeling of the vasculature. The effects of aldosterone on arachidonic acid metabolism and on the expression of thromboxane (TXA2) receptor (TP) were evaluated in the Dahl salt sensitive (DS) rat aorta, renal, femoral and carotid arteries. DS rats on a low salt (0.3% NaCl) diet were treated with or without ALDO for four weeks. Indirect blood pressure (BP), the release of TXA2, prostacyclin (PGI2) and prostaglandin E2, and the expression of COX‐2 and TP were measured. ALDO increased BP (17± 1%) and the basal release of PGE2 but reduced the basal release of TXA2. ALDO enhanced vascular reactivity to phenylephrine and up regulated the expression of COX‐2 in both aorta and renal vessels but reduced COX‐2 expression in the femoral artery. The TP expression was down regulated in the aorta but up regulated in the carotid by ALDO. These data reveal that the effect of ALDO in the vasculature is tissue specific and involves the release of vasoconstrictor prostanoids in the rat aorta by up regulating the expression of COX‐2 and TP in the vasculature. Therefore, it can be stated that the prostanoids play a pivotal role in the vasculopathic effect of aldosterone. Supported by NIDDK grant 1SC1DK082385.

Effects of 4-Hydroxy-2-Nonenal, a Major Lipid Peroxidation-Derived Aldehyde, and N-Acetylcysteine on the Cyclooxygenase-2 Expression in Human Uterine Myometrium

Background: Chorioamnionitis is one of the important causes of preterm labor. Preterm labor with chorioamnionitis is associated with oxidative stress. We reported that 4-hydroxy-2-nonenal (4-HNE), a major end product of oxidative fatty acid metabolism, is accumulated in the placenta with chorioamnionitis. The aim of this study was to confirm the effect of 4-HNE on cyclooxygenase-2 (COX-2) and prostaglandin (PG) induction in the uterine myometrial tissues. We also examined the effect of N-acetylcysteine (NAC) on 4-HNE-induced COX-2 expression. Methods: Uterine myometrial tissues were obtained from 5 patients. One of them underwent elective cesarean section without labor, and 4 of them underwent hysterectomy because of placental previa or atonic bleeding. We stimulated the uterine myometrial tissues with 4-HNE. In addition, the tissues were pretreated with NAC before 4-HNE treatment. The expression of COX-2 mRNA was observed by real-time PCR. PGE2 and prostacyclin release into the supernatants of the tissue cultures was measured by ELISA. Results: 4-HNE induced the COX-2 mRNA expression and PGE2 production in the uterine myometrial tissue culture in a dose-dependent and time-dependent manner. NAC inhibited 4-HNE-induced COX-2 expression. Conclusion: 4-HNE may play an important role in preterm labor. NAC might be protective against preterm labor under oxidative stress.

Influence of radiographic contrast media (Iodixanol und Iomeprol) on the morphology of human arterial and venous endothelial cells on extracellular matrix in vitro

After intra-arterial administration of radiographic contrast media (RCM), a disorder of the downstream microcirculation both with regard to blood flow velocity in microvessels and to tissue oxygen partial pressure was described. Possible factors contributing to this microcirculatory disorder are increase in plasma viscosity, a formation of echinocytes, a buckling and denudation of endothelial cells, and a disturbation of endothelial prostacyclin release. It is not known so far whether the reactions observed in the context of RCM applications are reactions of venous endothelial cells alone or also of arterial endothelial cells. Therefore, arterial ECs on ECM were exposed to the same RCMs under identical conditions. The decrease of cell-cell contacts with an increase of denuded subendothelial matrix areas in the functionally confluent endothelial cell layer on ECM were more pronounced after a five minute exposure of endothelial cells to Iomeprol compared to Iodixanol. Changes in arterial ECs after the incubation in culture media supplemented with RCM were very subtle in comparison to changes in venous ECs.

Endothelin-1 attenuates increases in hydraulic conductivity due to platelet-activating factor via prostacyclin release

We previously showed that endothelin-1 (ET-1) and prostacyclin (PGI(2)) similarly attenuate increases in microvascular permeability induced by platelet-activating factor (PAF). This led us to hypothesize that ET-1 attenuates trans-endothelial fluid flux during PAF through PGI(2) release. We tested this hypothesis in three phases. First, bovine pulmonary artery endothelial cells were exposed to 0.008-8 μM ET-1 and assayed for PGI(2) release. Second, to determine whether increased transmonolayer flux after PAF could be attenuated by ET-1 or PGI(2) and reversed by PGI(2) synthesis inhibition or PGI(2) receptor blockade, we measured endothelial cell transmonolayer flux after cells were exposed to 10 nM PAF plus 10 μM PGI(2) or 80 pM ET-1, with or without 500 μM tranylcypromine (PGI(2) synthase inhibitor) or 20 μM CAY-10441 (PGI(2) receptor blocker). Finally, hydraulic conductivity (L(p)) was measured in rat mesenteric venules in vivo after exposure to 10 nM PAF and 80 pM ET-1 with or without tranylcypromine (100 and 500 μM) or CAY-10441 (2 and 20 μM). We found that in vitro, ET-1 stimulated a dose-dependent increase in PGI(2) production (from 126 to 217 pg/ml, P < 0.01). Compared with PAF alone, PGI(2) plus PAF and ET-1 plus PAF decreased transmonolayer flux similarly by 52 and 46%, respectively (P < 0.01), while tranylcypromine and CAY-10441 reversed these effects by 92 and 47%, respectively (P < 0.05). In vivo, PAF increased L(p) fourfold (P < 0.01) and ET-1 attenuated this effect by 83% (P < 0.01). Tranylcypromine and CAY-10441 reversed the ET-1 attenuation in L(p) during PAF by 55 and 45%, respectively (P < 0.01). We conclude that ET-1 may stimulate endothelial cell PGI(2) release to attenuate the increases in transmonolayer flux and hydraulic conductivity secondary to PAF.

Emerging high-density lipoprotein infusion therapies: Fulfilling the promise of epidemiology?

High-density lipoprotein (HDL) plays a key role in reverse cholesterol transport but also activates nitric oxide synthase and stimulates prostacyclin release, enhances endothelial repair, inhibits cell adhesion molecule expression on vascular endothelium and monocyte recruitment into the arterial wall, and exerts antithrombotic effects. In experimental animals, infusions of HDL or apolipoprotein A-1 (apoA-1) halt the progression or induce regression of atherosclerosis, with favorable effects on plaque composition. Remarkably, a benefit is observed after a single infusion. In a pilot study, weekly infusions of ETC-216, a formulation of recombinant apoA-1 Milano, were administered at two doses for 5 weeks to patients beginning within 2 weeks of an acute coronary syndrome (ACS). Among the 47 patients completing the study, percent atheroma volume by intracoronary ultrasound was reduced in the combined active treatment groups but not in the placebo group. In a larger trial, the Effect of rHDL on Atherosclerosis-Safety and efficacy (ERASE), 183 post-ACS patients were randomized to 4 weekly infusions of placebo or one of two doses of CSL-111, which consists of apoA-1 derived from human plasma and combined with soybean phosphatidylcholine. The greater dose was discontinued because of a high incidence of hepatic enzyme elevation. Among the 136 patients with evaluable end point data, percent change in atheroma volume, the primary endpoint, improved significantly in the CSL-111 group but not in the placebo group. The secondary end points of plaque characterization indices and quantitative coronary angiographic changes both improved significantly in the CSL-111 group compared with the group receiving placebo. Taken together, this evidence suggests that infusions of HDL or apoA-1 may reduce events, particularly among patients with ACS.

Vasorelaxant Action of N-p-Nitrophenylmaleimide in the Isolated Rat Mesenteric Artery

The vasorelaxant response of N-p-nitrophenylmaleimide (4-NO2-NPM) was evaluated. The mesenteric rings (1-2 mm i.d.) were suspended by cotton thread for isometric tension recordings in a Tyrode's solution at 37 degrees C and gassed with a mixture of 95% O2 and 5% CO2, under a resting tension of 0.75 g. 4-NO2-NPM induced relaxation in mesenteric rings pre-contracted with phenylephrine (Phe; 10 microM, pD2 = 6.7 +/- 0.3) or KCl (80 mM, pD2 = 3.9 +/- 0.2). This effect was significantly attenuated after removal of the vascular endothelium, N(G)-nitro L-arginine methyl ester (L-NAME; 100 microM), atropine (1 microM), indomethacin (10 microM), L-NAME + indomethacin or 1H-[1,2,3]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10 microM). L-Arginine (1 mM) reversed the inhibitory effect of L-NAME. In endothelium-intact preparations pre-incubated with 20 mM KCl, tetraethylammonium bromide (TEA; 1 mM) or glibenclamide (Glib; 10 microM), the vasorelaxant effect was significantly attenuated when compared to controls (endothelium intact). In denuded rings, separate incubation with 20 mM KCl, TEA or Glib did not change the relaxation when compared with that obtained in denuded rings. 4-NO2-NPM inhibited in a concentration-dependent and non-competitive manner the concentration-response curves induced by CaCl2. In calcium-free medium, the transient contractions induced by Phe (10 microM) or caffeine (20 mM) were inhibited. The relaxant effect induced by 4-NO2-NPM appeared to be due to endothelial muscarinic receptors activation, NO and prostacyclin release and K(ATP) and BK(Ca) (Ca(2+)-activated K+ channels) endothelium-dependent activation. Inhibition of the Ca2+ influx and inhibition of the Ca2+ release from intracellular IP3- and caffeine-sensitive stores are also involved in the vasorelaxation.

Antihypertensive Properties of Angiotensin-Converting Enzyme Inhibitors (ACEI) Independent of the Renin-Angiotensin System

Angiotensin converting enzyme inhibitors (ACEi) lead to inhibition of angiotensin II formation and bradykinin inactivation. However, ACEi also have antihypertensive activity that is independent of the renin-angiotensin system. For example, the enhanced peripheral resistance due to smooth muscle cell hypertrophy and hyperplasia (related to lower apoptosis) increases vascular tonus in established hypertension. ACEi treatment restores susceptibility to apoptosis in these cells through stimulation of the Bax protein. Also, an altered function of the Na+/K+ ATPase leads to elevated levels of intracellular sodium concentration, and depolarization of smooth muscle membranes increasing their excitability. ACEi treatment normalizes this pump function, and the arterial tonus by release of endothelial nitric oxide and prostacyclin. Endothelium- dependent hyperpolarization (to acetylcholine) in mesenteric arteries mediated by release of the endotheliumderived hyperpolarizing factor, is impaired in hypertensive humans and animals. In this instance, ACEi restored this impaired response, since this treatment causes vascular remodeling in resistance SHR arteries through induction of apoptosis of vascular smooth muscle cells reducing the subendothelial thickening, which improves the EDHF circulation. The purpose of this review is to analyze the performance of ACEi in normalizing the vascular tonus during the hypertensive state, which may render new perspectives in basic and clinical research for the next years.

Basic Science of Pulmonary Arterial Hypertension for Clinicians

Pulmonary arterial hypertension (PAH) is a syndrome in which pulmonary arterial obstruction increases pulmonary vascular resistance, which leads to right ventricular (RV) failure and a 15% annual mortality rate. The present review highlights recent advances in the basic science of PAH. New concepts clarify the nature of PAH and provide molecular blueprints that explain how PAH is initiated and maintained. Five basic science concepts provide a framework to understand and treat PAH: (1) Endothelial dysfunction creates an imbalance that favors vasoconstriction, thrombosis, and mitogenesis. Restoration of this balance by inhibition of endothelin and thromboxane or augmentation of nitric oxide (NO) and prostacyclin is the paradigm on which most current therapy is based. (2) PAH has a genetic component. Mutations (bone morphogenetic protein receptor-2 [BMPR2]) and single-nucleotide polymorphisms (SNPs; ion channels and transporter genes) predispose to PAH. (3) Excess proliferation, impaired apoptosis, and glycolytic metabolism in pulmonary artery smooth muscle, fibroblasts, and endothelial cells suggest analogies to cancer. Many experimental therapies reduce PAH by decreasing the proliferation/apoptosis ratio; these include inhibitors of pyruvate dehydrogenase kinase (PDK), serotonin transporters (SERT), survivin, 3-hydroxy-3-methylglutaryl coenzyme A reductase, transcription factors (hypoxia-inducible factor [HIF]-1α and nuclear factor of activated T lymphocytes [NFAT]), and tyrosine kinases. Augmentation of voltage-gated K+ channels (Kv1.5) and BMPR2 signaling also addresses this imbalance. Tyrosine kinase inhibitors used to treat cancer are currently in phase 1 PAH trials. (4) Refractory vasoconstriction may occur due to rho kinase activation. Fewer than 20% of PAH patients respond to conventional vasodilators; however, refractory vasoconstriction may respond to rho kinase inhibitors. (5) The RV can be targeted therapeutically. Although increased afterload initiates RV failure, which is the major cause of death/dysfunction in PAH, the RV may be amenable to cardiac-targeted therapies. The RV in PAH has features of ischemic, hibernating myocardium. Guided by these new …

Aerobic Capacity Correlates with Prostacyclin Release in Hypertensive African Americans

Aerobic Capacity Correlates with Prostacyclin Release in Hypertensive African Americans

Endurance training increases exercise-induced prostacyclin release in young, healthy men – relationship with VO2max

In the present study, we evaluated the effect of 5 weeks of moderate-intensity endurance training on the basal and exercise-induced systemic release of prostacyclin (PGI2), as assessed by plasma 6-keto-PGF1α concentration. Twelve physically active young men with the following characteristics participated in this study (the mean±SD): age, 22.7 ±2.0 years; body mass, 76.8 ±8.9kg; BMI, 23.48±2.17kg x m-2; and maximal oxygen uptake (VO2max), 46.1±4.0ml x kg-1 x min-1. Plasma 6-keto-PGF1a concentrations were measured in venous blood samples taken prior to the exercise and at exhaustion (at VO2max) before and after completing the training protocol. On average, the training resulted in a significant increase in VO2max (p=0.03), power output at VO2max (p=0.001) and a significant increase (p=0.05) in the net-exercise-induced increase in plasma 6-keto-PGF1α concentration (Δ6-keto-PGF1α i.e., the difference between the end-exercise and pre-exercise 6-keto-PGF1α concentrations). No effect of training on the basal PGI2 concentration was found. Interestingly, within the study sample (n=12), two subgroups could be defined with a differential pattern of response with respect to Δ6-keto-PGF1α concentrations. In one subgroup (n=7), a significant increase in Δ6-keto-PGF1α concentration after training was found (p<0.02) (responders). This enhancement in the exercise-induced PGI2 release was accompanied by a significant (p<0.05) increase in VO2max after training. In contrast, in another subgroup (n=5), there was no observed effect of training on the Δ6-keto-PGF1a concentration and the VO2max after training (non-responders). In both of these subgroups, training did not influence the basal PGI2 concentration.In conclusion, the endurance training resulted in the adaptive augmentation of the systemic release of PGI2 in response to exercise, which plays a role in the training-induced increase in VO2max in young, healthy men. The impairment of the training-induced augmentation of PGI2 release in response to exercise demonstrated in the non-responders subgroup may predispose them to increased cardiovascular risk during vigorous exercise.

Indomethacin enhances reactivity to vasopressin in normotensive and hypertensive rats, while PGE2 receptor blockade only attenuates reactivity in normotensive rats.

Previously, we reported that in female (F) rats 17‐β‐estradiol and aortic coarctation‐induced hypertension (ACIH) increase release of thromboxane (TXA2) and prostacyclin from mesenteric arterioles (MA), and that constrictor responses of aorta to vasopressin (VP) are reduced ~40% by TP receptor antagonist SQ 29,548 (SQ). Thus, the roles of TXA2 and PGE2 in constrictor responses to VP were studied in MA. F Sprague‐Dawley rats (14–16 wks age) underwent ACIH (hypertensive; HT) or sham (normotensive; NT). Rats were sacrificed 12–14 days post‐ACIH and reactivity to VP was measured in MA (150–200 μm dia.) using isometric myography. Data are means ± S.E. (n = 4–5 rats/group). Maximal contractile responses of MA to VP did not differ between NT (9.97 ± 0.75 mN/mm) and HT (11.77 ± 1.40). SQ (40 μM) did not alter responses in NT (9.16 ± 1.53) or HT (12.69 ± 1.77). In separate rats, maximal responses to VP did not differ between NT and HT. AH6809, a PGE2 receptor blocker (EP1, 2, 3) reduced maximal responses of MA from NT (8.95 ± 0.36 vs. 10.24 ± 0.63) but not HT (9.73 ± 0.81 vs. 9.36 ± 0.61). Indomethacin (non‐specific COX inhibitor; 10 μM) increased contractions to VP in NT and HT (11.74 ± 0.84 and 12.75 ± 0.79, respectively). While TXA2 potentiates constrictor responses of aorta to VP, the role of TXA2 in reactivity of MA to VP is less certain. However, it appears that PGE2 may also play a role in modulating MA responses to VP in NT rats. (NIH:HL‐080402)

Analysis of cyclic AMP‐coupled signature molecules in human micro vascular smooth muscle cells shows link to stress‐associated proteins

Vascular stress or local injury may trigger an inflammatory response leading to increased production and release of prostaglandin E2 (PGE2) and prostacyclin (PGI2), activation of Gs‐coupled receptors, and increased intracellular concentrations of cyclic AMP (cAMP). This study elucidated the targets of cAMP signaling in the vessel wall, specifically in human vascular smooth muscle cells explanted from skin punch biopsy arterioles of healthy volunteers (microVSM). Intracellular concentrations of cAMP were increased by treating quiescent cells with forskolin (10 μM, a direct activator of adenylyl cyclase). cAMP activated both A‐kinase and Rap1 GTPase signaling (within 15 min), and increased reactive oxygen species (26±3 %,≤1h). Differential‐in‐Gel electrophoresis, utilized to identify global changes in protein profiles, showed detectable changes in known proteins associated with the cytoskeleton, gene expression, protein ‐synthesis, ‐folding, ‐targeting, ‐secretion, and the extracellular matrix. Notably, the cellular oxidative stress‐associated protein peroxiredoxin‐II and the p53 regulated growth and differentiation gene N‐myc downstream‐regulated gene 1(NDRG 1) were increased (≥2‐fold). These studies point to a crucial role of cAMP in eliciting a protective cellular response to maintain vessel wall integrity in response to stress or injury.

Evidence for prostacyclin and cAMP upregulation by bradykinin and insulin-like growth factor 1 in vascular smooth muscle cells

Although bradykinin (BK) and insulin like growth factor-1 (IGF-1) have been shown to modulate the functional and structural integrity of the arterial wall, the cellular mechanisms through which this regulation occurs is still undefined. The present study examined the role of second messenger molecules generated by BK and IGF-1 that could ultimately result in proliferative or antiproliferative signals in vascular smooth muscle cells (VSMC).Activation of BK or IGF-1 receptors stimulated the synthesis and release of prostacyclin (PGI2) leading to increased production of cAMP in VSMC. Inhibition of p42/p44mapk or src kinases prevented the increase in PGI2 and cAMP observed in response to BK or IGF-1, indicating a role for these kinases in the regulation of cPLA2 activity in the VSMC. Inhibition of PKC failed to alter production of PGI2 in response to BK, but further increased both p42/p44mapk activation and the synthesis of PGI2 produced in response to IGF-1. In addition, both BK and IGF-1 significantly induced the expression of c-fos mRNA levels in VSMC, and this effect of BK was accentuated in the presence a cPLA2 inhibitor. Finally, inhibition of cPLA2 activity and/or cyclooxygenase activity enhanced the expression of collagen I mRNA levels in response to BK and IGF-1 stimulation.These findings indicate that the effect of BK or IGF-1 to stimulate VSMC growth is an integrated response to the activation of multiple signaling pathways. Thus, the excessive cell growth that occurs in certain forms of vascular disease could reflect dysfunction in one or more of these pathways.

Arterial Stiffness and Endothelial Function

Functional assessment of the blood pressure waveform helps us to obtain an estimation of the arterial stiffness or its converse, arterial elasticity.1 Several epidemiological studies have clearly demonstrated that arterial stiffness is a significant predictor of cardiovascular disease incidence in the general population.2 There is clear evidence now that decreased arterial elasticity or increased arterial stiffness in normotensive and prehypertensive subjects induces increased risk for the development of arterial hypertension. In vitro and in vivo experiments have shown that the vascular endothelium plays a crucial role in vascular tone and consequently in arterial stiffness. However, there are no data available regarding the endothelial pathways involved in the adaptation of arterial mechanics during changes in blood flow. The elegant study by Bellien et al3 in this issue of Hypertension studied the endothelial pathways involved in the adaption of arterial mechanics during changes in blood flow. Besides identifying the “endothelial-derived relaxing factor” nitric oxide (NO) as important in this biological process, a unique aspect found in their study was the “endothelial-hyperpolarizing factor” EDHF. Endothelium-dependent relaxation/vasodilation in response to neurohumoral mediators and physical forces, such as the shear stress caused by blood flow, is generally attributed to the release of NO and/or prostacyclin. However, NO and prostacyclin cannot fully explain these endothelium-mediated vasodilator responses. The relaxations observed in the presence of NO synthase and cyclooxygenase inhibitors are often associated with hyperpolarization of the vascular smooth …

The in vitro effects of niacin on platelet biomarkers in human volunteers

Niacin is a natural pyridine derivative, proven to favorably modulate the blood lipid profile by increasing levels of high-density lipoprotein (HDL) cholesterol, and by reducing total cholesterol, low-density lipoprotein (LDL) cholesterol, triglycerides, and Lp (a) lipoprotein concentrations. Considering that platelet activity is important in predicting vascular outcomes, and that HDL heavily constitutes platelet cellular membranes, we sought to evaluate the effect of niacin on human platelet activity indices. The blood obtained from 30 aspirin-naïve volunteers was preincubated with escalating concentrations of niacin in vitro. Platelet tests included whole blood and plasma aggregometry, rapid cartridge-based analyser, expression of major surface receptors by flow cytometry, and plasma prostaglandins by ELISA. Preincubation of blood with niacin at 0.3, 1.0 and 3.0 mM resulted in significant inhibition of maximal adenosine diphosphate (ADP)- (p=0.03), and collagen-induced platelet aggregation (p=0.01), and reduced activity by VerifyNow (p=0.007) bedside analyser. Surface platelet PAR-1 (MoAb WEDE-15; p=0.04), and vitronectin (CD51/CD61; p=0.02) receptors were up-regulated. Niacin was associated with a two- to three-fold increase of thromboxane B2, prostaglandins D2, and E2. Formation of platelet-monocyte microparticles (CD14+CD151), and expression of PECAM-1 (CD31), thrombospondin (CD36), GP IIb/IIIa (CD41a) antigen, and activity with MoAb PAC-1, GPIb (CD42b), P-selectin (CD62p), LAMP-3 (CD63), LAMP-1 (CD107a), CD40-ligand (CD154), GP37 (CD165), were not affected by niacin, suggesting no effect on prostacyclin release. In conclusion, niacin in vitro affects platelet activity by mildly inhibiting aggregation, and stimulating significant prostaglandin release, with mostly intact major platelet receptor expression. The effect of niacin is unique, differs from other known antiplatelet agents, and suggests potential opportunities for therapeutic combination, particularly in patients with low levels of HDL-C. These preliminary data, while intriguing, require confirmation in subjects receiving orally dosed extended-release niacin in order to determine whether these findings are clinically relevant.

Pharmacological mechanisms underlying the vascular activities of Loranthus ferrugineus Roxb. in rat thoracic aorta

Aim of the study The present study was aimed to investigate the pharmacological basis for the use of Loranthus ferrugineus in hypertension. Materials and methods Loranthus ferrugineus methanol extract (LFME) was obtained using Soxhelt extractor and then successively fractionated using chloroform, ethyl acetate and n-butanol. The n-butanol fraction of LFME (NBF-LFME) was studied using isolated rat thoracic aorta. Results NBF-LFME (1.0 × 10 −5 to 3.0 mg/ml) was found to be the most potent to concentration-dependently relax the endothelium-intact phenyephrine (PE, 1 μM)- and high K + (80 mM)-precontracted rat aortic rings. Removal of the endothelium completely abolished the vascular relaxing properties of NBF-LFME. Pretreatment with atropine (1 μM), l-NAME (10 μM), indomethacin (10 μM) and methylene blue (10 μM) significantly blocked NBF-LFME-mediated relaxation. Endothelium-dependent and -independent relaxations induced by acetylcholine (ACh) and sodium nitroprusside (SNP), respectively, were significantly enhanced in aortic rings pretreated with NBF-LFME when compared to those observed in control aortic rings. On the contrary, glibenclamide (10 μM), propranolol (1 μM) and prazosin (0.01 μM) did not alter NBF-LFME-induced relaxation. Conclusions The results suggest that NBF-LFME induced vascular relaxation by stimulating muscarinic receptors, activating the endothelium-derived nitric oxide-cGMP-relaxant pathway, promoting prostacyclin release and/or possibly through its ability to lengthen the released nitric oxide half-life. The present data further supports previous in vivo findings and explain the traditional use of Loranthus ferrugineus as an anti-hypertensive agent.

Endothelin-1 attenuates increases in microvascular fluid leak due to platelet-activating factor via prostacyclin release

Endothelin-1 attenuates increases in microvascular fluid leak due to platelet-activating factor via prostacyclin release

Vitamin B6 Compounds are Capable of Reducing the Superoxide Radical and Lipid Peroxide Levels Induced by H2O2 in Vascular Endothelial Cells in Culture

Pyridoxamine, pyridoxine, and pyridoxal phosphate were tested to examine if they have antioxidant properties. Endothelial cells exposed to 0.5 mM H(2)O(2) for 2 hours increased the superoxide anion and lipid peroxide levels as biomarkers of oxidative stress. The increase of superoxide was mainly due to the activation of NADPH-oxidase by H(2)O(2). Preincubation of the endothelial cells with 0.1 or 1.0 mM of pyridoxamine or pyridoxal phosphate for one-half hour before H(2)O(2) exposure significantly reduced the superoxide and lipid peroxide compared to the cells exposed to H(2)O(2) only. Preincubation of the cells with 0.1 or 1.0 mM of pyridoxine also significantly reduced the lipid peroxide but did not significantly affect the superoxide level unless the preincubation time was extended to 24 hours. The prostacyclin release by endothelial cells was also significantly inhibited by H(2)O(2). However, the preincubation of endothelial cells with 1.0 mM of pyridoxamine, pyridoxine, or pyridoxal phosphate did not prevent that inhibition. These results indicate that pyridoxamine, pyridoxine, and pyridoxal phosphate acted as antioxidants and reduced the superoxide and lipid peroxides induced by H(2)O(2), but did not protect the cells from the effects directly related to H(2)O(2) itself.

Role of NO-synthases and cyclooxygenases in the hyperreactivity of male rabbit carotid artery to testosterone under experimental diabetes

Cardiovascular disease is the major cause of morbidity and mortality in diabetic patients, which in turn is also associated with low levels of serum testosterone. The working hypothesis was that diabetes might modify the mechanisms involved in the vascular actions of testosterone in isolated rabbit carotid arteries. Testosterone (10 −8–3 × 10 −4 M) induced a concentration-dependent relaxation of precontracted carotid arteries, which was higher in diabetic than in control rabbits. In control rabbits neither endothelium removal nor the nitric oxide synthase (NOS) inhibitor N G-nitro- l-arginine ( l-NOArg, 10 −5 M) modified the relaxant action of testosterone, and the cyclooxygenase (COX) inhibitor indomethacin (10 −5 M) enhanced this relaxation. In contrast, in diabetic rabbits endothelium removal, l-NOArg (10 −5 M) or indomethacin (10 −5 M) inhibited the testosterone induced relaxation. In arteries from diabetic rabbits, eNOS, iNOS and COX-2 expression and testosterone induced release of prostacyclin resulted enhanced in comparison with arteries from control rabbits. Testosterone (10 −4 M) strongly inhibited CaCl 2 (10 −5–3 × 10 −2 M) concentration-related contractions of the carotid artery both in control and diabetic rabbits. These results suggest that testosterone relaxes the rabbit carotid artery by blocking the extracellular calcium entry. Diabetes enhances the vasodilator response of the rabbit carotid artery to testosterone by a mechanism that at least includes an increased modulatory activity of the endothelial nitric oxide and an augmented release of COX-2 vasodilator, prostacyclin rather than the absence of COX-1 vasoconstrictor, thromboxane A 2. The hypotestosteronemia observed in diabetic rabbits could be a consequence of the increased expression of iNOS and could contribute to the hyperreactivity of the rabbit carotid artery to testosterone.