Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “ENDOTHELIUM”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources
PubMed2000

Nitric oxide mediated endothelium-dependent relaxation induced by glibenclamide in rat isolated aorta.

OBJECTIVES: Glibenclamide was found to act as both a selective ATP-sensitive K(+) channel blocker and a vasorelaxant. The exact mechanisms underlying the relaxant effect of glibenclamide are unknown. The present study was designed to examine the role of endothelium/nitric oxide in glibenclamide-induced relaxation in rat isolated aortic rings. METHODS: A combination of experimental approaches including isometric force measurement, cell culture, Ca(2+) fluorescence measurement and radioimmunoassay were used to examine the vascular effect of glibenclamide. RESULTS: Glibenclamide induced a concentration-dependent relaxation more effectively in rings with endothelium (IC(50) of 32+/-4 microM) than those without endothelium (IC(50) of 365+/-29 microM). Incubation with N(G)-nitro-L-arginine methyl ester (L-NAME) or methylene blue significantly reduced and L-arginine (3 mM) potentiated the glibenclamide-induced relaxation. L-Arginine (3 mM) partially antagonized the effect of L-NAME. Glibenclamide (100 microM) increased the cyclic GMP content of endothelium-intact tissues. Pretreatment with N(G)-nitro-L-arginine (100 microM) or removal of endothelium significantly suppressed the effect of glibenclamide on cyclic GMP production. Glibenclamide elevated the intracellular Ca(2+) levels in cultured rat aortic endothelial cells. Glibenclamide also inhibited the endothelium-independent contractile response to 60 mM K(+) (IC(50) of 137+/-21 microM) and caused a rightward shift in the concentration-contraction curve for CaCl(2). Besides, glibenclamide inhibited phorbol-12,13-diacetate (1 microM)-induced contraction in Ca(2+)-free Krebs solution. CONCLUSION: These results indicate that glibenclamide-induced endothelium-dependent relaxation involves nitric oxide release and this effect may be related to its stimulatory effect on endothelial Ca(2+) levels. However, the glibenclamide-induced endothelium-independent relaxation may be associated with its inhibitory effect on Ca(2+) influx through Ca(2+) channels and on the protein kinase C-mediated contractile mechanism.

Animals↗
PubMed1998

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.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2002

Medroxyprogesterone acetate does not antagonize estrogen-induced increases in endothelium-dependent vasodilation: potential clinical implications.

OBJECTIVE: Determine the effect of combined 17beta-estradiol benzoate (E2) and medroxyprogesterone acetate (MPA) administration on endothelium-dependent vasorelaxation to acetylcholine (ACh). DESIGN: Prospective, ex vivo study. SETTING: Academic research laboratory. ANIMAL(S): Mature female rats. INTERVENTION(S): Ovariectomized rats received one of the following interventions daily for 3 days: [1] corn oil via IM injection, [2] E2 (20 microg/kg IM), or [3] E2 (20 microg/kg IM) and MPA (10 mg/kg IM). MAIN OUTCOME MEASURE(S): Basal release of nitric oxide (NO) and endothelium-dependent and endothelium-independent vasodilation from thoracic aortas obtained from each group. RESULT(S): Estradiol treatment potentiated the endothelium-dependent relaxation to ACh when compared with the control group. Administration of MPA with E2 did not antagonize the beneficial effect of E2 on endothelium-dependent relaxation. Estradiol treatment alone or in combination with MPA did not affect endothelium-independent vasodilation as compared with the case of the control group. Administration of E2 resulted in increased basal NO release (assessed indirectly by measuring the constrictor response to N(G)-nitro-L-arginine [methyl ester (L-NAME)]) when compared with the case of the control group, and the addition of MPA to E2 did not alter the effect of E2 on basal NO release. CONCLUSION(S): Estradiol potentiates endothelium-dependent relaxant responses and increases basal endothelial NO release. Medroxyprogesterone acetate does not antagonize these effects of E2.

Acetylcholine↗
PubMed2001

A simple method for culturing mouse vascular endothelium.

Vascular endothelium is an important site for a wide array of immunological processes such as inflammation, atherosclerosis and allograft rejection. Culture methods of mouse vascular endothelium would provide an important in vitro correlate to immunological murine in vivo models. We describe a simple method to culture mouse vascular endothelium from thoracic aorta. Our cultured cells express typical phenotypic (CD105, CD31, CD106), morphological and ultrastructural (intercellular junctions, Weibel-Palade bodies) markers of vascular endothelium. They also possess functional receptors for uptake and processing of acetylated low-density lipoproteins. The mouse vascular endothelium within our system expresses high levels of MHC class I and MHC class II after activation with IFN-gamma. In addition, these cells express the accessory molecules CD80 and CD54, while they lack constitutive expression of CD86 and CD40, providing them the means to function as antigen presenting cells. Alloreactive CD4(+) and CD8(+) T lymphocytes demonstrate evidence of DNA synthesis after co-culture with activated vascular endothelium indicating their commitment to proliferation. In conclusion, we describe a simple culture system to isolate and grow mouse vascular endothelium, which provides a powerful tool to study biological interactions in vitro.

Animals↗
PubMed2003

Impaired endothelium-derived hyperpolarizing factor-mediated relaxation in porcine pulmonary microarteries after cold storage with Euro-Collins and University of Wisconsin solutions.

BACKGROUND: Endothelium plays an important role in mediating the function of transplanted organs. The widely used University of Wisconsin solution impairs the endothelium-derived hyperpolarizing factor-mediated relaxation in coronary arteries, but little is known about effects of lung preservation on endothelium-derived hyperpolarizing factor-mediated endothelial function. This study examined the effect of organ preservation solutions on the endothelium-derived hyperpolarizing factor-mediated relaxation in the pulmonary microarteries (diameter 200 to 450 microm). METHODS: Two segments (1 as control) from the same microartery were allocated in 2 chambers of a myograph. After incubation with hyperkalemia (potassium 115 mmol/L), University of Wisconsin, or Euro-Collins solution (at 4 degrees C for 4 hours), the endothelium-derived hyperpolarizing factor-mediated relaxation was induced by bradykinin (-10 to -6.5 log M, n = 8) or calcium ionophore (A(23187), -9 to -5.5 log M, n = 7) in U(46619) (-7.5 log M) precontracted rings in the presence of indomethacin (7 micromol/L), N(G)-nitro-L-arginine (300 micromol/L), and oxyhemoglobin (20 micromol/L). RESULTS: Exposure to hyperkalemia and storage with Euro-Collins or University of Wisconsin solution significantly decreased the relaxation to bradykinin (51.9 +/- 8.4% vs 60.3 +/- 6.1%, P =.02 or 49.3 +/- 7.3% vs 65.2 +/- 3.5%, P =.04) or A(23187) (12.5 +/- 0.02% vs 33.8 +/- 0.07%, P =.02 or 13.2 +/- 0.03% vs 31.0 +/- 0.05%, P =.03%). CONCLUSIONS: Endothelium-derived hyperpolarizing factor plays an important role in porcine pulmonary microarteries, and the endothelium-derived hyperpolarizing factor-mediated relaxation is impaired when the lung is preserved with University of Wisconsin or Euro-Collins solution. This impairment may affect the lung function during the reperfusion period after lung transplantation.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1996

Effects of cardiopulmonary bypass and circulatory arrest on endothelium-dependent vasodilation in the lung.

Endothelial injury with failure of pulmonary endothelium-dependent vasodilatation has been proposed as a possible cause for the increased pulmonary vascular resistance observed after cardiopulmonary bypass, but the mechanisms underlying this response are not understood. An in vivo piglet model was used to investigate the role of endothelium-dependent vasodilatation in postbypass pulmonary hypertension. The pulmonary vascular responses to acetylcholine, a receptor-mediated endothelium-dependent vasodilator, and nitric oxide, an endothelium-independent vasodilator, were studied in one group of animals after preconstriction with the thromboxane A2 analog U46619 (n = 6); a second group was studied after bypass with 30 minutes of deep hypothermic circulatory arrest (n = 6). After preconstriction with U46619, both acetylcholine and nitric oxide caused significant decreases in pulmonary vascular resistance (34% +/- 6% decrease, p = 0.007, and 39% +/- 4% decrease, p = 0.001). After cardiopulmonary bypass with circulatory arrest, acetylcholine did not significantly change pulmonary vascular resistance (0% +/- 8% decrease, p = 1.0), whereas nitric oxide produced a 32% +/- 4% decrease in pulmonary vascular resistance (p = 0.007). These results demonstrate a loss of receptor-mediated endothelium-dependent vasodilatation with normal vascular smooth muscle function after circulatory arrest. Administration of the nitric oxide synthase blocker Ngamma-nitro-L-arginine-methyl-ester after circulatory arrest significantly increased pulmonary vascular resistance; thus, although endothelial cell production of nitric oxide may be diminished, it continues to be a major contributor to pulmonary vasomotor tone after cardiopulmonary bypass with deep hypothermic circulatory arrest. In summary, cardiopulmonary bypass with deep hypothermic circulatory arrest results in selective pulmonary endothelial cell dysfunction with loss of receptor-mediated endothelium-dependent vasodilatation despite preserved ability of the endothelium to produce nitric oxide and intact vascular smooth muscle function.

Animals↗
PubMed2001

Effects of the ethanolic extract of Spirulina maxima on endothelium dependent vasomotor responses of rat aortic rings.

Dietary Spirulina decreases, endothelium-dependently, the responses to vasoconstrictor agonists and increases the endothelium-dependent, agonist-induced, vasodilator responses of rat aorta rings. The aim of this study was to analyze, in vitro, the effects of a raw ethanolic extract of Spirulina maxima on the vasomotor responses of rat aortic rings to phenylephrine and to carbachol. On rings with endothelium, the extract produced the following effects: (a) a concentration-dependent (60-1000 microg/ml) decrease of the contractile response to phenylephrine; (b) a rightward shift and a decrease in maximal developed tension, of the concentration--response curve to phenylephrine; (c) a concentration dependent relaxation of phenylephrine-precontracted rings. These effects were blocked by L-NAME, and not modified by indomethacin. The extract had no effect on the concentration-response curve to carbachol of rings with endothelium. On endothelium-denuded rings the extract caused a significant rightward shift of the concentration response curve to phenylephrine without any effect on maximal tension development. In the presence of the extract, indomethacin induced a marked decrease in the maximal phenylephrine-induced tension of endothelium-denuded rings. These results suggest that the extract increases the basal synthesis/release of NO by the endothelium and, also, the synthesis/release of a cyclooxygenase-dependent vasoconstricting prostanoid by vascular smooth muscle cells.

Animals↗
PubMed1997

HMG-CoA reductase inhibitors decrease CD11b expression and CD11b-dependent adhesion of monocytes to endothelium and reduce increased adhesiveness of monocytes isolated from patients with hypercholesterolemia.

OBJECTIVES: This study sought to determine whether inhibitors of 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase affect CD11b expression and adhesiveness of monocytes in vitro and after treatment of patients with hypercholesterolemia. BACKGROUND: HMG-CoA reductase inhibitors improve survival of patients with coronary heart disease (CHD) and prevent CHD in hypercholesterolemic men. Because these drugs have been shown to modulate monocyte functions, they may act by reducing monocyte adhesion to endothelium, which is crucial in atherogenesis. METHODS: Isolated human blood monocytes were subjected to flow cytometric detection of CD11b and adhesion assays on fixed human endothelial cells after treatment with lovastatin in vitro or ex vivo before and after treatment of hypercholesterolemic patients with HMG-CoA reductase inhibitors. RESULTS: The integrin heterodimer CD11b/CD18 expressed on monocytes interacts with intercellular adhesion molecule-1 on endothelium and is involved in monocyte adhesion to endothelium. Treatment of monocytes with lovastatin in vitro slightly and dose dependently reduced surface expression of CD11b on monocytes. Moreover, lovastatin inhibited CD11b-dependent adhesiveness to fixed endothelium of unstimulated monocytes or monocytes stimulated with monocyte chemotactic protein 1. Coincubation with mevalonate, but not with low density lipoprotein (LDL), reversed the effects of lovastatin, suggesting that early cholesterol precursors, but not cholesterol, are crucial for adhesiveness of CD11b. In hypercholesterolemic patients, adhesion of isolated monocytes to endothelium ex vivo was dramatically increased over values in healthy control subjects. Treatment of these patients with the HMG-CoA reductase inhibitors lovastatin or simvastatin (20 to 40 mg/day) for 6 weeks slightly decreased total and LDL cholesterol plasma levels and monocyte CD11b surface expression but resulted in a significant reduction of monocyte adhesion to endothelium (p < 0.01, n = 7). CONCLUSIONS: The reduction of CD11b expression and inhibition of CD11b-dependent monocyte adhesion to endothelium may crucially contribute to the clinical benefit of HMG-CoA reductase inhibitors in CHD, independent of cholesterol-lowering effects.

Cell Adhesion↗
PubMed1997

Leukotriene C4 from vascular endothelium enhances neutrophil adhesiveness.

We have examined the synthesis of leukotriene C4 from bovine aortic and pulmonary artery endothelium. Under basal conditions, neither aortic nor pulmonary artery endothelium revealed significant amounts of hydroxy fatty acids. Following incubation with ionophore A23187, several peaks including one which co-migrated with authentic LTC4 could be demonstrated from both aortic and pulmonary endothelium. LTC4 production was maximal after 30 min incubation, was inhibitable by the lipoxygenase inhibitor nordihydroguairetic acid, and was synthesized by bovine endothelium from tritiated arachidonic acid substrate. The putative LTC4 from endothelium was shown to be identical to authentic LTC4 by chromatography and scanning UV spectroscopy. Endothelial-derived LTC4 increased the adherence of bovine aortic endothelium for neutrophils in a concentration dependent pattern similar to authentic LTC4. These data suggest that vascular endothelium may influence leukocyte-endothelial interactions through synthesis of biologically active arachidonic acid metabolites such as LTC4.

Animals↗
PubMed2002

Endothelium-derived mediators and hypoxic pulmonary vasoconstriction.

The vascular endothelium synthesises, metabolises or converts a multitude of vasoactive mediators, and plays a vital role in the regulation of pulmonary vascular resistance. Its role in hypoxic pulmonary vasoconstriction (HPV) is however controversial. Although HPV has been demonstrated in both pulmonary arteries where the endothelium has been removed and isolated pulmonary artery smooth muscle cells, many reports have shown either partial or complete dependence on an intact endothelium for sustained HPV (> approximately 20 min). However, despite many years of study no known endothelium-derived mediator has yet been unequivocally shown to be essential for HPV, although several may either facilitate the response or act as physiological brakes to limit the extent of HPV. In this article we review the evidence for and against the role of specific endothelium-derived mediators in HPV. We make the case for a facilitatory or permissive function of the endothelium, that in conjunction with a rise in smooth muscle intracellular Ca(2+) initiated by a mechanism intrinsic to smooth muscle, allows the development of sustained HPV. In particular, we propose that in response to hypoxia the pulmonary vascular endothelium releases an as yet unidentified agent that causes Ca(2+) sensitisation in the smooth muscle.

Animals↗
PubMed1997

Hypoxic dilatation of porcine small coronary arteries: role of endothelium and KATP-channels.

1. The aim of the present study was to determine the cellular mechanims and potential mediators involved in hypoxic dilatation of porcine small coronary arteries. 2. Small coronary arteries were isolated from a branch of the left anterior descending artery of porcine hearts, cannulated with glass micropipettes and studied in a perfusion myograph system. At a transmural pressure of 40 mmHg, the arteries had an internal diameter of 167.8 +/- 6.6 microns (n = 37). 3. In arteries contracted with acetylcholine (ACh), hypoxia (0% O2, 30 min) caused dilatation (86.9 +/- 6.7% relaxation, n = 6) in vessels with endothelium but constriction in endothelium-denuded vessels. 4. Hypoxic vasodilatation occurring in arteries with endothelium was abolished by the KATP channel inhibitor, glibenclamide (0.44 microM), but was not affected by inhibition of nitric oxide synthase (L-NAME, 44 microM) or cyclo-oxygenase (indomethacin, 4.4 microM). 5. Bradykinin evoked endothelium-dependent relaxation that was inhibited by L-NAME (44 microM) but not glibenclamide 0.44 microM). Cromakalim (0.1-0.3 microM), a KATP channel opener, caused relaxation that was inhibited by glibenclamide, but was not affected by L-NAME (44 microM) and/or indomethacin (4.4 microM). 6. Endothelium-removal inhibited vasodilatation evoked by cromakalim, but increased vasodilator responses to the NO donor, SIN-1 (10(-8) to 10(-5) M). 7. These results indicate that hypoxia acted directly on vascular smooth muscle of small coronary arteries to cause contraction. However, this effect was overwhelmed by endothelium-dependent relaxation in response to hypoxia. This relaxation was most likely mediated by release of an endothelium-derived factor, distinct from nitric oxide or prostacyclin, that activated smooth muscle KATP-channels.

Animals↗
PubMed1997

Synergistic interaction between endothelium-derived NO and prostacyclin in pulmonary artery: potential role for K+ATP channels.

1. The aim of the present study was to assess interactions between nitric oxide (NO) and prostacyclin (PGI2) during endothelium-dependent relaxations evoked by bradykinin, calcium ionophore (A23187) and acetylcholine in canine isolated pulmonary artery. 2. Relaxations to low concentrations of bradykinin and A23187 were abolished by combined inhibition of NO-synthase (by N omega-nitro-L-arginine methyl ester L-NAME, 30 microM) and cyclo-oxygenase (indomethacin, 10 microM), suggesting mediation by NO and PGI2. The individual contributions of NO and PGI2 to the dilator responses were quantified by use of areas above the separate indomethacin-insensitive and L-NAME-insensitive components of the concentration-effect curves, respectively. Individually, NO and PGI2 accounted for only 53 +/- 5% and 16 +/- 9% of total bradykinin-induced relaxation, and 46 +/- 10% and 20 +/- 9% of total A23187-induced relaxation, suggesting that NO and PGI2 acted synergistically to cause endothelium-dependent relaxation. 3. Relaxation to low concentrations of acetylcholine was abolished by L-NAME but not affected by indomethacin, suggesting the response was mediated solely by NO with no interaction from PGI2. 4. Glibenclamide (1 microM), an inhibitor of ATP-sensitive potassium (K+ATP) channels, inhibited responses to bradykinin or A23187 but did not affect relaxations evoked by acetylcholine. Glibenclamide did not affect endothelium-independent relaxations to PGI2 or the NO-donor, 3-morpholinosydnonimine (SIN-1). 5. With bradykinin, glibenclamide attenuated total relaxation by 49 +/- 8%, but did not alter the individual NO and PGI2-mediated components of the response. Glibenclamide abolished the synergistic interaction between endothelium-derived NO and PGI2. 6. At high concentrations, bradykinin, A23187 or acetylcholine caused endothelium-dependent relaxation that was insensitive to L-NAME + indomethacin. With bradykinin or A23187, this component of relaxation was inhibited by glibenclamide, whereas with acetylcholine, glibenclamide had no effect. 7. The synergistic interaction between endothelium-derived NO and PGI2 in canine pulmonary artery is mediated by activation of K+ATP channels, presumably by an endothelium-derived hyperopolarizing factor (EDHF). The pattern of endothelial dilator mediators and the presence of this synergistic interaction is dependent on the nature of the endothelial stimulus.

Adenosine Triphosphate↗
PubMed1998

Endothelium-dependent sensory NANC vasodilatation: involvement of ATP, CGRP and a possible NO store.

1 Non-adrenergic non-cholinergic (NANC) vasodilator nerves regulate tone in certain vascular beds. We have investigated the mechanisms of the NANC dilator response in the isolated small mesenteric artery of the rabbit by use of the tension myograph. 2 Small second or third order (150-300 microm in diameter) arteries of the rabbit mesenteric bed were mounted in a Mulvany tension myograph. Responses to electrical field stimulation (EFS) and exogenous vasodilators were investigated. 3 EFS (0.5-16 Hz, 10 V, 0.3 ms for 5 s), in the presence of guanethidine (5 microM) and atropine (1 microM) produced frequency-dependent relaxation of small arteries. Pretreatment with tetrodotoxin (1 microM) abolished the relaxation and desensitization with capsaicin (10 microM) strongly inhibited the relaxation. 4 Pretreatment with a P2Y-purinoceptor antagonist, basilen blue (3 microM) or a human calcitonin gene-related peptide (hCGRP) receptor antagonist, hCGRP8-37 (1 microM) suppressed the NANC relaxation by approximately 40-60 % in each case and combined pretreatment almost abolished the relaxation. 5 The EFS-induced relaxation was suppressed by endothelium-removal, pretreatment with the soluble guanylyl cyclase inhibitor ODQ (1 microM) and the NO scavenger oxyhaemoglobin (OxyHb; 20 microM) but not by NO synthase inhibitors NG-nitro-L-arginine methyl ester (L-NAME; 300 microM) or NG-nitro-L-arginine (L-NOARG; 300 microM). Combined pretreatment with ODQ and CGRP8-37 almost abolished the relaxation. 6 A P2Y-purinoceptor agonist, 2-methylthio ATP, produced endothelium-dependent relaxation which was inhibited by L-NAME and ODQ (1 microM), whilst hCGRP produced endothelium-independent and ODQ-insensitive relaxation. 7 Ultraviolet light (320 nm, 5 shots over 20 s) produced relaxation that was blocked by both OxyHb and ODQ but not by NG-monomethyl-L-arginine (L-NMMA, 300 microM). 8 The present study suggests that EFS-induced NANC relaxation of the mesenteric small artery of the rabbit is mediated mainly by capsaicin-sensitive sensory C-fibres and that both ATP and CGRP are involved. The action of ATP released by EFS appears to be endothelium-dependent and involve activation of soluble guanylyl cyclase, but is resistant to inhibitors of NO synthase. The response to CGRP is endothelium-independent. These results show that ATP and CGRP account fully for the NANC relaxation of this vessel type and that the endothelium is involved in NANC-induced relaxation. The endothelium-dependent part of the response is consistent with the release of NO, either from NO synthase, incompletely inhibited by the NO synthase inhibitors, or by some preformed stores.

Adenosine Triphosphate↗
PubMed1998

Epoxyeicosatrienoic acids, potassium channel blockers and endothelium-dependent hyperpolarization in the guinea-pig carotid artery.

1. Using intracellular microelectrodes, we investigated the effects of 17-octadecynoic acid (17-ODYA) on the endothelium-dependent hyperpolarization induced by acetylcholine in the guinea-pig isolated internal carotid artery with endothelium. 2. In the presence of Nomega-nitro-L-arginine (L-NOARG, 100 microM) and indomethacin (5 microM) to inhibit nitric oxide synthase and cyclo-oxygenase, acetylcholine (1 microM) evoked an endothelium-dependent hyperpolarization which averaged -16.4 mV starting from a resting membrane potential of -56.8 mV. There was a negative correlation between the amplitude of the hyperpolarization and the absolute values of the resting membrane potential. 3. The acetylcholine-induced endothelium-dependent hyperpolarization was not altered by charybdotoxin (0.1 microM) or iberiotoxin (30 nM). It was partially but significantly reduced by apamin (0.5 microM) to -12.8+/-1.2 mV (n=10) or the combination of apamin plus iberiotoxin (-14.3+/-3.4mV, n=4). However, the combination of charybdotoxin and apamin abolished the hyperpolarization and under these conditions, acetylcholine evoked a depolarization (+ 7.1+/-3.7 mV, n = 8). 4. 17-ODYA (10 microM) produced a significant hyperpolarization of the resting membrane potential which averaged -59.6 mV and a partial but significant inhibition of the acetylcholine-induced endothelium-dependent hyperpolarization (-10.9 mV). 5. Apamin did not modify the effects of 17-ODYA but in the presence of charybdotoxin or iberiotoxin, 17-ODYA no longer influenced the resting membrane potential or the acetylcholine-induced hyperpolarization. 6. When compared to solvent (ethanol, 1% v/v), epoxyeicosatrienoic acids (EpETrEs) (5,6-, 8,9-, 11,12- and 14,15-EpETrE, 3 microM) did not affect the cell membrane potential and did not relax the guinea-pig isolated internal carotid artery. 7. These results indicate that, in the guinea-pig internal carotid artery, the involvement of metabolites of arachidonic acid through the cytochrome P450 pathway in endothelium-dependent hyperpolarization is unlikely. Furthermore, the hyperpolarization mediated by the endothelium-derived hyperpolarizing factor (EDHF) is probably not due to the opening of BK(Ca) channels.

8,11,14-Eicosatrienoic Acid↗
PubMed1998

Roles of calcium-activated and voltage-gated delayed rectifier potassium channels in endothelium-dependent vasorelaxation of the rabbit middle cerebral artery.

1. The cellular mechanism(s) of action of endothelium-derived vasodilator substances in the rabbit middle cerebral artery (RMCA) were investigated. Specifically, the subtypes of potassium channels involved in the effects of endothelium-derived relaxing factors (EDRFs) in acetylcholine (ACh)-induced endothelium-dependent vasorelaxation in this vessel were systematically compared. 2. In the endothelium-intact RMCA precontracted with histamine (3 microM), ACh induced a concentration-dependent vasorelaxation, which was sensitive to indomethacin (10 microM) or N(G)-nitro-L-arginine (L-NOARG; 100 microM); pD2 values 8.36 vs 7.40 and 6.38, P < 0.01 for both, n = 6 and abolished by a combination of both agents. ACh caused relaxation in the presence of high K+ PSS (40 mM KCl), which was not affected by indomethacin, but abolished by L-NOARG and a combination of indomethacin and L-NOARG. 3. In the presence of indomethacin, relaxation to ACh in the endothelium-intact RMCA precontracted with histamine was unaffected by either glibenclamide (10 microM), an ATP-sensitive K+ channel (K[ATP]) blocker, 4-aminopyridine (4-AP, 1 mM) or dendrotoxin (DTX, 0.1 microM), delayed rectifier K channel (Kv) blockers. However, relaxation responses to ACh were significantly inhibited by either LY83583 (10 microM) and 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 10 microM), guanylyl cyclase inhibitors, or charybdotoxin (CTX; 0.1 microM), iberiotoxin (ITX, 0.1 microM) and apamin (APA, 0.1 microM), large conductance Ca2+-activated K+ channels (BK[Ca]) blocker and small conductance Ca2+-activated K+ channel (SK[Ca]) blocker, respectively. 4. In the presence of L-NOARG, relaxation to ACh was unaffected by glibenclamide or the cytochrome P450 mono-oxygenase inhibitor, clotrimazole (1 microM), but was significantly inhibited by either 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ 22,536, 10 microM) and 2',3'-dideoxyadenosine (2',3'-DDA, 30 microM), adenylyl cyclase inhibitors, or 4-AP, DTX, CTX, ITX and APA. 5. In the endothelium-denuded RMCA precontracted with histamine, authentic NO-induced relaxation was unaffected by glibenclamide, 4-AP and DTX, but significantly reduced by ODQ, ITX and APA. Authentic prostaglandin I2 (PGI2)-induced relaxation was unaffected by glibenclamide, but significantly reduced by 2',3'-DDA, 4-AP, DTX, ITX and APA. Forskolin-induced relaxation was significantly inhibited by high K+, CTX and 4-AP. 6. These results indicate that: (1) in the RMCA the EDRFs released by ACh are NO and a prostanoid (presumably PGI2), and there is no evidence for the release of a non-NO/PGI2 endothelium-derived hyperpolarizing factor (EDHF), (2) K(Ca) channels are involved in NO-mediated relaxation of the RMCA but both K(Ca) and Kv channels are involved in PGI2-mediated relaxation.

Acetylcholine↗
PubMed1998

Cannabinoid CB1 receptor and endothelium-dependent hyperpolarization in guinea-pig carotid, rat mesenteric and porcine coronary arteries.

1. The purpose of these experiments was to determine whether or not the endothelium-dependent hyperpolarizations of the vascular smooth muscle cells (observed in the presence of inhibitors of nitric oxide synthase and cyclo-oxygenase) can be attributed to the production of an endogenous cannabinoid. 2. Membrane potential was recorded in the guinea-pig carotid, rat mesenteric and porcine coronary arteries by intracellular microelectrodes. 3. In the rat mesenteric artery, the cannabinoid receptor antagonist, SR 141716 (1 microM), did not modify either the resting membrane potential of smooth muscle cells or the endothelium-dependent hyperpolarization induced by acetylcholine (1 microM) (17.3 +/- 1.8 mV, n = 4 and 17.8 +/- 2.6 mV, n = 4, in control and presence of SR 141716, respectively). Anandamide (30 microM) induced a hyperpolarization of the smooth muscle cells (12.6 +/- 1.4 mV, n = 13 and 2.0 +/- 3.0 mV, n = 6 in vessels with and without endothelium, respectively) which could not be repeated in the same tissue, whereas acetylcholine was still able to hyperpolarize the preparation. The hyperpolarization induced by anandamide was not significantly influenced by SR 141716 (1 microM). HU-210 (30 microM), a synthetic CB1 receptor agonist, and palmitoylethanolamide (30 microM), a CB2 receptor agonist, did not influence the membrane potential of the vascular smooth muscle cells. 4. In the rat mesenteric artery, the endothelium-dependent hyperpolarization induced by acetylcholine (1 microM) (19.0 +/- 1.7 mV, n = 6) was not altered by glibenclamide (1 microM; 17.7 +/- 2.3 mV, n = 3). However, the combination of charybdotoxin (0.1 microM) plus apamin (0.5 microM) abolished the acetylcholine-induced hyperpolarization and under these conditions, acetylcholine evoked a depolarization (7.7 +/- 2.7 mV, n = 3). The hyperpolarization induced by anandamide (30 microM) (12.6 +/- 1.4 mV, n = 13) was significantly inhibited by glibenclamide (4.0 +/- 0.4 mV, n = 4) but not significantly affected by the combination of charybdotoxin plus apamin (17.3 +/- 2.3 mV, n = 4). 5. In the guinea-pig carotid artery, acetylcholine (1 microM) evoked endothelium-dependent hyperpolarization (18.8 +/- 0.7 mV, n = 15). SR 141716 (10 nM to 10 microM), caused a direct, concentration-dependent hyperpolarization (up to 10 mV at 10 microM) and a significant inhibition of the acetylcholine-induced hyperpolarization. Anandamide (0.1 to 3 microM) did not influence the membrane potential. At a concentration of 30 microM, the cannabinoid agonist induced a non-reproducible hyperpolarization (5.6 +/- 1.3 mV, n = 10) with a slow onset. SR 141716 (1 microM) did not affect the hyperpolarization induced by 30 microM anandamide (5.3 +/- 1.5 mV, n = 3). 6. In the porcine coronary artery, anandamide up to 30 microM did not hyperpolarize or relax the smooth muscle cells. The endothelium-dependent hyperpolarization and relaxation induced by bradykinin were not influenced by SR 141716 (1 microM). 7. These results indicate that the endothelium-dependent hyperpolarizations, observed in the guinea-pig carotid, rat mesenteric and porcine coronary arteries, are not related to the activation of cannabinoid CB1 receptors.

Animals↗
PubMed2000

An indirect influence of phenylephrine on the release of endothelium-derived vasodilators in rat small mesenteric artery.

1. The possibility that stimulation of smooth muscle alpha(1)-adrenoceptors modulates contraction via the endothelium was examined in rat small mesenteric arteries. 2. N(omega)-nitro-L-arginine methyl ester, (L-NAME, 100 microM to inhibit NO synthase) increased contraction to single concentrations of phenylephrine (1 - 3 microM) by approximately 2 fold (from a control level of 14.2+/-3.0 to 34. 1+/-4.2% of the maximum contraction of the artery, n=20). The action of L-NAME was abolished by disrupting the endothelium. 3. The subsequent addition of apamin (to inhibit small conductance Ca(2+)-activated K(+) channels, 50 nM) further augmented phenylephrine contractions, in an endothelium-dependent manner, to more than 3 fold above control (50.4+/-5.3% of the maximum contraction, n=11). 4.Charybdotoxin (non-selective inhibitor of large conductance Ca(2+)-activated K(+) channels, BK(Ca), 50 nM) plus L-NAME augmented the level of phenylephrine contraction to 4 - 5-fold above control (64.1+/-3.1%, n=5), but this effect was independent of the endothelium. The potentiation of contraction by charybdotoxin could be mimicked with the selective BK(Ca) inhibitor, iberiotoxin,. 5. Apamin together with L-NAME and charybdotoxin further significantly increased the phenylephrine contraction by 5 - 6-fold, to 79.9+/-3.5% of the maximum contraction of the artery (n=13). 6. Phenylephrine failed directly to increase the intracellular Ca(2+) concentration in endothelial cells freshly isolated from the small mesenteric artery. 7. Stimulation of smooth muscle alpha(1)-adrenoceptors in the mesenteric artery induces contraction that is markedly suppressed by the endothelium. The attenuation of contraction appears to reflect both the release of NO from the endothelium and the efflux of K(+) from both endothelial and smooth muscle cells. This suggests that the release of NO and endothelium-derived hyperpolarizing factor can be evoked indirectly by agents which act only on the smooth muscle cells.

Adrenergic alpha-1 Receptor Agonists↗
PubMed2002

Oxygen-derived free radicals mediate endothelium-dependent contractions to acetylcholine in aortas from spontaneously hypertensive rats.

Experiments were designed to investigate whether or not oxygen-derived free radicals mediate endothelium-dependent contractions to acetylcholine in the aorta of spontaneously hypertensive rat (SHR). Isometric tension was measured in aortic rings taken from adult male SHR and Wistar-Kyoto rat (WKY) in the presence of NG-nitro-L-arginine. Endothelium-dependent contractions to acetylcholine were significantly greater in rings from SHR compared to WKY. Oxygen-derived free radicals, generated from xanthine plus xanthine oxidase, induced contractions that were larger in aortas from SHR than from WKY. Contractions to acetylcholine and free radicals were abolished by a selective TP-receptor antagonist, S 18886, and a preferential inhibitor of cyclo-oxygenase-1, valeryl salicylate, but not by a preferential inhibitor of cyclo-oxygenase-2, NS-398. Allopurinol, deferoxamine and the combination of superoxide dismutase plus catalase inhibited the contractions to oxygen-derived free radicals but did not significantly affect those to acetylcholine. In contrast, diethyldithiocarbamic acid, an inhibitor of superoxide dismutase, or Tiron, a scavenger of superoxide anion, reduced endothelium-dependent contractions to acetylcholine in aortas from SHR. The effect of these two drugs was additive. In SHR chronically treated with dimethylthiourea endothelium-dependent contractions to acetylcholine were decreased, and reduced further by acute in vitro exposure to deferoxamine or the combination of superoxide dismutase plus catalase. These results suggest that in the SHR aorta acetylcholine-induced endothelium-dependent contractions involve endothelial superoxide anion production and the subsequent dismutation into hydroxyl radicals and/or hydrogen peroxide. The free radicals activate cyclo-oxygenase-1, most likely to produce endoperoxides. Activation of TP-receptors is required to observe endothelium-dependent contractions to acetylcholine or endothelium-independent contractions in response to free radical generation.

Acetylcholine↗