Role of endothelium in hypoxic contraction of canine basilar artery.

1. Reversible contraction of canine basilar artery, produced by hypoxia, persisted after mechanical and chemical removal of the endothelium. The removal of endothelium was confirmed by scanning electron microscopy as well as by the abolition or reversal of the relaxant response to acetylcholine or arginine8-vasopressin. 2. Hydroquinone, believed to block selectively endothelium-mediated relaxation, also preferentially attenuated hypoxic contractions even in the absence of endothelium but did not reduce responses to 5-hydroxytryptamine (5-HT) or high external potassium. 3. Contractions induced by red blood cell haemolysate, which occur independently of the endothelium, were also selectively attenuated by hydroquinone. 4. Contractions caused by hypoxia were inhibited by pretreatment with adenosine or by its application after contraction had developed. 5. Hypoxic contraction in canine basilar artery may result partly from a direct effect on smooth muscle as well as through the endothelium. 6. Hydroquinone may have an additional locus of action in smooth muscle cells besides its well known effect on the endothelium.     

Gamma-aminobutyric acid-induced contraction of the dog basilar artery

gamma-Aminobutyric acid (GABA) produced a biphasic action, that is, a relaxation followed by a contraction in the isolated dog basilar artery. Repeated applications of each concentration of GABA (10(-6), 10(-5), 10(-4), 10(-3) M) at regular intervals under resting conditions caused a stepwise increase in the contractile response. Marked reproducible contractile responses occurred (ED50: 1.3 X 10(-5) M), after at least 8-10 applications. The GABA-induced contraction as well as relaxation was blocked by bicuculline and picrotoxin. Pretreatment with inhibitors of prostaglandin synthesis such as aspirin (3 X 10(-6) to 3 X 10(-4) M) and indomethacin (3 X 10(-6) M) reduced the contractile response to GABA in an irreversible manner and without affecting the relaxation induced by GABA. These inhibitors increased the resting tone but reduced the tone in strips subjected to repeated applications of GABA. 15-Hydroperoxyarachidonic acid at concentrations of 1 X 10(-6) and 1 X 10(-5) M also attenuated the contractile response to GABA in a dose-dependent fashion. These observations suggest that GABA may modulate the contractile effect by inducing the production of contraction-causing prostaglandin(s) mediated through GABA receptors and/or by some as yet undefined mechanism.     

Role of ACE and NEP in bradykinin-induced relaxation and contraction response of isolated porcine basilar artery

The aim of the present study was to clarify the role of angiotensin converting enzyme (ACE) and neutral endopeptidase (NEP) in bradykinin (BK)-induced relaxation and contraction of isolated porcine basilar artery by measuring isometric tension, ACE and NEP activities and their localization. BK induced endothelium-dependent relaxation followed by contraction; however, in the presence of indomethacin BK induced relaxation but not contraction, in contrast, in the presence of L-nitro-arginine BK induced contraction but not relaxation. Captopril and thiorphan increased the p D(2) value for BK-induced relaxation from 8.11 to 9.55 and the p A(2) value for [Thi(5,8), D-Phe(7)]-BK (a B(2)-receptor antagonist) from 6.95 to 7.59. The same treatment increased the p D(2) value for BK-induced contraction from 7.93 to 8.97 and the p A(2) value for [Thi(5,8), D-Phe(7)]-BK from 6.86 to 7.50. Captopril inhibited ACE activity with an IC(50) of 38.0 nM, and thiorphan inhibited NEP and ACE activities with an IC(50) of 1.4 nM and 295.0 nM, respectively. Endothelial denudation decreased the ACE and NEP activities by 76.7% and 15.9%, respectively, and ACE mRNA level by 59.4%, but had no significant effect on NEP mRNA level. These results suggest that BK-induced relaxation and contraction in the porcine basilar artery are enhanced by captopril and thiorphan which predominantly inhibit ACE activity localized on endothelial cells.     

Differential modulation by basilar and mesenteric endothelium of angiotensin-induced contraction in canine arteries

The contraction of ring segments of canine mesenteric and basilar arteries in response to angiotensins II and III was investigated. Removal of the mesenteric endothelium resulted in markedly intensified contraction in response to angiotensin II but did not affect the contractile response to angiotensin III. This angiotensin II-induced contraction was augmented by indomethacin (10⁻⁵ M) and by methylene blue (5 × 10⁻⁶ M) in the intact rings. These findings suggest that mesenteric endothelium modulates the vasoconstriction induced by angiotensin II but not that induced by angiotensin III. They also indicate that the mesenteric endothelium may contain relaxing factors such as prostacyclin or endothelium-derived relaxing factor as mediators. In contrast with mesenteric endothelium, removal of the basilar endothelium produced a much reduced contraction in response to either angiotensin. Acetylcholine, which caused a dose-dependent contraction in the basilar artery, elicited only a low-grade response if the functional endothelium was absent. These results suggest that basilar endothelium may release a contracting factor. It is possible that the main modulator of the peripheral arteries is a relaxing factor but that of the cerebral arteries is a contracting factor.     

alpha,beta-MeATP augments the UTP contraction of rabbit basilar artery

The mechanism underlying the interaction between alpha,beta-methyleneadenosine 5'-triphosphate (alpha,beta-MeATP) and uridine 5'-triphosphate (UTP) was investigated using the basilar artery of a rabbit. UTP induced a concentration-dependent contraction, whereas P2X receptor agonists, such as alpha,beta-MeATP and 2-methylthioadenosine 5'-triphosphate (2-MeSATP), did not induce any contraction up to 100 microM. alpha,beta-MeATP augmented the UTP contraction two-fold, immediately and reversibly. This effect was observed with ectonucleotidase inhibition with 1 mM Ni(2+), the removal of extracellular Ca(2+) or Evans blue. The contractile response to adenosine 5'-O-(3-triphosphate) (ATPgammaS), a selective agonist for P2Y(4), was augmented by pretreatment with alpha,beta-MeATP also. ATPgammaS had no additional effect on the UTP contraction fully activated with alpha,beta-MeATP. UTP (100 microM) did not induce an increase in cytosolic Ca(2+) in a rabbit basilar arterial strip; however, in the presence of 1 mM alpha,beta-MeATP, UTP induced a significant increase in cytosolic Ca(2+). These results suggest that alpha,beta-MeATP facilitates the activation by UTP of the P2Y receptor (P2Y(4)) of the rabbit basilar artery through mechanisms other than nucleotidase inhibition, and that it does not do so via a P2X receptor.     

Possible role of leukotrienes in hypoxic contraction of canine isolated basilar artery.

1. Hypoxia reversibly increased isometric tension in unstimulated canine isolated basilar artery rings. 2. Nordihydroguaiaretic acid (NDGA; 5 x 10(-6) M), an inhibitor of lipoxygenase and quinacrine (10(-5) M), which blocks the release of arachidonic acid from phospholipids by inhibiting the enzyme phospholipase A2, blocked hypoxia-induced contractions. 3. The preferential leukotriene D4 (LTD4) antagonist, L-660,711, also inhibited the hypoxia-induced contractions in concentrations ranging from 10(-8) M to 10(-5) M. The effects seen were statistically significant (P less than 0.05). Two components of inhibition were seen. 4. Arachidonic acid (5 micrograms ml-1) caused contraction of the isolated basilar artery rings. This response was inhibited by NDGA (5 x 10(-6) M) and L-660,711 (10(-5) M). 5. The LTD4 (10(-8) M-10(-7) M)-induced contraction was relaxed by L-660,711 in a dose-dependent manner. Both the contraction caused by LTD4 as well as that caused by hypoxia were relaxed by 5 x 10(-6) M adenosine. 6. Leukotriene(s) may be involved in hypoxia-induced contraction of canine isolated basilar artery. However, they may not be the sole mediator(s).     

Mechanisms underlying diabetes enhancement of endothelin-1-induced contraction in rabbit basilar artery

The influence of alloxan-induced diabetes on the reactivity of rabbit basilar artery to endothelin-1 was examined. Endothelin-1 induced concentration-dependent contraction of basilar arteries that was higher in diabetic than in control rabbits. Endothelium removal produced a higher enhancement of the endothelin-1-induced contraction in control than in diabetic rabbits. N(G)-nitro-L-arginine (L-NOArg) enhanced the maximal contraction induced by endothelin-1 in control rabbits and potentiated this response in diabetic rabbits. Endothelin ETA receptor antagonist, cyclo(D-Asp-Pro-D-Val-Leu-D-Trp) (BQ-123), inhibited endothelin-1-induced contraction in both rabbit groups. Endothelin ETB receptor antagonist, 2,6-Dimethylpiperidinecarbonyl-gamma-Methyl-Leu-Nin-(Methoxycarbonyl)-D-Trp-D-Nle (BQ-788), enhanced endothelin-1-induced contraction in control rabbits and decreased the potency of endothelin-1 in diabetic rabbits. Sodium nitroprusside-induced relaxation of basilar arteries was lower in diabetic than in control rabbits. These results suggest that mechanisms underlying rabbit basilar artery hyperreactivity to endothelin-1 include decreased endothelial modulation of endothelin-1-induced contraction, with impaired endothelial endothelin ETB receptor activity; decreased sensitivity to nitric oxide (NO) in vascular smooth muscle; and enhanced participation of muscular endothelin ETA and ETB receptors.     

Pharmacological characterization of the alpha adrenoceptors of the dog basilar artery

Summary The effects of alpha adrenoceptor agonists and antagonists on the postsynaptic alpha receptors were examined in the dog basilar, mesenteric and renal arteries and the type of alpha adrenoceptors present was characterized. In the basilar artery, noradrenaline, clonidine and phenylephrine produced almost the same maximal contraction, the pD₂ values being 6.51±0.11, 5.49±0.16 and 5.65±0.13, respectively. Yohimbine (1–3×10^–8 M) inhibited the contractile responses to noradrenaline and clonidine competitively and the response to phenylephrine noncompetitively. Corynanthine (10^–6 M) had no effect on such contractile responses. In the mesenteric and renal arteries, the maximal responses to noradrenaline and phenylephrine were markedly greater than those to clonidine. Yohimbine (10^–7–10^–5 M) and corynanthine (10^–7–10^–5 M) both antagonized noradrenaline competitively in these vessels. In the basilar, mesenteric and renal arteries preloaded with ³H-noradrenaline, ³H-efflux induced by electrical transmural stimulation was attenuated by clonidine (10^–10–10^–7 M), while phenylephrine (10^–10–10^–8 M) was without effect. Yohimbine at considerably lower concentrations than corynanthine increased the ³H-efflux clicited by electrical stimulation. These results indicate that presynaptic and postsynaptic alpha receptors of the dog basilar artery are largely alpha₂ in contrast to those of peripheral arteries.This work was supported by a Grant-in-Aid for Co-operative Research (No. 00437006), by a Grant-in-Aid for Special Project Research (No. 56220016) and by a Grant-in-Aid for Encouragement of Young Scientists (No. 577106, 56770118) from the Ministry of Education, Science and Culture, Japan     

Modulatory effect of interleukin-1beta on rat isolated basilar artery contraction

An increased level of cytokine interleukin-1 (IL-1) has been detected around the site of stroke. However, the effect of IL-1beta on the basilar artery has received little attention. We evaluated the effects of IL-1beta on the contractile response of rat isolated basilar artery by measuring isometric tension change. IL-1beta (10 ng/ml) and phenylephrine (0.1 nM) markedly enhanced U46619 (30 and 100 nM)-induced basilar artery contraction. The IL-1beta-mediated potentiation was partly suppressed by zinc protoporphyrin (3 microM) and was abolished by tetrodotoxin (TTX, 100 nM), (-)-perillic acid (1 microM), PD98059 (0.3 microM), SB203580 (1 microM) and prazosin (1 microM). Our data suggest that IL-1beta (10 ng/ml) causes an enhancement of U46619-mediated basilar artery contraction that probably involves TTX-sensitive neuronal release of an alpha1-adrenoceptor agonist and activation of p42/p44 and p38 mitogen-activated protein kinases/p21(ras) pathways.     

Mechanisms of electrical field stimulation-induced vasodilatation in the guinea-pig basilar artery: the role of endothelium

1 The role of endothelium in neuronal vasodilatation elicited by electrical field stimulation (EFS) was investigated in preparations of the isolated guinea-pig basilar artery in which the tone was raised with prostaglandin F₂α. 2 In preparations with intact endothelium, EFS produced frequency-dependent dilatations which were not affected by guanethidine but were slightly yet significantly reduced by atropine (1 μm ), and were blocked by tetrodotoxin (1 μM ) and the nitric oxide synthase inhibitor l -NAME (10 μm ). 3 Dilatations were elicited by acetylcholine (3 μm ); these were blocked by l -NAME and atropine (1 μm ). 4 Dilatations were elicited by nicotine (100 μm ); these were blocked by l -NAME and hexamethonium (100 μm ). 5 Dilatation elicited by sodium nitroprusside (SNP, 3 μm ) was not affected by l -NAME. 6 The inhibitory effects of l -NAME were partially prevented by l -arginine (1 mm ). 7 Removal of the endothelium resulted in a significant reduction of dilatations elicited by EFS, elimination of the dilator action of acetylcholine, but enhancement of that to SNP. 8 The results suggest that EFS-induced vasodilatation is mediated in part by the nitrergic transmitter and in part by endothelium derived relaxing factor (EDRF) activated by acetylcholine released from cholinergic nerves.     

Mechanism of asynchronous Ca2+ waves underlying agonist-induced contraction in the rat basilar artery

Background and purpose:

Uridine 5''-triphosphate (UTP) is a potent vasoconstrictor of cerebral arteries and induces Ca²⁺ waves in vascular smooth muscle cells (VSMCs). This study aimed to determine the mechanisms underlying UTP-induced Ca²⁺ waves in VSMCs of the rat basilar artery.

Experimental approach:

Isometric force and intracellular Ca²⁺ ([Ca²⁺]_i) were measured in endothelium-denuded rat basilar artery using wire myography and confocal microscopy respectively.

Key results:

Uridine 5''-triphosphate (0.1–1000 µmol·L⁻¹) concentration-dependently induced tonic contraction (pEC₅₀ = 4.34 ± 0.13), associated with sustained repetitive oscillations in [Ca²⁺]_i propagating along the length of the VSMCs as asynchronized Ca²⁺ waves. Inhibition of Ca²⁺ reuptake in sarcoplasmic reticulum (SR) by cyclopiazonic acid abolished the Ca²⁺ waves and resulted in a dramatic drop in tonic contraction. Nifedipine reduced the frequency of Ca²⁺ waves by 40% and tonic contraction by 52%, and the nifedipine-insensitive component was abolished by SKF-96365, an inhibitor of receptor- and store-operated channels, and KB-R7943, an inhibitor of reverse-mode Na⁺/Ca²⁺ exchange. Ongoing Ca²⁺ waves and tonic contraction were also abolished after blockade of inositol-1,4,5-triphosphate-sensitive receptors by 2-aminoethoxydiphenylborate, but not by high concentrations of ryanodine or tetracaine. However, depletion of ryanodine-sensitive SR Ca²⁺ stores prior to UTP stimulation prevented Ca²⁺ waves.

Conclusions and implications:

Uridine 5''-triphosphate-induced Ca²⁺ waves may underlie tonic contraction and appear to be produced by repetitive cycles of regenerative Ca²⁺ release from the SR through inositol-1,4,5-triphosphate-sensitive receptors. Maintenance of Ca²⁺ waves requires SR Ca²⁺ reuptake from Ca²⁺ entry across the plasma membrane via L-type Ca²⁺ channels, receptor- and store-operated channels, and reverse-mode Na⁺/Ca²⁺ exchange.     

双苯氟嗪、氟桂利嗪、桂利嗪对5-羟色胺所致离体猪基底动脉收缩的拮抗作用(英文)

目的:探索双苯氟嗪(Dip,一种我国自行合成的桂利嗪衍生物),对5-羟色胺所致的脑动脉收缩的影响。方法:比较双苯氟嗪、氟桂利嗪(Flu)、桂利嗪(Cin)对5-羟色胺所致离体猪基底动脉收缩的抑制及两种收缩成分的影响。结果:三者的拮抗作用强度顺序(IC_(50))为Dip 4.0μmol·L~(-1)>Flu15.6μmol·L~(-1)>Cin 25.2umo·L~(-1)。这三种药对5-羟色胺所致离体猪基底动脉的两种收缩成分均有拮抗。Dip和Cin抑制收缩的快速相强于持续相,而Flu对二者的作用无显著差异。结论:在Dip,Flu和Cin三种药之中,Dip对脑血管的扩张作用最强,其原因主要与抑制内钙的释放有关。     

Chloride efflux is involved in ET-1 and 5-HT-induced contraction in rabbit basilar artery

Chloride (Cl-) efflux induces depolarization and contributes to contraction of cerebral arteries. We tested the effect of endothelin-1 and 5-hydroxytryptamine on isometric tension in rabbit basilar artery by inhibition of Na+-K+-2Cl- co-transporter and Cl-/HCO3- exchanger to decrease Cl-, by decreasing extracellular Cl- concentration, and by blocking Cl- channels using Cl- channel inhibitors. We have made the following observations: (i)endothelin-1 and 5-hydroxytryptamine produced contraction in the normal Cl- Krebs-Henseleit bicarbonate solution (123 mM Cl-); (ii)inhibition of Na+-K+-2Cl- co-transporter with bumetanide abolished the contractions; (iii) bicarbonate-free solution with HEPES reduced contractions to 5-hydroxytryptamine and endothelin-1; (iv) substitution of extracellular Cl- with methanesulfonate acid (MS- 113 mM, Cl- 10 mM) enhanced peak contraction to 5-hydroxytryptamine and endothelin-1 and decreased plateau contraction to 5-hydroxytryptamine, but did not affect the plateau contraction to endothelin-1 and KCl; and (v) blockade of Ca2+-dependent Cl- channel with niflumic acid and non-selective Cl- channel with 5-nitro-2-(3-phenylpropylamino) benzoic acid and indanyloxyacetic acid-94, R- (+)-methylindazone (R- (+)-IAA-94)decreased contractions to endothelin-1 and 5-hydroxytryptamine.However, removal of endothelium attenuated the effect of Cl-channel inhibitors. In conclusion, Cl- channels and Cl- flux are involved in endothelin-1-induced and 5-hydroxytryptamine-induced contraction in rabbit basilar artery. Cl- channel blockers might exert additional effects by releasing vasodilatation agents from endothelial cells.     

高血压对大鼠脑基底动脉收缩和钠泵活性的影响

目的探讨高血压对大鼠脑血管收缩性的影响及其与钠泵活性的关系。方法取♂Wistar大鼠(WR)和自发性高血压大鼠(SHR)基底动脉环,通过Multi Myograph张力换能系统记录血管张力变化,比较两种大鼠离体脑动脉对KCl和5-羟色胺(5-HT)的收缩反应,分析高血压病变对脑血管收缩性和钠泵活性的影响。结果与WR基底动脉相比,SHR基底动脉的KCl和5-HT量效曲线明显右移,再复K+所致血管舒张作用减弱,提示高血压病变可明显降低脑血管钠泵活性及KCl和5-HT的收缩反应;哇巴因(Ouabain,OUA)浓度依赖性收缩SHR脑血管,其量效关系曲线可经两点结合模型进行最佳拟合,Kd分别为:1.7×10~(-8)mol·L~(-1)和1.6×10~(-5)mol·L~(-1),表明SHR脑基底动脉上存在高、低亲和力两种不同功能的钠泵。用5×10~(-7)mol·L~(-1)和10~(-4)mol·L~(-1)的OUA分别抑制高、低亲和力钠泵,仅能在SHR而非WR脑血管明显左移KCl和5-HT量效曲线,表明OUA可明显增强KCl和5-HT对脑血管的收缩作用,且OUA增强5-HT收缩SHR脑血管的作用呈明显的浓度依赖性(r=0.9393,P<0.05);在SHR脑血管,这两个浓度OUA对KCl量效曲线的左移幅度无明显差别,而对5-HT收缩量效曲线的左移幅度却有明显不同,提示仅高亲和力钠泵介导了SHR脑血管对KCl的收缩反应,而SHR脑血管对5-HT的收缩反应则由高、低亲和力两种钠泵共同参与。结论高血压病变可明显降低脑血管对血管收缩剂的反应性,其机制可能与高血压所致钠泵活性降低或钠泵对OUA敏感性增加有关。     

Chemical removal of the endothelium by saponin in the isolated dog femoral artery

Chemical removal of the endothelium by saponin in the isolated dog femoral artery was investigated by comparing the relaxant responses to endothelium-dependent and -independent vasodilators of saponin-treated rings with the responses of non-treated rings. Saponin treatment was done by incubating rings with Krebs-Henseleit solution containing 0.1, 0.3 or 1 mg/ml of saponin for 45 min at 37 degrees C. In non-treated rings, acetylcholine (10(-8)-3 X 10(-6) M) caused a concentration-dependent relaxation of rings precontracted with prostaglandin F2 alpha (3 X 10(-6) M). The acetylcholine-induced relaxation was reduced in rings pretreated with 0.1 mg/ml of saponin and almost abolished with 0.3 or 1 mg/ml. Prostaglandin F2 alpha-induced contraction was suppressed weakly by treatment with 0.3 mg/ml and markedly with 1 mg/ml saponin. The treatment with 0.3 mg/ml saponin markedly reduced relaxations caused by substance P (10(-9)-3 X 10(-8) M) and by Ca2+-ionophore A23187 (10(-6) M). Relaxant responses of saponin-treated rings to nitroglycerin and to nitroprusside were almost identical with those of non-treated rings. These results showing selective suppression by saponin of the endothelium-dependent relaxation suggest that saponin removes the endothelial cells from the intimal surface of the artery, and this was confirmed by electron microscopy. The endothelium removing method with saponin seems to be useful as a pharmacological tool for vascular investigations.     

Role of endothelium and calcium channels in endothelin-induced contraction of human cerebral arteries.

Endothelin constricted human isolated cerebral arteries in a concentration-dependent manner. The maximal tension developed, as well as EC50 values were similar in arteries with and without endothelium. Removal of extracellular calcium or addition of the calcium antagonist nicardipine (10(-6)M), attenuated but did not abolish responses to endothelin. These experiments show that the endothelin-induced contraction in human cerebral arteries is not linked to the presence of intact endothelial cells. The data also show that the contractile effects of endothelin cannot be explained solely by an action on voltage-dependent calcium channels.     

5-HT1-like receptors mediate 5-hydroxytryptamine-induced contraction of human isolated basilar artery

1. The 5-hydroxytryptamine (5-HT) receptor mediating contraction of endothelium denuded human basilar artery has been characterized in vitro. 2. 5-HT and a variety of 5-HT agonists contracted human isolated basilar artery with a rank order of agonist potency, 5-carboxamidotryptamine (5-CT) greater than 5-HT identical to methysergide greater than GR43175 much greater than 8-OHDPAT much greater than 2-methyl-5-HT. The maximum response produced by these agonists differed. 3. None of the agonists relaxed human basilar artery when tone was elevated with prostaglandin F2 alpha, indeed further contraction was seen. 4. The contractile responses of human basilar artery to 5-HT and the selective 5-HT1-like agonist GR43175 were highly reproducible whilst those to 5-CT were not. 5. The contractile response to both 5-HT and GR43175 was resistant to antagonism by ketanserin and GR38032, thus excluding activation of 5-HT2 and 5-HT3 receptors. The contractile action of 5-HT and GR43175 was also not antagonized by (+/-)-cyanopindolol, excluding the activation of receptors similar to 5-HT1A and 5-HT1B recognition sites identified in ligand binding studies. 6. In marked contrast, methiothepin was a potent antagonist of the contractile actions of both 5-HT and GR43175, with a pA2 value of 8.8 against both agonists. Methiothepin (100 nM) had no effect on the contractile response to the thromboxane A2-mimetic U46619. 7. We conclude that 5-HT and GR43175 contract the human isolated basilar artery by activating the same receptor type.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mitochondrial monoamine oxidase-A-mediated hydrogen peroxide generation enhances 5-hydroxytryptamine-induced contraction of rat basilar artery

BACKGROUND AND PURPOSE

We evaluated the role(s) of monoamine oxidase (MAO)-mediated H₂O₂ generation on 5-hydroxytryptamine (5-HT)-induced tension development of isolated basilar artery of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats.

EXPERIMENTAL APPROACH

Basilar artery (endothelium-denuded) was isolated for tension measurement and Western blots. Enzymically dissociated single myocytes from basilar arteries were used for patch-clamp electrophysiological and confocal microscopic studies.

KEY RESULTS

Under resting tension, 5-HT elicited a concentration-dependent tension development with a greater sensitivity (with unchanged maximum tension development) in SHR compared with WKY (EC₅₀: 28.4 ± 4.1 nM vs. 98.2 ± 9.4 nM). The exaggerated component of 5-HT-induced tension development in SHR was eradicated by polyethylene glycol-catalase, clorgyline and citalopram whereas exogenously applied H₂O₂ enhanced the 5-HT-elicited tension development in WKY. A greater protein expression of MAO-A was detected in basilar arteries from SHR than in those from WKY. In single myocytes and the entire basilar artery, 5-HT generated (clorgyline-sensitive) a greater amount of H₂O₂ in SHR compared with WKY. Whole-cell iberiotoxin-sensitive Ca²⁺-activated K⁺ (BK_Ca) amplitude measured in myocytes of SHR was approximately threefold greater than that in WKY (at +60 mV: 7.61 ± 0.89 pA·pF⁻¹ vs. 2.61 ± 0.66 pA·pF⁻¹). In SHR myocytes, 5-HT caused a greater inhibition (clorgyline-, polyethylene glycol-catalase- and reduced glutathione-sensitive) of BK_Ca amplitude than in those from WKY.

CONCLUSIONS AND IMPLICATIONS

5-HT caused an increased generation of mitochondrial H₂O₂ via MAO-A-mediated 5-HT metabolism, which caused a greater inhibition of BK_Ca gating in basilar artery myocytes, leading to exaggerated basilar artery tension development in SHR.     

神经肽Y对离体兔脑血管的作用及其内皮依赖关系

神经肽Y对离体兔脑基底动脉的作用表现在:(1)直接收缩;(2)增强组胺的收缩效应;(3)抑制乙酰胆碱和腺苷的舒张效应。作用(1)和(3)不依赖于血管内皮的存在,而作用(2)依赖血管内皮,其机理可能是由于神经肽Y对血管内皮舒张因子(EDRF)的释放或作用具有抑制性影响。     

Pharmacological nature of nicotine-induced contraction in the rat basilar artery: involvement of arachidonic acid metabolites

The pharmacological nature of nicotine-induced contraction in the rat basilar artery is poorly understood. The purpose of this study was to investigate the endothelium dependency and involvement of arachidonic acid metabolites in nicotine-induced contraction in the rat basilar artery. The rat basilar artery was removed from the brain and cut into a spiral preparation. Nicotine (3x10(-5) to 10(-2) M) induced the concentration-dependent contraction in the rat basilar artery, and the maximal contraction was obtained at 3x10(-3) M. The contraction induced by nicotine (3x10(-3) M) was significantly attenuated by the presence of saponin (0.05 mg/ml, 15 min). Phospholipase C (PLC) inhibitors (NCDC and U-73122), calcium-independent phospholipase A(2) (iPLA(2)) inhibitor (BEL), cyclooxygenase-2 (COX-2) inhibitors (nimesulide, L-745,337 and celecoxib), and a 5-lipoxygenase (5-LOX) inhibitor (ZM-230487) concentration-dependently attenuated the nicotine-induced contraction. A cytosolic phospholipase A(2) (cPLA(2)) inhibitor (AACOCF3), secretory phospholipase A(2) (sPLA(2)) inhibitor (indoxam), and cyclooxygenase-1 (COX-1) inhibitors (flurbiprofen and ketoprofen) did not affect the nicotine-induced contraction. From these results, it was suggested that nicotine-induced contraction in the rat basilar artery is endothelium-dependent and is due to arachidonic acid metabolites.