Physiologic functions of normal endothelial cells

Juglone as antihypertensive agent acts through multiple vascular mechanisms

Background: Juglone, a natural phenolic compound obtained from the walnut tree, is known for its wide range of biological activities. However, it has yet to be tested for its effects on hypertension and vascular tone. This investigation was aimed to explore the antihypertensive effect and the nature of vascular reactivity of juglone in rat models.Methods: Juglone was tested in in vivo and in vitro experiments in rats. The responses were analyzed and recorded through a PowerLab data acquisition system.Results: Intravenous injection of juglone significantly decreased the mean arterial blood pressure (MAP) in normotensive and hypertensive rats (Max. fall, 43.50 ± 2.96 vs 49.66 ± 3.28 mmHg). In rats pretreated with Nω-Nitro l-arginine methyl ester (_L-NAME), the effect of juglone on MAP was reduced as compared to the control. However, in rats pretreated with atropine the fall in MAP by juglone was not altered. Juglone induced relaxation in the phenylephrine, K⁺ (80 mM), and angiotensin II pretreated isolated rat aortic rings. This vasorelaxant effect was reduced with _L-NAME pretreatment. Atropine pretreatment did not modify the vasorelaxant effect of juglone. Pre-incubation with juglone attenuated the intracellular Ca²⁺ release by suppressing phenylephrine peak formation and also shifted CaCl₂ concentration-response curves (CRCs) to the right. Of note, combined treatment with 4-aminopyridine and barium chloride also reduced juglone-mediated vasorelaxation suggesting a role of K⁺-channels as well.Conclusion: In conclusion, juglone exerts its antihypertensive effect through vasorelaxation, which is mediated by nitric oxide, inhibition of intracellular calcium release and opening of K⁺-channels.

In Vitro Endothelialization of Carbon-Coated Dacron Vascular Grafts

Physical vapour deposition is used to coat vascular prostheses with pyrolytic carbon. This coating may facilitate the development of an endothelial monolayer in grafts implanted in laboratory animals. This in vitro study compared the adherence and growth of cultured porcine aortic endothelial cells (EC) seeded in vitro on carbon-coated Dacron, to uncoated prostheses. The cells were incubated at 5 × 104 cells/cm2. Progress was monitored at different times (TO + 2 hours, D 1, D 4, D 8) by microscopic observation, when cell counts were made; and by scanning electronic microscopy (SEM) to evaluate morphological EC-graft interactions. Cell adherence was independent of the carbon coating but cellular growth occurred only on carbon-coated Dacron. The SEM observations showed both the shape of the adherent cells, which were rounded on uncoated Dacron and extensively spread on carbon-coated prostheses, and the morphology of the carbon coating.

Biochemical changes of the endothelium in the murine model of NO-deficient hypertension

Alterations in the α-helix and β-sheet content and the lipid-to-protein ratio are the most striking features of hypertension development in the vascular endothelium.

The mechanism of vasorelaxation induced by ethanol extract of Sophora flavescens in rat aorta

AIM OF THE STUDY

Sophora flavescens (SF) is a known medicinal herb for the treatment of cardiovascular symptoms associated with arrhythmia in China. However, the pharmacological action mechanisms involved have not been well studied. The aim of the present study was to define effects of roots of SF on the vascular tension and responsible mechanisms in rat thoracic aorta.

MATERIALS AND METHODS

Ethanol extract of the roots of SF (ESF) was examined for their vascular relaxant effect in isolated phenylephrine-precontracted rat thoracic aorta.

RESULTS

ESF (0.1-100 μg/ml) induced relaxation of the phenylephrine-precontracted aortic rings in a concentration-dependent manner. Endothelium-denudation abolished the ESF-induced vasorelaxation. Pretreatment of the endothelium-intact aortic rings with l-NAME, an inhibitor of nitric oxide synthase, and ODQ, an inhibitor of soluble guanylyl cyclase (sGC), inhibited ESF-induced vasorelaxation. ESF increased cGMP levels of the aortic rings in a concentration-dependent manner and the effect was blocked by l-NAME and ODQ. Inhibition of K(+) channels with glibenclamide and tetraethylammonium, cyclooxygenase inhibition with indomethacin, and β-adrenergic and muscarinic receptors blockade had no effect on the ESF-induced vasorelaxation.

CONCLUSION

These findings suggest that ESF relaxes vascular smooth muscle via endothelium-dependent NO-sGC-cGMP signaling pathway.

Vascular relaxation induced by aqueous extract of Lespedeza cuneata via the NO-cGMP pathway

The aqueous extract of Lespedeza cuneata G. Don. (ALC) induced vasorelaxation of phenylephrine precontracted aorta in a dose-dependent manner. This effect disappeared in the absence of functional endothelium. Pretreatment of the aortic tissues with N(G)-nitro-L-arginine methyl ester (L-NAME), or 1H-[1,2,4]-oxadiazole-[4,3-α]-quinoxalin-1-one (ODQ) blocked ALC-induced vascular relaxation. Incubation of endothelium-intact thoracic aortic rings with ALC increased cGMP production. ALC-induced cGMP production was blocked by pretreatment with L-NAME or ODQ. ALC-induced vascular relaxation was also markedly attenuated by addition of verapamil or diltiazem, but was not blocked by pretreatment with indomethacine, glibenclamide, tetraethylammonium, atropine, or propranolol. The results suggest that ALC dilates vascular smooth muscle via endothelium-dependent NO-cGMP signaling.

Ethanol extract of seeds of Oenothera odorata induces vasorelaxation via endothelium-dependent NO-cGMP signaling through activation of Akt-eNOS-sGC pathway

AIM OF STUDY

The vasorelaxant effect of ethanol extract of seeds of Oenothera odorata (Onagraceae) (one species of evening primroses) (ESOO) and its mechanisms involved were defined.

MATERIALS AND METHODS

Changes in vascular tension, guanosine 3',5'-cyclic monophosphate (cGMP) levels, and Akt expression were measured in carotid arterial rings from rats. Seeds of Oenothera odorata were extracted with ethanol (94%) and the extract was filtered, concentrated and stored at -70°C.

RESULTS

ESOO relaxed endothelium-intact, but not endothelium-denuded, carotid arterial rings in a concentration-dependent manner. Similarly, ESOO increased cGMP levels of the carotid arterial rings. Pretreatment of endothelium-intact arterial rings with L-NAME, an inhibitor of nitric oxide synthase (NOS), or ODQ, an inhibitor of soluble guanylyl cyclase (sGC), blocked the ESOO-induced vasorelaxation and increase in cGMP levels. Nominally Ca(2+)-free but not L-typed Ca(2+) channel inhibition attenuated the ESOO-induced vasorelaxation. Thapsigargin, Gd(3+), and 2-aminoethyl diphenylborinate, modulators of store-operated Ca(2+) entry (SOCE), significantly attenuated the ESOO-induced vasorelaxation and increase in cGMP levels. Further, wortmannin, an inhibitor of Akt, attenuated the ESOO-induced vasorelaxation and increases in cGMP levels and phosphorylated Akt2 expression. K(+) channel blockade with TEA, 4-aminopyridine, and glibenclamide attenuated the ESOO-induced vascular relaxation.

CONCLUSION

Taken together, the present study demonstrates that ESOO relaxes vascular smooth muscle via endothelium-dependent NO-cGMP signaling through activation of the Akt-eNOS-sGC pathway.

Vascular relaxation by ethanol extract of Xanthoceras sorbifolia via Akt- and SOCE-eNOS-cGMP pathways

AIM OF THE STUDY

The aim of the present study was to define the effect of Xanthoceras sorbifolia extracts (XS) on vascular tension and responsible mechanisms in rat thoracic aortic rings.

MATERIALS AND METHODS

Ethanol extract of the leaves of XS (EXS) was examined for their vascular relaxant effects in isolated phenylephrine-precontracted rat thoracic aorta.

RESULTS

EXS (0.1-100 μg/ml) induced relaxation of the phenylephrine-precontracted aortic rings in a concentration-dependent manner. Endothelium-denudation abolished EXS-induced vasorelaxation. Pretreatment of the endothelium-intact aortic rings with N(G)-nitro-L-arginine methylester (L-NAME) and 1H-[1,2,4]-oxadiazolo-[4,3-α]-quinoxalin-1-one (ODQ) inhibited EXS-induced vasorelaxation. Inhibition of Ca(2+) entry via L-type Ca(2+) channels failed to block the EXS-induced vasorelaxation. Extracellular Ca(2+) depletion significantly attenuated EXS-induced vasorelaxation. Modulators of the store-operated Ca(2+) entry (SOCE), thapsigargin, 2-aminoethyl diphenylborinate (2-APB) and Gd(3+), and an inhibitor of Akt, wortmannin, markedly attenuated the EXS-induced vasorelaxation. EXS increased cGMP levels of the aortic rings in a concentration-dependent manner and the effect was blocked by L-NAME, ODQ, thapsigargin, Gd(3+), 2-APB, and wortmannin. Further, EXS-induced vasorelaxation was significantly attenuated by tetraethylammonium, a non-selective K(ca) channels blocker, but not by glibenclamide, an ATP-sensitive K(+) channels inhibitor. Inhibition of cyclooxygenase with indomethacin, and adrenergic and muscarinic receptors blockade had no effects on EXS-induced vasorelaxation.

CONCLUSIONS

The present study suggests that EXS relaxes vascular smooth muscle via endothelium-dependent NO-cGMP signaling through activation of the Akt- and SOCE-eNOS-sGC pathways, which may, at least in part, be related to the function of K(+) channels.

Water extract of Zanthoxylum piperitum induces vascular relaxation via endothelium-dependent NO-cGMP signaling

AIM OF THE STUDY

The aim of the present study was to define the effects of extracts of leaves of Zanthoxylum piperitum (ZP) on the vascular tension and its mechanisms responsible in rat thoracic aortic rings.

MATERIALS AND METHODS

Methanol extract of ZP and aqueous fraction of the methanol extract (AZP) were examined for their vascular relaxant effects in isolated phenylephrine-precontracted aortic rings.

RESULTS

Methanol extract of ZP and aqueous fraction of the methanol extract (AZP) induced relaxation of the phenylephrine-precontracted aortic rings in a concentration-dependent manner. Endothelium-denudation abolished the AZP-induced vasorelaxation. Pretreatment of the endothelium-intact aortic rings with N(G)-nitro-L-arginine methylester (L-NAME) and 1H-[1,2,4]-oxadiazolo-[4,3-alpha]-quinoxalin-1-one (ODQ) inhibited the AZP-induced vasorelaxation. Inhibition of Ca(2+) entry via L-type Ca(2+) channels failed to block the AZP-induced vasorelaxation. Extracellular Ca(2+) depletion slightly but significantly attenuated the AZP-induced vasorelaxation. Thapsigargin significantly attenuated the AZP-induced vasorelaxation. Further, Gd(3+) and 2-aminoethyl diphenylborinate (2-APB), inhibitors of store-operated Ca(2+) entry (SOCE), markedly attenuated the AZP-induced vasorelaxation. Also, wortmannin, an inhibitor of Akt, an upstream signaling molecule of eNOS, attenuated the AZP-induced vasorelaxation. AZP increased cGMP levels of the aortic rings in a concentration-dependent manner and the effect was blocked by L-NAME, ODQ, thapsigargin, Gd(3+), 2-APB, and wortmannin. K(+) channel inhibition with glibenclamide and tetraethylammonium, cyclooxygenase inhibition with indomethacin, and adrenergic and muscarinic receptors blockade had no effects on the AZP-induced vasorelaxation.

CONCLUSION

Taken together, the present study suggests that AZP relaxes vascular smooth muscle via endothelium-dependent activation of NO-cGMP signaling through the Akt- and SOCE-eNOS pathways.

A biomimetic peptide fluorosurfactant polymer for endothelialization of ePTFE with limited platelet adhesion

Endothelialization of expanded polytetrafluoroethylene (ePTFE) has the potential to improve long-term patency for small-diameter vascular grafts. Successful endothelialization requires ePTFE surface modification to permit cell attachment to this otherwise non-adhesive substrate. We report here on a peptide fluorosurfactant polymer (FSP) biomimetic construct that promotes endothelial cell (EC)-selective attachment, growth, shear stability, and function on ePTFE. The peptide FSP consists of a flexible poly(vinyl amine) backbone with EC-selective peptide ligands for specific cell adhesion and pendant fluorocarbon branches for stable anchorage to underlying ePTFE. The EC-selective peptide (primary sequence: Cys-Arg-Arg-Glu-Thr-Ala-Trp-Ala-Cys, CRRETAWAC) has demonstrated high binding affinity for the alpha(5)beta(1) integrin found on ECs. Here, we demonstrate low affinity of CRRETAWAC for platelets and platelet integrins, thus providing it with EC-selectivity. This EC-selectivity could potentially facilitate rapid in vivo endothelialization and healing without thrombosis for small-diameter ePTFE vascular grafts.

The effect of RGD fluorosurfactant polymer modification of ePTFE on endothelial cell adhesion, growth, and function

We have synthesized and characterized a novel peptide fluorosurfactant polymer (PFSP) modification that facilitates the adhesion and growth of endothelial cells on expanded polytetrafluoroetheylene (ePTFE) vascular graft material. This PFSP consists of a poly(vinyl amine) (PVAm) backbone with integrin binding Arg-Gly-Asp (RGD) peptides and perfluorocarbon pendant branches for adsorption and stable adhesion to underlying ePTFE. Aqueous PFSP solution was used to modify the surface of fluorocarbon substrates. Following subconfluent seeding, endothelial cell (EC) adhesion and growth on PFSP was assessed by determining cell population at different time points. Spectroscopic results indicated successful synthesis of PFSP. PFSP modification of ePTFE reduced the receding water contact angle measurement from 120 degrees to 6 degrees , indicating successful surface modification. Quantification of cell population demonstrated reduced EC attachment efficiency but increased growth rate on RGD PFSP compared with fibronectin (FN). Actin staining revealed a well-developed cytoskeleton for ECs on RGD PFSP indicative of stable adhesion. Uptake of acetylated low-density lipoprotein and positive staining for VE-Cadherin confirm EC phenotype for adherent cells. Production of prostacyclin, a potent antiplatelet agent, was equivalent between ECs on FN and RGD PFSP surfaces. Our results indicate successful synthesis and surface modification with PFSP; this is a simple, quantitative, and effective approach to modifying ePTFE to encourage endothelial cell attachment, growth, and function.

Vascular relaxation by the methanol extract of Sorbus cortex via NO-cGMP pathway

The methanol extract of Sorbus commixta cortex (MSC) induced relaxation of the phenylephrine-precontracted aorta in a dose-dependent manner, which was disappeared by removal of functional endothelium. Pretreatment of the aortic tissues with N(G)-nitro-L-arginine methyl ester (L-NAME), methylene blue, or 1H-[1,2,4]-oxadiazole-[4,3-alpha]-quinoxalin-1-one (ODQ) inhibited the vascular relaxation induced by MSC. MSC-induced vascular relaxations were also markedly attenuated by addition of verapamil or diltiazem, while the relaxant effect of MSC was not blocked by pretreatment with indomethacine, glibenclamide, tetraethylammonium (TEA), atropine, or propranolol, respectively. Incubation of endothelium-intact carotid arteries or of human umbilical vein endothelial cells (HUVECs) with MSC increased the production of guanosine 3',5'-cyclic monophosphate (cGMP). Moreover, MSC-induced cGMP production was effect was blocked by pretreatment with L-NAME or ODQ. These results suggest that MSC dilates vascular smooth muscle via endothelium-dependent nitric oxide-cGMP signaling pathway, possible involvement of L-type Ca(2+) channel.

Vasodilatory and anti-inflammatory effects of the aqueous extract of rhubarb via a NO-cGMP pathway

While conducting an in vitro screen of various medicinal plant extracts, an aqueous extract of rhubarb (Rheum undulatum L, AR) was found to exhibit a distinct vasorelaxant activity. AR induced a concentration-dependent relaxation of the phenylephrine-precontracted aorta. This effect disappeared with the removal of functional endothelium. Pretreatment of the aortic tissues with N(G)-nitro-L-arginine methyl ester (L-NAME), methylene blue, or 1H-[1,2,4]-oxadiazole-[4,3-alpha]-quinoxalin-1-one (ODQ) inhibited the relaxation induced by AR. Incubation of human umbilical vein endothelial cells (HUVECs) with AR increased the production of cGMP in a dose-dependent manner, but this effect was blocked by pretreatment with L-NAME and ODQ, respectively. AR treatment attenuated TNF-alpha-induced NF-kappaB p65 translocation in HUVECs in a dose-dependent manner. In addition, AR suppressed the expression levels of adhesion molecules including ICAM-1 and VCAM-1 induced by TNF-alpha in HUVECs. TNF-alpha-induced MCP-1 expression was also attenuated by the addition of AR. This attenuation was blocked by pretreatment with either L-NAME or ODQ. AR treatment inhibited cellular adhesion of U937 cells onto HUVECs induced by TNF-alpha. Taken together, the present study suggests that AR dilates vascular smooth muscle and suppresses the vascular inflammatory process via endothelium-dependent NO/cGMP signaling.

Vasodilatory and anti-inflammatory effects of the 1,2,3,4,6-penta-O-galloyl-beta-D-glucose (PGG) via a nitric oxide-cGMP pathway

Vasorelaxant and anti-inflammatory effects of a 1,2,3,4,6-penta-O-galloyl-beta-d-glucose (PGG) isolated from the root barks of Paeonia suffruticosa and possible mechanisms responsible were investigated. PGG induced a concentration-dependent relaxation of the phenylephrine-precontracted rat aorta. This effect disappeared with the removal of functional endothelium. Pretreatment of the aortic tissues with either N(G)-nitro-L-arginine methyl ester (L-NAME) or 1H-[1,2,4]-oxadiazole-[4,3-alpha]-quinoxalin-1-one (ODQ) inhibited the relaxation induced by PGG. Incubation of human umbilical vein endothelial cells (HUVECs) or carotid arteries isolated from rats with PGG increased the production of cGMP in a dose-dependent manner, but this effect was blocked by pretreatment with L-NAME and ODQ, respectively. PGG treatment attenuated tumor necrosis factor-alpha (TNF-alpha)-induced nuclear factor-kappaB (NF-kappaB) p65 translocation in human umbilical vein endothelial cells. In addition, PGG suppressed the expression levels of adhesion molecules including intracellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) induced by TNF-alpha. TNF-alpha-induced monocyte chemoattractant protein-1 (MCP-1) expression was also attenuated by addition of PGG. PGG treatment inhibited cellular adhesion of U937 cells onto human umbilical vein endothelial cells induced by TNF-alpha. Taken together, the present study suggests that PGG dilates vascular smooth muscle and suppresses the vascular inflammatory process via endothelium-dependent nitric oxide (NO)/cGMP signaling.

Time to abandon dogma: CD14 is expressed by non‐myeloid lineage cells

CD14 is a pattern recognition receptor; its important role in innate immunity is reviewed here. Since its discovery and subsequent classification at the first leucocyte typing workshop in 1982, CD14 has been thought of as a leucocyte differentiation antigen. However, it has become clear that CD14 is also expressed by many non-myeloid cells, and the evidence for this is presented. The possible role of the presence of low copy number CD14 on non-myeloid cells is discussed. It is time to acknowledge CD14 as an ubiquitous molecule and abandon the position that it is expressed by myeloid cells alone.

Ginger lowers blood pressure through blockade of voltage-dependent calcium channels

Ginger (Zingiber officinale Roscoe), a well-known spice plant, has been used traditionally in a wide variety of ailments including hypertension. We report here the cardiovascular effects of ginger under controlled experimental conditions. The crude extract of ginger (Zo.Cr) induced a dose-dependent (0.3-3 mg/kg) fall in the arterial blood pressure of anesthetized rats. In guinea pig paired atria, Zo.Cr exhibited a cardiodepressant activity on the rate and force of spontaneous contractions. In rabbit thoracic aorta preparation, Zo.Cr relaxed the phenylephrine-induced vascular contraction at a dose 10 times higher than that required against K (80 mM)-induced contraction. Ca2+ channel-blocking (CCB) activity was confirmed when Zo.Cr shifted the Ca2+ dose-response curves to the right similar to the effect of verapamil. It also inhibited the phenylephrine (1 microM) control peaks in normal-Ca2+ and Ca2+-free solution, indicating that it acts at both the membrane-bound and the intracellular Ca2+ channels. When tested in endothelium-intact rat aorta, it again relaxed the K-induced contraction at a dose 14 times less than that required for relaxing the PE-induced contraction. The vasodilator effect of Zo.Cr was endothelium-independent because it was not blocked by L-NAME (0.1 mM) or atropine (1 microM) and also was reproduced in the endothelium-denuded preparations at the same dose range. These data indicate that the blood pressure-lowering effect of ginger is mediated through blockade of voltage-dependent calcium channels.

Alpha-naphthoflavone induces vasorelaxation through the induction of extracellular calcium influx and NO formation in endothelium

The effect of alpha-naphthoflavone (alpha-NF) on vascular function was studied in isolated ring segments of the rat thoracic aorta and in primary cultures of human umbilical vein endothelial cells (HUVECs). alpha-NF induced concentration-dependent relaxation of the phenylephrine-precontracted aorta endothelium-dependently and -independently at lower and higher concentrations, respectively. The cGMP, but not cAMP, content was increased significantly in alpha-NF-treated aorta. Pretreatment with N(omega)-nitro- l-arginine methyl ester (L-NAME) or methylene blue attenuated both alpha-NF induced vasorelaxation and the increase of cGMP content significantly. The increase of cGMP content induced by alpha-NF was also inhibited by chelating extracellular Ca(2+) with EGTA. These results suggest that the endothelium-dependent vasorelaxation induced by alpha-NF is mediated most probably through Ca(2+)-dependent activation of NO synthase and guanylyl cyclase. In HUVECs, alpha-NF induced concentration-dependent formation of NO and Ca(2+) influx. alpha-NF-induced NO formation was abolished by removal of extracellular Ca(2+) and by pretreatment with the Ca(2+) channel blockers SKF 96365 and Ni(2+), but not by the L-type Ca(2+) channel blocker verapamil. The Ca(2+) influx, as measured by (45)Ca(2+) uptake, induced by alpha-NF was also inhibited by SKF 96365 and Ni(2+). Our data imply that alpha-NF, at lower concentrations, induces endothelium-dependent vasorelaxation by promoting extracellular Ca(2+) influx in endothelium and the activation of the NO-cGMP pathway.

Induction of vasorelaxation through activation of nitric oxide synthase in endothelial cells by brazilin

The vasorelaxant activity of Caesalpinia sappan L., a traditional Chinese medicine, and its major component brazilin were investigated in isolated rat aorta and human umbilical vein endothelial cells. In isolated rat aorta, C. sappan L. extract and brazilin relaxed phenylephrine-induced vasocontraction and increased cyclic guanosine 3',5'-monophosphate (cGMP) content. Induction of vasorelaxation of brazilin was endothelium-dependent and could be markedly blocked by pretreatment with nitric oxide synthase (NOS) inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME); N(G)-monomethyl-L-arginine acetate (L-NMMA) and guanylyl cyclase inhibitor, methylene blue; 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and nitric oxide (NO) scavenger, hemoglobin. The increasing cGMP content induced by brazilin was also blocked by pretreatment with L-NAME, methylene blue, and the removal of extracellular Ca(2+). In human umbilical vein endothelial cells, brazilin dose-dependently induced an increase in NO formation and NOS activity, which were greatly attenuated by either the removal of extracellular Ca(2+) or the chelating of intracellular Ca(2+) chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM). Moreover, brazilin dose-dependently induced the influx of extracellular Ca(2+) in human umbilical vein endothelial cells. Collectively, these results suggest that brazilin induces vasorelaxation by the increasing intracellular Ca(2+) concentration in endothelial cells of blood vessels and hence activating Ca(2+)/calmodulin-dependent NO synthesis. The NO is released and then transferred into smooth muscle cells to activate guanylyl cyclase and increase cGMP content, resulting in vasorelaxation.

Ca(2+) removal mechanisms in freshly isolated rabbit aortic endothelial cells

Calcium removal from the cytoplasm was investigated in freshly isolated aortic endothelial cells by monitoring changes in intracellular calcium ([Ca(2+)](i)) using ratiometric fura-2 fluorimetry. Blockade of the Na(+)/Ca(2+) exchanger (NCX) by replacement of external sodium with equi-molar N-methyl-D-glutamine (0Na PSS) decreased the removal rate by 52%. Blockade of the sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA) by cyclopiazonic acid (CPA) decreased the removal rate by 50%. Simultaneous application of CPA and 0Na PSS did not reduce the removal rate any further (53%). The lack of additivity of these two procedures, suggests that SERCA and the NCX function in series to lower [Ca(2+)](i). In addition, in the absence of extracellular Ca(2+), removal of external Na(+) markedly reduced the rate of loss of Ca(2+) from the ER further supporting the hypothesis that NCX is functionally linked to ER calcium release channels, and thus, plays an important role in ER calcium unloading. To investigate the mechanism for the coupling of NCX and SERCA, the same protocols as described above were repeated after treating the cells with cytochalasin D, which disrupts the cytoskeleton. This treatment uncoupled the NCX from SERCA, as evidenced by the resulting additive inhibitory effects of application of CPA and removal of extracellular Na(+) on the rate of Ca(2+) removal from the cytoplasm. These data suggest that in endothelial cells NCX and SERCA function in series to remove about half of the free Ca(2+) from the cytosol, while PMCA contributes to the other half of the Ca(2+) removal process.

Human saphenous vein endothelial cells express a tetrodotoxin-resistant, voltage-gated sodium current

Whole-cell patch-clamp electrophysiological investigation of endothelial cells cultured from human saphenous vein (HSVECs) has identified a voltage-gated Na+ current with a mean peak magnitude of -595 +/- 49 pA (n = 75). This current was inhibited by tetrodotoxin (TTX) in a concentration-dependent manner, with an IC50 value of 4.7 microM, suggesting that it was of the TTX-resistant subtype. An antibody directed against the highly conserved intracellular linker region between domains III and IV of known Na+ channel alpha-subunits was able to retard current inactivation when applied intracellularly. This antibody identified a 245-kDa protein from membrane lysates on Western blotting and positively immunolabeled both cultured HSVECs and intact venous endothelium. HSVECs were also shown by reverse transcription-polymerase chain reaction to contain transcripts of the hH1 sodium channel gene. The expression of Na+ channels by HSVECs was shown using electrophysiology and cell-based enzyme-linked immunosorbent assay to be dependent on the concentration and source of human serum. Together, these results suggest that TTX-resistant Na+ channels of the hH1 isoform are expressed in human saphenous vein endothelium and that the presence of these channels is controlled by a serum factor.

Vasorelaxation of rat thoracic aorta caused by 14-deoxyandrographolide

1. The pharmacological effects of 14-deoxyandrographolide on rat isolated thoracic aorta were examined. 2. 14-Deoxyandrographolide (2.5-120 mumol/L) inhibited contractions induced by phenylephrine (PE; 0.1 mumol/L) and high K+ (80 mmol/L) in a concentration-dependent manner in endothelium-intact aorta. The effect was attenuated in endothelium-denuded aorta without modifying the maximal response. Like verapamil, 14-deoxyandrographolide produced a much greater vasorelaxant effect in aorta precontracted by KCl than by PE. 14-Deoxyandrographolide (20-60 mumol/L) also inhibited responses of the rat aorta to PE. 3. In Ca(2+)-free medium (KCl 55 mmol/L), 14-deoxyandrographolide (20-80 mumol/L) antagonized Ca(2+)-induced vasocontraction in a concentration-dependent manner and transient contractions induced by both caffeine (10 mmol/L) and nor-adrenaline (1 mumol/L) were suppressed or almost abolished by 14-deoxyandrographolide. 4. The vasorelaxant effect of 14-deoxyandrographolide was partially antagonized by NG-nitro-L-arginine methyl ester (25 mumol/L), a specific and competitive nitric oxide synthase (NOS) inhibitor, and methylene blue (10 mumol/L), a soluble guanylate cyclase inhibitor, but was not affected by indomethacin (20 mumol/L), a cyclo-oxygenase inhibitor, or glibenclamide (10 mumol/L), an ATP-sensitive K(+)-channel blocker. 5. These results suggest that the vasorelaxant activity of 14-deoxyandrographolide may be mediated via the activation of NOS and guanylate cyclase, as well as the blockade of Ca2+ influx through both voltage- and receptor-operated Ca2+ channels.

Effect of aescine on hypoxia-induced neutrophil adherence to umbilical vein endothelium

Although venous stasis due to blood stagnation in lower limbs has been recognised as an important etiological factor for the development of varicose veins, the mechanism linking this ischemic situation to the modifications of the venous wall in varicose veins is still unclear. There is evidence that the activation of the endothelium during blood stasis and its subsequent cascade of interactions with other cell types could alter the structure of the vein wall and could possibly be at the origin of the disease. While phlebotonic drugs are often used to improve symptoms in chronic venous insufficiency, their precise mechanism of action is not well understood. We now tested aescine (Reparil i.v. form) in an ex vivo model which mimics this situation, i.e., perfused human umbilical vein exposed to hypoxic conditions. To study the effect of aescine on neutrophil activation and adhesion to the endothelium, human umbilical veins were incubated under hypoxic conditions with or without aescine and the interactions between the endothelium and neutrophil-like cells, HL60, were investigated. We observed that a large number of HL60 became adherent to the endothelium of veins after 2 h hypoxia and that these adherent HL60 were activated: they released high amounts of superoxide anion and of leukotriene B4. Aescine (250 ng/ml or 0.22 microM) was shown to markedly inhibit HL60 adherence to hypoxic endothelium. By decreasing the number of adherent HL60, aescine also decreased the subsequent production of superoxide anion and of leukotriene B4. Scanning electron microscopy confirmed the increased HL60 adherence to the endothelium, as well as the inhibitory effect of aescine. These results support results of in vitro studies on isolated endothelial cells in which aescine was shown to inhibit the hypoxia-induced activation of endothelial cells and the subsequent increased adherence of neutrophils. In vivo, the activated and infiltrated leukocytes release free radicals, chemotactic molecules such as leukotriene B4 and proteases which then can degrade the extracellular matrix. These processes could contribute to alterations of the venous wall similar to those observed in varicose veins. By maintaining an intact endothelium during in vivo blood stasis in the lower limbs and preventing neutrophil recruitment, adherence and activation, aescine could prevent the resulting alterations of the venous wall. These results could explain at least in part the potential benefit of the drug in the prevention of venous insufficiency.

Role of vascular nitric oxide in physiological and pathological conditions

This review describes the ability of certain diseases, such as essential hypertension, atherosclerosis, angina, and vasospasm, to reduce vascular nitric oxide (NO) formation or to increase its metabolism. In contrast, others, such as hypotension, sepsis, stroke, myocardial depression, and inflammatory responses, increase NO synthesis. The mechanism implicated in the changes in the formation and metabolism of NO are described. To prevent or treat these pathological processes, in which a deficiency in vascular NO formation plays a causative role, NO may be provided through methods such as direct NO administration or indirect NO supply through either NO donors or L-arginine, which facilitates NO formation.

The effect of S-(+)-boldine on the alpha 1-adrenoceptor of the guinea-pig aorta

1. The cardiovascular activity of S-(+)-boldine, an aporphine alkaloid structurally related to papaverine, was determined. The work includes functional studies on guinea-pig isolated aorta contracted with noradrenaline, caffeine, KCl or Ca2+, and on guinea-pig trachea contracted with acetylcholine or histamine. 2. S-(+)-boldine inhibited in a concentration-dependent manner the contractile response evoked by noradrenaline (10 microM) in guinea-pig aorta (IC50 = 1.4 +/- 0.2 microM) while the KCl depolarizing solution (60 mM)- or the Ca2+ (1 mM)-induced contractions were only partially affected by boldine up to 300 microM. In contrast, papaverine relaxed noradrenaline (NA), KCl or Ca2+ induced contractions showing similar IC50 values in all cases. S-(+)-boldine had a greater potency on the contraction elicited by NA whereas papaverine acted in a non-selective manner. 3. S-(+)-boldine was found to be an alpha 1-adrenoceptor blocking agent in guinea-pig aorta as revealed by its competitive antagonism of noradrenaline-induced vasoconstriction (pA2 = 5.64 +/- 0.08), and its potency was compared with that of prazosin (pA2 = 8.56 +/- 0.24), a known potent alpha 1-adrenoceptor antagonist. In contrast, papaverine caused rightward shifts of the NA concentration-response curves with depression of maximal response indicating that it acts as a non-competitive antagonist. 4. Contraction of guinea-pig aorta induced by caffeine (60 mM) in a Ca(2+)-containing Krebs solution was not affected by a 60 min incubation period with different doses of S-(+)-boldine (1-300 microM). Papaverine inhibited partially this caffeine-induced contraction at the maximal dose used (100 microM). 5. Inositol phosphates formation induced by noradrenaline (10 microM) in guinea-pig thoracic aorta was inhibited by S-(+)-boldine (30 microM) but not by papaverine (10 microM). 6. Contractions of guinea-pig trachea caused by acetylcholine (100 microM) or histamine (10 microM) were not modified by S-(+)-boldine (0.1-100 microM). 7. These results provide evidence that S-(+)-boldine, an aporphine alkaloid, has interesting properties as an alpha 1-adrenoceptor blocker in vascular smooth muscle, and acts as a competitive antagonist of the alpha 1-adrenoceptor present in the guinea pig aorta.

Endothelial cell oxidant generation during K(+)-induced membrane depolarization

We tested the hypothesis that membrane depolarization may initiate oxidant generation in the endothelial cell. Depolarization was produced in bovine pulmonary arterial endothelial cells (BPAEC) in monolayer culture with varying external K+, or with glyburide (10 microM), tetraethylammonium (TEA, 10 mM), gramicidin (1 microM), or nigericin (2 microM). Evaluation of bisoxonol fluorescence of BPAEC indicated concentration-dependent depolarization by high K+ (2% change in fluorescence/mV change in membrane potential in the 5.9-48 mM range of K+) and essentially complete depolarization with glyburide. Generation of oxidants was assessed with o-phenylenediamine dihydrochloride (o-PD) oxidation in the presence of horseradish peroxidase (HRP). There was a time-dependent increase in o-PD oxidation with 24 mM K+, nigericin, and gramicidin over 2 hours compared with control. In 1 hour o-PD oxidation increased 2.8-fold for 24 mM and 3.7-fold for 48 mM K+ compared with control. Catalase reduced 24 mM K(+)-induced o-PD oxidation by 50%, while Cu/Zn-superoxide dismutase (SOD) abolished the increase. Oxidation of o-PD was reduced by 57% in the absence of HRP in the system. With K+ channel blockade, o-PD oxidation increased 3.8-fold with glyburide and 4.6-fold with TEA compared with control. These data indicate formation of H2O2 and possibly other oxidants with depolarization and suggest involvement of K(+)-channels in this process.

Pharmacological activity of DC-015, a novel potent and selective alpha 1-adrenoceptor antagonist

The pharmacological activity of 3-((4-(2-methoxyphenyl)piperazin-1-yl)methyl)-2,3-dihydroimidaz o(1,2 -c)quinazolin-5(6H)-one (DC-015), a newly synthesized quinazoline derivative, was determined in rat isolated thoracic aorta and pressor responses were determined in spontaneously hypertensive rats (SHR). Experimental results indicated that DC-015 is an alpha 1-adrenoceptor-blocking agent in rat thoracic aorta as revealed by its competitive antagonism of phenylephrine-induced vasocontraction (pA2 = 10.54 +/- 0.55). These effects still persisted in denuded aorta. It was as potent as prazosin (pA2 = 10.04 +/- 0.63). At higher concentration (1.0 microM), DC-015 also expressed 5-hydroxytryptamine (5-HT) receptor competitive antagonism, but this 5-HT blocking effect was not found in the prazosin-administration group. [3H]Inositol monophosphate formation stimulated by phenylephrine (30 microM) in rat thoracic aorta was diminished by DC-015 (3 and 10 nM) and prazosin (10nM); whereas the cAMP content of rat thoracic aorta was not altered by DC-015 and prazosin. Furthermore, intravenous administration of DC-015 and prazosin (both at 0.01, 0.05 and 0.1 mg/kg-1) induced a dose-dependent reduction of mean arterial pressure which reached a maximal effect at 5 mm after injection and persisted over 2 h in SHR. A higher dose of DC-015 (0.1 mg/kg-1, i.v.) did not cause any significant changes in heart rate, whereas, the same dose of prazosin (0.1 mg/kg-1, i.v.) produced a decrease which seems to parallel the time course of the hypotensive response. We can conclude that the DC-015 is a potent, highly selective alpha 1-adrenoceptor antagonist in vascular smooth muscle.

Protection of hypoxia-induced ATP decrease in endothelial cells by ginkgo biloba extract and bilobalide

Due to their localization at the interface between blood and tissue, endothelial cells are the first target of any change occurring within the blood, and alterations of their functions can seriously impair organs. During hypoxia, which mimics in vivo ischemia, a cascade of events occurs in the endothelial cells, starting with a decrease in ATP content and leading to their activation and release of inflammatory mediators. EGb 761 and one of its constituents, bilobalide, were shown to inhibit the hypoxia-induced decrease in ATP content in endothelial cells in vitro. Under these conditions, glycolysis was activated, as evidenced by increased glucose transport, as well as increased lactate production. Bilobalide was found to increase glucose transport under normoxic but not hypoxic conditions. In addition, EGb and bilobalide prevented the increase in total lactate production observed after 60 min of hypoxia. However, after 120 min of hypoxia, the total lactate production was similar under normoxic and hypoxic conditions, and both compounds increased this production. These results indicate that glycolysis slowed down between the 60th and 120th minute of hypoxia, while EGb and bilobalide delayed the onset of glycolysis activation. In another experimental model, both compounds were shown to increase the respiratory control ratio of mitochondria isolated from liver of rats treated orally. Since ischemia is known to uncouple mitochondria, the protection of ATP content and the delay in glycolysis activation observed during hypoxia in the presence of EGb 761 or bilobalide is best explained by a protection of mitochondrial respiratory activity, at least during the first 60 min of hypoxia incubation. Both products retain the ability to form ATP, thereby reducing the cell's need to induce glycolysis, probably by preserving ATP regeneration by mitochondria as long as oxygen is available.

Evidence for the presence of endothelin ETA receptors in endothelial cells in situ on the aortic side of porcine aortic valve

1. In the present study, we determined whether ETA receptors are present on endothelial cells in situ, by use of front-surface fluorometry of fura-2-loaded porcine aortic valvular strips and reverse transcription polymerase chain reaction (RT-PCR). 2. Although endothelin-1 (ET-1) and endothelin-3 (ET-3) induced maximum elevations of cytosolic Ca2+ concentrations ([Ca2+]i) at 10(-7) M, the peak elevations of [Ca2+]i induced by ET-1 were much greater than those induced by ET-3. 3. The application of ET-1 after ET-3 induced an additional increase in [Ca2+]i, while the application of ET-3 after ET-1 had no effect. A selective ETA receptor antagonist, BQ-123, partially inhibited the ET-1-induced Ca2+ transient but had no effect on ET-3-induced Ca2+ transients. These experiments indicated the presence of functioning ETA receptors in addition to ETB receptors in endothelial cells in situ. 4. The sequence of pig lung ETA receptor complimentary DNA (cDNA) was determined by PCR. RT-PCR, using specific primers for pig ETA receptor sequence and total RNA from endothelial cells on the aortic side of the aortic valve, gave the expected size of band. This PCR product was sequenced and was found to be identical to the sequence of the pig lung ETA receptor. 5. The partial sequence of the pig lung ETB receptor was also determined. RT-PCR for the pig ETB receptor revealed that endothelial cells of the aortic valve express ETB receptor messenger RNA (mRNA). 6. We confirmed that functioning ETA receptors and expression of ETA receptor mRNA exist in the endothelial cells on the aortic side of porcine aortic valves.

Endothelium-dependent relaxation of rat aorta by butein, a novel cyclic AMP-specific phosphodiesterase inhibitor

Butein, isolated from Dalbergia odorifera T. Chen, caused endothelium-dependent relaxation of rat aorta precontracted with phenylephrine. This effect was abolished in endothelium-denuded aorta and in endothelium-intact aorta in the presence of NG-monomethyl-L-arginine, oxyhemoglobin and methylene blue, whereas the effect was unaltered by indomethacin or charybdotoxin. These results indicate that the vasorelaxant effect of butein depended on the endothelium and was mediated by endothelium-derived relaxing factor (EDRF). Incubation of endothelium-intact aorta with butein increased not only cAMP but also cGMP content. Four phosphodiesterase forms were isolated by diethylaminoethyl (DEAE)-Sephacel chromatography from rat aorta. cAMP-specific phosphodiesterase (type IV) activity was potently inhibited by butein with an IC50 of 10.4 +/- 0.4 microM. In contrast, phosphodiesterase I, III and V activities were inhibited by butein above 100 microM. Adenylate cyclase and guanylate cyclase activities were unchanged by butein. These results suggest that the increase of cAMP formation elicited by butein is due to the inhibition of cAMP-specific phosphodiesterase. The specific phosphodiesterase IV inhibitor (rolipram) and V inhibitor (zaprinast) both produced endothelium-dependent relaxations, whereas the phosphodiesterase III inhibitor (trequinsin) produced relaxation of rat aorta independent of the endothelium. In the presence of a functional endothelium, relaxations produced by butein were significantly potentiated by isoprenaline, forskolin, trequinsin and sodium nitroprusside. It is concluded that butein, a novel cAMP-specific phosphodiesterase inhibitor, produced relaxation of rat aorta, an effect dependent on an intact endothelium. The relaxant effect of butein was markedly enhanced by cGMP-elevating agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological evaluation of N-methyl-actinodaphnine, a new vascular alpha-adrenoceptor antagonist, isolated from Illigera luzonensis

The pharmacological activity of N-methyl-actinodaphnine, isolated from Illigera luzonensis, was determined by functional and binding experiments with peripheral tissues. In a functional study, N-methyl-actinodaphnine was a simple competitive antagonist of contractions elicited by phenylephrine (pA2 = 7.11) in rat thoracic aorta; it also competitively antagonised the clonidine-induced inhibition of the twitch response of rat vas deferens (pA2 = 5.01). In addition, [3H]inositol monophosphate formation caused by noradrenaline (3 microM) in rat isolated thoracic aorta was concentration dependently inhibited by N-methyl-actinodaphnine (1 and 10 microM); however, it had no effect on cyclic AMP and cyclic GMP contents. Additionally, N-methyl-actinodaphnine had extremely low affinity for thromboxane receptors, prostaglandin receptors, Ca2+ channels, muscarinic receptors, histamine receptors, beta-adrenoceptors, neurokinin and leukotriene receptors in vitro. However, N-methyl-actinodaphnine also possessed 5-hydroxytryptamine (5-HT) receptor blocking activity. Its potency for blocking 5-HT receptors was about 14 times less than that for blocking alpha 1-adrenoceptors. In binding experiments, N-methyl-actinodaphnine displaced biphasically the binding of 0.2 nM [3H]prazosin to cultured A10 cells. The selectivity for alpha 1-adrenoceptor subtypes was also investigated in rat vas deferens and spleens. The contractile response in rat vas deferens to noradrenaline was competitively inhibited by N-methyl-actinodaphnine with a pA2 value of 6.58; N-methyl-actinodaphnine also competitively antagonized the phenylephrine-induced contraction in rat spleen with a pA2 value of 7.38. These results indicate that N-methyl-actinodaphnine is a selective alpha 1-adrenoceptor antagonist. Furthermore, it is more selective for the alpha 1B- than for the alpha 1A-adrenoceptor subtype.

Vasorelaxant effect of isoliquiritigenin, a novel soluble guanylate cyclase activator, in rat aorta

1. The vasorelaxant activity of isoliquiritigenin, isolated from Dalbergia odorifera T, was investigated in the phenylephrine-precontracted rat aorta by measuring tension, guanylate and adenylate cyclase activities, guanosine 3':5'-cyclic monophosphate (cyclic GMP) and adenosine 3':5'-cyclic monophosphate (cyclic AMP) levels. 2. Isoliquiritigenin concentration-dependently relaxed rat aorta contracted with phenylephrine, KCl, U-46619, endothelin and 5-hydroxytryptamine, with EC50s of 7.4 +/- 1.6, 10.5 +/- 2.3, 14.3 +/- 3.3, 11.8 +/- 2.0 and 13.6 +/- 3.7 microM, respectively. 3. Isoliquiritigenin caused endothelium-independent relaxation of phenylephrine-precontracted rat aortic rings. Neither NG-monomethyl-L-arginine (L-NMMA) (an inhibitor of the L-arginine-NO pathway) nor oxyhaemoglobin (which binds NO) modified the relaxant effect of isoliquiritigenin. The relaxant action of isoliquiritigenin also persisted in intact aorta in the presence of indomethacin or glibenclamide. However, methylene blue, an inhibitor of soluble guanylate cyclase, abolished relaxation induced by isoliquiritigenin. 4. Incubation of rat aorta with isoliquiritigenin not only increased aortic cyclic GMP content but also caused small increases in aortic cyclic AMP content, and greatly potentiated the increases in cyclic AMP observed in the presence of forskolin. The maximum increase in cyclic GMP by isoliquiritigenin was reached earlier than the increase in cyclic AMP. This result suggests that the increases in cyclic GMP caused by isoliquiritigenin might stimulate the accumulation of cyclic AMP. 5. Concentration-dependent increases in soluble guanylate cyclase activity were observed in isoliquiritigenin (1-100 microM)- or sodium nitroprusside (SNP)-treated rat aortic smooth muscle cells, while adenylate cyclase activity was unchanged in isoliquiritigenin (100 microM)-treated cells. 6. Relaxation and cyclic AMP formation of rat aorta caused by isoliquiritigenin was potentiated in the presence of forskolin (10 nM), which had little effect when given alone. 2',5'-Dideoxyadenosine (DDA,200 microM), an adenylate cyclase inhibitor, diminished the relaxation and cyclic AMP formation of rat aorta by isoliquiritigenin only in the presence of forskolin. DDA did not affect the increases in cyclic GMP formation induced by isoliquiritigenin. These results suggest that elevated levels of cyclic GMP may mediate the majority of the relaxation of the phenylephrine-precontracted aorta induced byisoliquiritigenin, while the synergistic interaction with a low concentration of forskolin depends on an enhanced accumulation of cyclic AMP.7. Relaxation of phenylephrine-precontracted rat aorta and carbachol-precontracted guinea-pig trachea by rolipram (phosphodiesterase, PDE IV inhibitor) was markedly enhanced by isoliquiritigenin, while response to cilostamide (PDE III inhibitor) was not significantly changed by isoliquiritigenin.8. It is concluded that isoliquiritigenin exerts a vasorelaxant effect by activating soluble guanylatecyclase and increasing cyclic GMP. Synergistic effects of isoliquiritigenin and forskolin on muscle relaxation and cyclic AMP accumulation indicate that inhibition of cyclic AMP breakdown by cyclic GMP via the inhibition of PDE III (cyclic GMP-inhibited PDE) is the dominant mechanism.

Relaxation of rat thoracic aorta induced by pyridine

The pharmacological and toxicological activity of pyridine was determined in rat thoracic aorta. Pyridine inhibited norepinephrine (3 microM)-induced phasic and tonic contractions in the thoracic aorta as well as the endothelium-denuded aorta of the rat. The tonic pre-contraction elicited by norepinephrine was also relaxed by the addition of pyridine and this relaxing effect was not affected by indomethacin (20 microM), NG-monomethyl-L-arginine acetate (50 microM) or methylene blue (50 microM). In high-K+ medium (80 mM), pyridine inhibited the Ca2+ concentration-dependent vasocontraction. Moreover, in Ca(2+)-free medium, the norepinephrine (3 microM)-induced phasic contraction was also suppressed by pyridine, while the caffeine (10 mM)-induced contraction remained unaffected. The cAMP and cGMP levels of rat aorta were not changed by pyridine. The 45Ca2+ influx elicited by either norepinephrine or high-K+ was inhibited by pyridine in a concentration-dependent manner. All of these findings indicated that pyridine relaxes rat thoracic aorta by virtue of its Ca2+ channel-blocking properties in vascular smooth muscle.

Na(+)-Ca2+ exchange in intact endothelium of rabbit cardiac valve

A new method of measuring cytoplasmic free Ca2+ ([Ca2+]i) of individual intact cardiovascular endothelial cells by using imaging fluorescence microscopy was designed. Application of agonist to the aortic or pulmonary valve of the rabbit triggered an increase in [Ca2+]i, which depended on the existence of endothelium on the surface of the valve. Under resting conditions, sudden reversal of the Na+ gradient by substituting external Na+ with N-methyl D-glucamine (NMDG) resulted in a [Ca2+]i spike, which then returned toward the resting level. Increasing intracellular Na+ concentration ([Na+]i) by application of ouabain or monensin induced a sustained [Ca2+]i increase. Na+ substitution by NMDG during the agonist- or monensin-induced [Ca2+]i increase gave rise to a further [Ca2+]i spike, which subsequently declined to a level higher than that before removal of external Na+. A selective inhibitor of Na(+)-Ca2+ exchange, 3',4'-dichlorobenzamyl (DCB), abolished the transient [Ca2+]i increase induced by Na+ substitution, and Mg2+, an inorganic inhibitor of Na(+)-Ca2+ exchanger, markedly reduced this transient [Ca2+]i increase. On the other hand, the selective Na(+)-H+ exchanger blocker 5-(N,N-hexamethylene)amiloride (HMA) did not abolish the transient [Ca2+]i increase caused by Na+ substitution. In summary, decreasing the Na+ gradient of the endothelial cells through either receptor stimulation (agonist), Na(+)-K+ pump inhibition (ouabain), pretreatment with Na+ ionophore (monensin), or reversing the Na+ gradient through Na+ substitution (NMDG) all increased [Ca2+]i. This raised [Ca2+]i was antagonized by agents such as DCB or Mg2+, which are thought to inhibit Na(+)-Ca2+ exchange, but not by HMA, an inhibitor of Na(+)-H+ exchange.(ABSTRACT TRUNCATED AT 250 WORDS)

Involvement of von Willebrand factor and PGI2 in platelet binding to a partially denuded endothelial monolayer

Platelet binding to an endothelial monolayer was examined after denudation. The binding increased for up to 10 min and thereafter declined gradually. Antibodies against von Willebrand factor (vWF) inhibited the binding. Production of prostacyclin (PGI2) occurred 10 min after endothelial denudation. This study suggests that vWF is involved in the binding during the first 10 min and that PGI2 suppresses the binding thereafter.

Mechanisms of vasorelaxation induced by N-allylsecoboldine in rat thoracic aorta

N-Allylsecoboldine was shown to be the most effective of several boldine derivatives that were tested for their vasorelaxing effect on the rat aorta. In KCl (60 mmol/l) medium, Ca2+ (0.03-3 mmol/l)-induced vasoconstriction was inhibited, concentration-dependently, by N-allylsecoboldine. The IC50 for N-allylsecoboldine was calculated to be about 4 mumol/l (for a Ca2+ concentration of 1 mmol/l). The vasorelaxant effect on KCl-induced responses was more pronounced at 60 mmol/l KCl than at 15 mmol/l KCl. Contraction of rat aorta in response to phenylephrine (0.01-100 mumol/l) was concentration-dependently inhibited by N-allylsecoboldine and by verapamil (3-30 mumol/l), while contraction in response to B-HT 920, serotonin or PGF2 alpha was not affected. This relaxing effect of N-allylsecoboldine persisted in endothelium-denuded aorta. In cultured A10 vascular smooth muscle cells, N-allylsecoboldine and verapamil displaced the binding of [3H]-prazosin (Ki values = 0.4 +/- 0.2 and 0.6 +/- 0.2 mumol/l, respectively). The increase of inositol monophosphate caused by phenylephrine in rat aorta was completely suppressed by chloroethylclonidine, but only slightly inhibited by N-allylsecoboldine and by verapamil. Glibenclamide or charybdotoxin did not affect the relaxation induced by N-allylsecoboldine of aortic rings precontracted with phenylephrine. Neither the cGMP nor the cAMP content was changed by N-allylsecoboldine. We conclude that N-allylsecoboldine relaxes the rat aorta by blocking Ca2+ channels and that it also has an antagonistic effect at alpha 1-adrenoceptors.

Vasorelaxing effect in rat thoracic aorta caused by laurotetanine isolated from Litsea cubeba Persoon

The pharmacological effects of laurotetanine on rat isolated thoracic aorta were examined. The contraction of aortic rings caused by high potassium (60 mM) and cumulative concentrations of calcium (0.03-3 mM) was inhibited by 3-50 microM laurotetanine in a dose-dependent manner with an IC50 value of 19.8 +/- 3.6 microM (n = 6) in a 1 mM Ca2+ medium. The phenylephrine (3 microM)-induced contraction was also inhibited by laurotetranine. Its effect was more marked on the tonic contraction than on the phasic contraction and was not easily washed-out. On addition of laurotetanine during the tonic contraction, relaxation could also be observed. This relaxing effect was not antagonized by indomethacin (20 microM) and was still seen in denuded aorta or in the presence of nifedipine (1 microM). The caffeine (20 mM)-induced contraction was not affected by laurotetanine. cAMP and cGMP levels of aorta were not changed by laurotetanine. It is concluded that laurotetanine relaxed the rat thoracic aorta mainly by suppressing the Ca2+ influx through both voltage- and receptor-operated calcium channels.

Mechanisms by which Candida albicans induces endothelial cell prostaglandin synthesis

One strategy for improving resistance to opportunistic pathogens is to determine host cellular responses during the invasion process and upregulate those responses that are relevant to host defense mechanisms. Within this context, we have shown previously that invasion of endothelial cells by Candida albicans in vitro causes increased production of prostaglandins. As a prerequisite for modulating endothelial cell prostaglandin production, we now characterize the mechanisms through which this process occurs. Endothelial cell invasion by C. albicans appeared to stimulate the conversion of arachidonic acid into prostaglandins by upregulating the synthesis of endothelial cell cyclooxygenase and increasing the activity of the endothelial cell phospholipase. The enhanced activities of these two enzymes were independent of calphostin C-sensitive protein kinase C and resulted in the increased production and extracellular secretion of prostaglandin I2 (PGI2), PGF2 alpha, and PGE2. The secretion of these prostaglandins had no effect on the amount of endothelial cell injury induced by C. albicans. The role of the increased prostaglandin secretion by endothelial cells is likely related to modulation of the leukocyte response at the candida-leukocyte-endothelial cell interface.

Relaxation of rat thoracic aorta induced by 2,2',2''-tripyridine

The pharmacological and toxicological activity of 2,2',2''-tripyridine was determined in rat thoracic aorta. 2,2',2''-Tripyridine inhibited norepinephrine (3 microM)-induced phasic and tonic contractions in the thoracic aorta as well as the endothelium-denuded aorta of the rat. The tonic pre-contraction elicited by norepinephrine was also relaxed by the addition of 2,2',2''-tripyridine and this relaxing effect was not affected by indomethacin (20 microM) but partially antagonized by methylene blue (50 microM). In high-K+ medium (80 mM), 2,2',2''-tripyridine inhibited the Ca2+ concentration dependent vasocontraction. Moreover, in Ca(2+)-free medium, the phasic contraction induced by either norepinephrine (3 microM) or caffeine (10 mM) was also suppressed by 2,2',2''-tripyridine. Although the cAMP level of rat aorta was not changed by 2,2',2''-tripyridine, cGMP level was significantly increased by 2,2',2''-tripyridine. The increase in cGMP level caused by 2,2',2''-tripyridine was completely blocked by methylene blue (50 microM). The 45Ca2+ influx elicited by either norepinephrine or high-K+ was inhibited by 2,2',2''-tripyridine. All of these findings indicate that 2,2',2''-tripyridine relaxes rat thoracic aorta by virtue of its Ca(2+)-channel blocking properties and by elevating cGMP levels in vascular smooth muscle.

Pharmacological activity of (-)-discretamine, a novel vascular alpha-adrenoceptor and 5-hydroxytryptamine receptor antagonist, isolated from Fissistigma glaucescens

1. The pharmacological activity of (-)-discretamine, isolated from Fissistigma glaucescens, was determined in rat isolated thoracic aorta, cardiac tissues and ventricular myocytes and guinea-pig isolated trachea. 2. (-)-Discretamine was found to be an alpha 1-adrenoceptor blocking agent in rat thoracic aorta as revealed by its competitive antagonism of noradrenaline (pA2 = 7.20 +/- 0.10)- or phenylephrine (pA2 = 7.60 +/- 0.09)-induced vasoconstriction. It was as potent as phentolamine (pA2 = 7.51 +/- 0.10), but was more potent than yohimbine (pA2 = 6.18 +/- 0.06). Removal of endothelium significantly increased the antagonistic potency of (-)-discretamine on noradrenaline (pA2 = 7.52 +/- 0.09)- or phenylephrine (pA2 = 7.90 +/- 0.09)-induced vasoconstriction. 3. (-)-Discretamine was also an alpha 2-adrenoceptor blocking agent (pA2 = 6.30 +/- 0.15) and a 5-hydroxytryptamine antagonist (pA2 = 6.87 +/- 0.06), both in rat aorta denuded of endothelium. 4. (-)-Discretamine protected alpha-adrenoceptors from alkylation by the irreversible blocking agent, phenoxybenzamine. 5. [3H]-inositol monophosphate formation caused by noradrenaline (3 microM) in rat thoracic aorta was suppressed by (-)-discretamine (10 and 30 microM) and prazosin (3 microM). 6. A high concentration of (-)-discretamine (30 microM) did not affect the contraction induced by the thromboxane receptor agonist U-46619, prostaglandin F2 alpha (PGF2 alpha), angiotensin II, high K+ or endothelin in rat aorta denuded of endothelium. Neither cyclic AMP nor cyclic GMP content of rat thoracic aorta was changed by (-)-discretamine. 7. Contraction of guinea-pig trachea caused by histamine, leukotriene C4 or carbachol was not affected by (-)-discretamine (30 microM). (-)-Discretamine also did not block beta l- or beta2-adrenoceptor-mediated responses induced by isoprenaline in rat right atria and guinea-pig trachea.8. A voltage clamp study in rat ventricular single myocytes revealed that sodium inward current, slow inward Ca2+ current or transient (ItO) and steady state (I800) outward current was not affected by(-)-discretamine (30 microM).9. It is concluded that (-)-discretamine is a selective x-adrenoceptor and 5-HT receptor antagonist in vascular smooth muscle.

Ca(2+)-channel blockade in rat thoracic aorta by crychine isolated from Cryptocarya chinensis Hemsl

The pharmacological effects of crychine, isolated from Cryptocarya chinensis Hemsl, on rat thoracic aorta were examined. In the high-K+ medium (60 mM), Ca2+ (0.03-3 mM)-induced vasoconstriction was inhibited by crychine in a concentration-dependent manner (10-100 micrograms mL-1). Increasing the incubation time from 5 to 30 min did not cause more pronounced inhibitory effect on KCl-induced contraction. The tonic contractions elicited by KCl (60 mM) and Bay K 8644 (0.1 microM) were also relaxed by the addition of crychine and were more marked in the 1.9 mM than in the 5 mM Ca2+ medium. The noradrenaline concentration-response curves were antagonized non-competitively by crychine (10-100 micrograms mL-1). At the plateau of noradrenaline-induced tonic contraction, the addition of crychine also caused relaxation. This relaxing effect of crychine was not antagonized by indomethacin (20 microM) or methylene blue (50 microM), and was still present in denuded aorta or in the presence of nifedipine (2 microM). Caffeine (10 mM)-induced contraction and cAMP or cGMP levels were not affected by crychine. It is concluded that crychine relaxes the rat thoracic aorta mainly by suppressing the Ca2+ influx through both voltage- and receptor-operated calcium channels.

Hypoxia-induced activation of endothelial cells as a possible cause of venous diseases: hypothesis

Blood stasis in leg veins is a situation commonly linked to the development of venous diseases such as varicoses. Such a stasis will provoke an ischemia, thus decreasing oxygen availability to tissues. Owing to its localization between blood and tissue, endothelium is the first target of this insult. The authors develop here a hypothesis in which the effect of oxygen deprivation on the functional state of the endothelium is the starting point of a cascade of events leading to the disorganization of the vessel wall typical of these pathologies. When venous human endothelial cells obtained from umbilical cords (HUVEC) are exposed to hypoxic conditions they become activated without change in their viability. The synthesis of a proinflammatory molecule (PAF, platelet-activating factor) and the adhesion of human polymorphonuclear neutrophils (PMN) on HUVEC are markedly increased during hypoxia incubation. These two processes are related to a calcium-dependent activation of endothelial cells due to a decrease of adenosine triphosphate (ATP) availability during hypoxia. Adherence of neutrophils to endothelial cells is the first step of diapedesis, which leads to the infiltration of these cells in the media of the veins, where they affect the smooth muscle cells and the connective tissue, leading to tissue alterations typical of the venous pathologies. The authors propose that this sequential process which originates from a reduction in oxygen availability and which involves different cell type as one main cause of the venous disorders, in addition to genetic, hormonal, and mechanical factors.