Calcitonin gene-related peptide activates different signaling pathways in mesenteric lymphatics of guinea pigs

The effects of calcitonin gene-related peptide (CGRP) on constriction frequency, smooth muscle membrane potential (V(m)), and endothelial V(m) of guinea pig mesenteric lymphatics were examined in vitro. CGRP (1-100 nM) caused an endothelium-dependent decrease in the constriction frequency of perfused lymphatic vessels. The endothelium-dependent CGRP response was abolished by the CGRP-1 receptor antagonist CGRP-(8-37) (1 microM) and pertussis toxin (100 ng/ml). This action of CGRP was also blocked by the nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine (L-NNA; 10 microM), an action that was reversed by the addition of L-arginine (100 microM). cGMP, adenylate cyclase, cAMP-dependent protein kinase (PKA), and ATP-sensitive K+ (K+(ATP)) channels were all implicated in the endothelium-dependent CGRP response because it was abolished by methylene blue (20 microM), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10 microM), dideoxyadenosine (10 microM), N-[2-(p-bromociannamylamino)-ethyl]-5-isoquinolinesulfonamide-dichloride (H89; 1 microM) and glibenclamide (10 microM). CGRP (100 nM), unlike acetylcholine, did not alter endothelial intracellular Ca2+ concentration or V(m). CGRP (100 nM) hyperpolarized the smooth muscle V(m), an effect inhibited by L-NNA, H89, or glibenclamide. CGRP (500 nM) also caused a decrease in constriction frequency. However, this was no longer blocked by CGRP-(8-37). CGRP (500 nM) also caused smooth muscle hyperpolarization, an action that was now not blocked by L-NNA (100 microM). It was most likely mediated by the activation of the cAMP/PKA pathway and the opening of K+(ATP) channels because it was abolished by H89 or glibenclamide. We conclude that CGRP, at low to moderate concentrations (i.e., 1-100 nM), decreases lymphatic constriction frequency primarily by the stimulation of CGRP-1 receptors coupled to pertussis toxin-sensitive G proteins and the release of NO from the endothelium or enhancement of the actions of endogenous NO. At high concentrations (i.e., 500 nM), CGRP also directly activates the smooth muscle independent of NO. Both mechanisms of activation ultimately cause the PKA-mediated opening of K+(ATP) channels and resultant hyperpolarization.     

Cardiovascular pharmacology of anandamide

The fatty acid amide anandamide produces hypotension and a decrease in systemic vascular resistance in vivo. A drop in blood pressure is also seen with synthetic cannabinoid (CB) receptor agonists. The hypotensive responses to anandamide and synthetic cannabinoids are absent in CB1 receptor gene knockout mice. In isolated arteries and perfused vascular beds, anandamide induces vasodilator responses, which cannot be mimicked by synthetic cannabinoids. Instead, vanilloid receptors on perivascular sensory nerves play a key role in these effects of anandamide. Activation of vanilloid receptors by anandamide triggers the release of sensory neuropeptides such as the vasodilator calcitonin gene-related peptide (CGRP). Anandamide is detected in blood and in many cells of the cardiovascular system, and macrophage-derived anandamide may be involved in several hypotensive clinical conditions. Interestingly, cannabinoid and vanilloid receptors display an overlap in ligand recognition properties, and the frequently used CB1 receptor antagonist SR141716A also inhibits vanilloid receptor-mediated responses. The presence of anandamide in endothelial cells, neurones and activated macrophages (monocytes), and its ability to activate CB and vanilloid receptors make this lipid a potential bioregulator in the cardiovascular system.     

胍丁胺对离体大鼠主动脉张力的影响及其受体机制

采用离体血管环灌流方法,观察了胍丁胺（agmatine,Agm)对大鼠胸主动脉张力的影响,并探讨其受体机制,实验结果如下：（1）在苯肾上腺素PE,10^-6mol/L)引起血管预收缩的 基础上,Agm(10^-7-10^-2mol/L)剂量依赖性地舒张大鼠胸主动脉。（2）上述舒张反应在去除内皮和应用NOS抑制剂N^-G-mnitro-L-arginine methyl ester(L-NAME,0.5mmol/L)后依然存在,提示Agm的舒血管作用为非内皮依赖性,并无NO的参与。（3）在高Ca^2 (3mmol/L)引起血管预收缩的基础上,Agm也可剂量依赖性地舒张大鼠主动脉。（4）预先应用α2－肾上腺素能受体（α2－adrenergic receptor,α2－AR）和咪唑啉受体（IR）阻断剂idazoxan(10^-4mol/L)则可完全阻断Agm的上述作用。（5）应用α2－AR拮抗剂yohimbine(10^-4mol/L)可部分阻断Agm对大鼠主动脉的舒张反应,以上结果表明,Agm对大鼠主动脉血管的舒张作用是由α2－AR和IR共同介导。     

Characterization of the vasorelaxation to methanandamide in rat gastric arteries

In the present study, the relaxant effect of the cannabinoid methanandamide was explored in rat gastric arteries. Since in some vessels cannabinoids have been shown to release calcitonin gene-related peptide (CGRP) from perivascular nerves, the influence of methanandamide was compared with that of exogenous CGRP. Methanandamide and CGRP elicited concentration-dependent, endothelium-independent relaxations. Methanandamide-induced relaxations were unaffected by the CB1 receptor antagonist AM251, the CB2 receptor antagonists AM630 and SR144528, and combined pre-exposure to AM251 and SR144528. Pre-exposure to O-1918, an antagonist of a novel nonCB1/nonCB2 cannabinoid receptor, did not influence the relaxations to methanandamide. Capsaicin or capsazepine treatment slightly inhibited methanandamide-induced relaxations. Preincubation with 30 mmol/L extracellular K+ or 3 mmol/L TEA had no significant effect on the responses elicited by methanandamide, but reduced CGRP-induced relaxations. Relaxation to 10(-5) mol/L methanandamide was significantly blunted by Bay K8644 and by preincubation with nifedipine. Furthermore, 10(-5) mol/L methanandamide significantly inhibited CaCl2-induced contractions in norepinephrine-stimulated vessels previously depleted of intra- and extracellular Ca2+. Finally, preincubation with 10(-5) mol/L methanandamide almost completely abolished high K+-induced contractions. These findings suggest that the vasorelaxant action of methanandamide in rat gastric arteries is not mediated by stimulation of known cannabinoid receptors and only partly related to stimulation of TRPV1 receptors on perivascular nerves. At high concentrations, methanandamide might induce relaxation by reducing calcium entry into the smooth muscle cells.     

Analysis of responses to endothelins in isolated porcine blood vessels by using a novel endothelin antagonist, BQ-153.

We examined the effects of a novel ETA-selective endothelin (ET) antagonist, BQ-153, on vascular responses to ET-1 and ET-3 in isolated porcine coronary and pulmonary blood vessels, to clarify the roles of ET receptor subtypes in the regulation of vascular smooth muscle tension. With endothelium-denuded vascular tissues, the concentration-contraction curve (CCC) for ET-1 appeared as a single sigmoidal shape for all types of tissue. The CCC for ET-1 was antagonized by BQ-153 (2 and 10 microM) in all tissues, but part of the contraction was resistant. The CCC for ET-3 usually consisted of two different phases with higher (first phase) and lower (second phase) sensitivities to the peptide. Only the second phase of CCC for ET-3 was completely inhibited by BQ-153 (2 microM) in all tissues, while the first phase was resistant. The BQ-153-resistant contractile phases of ET-1 and ET-3-induced vasoconstriction appeared to have similar sensitivity in all tissues, and the contractile activity varied with each type of tissue. With endothelium-intact materials, the potencies of ET-1 and ET-3 for endothelium-dependent vasorelaxation in pulmonary artery were almost equivalent. BQ-153 (10 microM) did not inhibit ET-induced vasorelaxation. These results indicate that ET-induced vasoconstriction is mediated not only through ETA but also through ETnonA (probably ETB), and that the relative proportions of the ET-receptor subtypes mediating contractions vary in different vascular areas. In addition, results showed that ET-induced endothelium-dependent vasorelaxation is mediated through ETB.     

三羟异黄酮对离体家兔股动脉张力的影响及其机制

植物雌激素三羟异黄酮（genistein,GST)使离体的预先收缩的动脉舒张,其舒张的机制仍然不完全清楚。本研究旨在观察植物雌激素三羟异黄酮对离体家兔股动脉的作用及其机制,结果如下：（1）在苯肾上腺素（PE,1umol/L)引起血管收缩的基础上,GST（10－40umol/L)剂量依赖性地舒张离体家兔股动脉;（2）去除血管内皮显著地抑制GST引起的舒张;（3）在内皮完整情况下,预先应用NOS抑制剂L－NAME（100umol/L)也可显著地抑制GST引起的舒张,提示GST的舒血管作用是内皮依赖的,并与一氧化氮有关;（4）在内皮完整的扣去除内皮的股动脉环,预先应用L－型钙通道激动剂Bay M8644(0.5umol/L)也显著抑制由GST引起的血管舒张,以上结果表明,GST引起的兔股动脉的舒张是部分内皮依赖的,且与拮抗钙有关。     

Activation of capsaicin-sensitive primary sensory neurones induces anandamide production and release

The inhibitory cannabinoid 1 receptor and the excitatory vanilloid receptor 1, both of which are responsive to the endogenous ligand anandamide, are co-expressed on a subpopulation of primary sensory neurones. We report that activation of the cannabinoid 1 receptor/vanilloid receptor 1-co-expressing primary sensory neurones induces the production and release of anandamide. Application of capsaicin (3 nm-1 micro m) to cultured primary sensory neurones evoked calcitonin gene-related peptide release, which was significantly increased by the selective cannabinoid 1 receptor antagonist, SR141716A (200 nm). Mass spectrometric analyses of the extracellular solution revealed that exposure to capsaicin (10 nm or 100 nm) enhanced the anandamide concentration of the medium from less then 0.05 pmol/ micro L to more then 2 pmol/ micro L. Depolarization of the neurones with 50 mm KCl also enhanced the anandamide content of the buffer. Both the capsaicin- and KCl-induced anandamide release depended on extracellular Ca2+. Prolonged treatment of the cultures with capsaicin (10 micro m) reduced both the capsaicin- and KCl-induced anandamide release. These findings indicate that activation of capsaicin-sensitive primary sensory neurones evokes anandamide production and release, and that anandamide might be a key endogenous regulator of the excitability of these neurones.     

The endocannabinoid arachidonyl ethanolamide (anandamide) increases pulmonary arterial pressure via cyclooxygenase-2 products in isolated rabbit lungs

Several cannabinoids elicit systemic vasodilation, mainly via CB1 cannabinoid and vanilloid receptors. However, effects in the pulmonary circulation are unknown. Using the isolated, ventilated, buffer-perfused rabbit lung, we have shown that the endocannabinoids arachidonyl ethanolamide (anandamide) and 2-arachidonyl glycerol (2-AG) dose-dependently increase pulmonary arterial pressure (+19.9 +/- 3.4 mmHg, 5 microM, and +39.5 +/- 10.8 mmHg, 0.4 microM, respectively). 2-AG induced lung edema. The CB1 receptor antagonist AM-251 (0.1 and 5 microM) and the VR1 vanilloid receptor antagonist capsazepine (10 microM) failed to reduce anandamide's effects. The metabolically stable anandamide and 2-AG analogs R-methanandamide and noladin ether, Delta9-tetrahydrocannabinol, and the synthetic cannabinoid HU-210, which is no arachidonic acid product, were without effect. The unspecific cyclooxygenase (COX) inhibitor aspirin (100 microM, P < 0.001) and the specific COX-2 inhibitor nimesulide (10 microM, P < 0.01) completely prevented pulmonary hypertension after 5 microM anandamide. COX-2 RNA was detected in rabbit lungs. The synthetic thromboxane receptor antagonist SQ 29,548 was without effect, but the specific EP1 prostanoid receptor antagonist SC-19220 (100 microM) inhibited the pressure increase after anandamide (P < 0.05). PCR analysis detected fatty acid amidohydrolase (FAAH), an enzyme that degrades endocannabinoids, in rabbit lung tissue. Furthermore, the specific FAAH inhibitor methyl arachidonyl fluorophosphonate (0.1 microM) blocked pressure effects of anandamide (P < 0.01). Finally, anandamide (99 +/- 55 pmol/g) and 2-AG (19.6 +/- 8.4 nmol/g) were found in native lungs. We conclude that anandamide increases pulmonary arterial pressure via COX-2 metabolites following enzymatic degradation by FAAH into arachidonic acid products.     

Inhibition of endothelium-dependent vascular relaxation by tetrandrine.

The effects of tetrandrine, a Ca2+ antagonist of bis-benzylisoquinoline alkaloid origin, on endothelium-dependent and -independent vascular responsiveness were investigated in perfused rat mesenteric artery. In endothelium-intact preparations pre-contracted with 3 microM phenylephrine and fully relaxed by 0.3 microM acetylcholine tetrandrine caused a rapid transient contraction. In endothelium-denuded preparations, tetrandrine caused only vasorelaxation of phenylephrine-contraction. The biphasic effect of tetrandrine in acetylcholine-relaxed preparations could also be mimicked by sequential applications of atropine/tetrandrine or N(G)-nitro-L-arginine-methylester (L-NAME)/tetrandrine, but atropine or L-NAME alone caused only vasoconstriction. This tetrandrine-induced transient vasoconstriction was also observed in preparations relaxed with ATP, histamine or thapsigargin (TSG), but not those relaxed with A23187, sodium nitroprusside or nifedipine. The present results suggest that tetrandrine, in addition to its known inhibitory effects on vascular smooth muscle by virtue of its Ca2+ antagonistic actions, also inhibits NO production by the endothelial cells possibly by blockade of Ca2+ release-activated Ca2+ channels.     

Endothelium-dependent and -independent vasorelaxation by a theophylline derivative MCPT: roles of cyclic nucleotides, potassium channel opening and phosphodiesterase inhibition

The vasorelaxation activities of MCPT, a newly synthesized xanthine derivative, were investigated in this study. In phenylephrine (PE)-precontracted rat aortic rings with intact endothelium, MCPT caused a concentration-dependent relaxation, which was inhibited by endothelium removed. This relaxation was also reduced by the presence of nitric oxide synthase inhibitor Nomega-nitro-L-arginine methylester (L-NAME, 100 microM), soluble guanylyl cyclase (sGC) inhibitors methylene blue (10 microM), 1 H-[1,2,4] oxidazolol [4,3-a] quinoxalin-1-one (ODQ, 1 microM), adenylyl cyclase (AC) blocker SQ 22536 (100 microM), ATP-sensitive K+ channel blocker (KATP) glibenclamide (1 microM), a Ca2+ activated K+ channels blocker tetraethylammonium (TEA, 10 mM) and a voltage-dependent potassium channels blocker 4-aminopyridine (4-AP, 100 microM). The vasorelaxant effects of MCPT together with IBMX (0.5 microM) had an additive action. In PE-preconstricted endothelium-denuded aortic rings, the vasorelaxant effects of MCPT were attenuated by pretreatments with glibenclamide (1 microM), SQ 22536 (100 microM) or ODQ (1 microM), respectively. MCPT enhanced cAMP-dependent vasodilator isoprenaline- and NO donor/cGMP-dependent vasodilator sodium nitroprusside-induced relaxation activities in endothelium-denuded aortic rings. In A-10 cell and washed human platelets, MCPT induced a concentration-dependent increase in intracellular cyclic GMP and cyclic AMP levels. In phosphodiesterase assay, MCPT displayed inhibition effects on PDE 3, PDE 4 and PDE 5. The inhibition % were 52 +/- 3.9, 32 +/- 2.6 and 8 +/- 1.1 respectively. The Western blot analysis on HUVEC indicated that MCPT increased the expression of eNOS. It is concluded that the vasorelaxation by MCPT may be mediated by the inhibition of phosphodiesterase, stimulation of NO/sGC/ cGMP and AC/cAMP pathways, and the opening of K+ channels.     

Effects of econazole on receptor-operated and depolarization-induced contractions in rat isolated aorta

In our previous study, econazole caused a decrease in serum nitrite levels in septic mice in vivo, but it enhanced the mortality rate. The aim of the study was to investigate the in vitro effects of econazole on receptor-operated and depolarization-induced contractions on endothelium-intact and -denuded rat isolated aorta. Econazole (0.1, 1 and 10 microM) significantly inhibited receptor-operated (phenylephrine, Phe) and depolarization (KCl)-induced contractions of endothelium-intact or -denuded rings in a noncompetitive and concentration-dependent manner. Removal of endothelium changed the pD'2 values only for KCl-induced responses. The pD'2 values of L-type calcium channel blocker nifedipine were significantly higher than the econazole on Phe concentration-response curves in endothelium-intact and -denuded rings. Econazole caused a biphasic response in precontracted by Phe or KCl in endothelium-intact and -denuded rings, first a transient contraction following sustained relaxation. Removal of endothelium did not affect the contractile responses induced by Phe. The contractile responses induced by 10 microM econazole in the KCl-precontracted rings were antagonized by the treatment of alpha-adrenergic receptor antagonist, phentolamine (10 microM). Deendothelization was significantly increased the IC50 values of econazole obtained from Phe- and KCl-precontractions. The relaxations induced by 10 microM econazole in endothelium-intact rings precontracted with Phe or KCl were not changed by NO synthase inhibitor, L-N(G)-nitroarginine (100 microM). The IC50 values of econazole were significantly higher than nifedipine in endothelium-intact and -denuded rings. These results suggest that econazole is a noncompetitive antagonist on alpha1-adrenoceptor-mediated and depolarization-induced contractions in rat isolated aorta by inhibiting Ca2+ entry through L-type calcium channels, and the endothelium seems to modulate vascular responses induced by this agent. The vascular effects of econazole may limit the usage of this agent in septic shock.     

Endothelium-dependent vasorelaxation effect of rutin-free tartary buckwheat extract in isolated rat thoracic aorta

The aim of this study was to point out the potential of tartary buckwheat on vascular functions. A nonabsorbed fraction of hot-water extract of tartary buckwheat on a SP70 column (TBSP-T), which was free from rutin, was used for this aim. In a contractile experiment using Sprague-Dawley rat thoracic aorta rings contracted by 1.0 microM phenylephrine (PE) or 50 mM KCl, TBSP-T evoked a significant vasorelaxation [EC50 (mg/ml): PE; 2.2; KCl, 1.9]. By a further fractionation of TBSP-T by liquid-liquid partitioning into basic, neutral and acidic fractions, a marked enhancement of vasorelaxation effect was observed only for acidic fraction (EC50, 0.25 mg/ml). The action of acidic fraction was significantly attenuated in endothelium-denuded aortic rings and in the presence of nitric oxide synthase inhibitor, NG-monomethyl-L-arginine (100 microM). The fraction also enhanced the cyclic guanosine monophosphate (cGMP) production in aortic rings contracted with PE [cGMP (pmol/mg protein): PE, 7.2+/-2.3; PE+Acidic fraction, 35+/-8]. These results indicate that acidic fraction could mediate NO/cGMP pathways, thereby exerting endothelium-dependent vasorelaxation action. In conclusion, tartary buckwheat was proven to regulate vascular tones and have latent acidic candidates except for rutin.     

Nebivolol: a selective beta(1)-adrenergic receptor antagonist that relaxes vascular smooth muscle by nitric oxide- and cyclic GMP-dependent mechanisms.

Nebivolol is a highly selective beta(1)-adrenergic receptor antagonist that also possesses vasodilator properties that are attributed largely to nitric oxide (NO). The objective of the present study was to elucidate in more detail the mechanisms by which nebivolol relaxes vascular smooth muscle. In the canine species, nebivolol caused relaxation of isolated precontracted rings of coronary artery and pulmonary artery largely by endothelium-dependent, NO-dependent, and cyclic GMP-dependent mechanisms. Vasorelaxation was inhibited by N(G)-methylarginine, and this inhibition was reversed by addition of excess L-arginine. Moreover, the vasorelaxant responses to nebivolol were markedly inhibited by oxyhemoglobin, methylene blue, and 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ), whereas vasorelaxation was enhanced by zaprinast. Rat aortic ring preparations, however, relaxed in response to nebivolol by both endothelium-dependent and endothelium-independent mechanisms, both involving NO, and cyclic GMP. Endothelium-dependent and endothelium-independent vasorelaxation were inhibited by oxyhemoglobin, methylene blue, and ODQ. However, only endothelium-dependent vasorelaxation in response to nebivolol was inhibited by N(G)-methylarginine. Additional experiments ruled out other endothelium-independent vasorelaxant mechanisms. In conclusion, the vasodilator responses to nebivolol involve NO and cyclic GMP in both vascular endothelial and smooth muscle cells.     

In-Vitro and In-Vivo Action of Cannabinoids

The discovery of endocannabinoids such as anandamide and the wide spread localization of cannabinoid receptors in the brain and peripheral tissues, suggests that the cannabinoid system represents a previously unrecognized ubiquitous net work in the nervous system, whose physiology and function is unfolding. In this study, we tested the hypothesis that some of the actions of anandamide are independent of a cannabinoid receptor mechanism. This was accomplished by the use of cannabinoid agonist and antagonist interaction in an in-vitro and in-vivo test systems. In-vitro, we used Xenopus laevis oocytes expression system and two-voltage clamp technique in combination with differential display polymerase chain reaction to determine whether the differential display of genes following treatment with anandamide may be linked to AMPA glutamate receptor. The differential expression of genes in vivo after the sub-acute administration of anandamide could not be directly linked with the AMPA glutamate receptor. In the voltage clamp studies we investigated the effects of anandamide on recombinant AMPA GluR3 sub-unit currents generated by kainic acid in oocytes expressing the AMPA glutamate receptor. In the in-vitro studies, we present evidence that anandamide inhibited the kainate activated currents in oocytes expressing AMPA glutamate receptor involves cAMP transduction via a cannabinoid receptor independent mechanism. In the in-vivo studies, SR141716A, the CB1 antagonist, induced anxiolysis, that was dependent on the mouse strain used in the anxiety model and blocked the anxiogenic effects of anandamide or methanandamide whereas SR141716A had no effect on the anandamide inhibition of kainate activated currents in-vitro.     

Vascular effects of 7-epiclusianone, a prenylated benzophenone from Rheedia gardneriana, on the rat aorta.

The vascular effects of 7-epiclusianone on the rat aorta were investigated. In the rat aortic rings with functional endothelia, 7-epiclusianone up to 10microM induced a concentration-dependent vasodilatation of the sustained contractions induced by phenylephrine (0.3microM). At concentrations higher than 10microM, 7-epiclusianone induced a concentration-dependent contraction in the aortic rings. The vasodilator effect of 7-epiclusianone was drastically decreased with L-NAME (100microM) as well as in endothelium-denuded aortic rings. Moreover, indomethacin (10microM) induced a significant shift to the left in the vasodilator but did not modify the vasoconstrictor effect of 7-epiclusianone. In arteries without pre-contraction, 7-epiclusianone (3-100microM) induced concentration-dependent contraction only in endothelium-intact and in the presence of L-NAME (100microM). This effect was inhibited by indomethacin (10microM) and ZM230487 (1microM), selective inhibitors of cyclooxygenase and of 5-lipoxygenase, respectively. We can conclude that at low concentrations 7-epiclusianone induces an endothelium-dependent vasodilator effect in rat aortic rings. At higher concentrations and in conditions where NO synthase was inhibited, 7-epiclusianone induces a vasocontractile effect. Nitric oxide seems to participate in the vasodilatation, while endothelial cyclooxygenase- and 5-lipoxygenase-derived products play a role in the vasoconstrictor effect.     

Vasoconstrictive effect of hydrogen sulfide involves downregulation of cAMP in vascular smooth muscle cells

Hydrogen sulfide (H(2)S), a new endogenous mediator, produces both vasorelaxation and vasoconstriction. This study was designed to examine whether cAMP mediates the vasoconstrictive effect of H(2)S. We found that NaHS at a concentration range of 10-100 microM (yields approximately 3-30 microM H(2)S) concentration-dependently reversed the vasodilation caused by isoprenaline and salbutamol, two beta-adrenoceptor agonists, and forskolin, a selective adenylyl cyclase activator, in phenylephrine-precontracted rat aortic rings. Pretreatment with NaHS (10-100 microM) for 5 min also significantly attenuated the vasorelaxant effect of salbutamol and forskolin. More importantly, NaHS (5-100 microM) significantly reversed forskolin-induced cAMP accumulation in vascular smooth muscle cells. However, NaHS produced significant, but weaker, vasoconstriction in the presence of N(G)-nitro-l-arginine methyl ester (100 microM), a nitric oxide synthase inhibitor, or in endothelium-denuded aortic rings. Blockade of ATP-sensitive potassium channels with glibenclamide (10 microM) failed to attenuate the vasoconstriction induced by H(2)S. Taken together, we demonstrated for the first time that the vasoconstrictive effect of H(2)S involves the adenyly cyclase/cAMP pathway.     

一氧化碳对大鼠离体肺动脉的舒张作用

本研究观察了一氧化碳 (CO)对离体大鼠肺动脉的舒张作用。制备Wistar大鼠肺动脉环 ,作出ACh浓度效应曲线之后 ,肺动脉环用一氧化氮合成酶抑制剂L NAME 3 0 μmol/L (n =10 )或血红素氧化酶抑制剂ZnPPIX 10μmol/L +L NAME 3 0 μmol/L (n =10 )孵育 3 0min ,再制备一个ACh的浓度效应曲线 ,观察ZnPPIX对ACh的浓度效应曲线的影响。另取一组肺动脉环 ,分为内皮完整组和去内皮组 ,观察外源性CO对肺动脉环张力的影响。结果表明 ,用L NAME孵育后 ,ACh的血管舒张反应受抑 ,最大抑制率为 5 0 4± 9 2 % ;用ZnPPIX +L NAME孵育后 ,ACh的血管舒张反应进一步受抑 ,最大抑制率为 84 4± 11 2 %。外源性CO无论对内皮完整组还是去内皮组肺动脉都有舒张作用。本研究提示 ,ZnPPIX可抑制ACh的内皮依赖性肺动脉舒张反应 ,CO是一个内皮源性的血管舒张因子 ,外源性CO可舒张肺动脉     

Evidence for the involvement of nitric oxide in A2B receptor-mediated vasorelaxation of mouse aorta

We have investigated the role of adenosine and its analogs on vasorelaxation of mouse aorta in intact endothelium with rank order of potency as follows: 5'-N-ethylcarboxamidoadenosine (NECA) > 2-chloroadenosine > adenosine > CGS-21680, which is consistent with the profile of A(2B)-adenosine receptor (A(2B)AR). In endothelium-intact tissues, acetylcholine produced relaxation ranging from 65 to 80% in phenylephrine (PE, 10(-7) M)-precontracted mouse aorta, whereas no relaxation was observed in endothelium-denuded tissues. The A(2B)AR antagonist alloxazine (10(-5) M) shifted concentration-response curve for NECA (EC(50) = 0.005 x 10(-5) M) to the right with an EC(50) of 2.8 x 10(-5) M, demonstrating that this relaxation is partially dependent on functional endothelium mediated predominantly via A(2B)AR in this tissue. This conclusion was further supported by the following findings: 1) in the endothelium-intact mouse aorta, the EC(50) values for NECA and adenosine were found to be 0.05 and 1.99 x 10(-4) M, respectively; however, in denuded endothelium, these values were 0.098 and 3.55 x 10(-4) M, respectively; 2) NECA-induced relaxation was significantly blocked by N(G)-nitro-l-arginine methyl ester (l-NAME; 10(-4) M) in endothelium-intact tissues, which was reversed by pretreatment with l-arginine (10(-4) M), whereas no significant inhibition was found in endothelium-denuded tissues; 3) total nitrites and nitrates (NOx) in intact endothelium with l-NAME (10(-4) M) alone and in combination with l-arginine were 59% (P < 0.05) and 96%, respectively, in comparison with control (PE + NECA); and 4) endothelial nitric oxide synthase gene expression was found to be 67% (P < 0.05) less in endothelium-denuded as opposed to endothelium-intact mouse aorta. Thus these data demonstrate that adenosine-mediated vasorelaxation is partially dependent on A(2B)AR in mouse aorta.     

Effects of 17ß-estradiol on endothelium-dependent relaxation induced by acetylcholine in female rat aorta

Estrogens have been postulated to play an important role in modulation of vascular responses to endogenous reactive substances. The effects of chronic in vivo treatment with 17ß-estradiol on relaxant responses to acetylcholine were investigated in the rat aorta isolated from prepubertal female rats. The selectivity of effects of 17ß-estradiol on acetylcholine-induced relaxation was evaluated using histamine, another endothelium-dependent relaxant in the rat aorta. 17ß-Estradiol significantly enhanced endothelium-dependent relaxation induced by acetylcholine, but did not alter the vascular responses to acetylcholine in endothelium-denuded aortic rings isolated from prepubertal female rats. In contrast, 17ß-estradiol did not change endothelium-dependent relaxation induced by histamine in endothelium-intact aortic rings. The results of the present study demostrate that 17ß-estradiol selectively enhanced acetylcholine-induced endothelium-dependent relaxation in the rat aorta.     

Endothelium-dependent vasodilation induced by Hancornia speciosa in rat superior mesenteric artery

The vasodilator effect of the ethanolic extract of leaves from Hancornia speciosa Gomes (HSE) was evaluated in superior mesenteric artery rings. HSE produced a concentration-dependent vasodilation (IC50 = 10.8 +/- 4.0 microg/mL) in arterial rings pre-contracted with phenylephrine, which was completely abolished in endothelium-denuded vessels. Endothelium-dependent vasodilation induced by HSE was strongly reduced by L-NAME (100 microM), a nitric oxide (NO) synthase inhibitor, but neither by atropine, a muscarinic receptor antagonist (1 microM), nor by indomethacin (10 microM), a cyclooxygenase inhibitor. In rings pre-contracted with 80 mM KCl, the vasodilator effect of HSE was shifted to the right and was completely abolished in the presence of L-NAME (100 microM). Similar effects were obtained in mesenteric rings pre-contracted with phenylephrine in the presence of KCl 25 mM alone or in addition to 100 microM L-NAME. In addition, BaCl2 (1 mM) dramatically reduced the vasodilation induced by HSE. Together, these findings led us to conclude that HSE induces an endothelium-dependent vasodilation in rat mesenteric artery, by a mechanism dependent on NO, on the activation of potassium channels and endothelium-derived hyperpolarizing factor release. Rutin, identified as a major peak in the HPLC fingerprint obtained for HSE, might contribute for the observed vasodilator effect, since it was able to induce an endothelium-dependent vasodilation in rat superior mesenteric arteries.