前列腺素而非一氧化氮是鳟主动脉内皮细胞舒血管因子(英文)

AIM:To identify the type of prostanoids produced by endothelial cells of trout aorta and to determine whether or not the smooth muscle responds to nitric oxide. METHODS:Ventral aortas, with and without endotheli-um from rainbow trout (S gairdneri), were incubated in a buffered salt solution. RESULTS:Addition of the calcium ionophore A23187 caused a significant increase in prostaglandin E's and a consistent increase in the stable metabolite of prostacyclin (6-keto-prostaglandin F1a) in the incubation media only when the endothelium was present. This production was inhibited by methylene blue (10umol/L). In rings of trout aorta without endothelium suspended for the measurement of isometric force in organ chambers,prostacyclin and prostaglandin E1 but not prostaglandin E2 caused concentration-dependent decreases in tension when the rings were contracted with acetyl-choline. The smooth muscle did not relax to nitric oxide but did so to sodium nitroprusside. Relaxations to the latter nitrovasodilator were no     

（—）Epicatechin induces and modulates endotheliumdependent relaxation in isolated rat mesenteric artery rings

AIM:The present study was aimed to examine the role of endothelial nitric oxide in the relaxant response to green tea (-)epicatechin and its modulation of endothelium-mediated relaxation in the isolated rat mesenteric artery rings.METHODS:Changes in the isometric tension were measured with Grass force-displacement transducers.RESULTS:The (-)epicatechin-induced relaxation was largely dependent on the presence of intact endothelium and was reversed by N^G-nitro-L-arginine methyl ester 10μmol/L or methylene blue 10μmol/L,the inhibitors of nitric oxidemediated relaxation.L-Arginine at 1mmol/L antagonized the effect of L-NAME or methylene blue.Pretreatment of endothelium-intact rings with (-)epicatechin 10μmol/L enhanced the relaxation induced by endothelium-dependent vasodilator,acetylcholine,while this concentration did not influence the endothelium-independent relaxation induced by sodium nitroprusside in the endothelium-denuded artery rings.CONCLUSION:The results indicate that the endothelium-dependent vasodilation by (-)epicatechin is mainly mediated through nitric oxide and low concentration of (-)epicatechin augments endothelium-dependent vasorelaxation in the rat mesenteric arteries.     

Effect of pravastatin on impaired endothelium-dependent relaxation induced by lysophosphatidylcholine in rat aorta

Aim: To investigate the effects of pravastatin, a potent 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, on impaired endothelium-dependent relaxation induced by lysophosphatidylcholine (LPC), the major component of oxidized low-density lipoprotein, in rat thoracic aorta. Methods: Both the endothelium-dependent relaxation response to acetylcholine and the endotheliumindependent relaxation response to sodium nitroprusside of aortic rings were measured by recording isometric tension after the rings were exposed to LPC in the absence or presence of pravastatin to estimate the injury effect of LPC and the protective effect of pravastatin on the aortic endothelium, respectively. Results: Exposure of aortic rings to LPC (1-10μmol/L) for 30 min induced a significant concentration-dependent inhibition of endothelium-dependent relaxation to acetylcholine, but did not affect endothelium-independent relaxation in response to sodium nitroprusside. Pre-incubation of aortic rings with pravastatin (0.3-3mmol/L) for 15 min and then co-incubation of the rings with LPC (3 μmol/L) for another 30 min significantly attenuated the inhibition of endothelium-dependent relaxation induced by LPC. This protective effect of pravastatin (1 mmol/L) was abolished by N^G-nitro-L-arginine methyl ester (30 μmol/L), an inhibitor of nitric oxide synthase, but not by indomethacin (10 μmol/L), an inhibitor of cyclooxygenase. Moreover, protein kinase C inhibitor chelerythrine (1μmol/L) the superoxide anion scavenger superoxide dismutase (200 kU/L), and the nitric oxide precursor L-arginine (3 mmol/L) also improved the impaired endotheliumdependent relaxation induced by LPC, similar to the effects of pravastatin.C onclusion: Pravastatin can protect the endothelium against functional injury induced by LPC in rat aorta, a fact which is related to increasing nitric oxide bioavailability.     

Role of endothelium/nitric oxide in vascular response to flavonoids and epicatechin

AIM: To examine the role of endothelium in the vascular responses to flavonoids, baicalein, baicalin, cardamonin, alpinetin, and to purified jasmine green tea (-)epicate-chin in the isolated rat mesenteric artery rings. METHODS: The isometric contraction was measured by Grass force-displacement transducers. RESULTS: Both baicalein and baicalin enhanced the phenylephrine-induced contractile response in the endothelium-intact rings. This enhancement was abolished by pretreatment with the nitric oxide inhibitor NG-nitro-L-arginine or in the absence of the endothelium. Both flavonoids also inhibited the acetylcholine-induced endothelial nitric oxide-dependent relaxation. In contrast, cardamonin, alpinetin or (-)epicatechin induced both endothelium-dependent and -independent relaxation. NG-nitro-L-arginine meyhyl ester or endothelium denudation attenuated the endothelium-dependent relaxation to the same extent. CONCLUSION: Baicalein and baicalin enhanced the phenylephrine-induced contraction most likely thro     

Protective effects of cariporide on endothelial dysfunction induced by high glucose

Aim: To explore the effects of cariporide, a selective sodium-hydrogen antiporter inhibitor, on endothelial dysfunction induced by high glucose. Methods: Acetylcholine (ACh)-induced endothelium-dependent relaxation (EDR), sodium nitroprusside (SNP)-induced endothelium-independent relaxation and biochemical parameters including malondialdehyde (MDA), superoxide dismutase (SOD), and nitric oxide (NO) were measured in rat isolated aorta. Results: A 6-h incubation of aortic rings with high glucose (44 mmol/L) resulted in a significant inhibition of EDR, but had no effects on endothelium-independent relaxation. After the 6-h incubation of aortic rings in the co-presence of cariporide (0.01, 0.1, and 1μmol/L) with high glucose, cariporide prevented the inhibition of EDR caused by high glucose in concentration-dependent manners. Similarly, high glucose decreased SOD activity and contents of NO, and increased MDA concentration in aortic tissue. Cariporide (1 μmol/L) significantly resisted the decrease of NO content and SOD activity, and elevation of MDA concentration caused by high glucose in aortic tissues. Mannitol (44 mmol/L) or cariporide (1μmol/L) alone had no effect on EDR, endothelium-independent relaxation and biochemical parameters. Conclusion: Cariporide significantly prevented endothelial dysfunction induced by high glucose. The mechanisms of endothelial dysfunction induced by high glucose may involve the activation of sodium-hydrogen antiporter and the generation of oxygen-free radicals, but it is not related to the change of osmolarity.     

Rilmenidine prevents blood pressure increase in rats with compromised nitric oxide production

AIM: To search tools of high blood pressure in the model of nitric oxide (NO)-defective hypertension, and thestudy focused on the effect of rilmenidine, agonist of imidazoline receptors, which was suggested to modulatecentral sympathetic outflow. METHODS: Three experimental groups, each consisting of 7 rats, were used: (I) ratswith inhibition of NO synthase (NOS) by Nr-nitro-L-arginine methyl ester (L-NAME) 40 mg.kg-~.d~ for 4 weeks indrinking water, (II) rats with inhibited NOS as in group I, plus agonist of imidazoline receptors rilmenidine 3mg.kg^-1.d^-1 for 4 weeks by garage, and (Ⅲ) control rats. Systolic blood pressure was measured weekly noninvasively.At the end of experiment aortic ring isometric tension was followed, NOS expression (aorta, left ventricle), andNOS activity (left ventricle and brain) were determined. RESULTS: In the group I systolic blood pressure in-creased significantly, aortic ring relaxation to acetylcholine was significantly attenuated. Rilmenidine administeredsimultaneously with L-NAME (group II) prevented the increase of blood pressure which did not differ significantlyfrom control values; aortic ring relaxation to acetylcholine did not differ from control. No change in NOS expres-sion (aorta and left ventricle) was found in groups I and II. Significant decline in NOS activity (left ventricle andbrain) was found in groups I and II. CONCLUSION: Rilmenidine has a remarkable role in NO-defective hypertension,possibly by inhibiting central sympathetic outflow and by affecting receptors in vascular smooth muscle also. Theprime cause of hypertension in this experimental model - the compromised production of NO due to inhibition ofNOS - was not affected by rilmenidine.     

环GMP抑制的环AMP磷酸二酯酶产生的内皮源性NO的基础释放促进前列环素引起的小猪肺动脉舒张(英文)

AIM: To study the interactions between prostacyclin and endothelium-derived nitric oxide in porcine pulmonary arteries. METHODS: Rings of 5th order of porcine pulmonary arteries were studied in vitro for the measurement of tension and the content in cyclic nucleotides. RESULTS: Prostacyclin, given exogenously, caused en-dothelium-potentiated relaxations (inhibition of phenyle-phrine contraction) that were inhibited by the inhibitors of the L-arginine nitric oxide pathway, oxyhemoglobin and Nω-nitro-L-arginine. These inhibitors did not affect the tension in rings without endothelium. Cyclic GMP-con-centrations were not increased above basal concentrations in the presence of prostacyclin. Increases were seen with acetylcholine and sodium nitroprusside. Prostacyclin-stimulated cyclic AMP concentrations did not reach statistical significance compared to controls. The addition of 8-bromo-cyclic GMP to prostacyclin, however, increased the cyclic AMP content. The nitric oxide synthase inhibitor, nitro-L-argin     

Chronic 17β-estradiol augments relaxant role of basal nitric oxide in blood vessels from rats with heart failure

The effects of chronic 17β-estradiol on endothelium-dependent relaxation to acetylcholine (ACh) and contraction to N ^G-nitro-l-arginine methyl ester (l-NAME), and endothelium-independent relaxation to sodium nitroprusside (SNP) were examined on blood vessels from rats with chronic heart failure (CHF). Two groups of ovariectomized female (50–60 days) rats were implanted with pellets containing 17β-estradiol (25 μg/day) or vehicle, and given ligation of the left main coronary artery 1 week later. Another group of ovariectomized rats was implanted with vehicle pellets, and sham-operated. After 7 weeks, thoracic aortic rings, pulmonary artery rings, and portal vein strips were prepared for in vitro studies. Relative to sham-operated rats treated with the vehicle, vessels from vehicle-treated, coronary-ligated rats had similar relaxation to ACh and SNP but reduced response to l-NAME that was significant (P<0.05) for the aorta and portal vein but not pulmonary artery. Treatment of ligated rats with 17β-estradiol augmented responses to l-NAME in the aorta, pulmonary artery and portal vein to values above those in sham-operated rat. 17β-Estradiol did not affect relaxation of any vessels to SNP and increased maximum relaxation to ACh only in the portal vein. Hence, 17β-estradiol enhances the relaxant role of basal nitric oxide in CHF. Received: 17 June 1998 / Accepted: 21 September 1998     

Neurotransmitter release evoked by α-latrotoxin in the smooth muscle of the female pig urethra

Neuronal regulation of smooth muscle tone in the female pig urethra has mainly been studied in vitro using electrical field stimulation (EFS) of nerves. Excitatory control is considered to be exerted by released noradrenaline, whereas inhibitory control is non-adrenergic non-cholinergic (NANC), and mediated by nitric oxide (NO), and an as yet unidentified agent. We investigated the functional and morphological effects of α-latrotoxin (αLTX), a spider neurotoxin believed to cause massive release of vesicle-stored neurotransmitters, on spontaneously developed urethral smooth muscle tone. The effects were compared to those of EFS and high potassium. In the presence of the NO-synthesis inhibitor N^ω-nitro-L-arginine (L-NOARG: 0.3 mM) both αLTX and EFS evoked contractions. After treatment with scopolamine and phentolamine, no contraction was observed, and under these conditions αLTX and EFS induced relaxation. At low frequencies (<12 Hz), the EFS-induced relaxations were rapid, whereas at higher frequencies (>12 Hz), they were biphasic, consisting of a rapid first phase followed by a more long-lasting second phase. L-NOARG abolished the relaxations at low frequencies, as well as the first phase of the biphasic relaxation. The second phase was not affected by treatment with L-NOARG, but 0.1 μM ω-conotoxin GVIA, blocker of N-type voltage-operated calcium- channels (VOCCs), markedly reduced or abolished the response. In the presence of L-NOARG or ω-conotoxin GVIA, the αLTX-induced relaxation was significantly decreased, and the combination of L-NOARG and ω-conotoxin GVIA further reduced or abolished the relaxation. In preparationstreated with tetrodotoxin or scorpion venom, believed to inactivate nerves by acting on sodium channels, αLTX and EFS had no effects. αLTX-induced relaxation was not associated with changes in cyclic GMP or cyclic AMP content. High (80 mM) potassium solution induced a triphasic response of the preparation. A transient relaxation was followed by a restoration of tone, and then by a persistent relaxation. The persistent relaxation was slightly reduced by scorpion venom or L-NOARG, but reduced by 50% by a combination of L-NOARG and ω-conotoxin GVIA. Ultrastructural analysis of the urethral circular smooth muscle layer revealed a moderate amount of nerve profiles supplying the smooth muscle. In control preparations, the nerve profiles contained both small synaptic vesicles and large dense core vesicles. αLTX caused a major loss of both types of vesicle. The present data suggest that αLTX has the ability to release not only adrenergic and cholinergic transmitters, but also NANC mediators of relaxation, including NO, from nerve terminals in the urethra. Received: 13 January 1997 / Accepted: 17 April 1997     

Role of gap junctions in endothelium-derived hyperpolarizing factor-mediated vasodilatation in rat renal artery

AIM: To investigate the effects of gap junction inhibitors on endothelium-derived but nitric oxide (NO)- and prostacyclin (PGI2)-independent vasodilatations induced by carbachol in the rat isolated renal artery. METHODS: Isolated renal arteries were mounted on a wire myograph apparatus were tissues treated with the nitric oxide synthase inhibitor N^ω-nitro-L-arginine methyl ester hydrochloride (NAME; 100 μmol/L) and indomethacin (10 μmol/L) and precontracted with phenylephrine (0.1 μmol/L). NAME and indomethacin treated Carbachol (0.01-10 μmol/L)- or sodium nitroprusside (SNP; 1-300 nmol/L)-induced mediated relaxations were observed in the presence of gap junction inhibitors. RESULTS: Carbachol produced a concentration-dependent relaxation in tissues treated with NAME (100 μmol/L) and indomethacin (10 μmol/L). This relaxation was not affected by hemoglobin (3 μmol/L), but was inhibited by charybdotoxin (200 nmol/L) and ouabain (30 μmol/L). The putative gap junction inhibitors, GAP 27 peptides with sequence homology to connexins 40 and 43 respectively reduced carbachol- but not SNP-induced relaxations mediated by endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxations. The inhibition by the connexin 43 inhibitor was greater than that of the connexin 40 inhibitor. CONCLUSION: The results indicate the presence of gap junctions sensitive to 43^GAP 27 and 43^GAP 27 in the rat renal artery and each of these different types of gap junctions plays a role in the NO- and PGI2-independent relaxations induced by carbachol in this blood vessel. However, connexin 43 appears to play a more predominant role in mediating gap junction communications in the rat renal artery.     

镰状细胞对内皮诱导一氧化氮的清除能力低下

AIM: To assess the ability of sickle cells to interfere with the release or transfer of endothelium-derived relaxing factor (EDRF) in comparison to normal erythrocytes. METHODS: A perfusion-superfusion bioassay system was used a canine carotid artery with endothelium (donor of EDRF) and a ring of the same vessel without endothelium (detector) were separated by tubing resulting in a five second interval for transfer of EDRF from donor to detector. Changes in isometric tension were monitored in both the donor and the detector preparations. Release of EDRF, as determined by sustained relaxations during the contractions to phenylephrine, was induced by infusing acetylcho-line through the donor artery. RESULTS: Supervision with normal and sickle erythrocytes caused impairment of the endothelium-dependent relaxations in both detector and donor tissues. When infused through the transfer line, sickle cells were less potent than normal erythrocytes in inhibiting relaxation in the detector tissues. In contrast, i     

Differential mechanisms of urethral smooth muscle relaxation by several NO donors and nitric oxide

We have examined the mechanisms of action of a broad spectrum of nitric oxide (NO) donors, including several S-nitrosothiols, sodium nitroprusside (SNP) and nitroglycerine (GTN), in relation to their relaxant activity of urethral smooth muscle. For all the compounds examined, NO release (in solution and in the presence of urethral tissue), relaxation responses, elevations in cGMP levels and the effect of thiol modulators were evaluated and compared with the effect of NO itself. Whilst all NO donors, except GTN, released NO in solution due to photolysis or chemical catalysis, this release was not correlated with their relaxant activity in sheep urethral preparations, which were furthermore not affected by the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (cPTIO; 0.3 mM). A substantial NO-generating activity was found for S-nitroso-L-cysteine (CysNO) and S-nitroso-N-acetyl-D,L-penicillamine (SNAP) in the presence of urethral cytosolic fractions, suggesting metabolic activation to NO in the cytosol of the target tissue. In contrast, NO generation from S-nitroso-N-acetyl-L-cysteine (N-ac-CysNO), S-nitrosoglutathione (GSNO) and SNP were reduced by the presence of urethral homogenate and/or subcellular fractions, suggesting direct NO transfer to tissue constituents. NO donors and NO gas induced dissimilar degrees of cGMP accumulation in urethral tissue, while they were essentially equipotent as urethral relaxants. Furthermore, 1H-[1,2,4]-oxadiazole-[4,3-a]-quinoxalin-1-one (ODQ; 10 μM) inhibited both relaxation and cGMP accumulations, but with different potency for the different compounds. Oxidation of sarcolemmal thiol groups with 5-5′-dithio-bis[2-nitrobenzoic acid] (DTNB; 0.5 mM) enhanced relaxations to GSNO, an effect that was reversed by dithiotreitol (DTT; 1 mM), suggesting a direct effect through nitrosylation/oxidation reactions at the cell membrane, while relaxations to NO and to all the other compounds were not affected by these treatments. Finally, photodegradation of SNP induced the formation of a stable intermediate that still evoked NO-cGMP-mediated relaxations. This indicates that the assumption that SNP is fully depleted of NO by exposure to light should be revised. It can be concluded that important differences exist in the mechanisms by which distinct NO donors relax urethral smooth muscle and they cannot be regarded simply as NO-releasing prodrugs. Received: 28 December 1998 / Accepted: 14 April 1999 / Published online: 22 June 1999     

转换酶抑制剂培哚普利拉非激肽酶依赖性地加强由激肽引起的内皮依赖性血管松弛

The present study examined whether or not the resistance to degradation of bradykinin analogs affects the kinin-potentiating action of the inhibitor of converting enzyme, perindoprilat. METHODS: Hydrolysis of [Hyp3,Tyr(Me)8]-bradykinin by ACE present in isolated canine coronary arteries was assessed by determination of peptide metabolites using electrospray mass spectrometry, and compared to that of bradykinin. Contractions and relaxations of isolated rings of coronary arteries, with and without endothelium, were recorded as changes in isometric force. RESULTS: After a 30 min incubation, most of the bradykinin was degraded by the arteries, while less than 10 % of [Hyp3 Tyr(Me)8]-bradykinin was hydrolysed. In organ chambers, [Hyp3, Tyr(Me)8]-bradykinin like bradykinin caused relaxations of isolated canine coronary arteries with endothelium that could be attributed to both NO and endothelium-derived hyperpolarizing factor (EDHF). Perindoprilat caused a comparable leftward shift in the concentration-relaxa     

Effects of resveratrol,curcumin and their derivatives on the activation of microglia induced by LPS

Objective To determine the inhibitory effects of 21 resveratrol derivatives and 3 natural curcuminoids on lipopolysaccharide(LPS)-induced Nitric oxide(NO)and tumor necrosis factor-alpha(TNF-α)production in microglia and their structure-activity relationships.Methods Cell viability was evaluated by the MTT reduction assay.Accumulation of nitrite(NO2-)in culture supernatant fluids was measured by the Griess reaction.Sodium nitroprusside(SNP)(2.5 mM)solution was used to determine the scavenging activities of these compounds.The levels of TNF-α in the culture medium were measured by using an ELISA kit.Semi-quantitative RT-PCR analysis was used to determine the mRNA levels of inducible NOS(iNOS)and TNF-α.Results It was found,for the first time,that certain resveratrol derivatives that have 3,5-dimethoxyl groups in the A-ring,such as(E)-4-(3,5-dimethoxystyryl)phenol(pterostilbene,compound 2),or have substituted the B-ring of resveratrol with quinolyl,such as(E)-5-[2-(quinolin-4-yl)vinyl]benzene-1,3-diol(compound 18)and(E)-4-(3,5-dimethoxystyryl)quinoline(compound 19),strongly inhibited NO production.Compounds 2,18,and 19 reduced LPS-induced protein and mRNA expression of inducible NO synthase(iNOS),but did not display direct NO-scavenging activity up to 30 μM in sodium nitroprusside(SNP)solution.Moreover,compounds 2,18,and 19 could also significantly inhibit the production of TNF-α by LPS-activated microglia.Furthermore,we found the demethoxy derivatives of curcumin have more potent inhibition activity on NO and TNF-α releasing in activated-microglia.Conclusions In the present study we compared the activated-microglia inhibition effect of resvertrol,curcumin and their derivatives and provided a glance of the structure-activity relationships of these compounds,the information is beneficial to design new potent compounds which can provide better therapeutic implications for various neurodegenerative diseases.     

Nitric oxide and ATP co-mediate the NANC relaxant response in the guinea-pig taenia caeci

The effect of the nitric oxide synthase inhibitor N ^G-nitro-l-arginine (l-NOARG; 100 μM) and the P₂ purinoceptor antagonist pyridoxalphosphate-6-azophenyl-2’,4’-disulfonic acid (PPADS; 50 μM) was investigated on the non-adrenergic, non-cholinergic (NANC) relaxant response of the guinea-pig isolated taenia caeci to electrical field stimulation at 1 or 10 Hz, under isotonic recording conditions. Either drug alone caused an about 50% inhibition, while combining the two drugs nearly abolished the response at both frequencies. The inhibitory effect of l-NOARG (100 μM) was partly reversed by l-arginine (30 mM). PPADS, but not l-NOARG, inhibited the relaxant effect of exogenous ATP, but not that of the nitric oxide donor sodium nitroprusside. It is concluded that both nitric oxide and ATP are involved in the mediation of NANC relaxation in the taenia caeci, in an apparently additive manner. Received: 23 June 1998 / Accepted: 3 July 1998     

高浓度曲马朵通过内皮依赖与非依赖机制诱导家兔主动脉舒张(英文)

AIM: The mechanism of tramadol-induced vasodilation was investigated using isolated rabbit thoracic aortic rings. METHODS: Aortic rings from 8 rabbits were placed in organ bath and precontracted with phenylephrine(10~(-5) mol/L) before addition of tramadol. Relaxation responses by tramadol were evaluated in the presence and absence of endothelium, indomethacin (an inhibitor of cyclooxygenase), N~G-nitro-L-arginine methyl ester (L-NAME, a specific inhibitor of nitric oxide synthase), glibenclamide (an inhibitor of ATP-sensitive potassium channels), tetraethylammonium chloride (TEA, an inhibitor of calcium-sensitive potassium channels), and naloxone (an antagonist of opioid receptors). RESULTS: Tramadol(10~(-4) mol/L and 3×10~(-4) mol/L) caused significant vasodilation in endothelium-intact and endothelium-denuded aortic rings (P<0.05). The relaxation response to tramadol was significantly greater in endothelium-intact rings than in endothelium-denuded rings. Pretreatment of aortic rings with indomethaci     

Effects of tetrandrine on smooth muscle contraction induced by mediators in pulmonary hypertension

AIM: In attempt to characterize tetrandrine on pulmonary hypertension, biological activities induced by a range of mediators implicated in the pathogenesis of pulmonary hypertension were investigated. METHODS: Pulmonary artery rings and tracheal segments were contracted with couples of bioactive substances in which a series experi-ments including effects of tetrandrine on calcium agonist, endothelin, thromboxane A2, angiotensin II, neuropeptide Y, histamine, 5-methyl furmethide were performed, the influences of tetrandrine in the concentration of 1 to 30 μmol/L were investigated. RESULTS: Tetrandrine inhibited calcium agonist BayK8644, endothelin-1 and throm-boxane A2 mimetic U46619, angiotensin II- and neuropeptide Y-induced contractile responses with depression of the maximal contraction of pulmonary artery rings in a varying extent. Tetrandrine inhibited leukotriene E4-induced concentration-response curve in a competitive antagonist manner with a pKB of (5.29 ±0.11) without any influence leukotrien     

抗高血压中草药罗布麻NO释放作用的内皮保护作用和机制（英文）

OBJECTIVE The extracts of the Apocynum venetumleaves(AVLE),also known as Luobuma,is an antihypertensive medicinal herb used widely in TCM.AVLE has been reported to exert antihypertensive action by dilating the blood vessels in an endothelium-dependent and concentration-dependent manner with optimal effect seen at as low as 10μg·mL.The present study seeks to further evaluate the free radical scavenging actions and cellular mechanism underlying the nitric oxide(NO)-releasing property of AVLE in rat aorta and human umbilical vein endothelial cells(HUVECs).METHODS Endothelium-dependent relaxation induced by AVLE was assessed in organ chambers in the presence or absence of NG-nitro-L-arginine(LNAME,100μmol·L-1),endothelial NO synthase inhibitor(eNOS),ODQ(1μmol·L-1),soluble guanylyl cyclase inhibitor,polyethyleneglycol catalase(PP2,20μmol·L-1),inhibitor of Src kinase and wortmannin(30nmol·L-1),and LY294002(20μmol·L-1),PI3-Kinase inhibitor.Total nitrite and nitrate(NOx)level were measured by Greiss reagent.The cellular effects of AVLE was tested in HUVECs at different concentration with or without inhibitors.The phosphorylation level of Akt and eNOS were assessed by Western blotting.RESULTS In the rat aorta,AVLE(0.3-10μg·mL-1)dose-dependently inhibited the contraction to phenylephrine(1μmol·L-1)and significantly suppressed theβ-NADPH-induced generation of superoxide anion(SOA).Removal of endothelium,treatment with L-NAME or ODQ prevented the vasorelaxant effects of AVLE.Similarly,pre-treatment with PP2,wortmannin and LY294002 reduced the vasorelaxant effects of AVLE.AVLE significantly increased of total NOx level in rat aorta compared to control.It also caused phosphorylation of AKT and eNOS in cultured HUVECs in a dose-dependent manner and which were markedly suppressed by PP2,wortmannin and LY294002.CONCLUSION The present results suggest that the vasorelaxant effect of AVLE is due to its dual ability of releasing NO and protecting it from the scavenging actions of the SOA.Furthermore,AVLE causes endothelium-dependent NO mediated relaxations of rat aortas through Src/PI3K/Akt dependent NO signalling pathway.     

Activators of protein kinase A induce a glibenclamide-sensitive 86Rb+ efflux in rat isolated aorta

The effect of activators of protein kinase A on membrane K⁺ permeability and the interaction of these compounds with cromakalim, an opener of ATP-sensitive K⁺ channels (K_ATP channels), were investigated. Membrane K⁺ permeability was assessed by measuring ⁸⁶Rb⁺ efflux from rings of rat aorta. Forskolin, an activator of adenylate cyclase, and isobutylmethylxanthine (IBMX), a nonselective phosphodiesterase inhibitor, induced small, concentration-dependent increases in tracer efflux up to 20-40% over the basal level. The effect of forskolin was abolished by the K⁺ channel blocker tedisamil (1 μM) and partially inhibited by glibenclamide (1 μM), a relatively selective blocker of K_ATP channels. Further studies were conducted in the presence of 35mM KCl in the bath in order to increase the size of the ⁸⁶Rb⁺ efflux stimulated by forskolin and IBMX. At high concentrations, these compounds produced a biphasic effect with a peak increase being followed by a lower plateau value. Glibenclamide inhibited the ⁸⁶Rb⁺ efflux response to forskolin and IBMX by 50-80%. The K⁺ channel blockers tedisamil (1 μM), Ba²⁺ (1mM) and tetraethylammonium (10mM) also reduced the peak response to forskolin by about 50% and abolished or greatly inhibited the plateau response. In addition to the small effect on basal ⁸⁶Rb⁺ efflux, forskolin (0.3 μM) increased cromakalim-induced ⁸⁶Rb⁺ efflux 3.4 times. At higher concentrations, however, a concentration-dependent inhibition was observed with an IC₅₀ value of 7.6 ±0.4 μM. 1,9-dideoxyforskolin, which does not increase cAMP, increased neither basal nor cromakalim-induced ⁸⁶Rb⁺ efflux; however, it inhibited cromakalim-stimulated tracer efflux with an IC₅₀ value of 22 ±2 μM. It is concluded that forskolin and IBMX, probably by increasing intracellular cAMP levels, induce a ⁸⁶Rb⁺ efflux from rat aorta, the major part of which is glibenclamide-sensitive and may pass through K_ATP channels. In addition, low concentrations of forskolin greatly facilitate the K_ATP channel opening effect of cromakalim whereas high concentrations block the channel; this blocking effect of forskolin is unrelated to the cAMP elevating action. Received: 25 September 1996 / Accepted: 20 December 1996     

Impairment of nitric oxide-mediated relaxations in anaesthetized autoperfused streptozotocin-induced diabetic rats

This work was designed to determine in vivo the influence of the metabolic control of streptozotocin-induced diabetic rats, measured by the levels of haemoglobin glycosylation in blood (HbA_1c), on developing vascular endothelial dysfunction. For this, the vasoactive responses to basal and stimulated endothelial nitric oxide (NO) were studied using the technique of the anaesthetized autoperfused rat, analyzing the responses to acetylcholine (ACh) and N^G-nitro-l-arginine methyl ester (l-NAME) in non-diabetic and diabetic rats with different degrees of metabolic control (four groups with HbA_1c levels of 5.5–7.4%, 7.5–9.4%, 9.5–12%, and >12%, respectively). When administered over a noradrenaline-induced vasopressor tone, ACh (0.25, 0.75, 2.5, 7.5 and 25 μg kg^-1) induced dose-dependent vasodilatatory responses in all rat groups, reducing both mean arterial pressure and perfusion pressure of the left hindlimb. These responses were similar in non-diabetic and in diabetic rats with good metabolic control (HbA_1c 5.5–7.4%), while diabetic rats with levels of HbA_1c higher than 7.5% showed significantly lower vasodilatatory responses to ACh. In untreated diabetic rats, the relaxant responses evoked by the NO donor sodium nitroprusside were also impaired. On the other hand, increasing doses of l-NAME (0.1 to 10 mg kg^-1) enhanced both mean arterial pressure and left hindlimb perfusion pressure in diabetic and non-diabetic rats. As with ACh, the responses to l-NAME were significantly reduced in diabetic rats with HbA_1c levels higher than 7.5%. To determine the mechanism underlying the NO-mediated endothelial dysfunction, the responses to ACh in untreated diabetic rats (HbA_1c >12%) were studied in the presence of the NO substrate l-arginine, in the presence of the oxygen-derived free radical scavenger superoxide dismutase (SOD), or in the presence of both compounds. Both l-arginine and SOD produced a partial improvement of the ACh-induced vasodilatatory responses, but the effects of these agents were not additive. In this group of animals, SOD also induced a partial recovery of the l-NAME-evoked vasoconstrictions. In non-diabetic and untreated diabetic rats, the plasma levels of NO derivatives and arginine were measured. No significant differences were obtained in the amount of nitrites plus nitrates, while plasma levels of arginine were markedly reduced in the untreated diabetic animals. The results indicate that the endothelial dysfunction associated to diabetes is closely related to the level of metabolic control of the disease. Therefore, it is possible to establish a threshold for developing endothelium impairment from percentages of HbA_1c higher than 7.5%. As the responses to the NO synthase blocker l-NAME were analogously impaired, it is reasonable to suggest that diabetic endothelial dysfunction is related to the interference with mechanisms linked both to stimulated and basal production of NO. We suggest that this interference is partially due to a deficit in the substrate availability for NO and to an increased generation of superoxide anions. Received: 22 December 1997 / Accepted: 20 July 1998