Pharmacological neutropenia prevents endothelial dysfunction but not smooth muscle functions impairment induced by middle cerebral artery occlusion

1. The polymorphonuclear neutrophils (PMN) activation and mobilization observed in acute cerebral infarction contribute to the brain tissue damage, but PMN could also be involved in postischemic functional injury of ischemied blood vessel. 2. This study was undertaken to investigate whether pharmacological neutropenia could modify the postischemic endothelial dysfunction in comparison to smooth muscle whose impairment is likely more related to reperfusion and oxidative stress. 3. A cerebral ischemia-reperfusion by endoluminal occlusion of right middle cerebral artery (MCA) was performed 4 days after intravenous administration of vinblastine or 12 h after RP-3 anti-rat neutrophils monoclonal antibody (mAb RP-3) injection into the peritoneal cavity, on male Wistar rats with 1-h ischemia then followed by 24-h reperfusion period. Brain infarct volume was measured by histomorphometric analysis and vascular endothelial and smooth muscle reactivity of MCA was analysed using Halpern myograph. 4. Neutropenia induced a neuroprotective effect as demonstrated by a significant decrease of brain infarct size. In parallel to neuroprotection, neutropenia prevented postischemic impairment of endothelium-dependent relaxing response to acetylcholine. In contrast, smooth muscle functional alterations were not prevented by neutropenia. Ischemia-reperfusion-induced myogenic tone impairment remained unchanged in vinblastine and mAb RP-3-treated rats. Postischemic Kir2.x-dependent relaxation impairment was not prevented in neutropenic conditions. The fully relaxation of smooth muscle response to sodium nitroprusside was similar in all groups. 5. Our results evidenced the dissociate prevention of pharmacologically induced neutropenia on postischemic vascular endothelial and smooth muscle impairment. The selective endothelial protection by neutropenia is parallel to a neuroprotective effect suggesting a possible relationship between the two phenomena.     

Role of membrane potential in endothelium-dependent relaxation of isolated mouse main pulmonary artery

The physiology of smooth muscle and endothelial cells of a particular vascular bed and from different species differs from each other. Acetylcholine causes an endothelium-dependent relaxation of preconstricted pulmonary arteries from the rat. This relaxation is mediated by nitric oxide (NO) plus a yet-unidentified endothelium-derived hyperpolarizing factor, which relaxes the smooth muscles by hyperpolarizing them. Our aim is to test whether these observations could be generalized to the smooth muscle cells from the mouse pulmonary artery. Smooth muscle or endothelial cell membrane potential of strips of murine pulmonary artery were measured simultaneously with the force developed by the strip. Acetylcholine hyperpolarized the endothelial cells. However, acetylcholine did not induce an endothelium-dependent hyperpolarization of the smooth muscle, while it relaxed the strip in an endothelium-dependent manner. This relaxation was abolished by an inhibitor of NO synthesis, nitro-L-arginine. Moreover, nitroglycerin relaxed the strips without changing the membrane potential of the smooth muscle cells. Injection of Lucifer yellow into the endothelial cells and the smooth muscle cells did not show heterocellular dye coupling. Furthermore, electron microscopy did not show gap junction plate at the myoendothelial junctions. We conclude that in the mouse main pulmonary artery, NO alone is responsible for the acetylcholine-induced endothelium-dependent vasodilatation, whereas the phenomenon called endothelium-derived hyperpolizing factor is not present. Therefore, caution should be taken when comparing different animal models to study pulmonary circulation and its reactivity.     

Effects of chronic treatment with SQ29852 on spontaneous smooth muscle tone and endothelium-dependent relaxation in aorta of stroke-prone spontaneously hypertensive rats.

The effects of chronic treatment with SQ29852, an angiotensin-converting enzyme inhibitor, on spontaneous smooth muscle tone and endothelium-dependent relaxation of aorta from stroke-prone spontaneously hypertensive rats (SHRSP) were studied and compared with those of captopril. Endothelium-removed aorta from 16-week-old SHRSP exhibited a high amplitude of spontaneously developed active tension (active tone), whereas no active tone was observed in the preparation from control normotensive Wistar-Kyoto (WKY) rats. Treatment with SQ29852 or captopril at age 5-16 weeks prevented the development of hypertension. No active tone could be detected in the preparation from SQ29852-treated SHRSP. Endothelium-dependent relaxation was markedly reduced in the preparation from nontreated SHRSP compared with WKY rats. Treatment with SQ29852 prevented the impairment of endothelium-dependent relaxation. It was also shown that norepinephrine-induced contraction was markedly depressed in endothelium-intact aorta from SQ29852-treated rats. The effects of SQ29852 were more prominent than those of hydralazine when blood pressure was maintained at similar levels. It was suggested that SQ29852 exerts an action on both vascular smooth muscle and endothelium that is mediated by the inhibition of angiotension-converting enzyme in addition to indirect actions of SQ29852 that are brought about by blood pressure lowering.     

Endothelium-dependent relaxation to acetylcholine in the rabbit basilar artery: importance of membrane hyperpolarization.

1. Muscarinic stimulation of isolated, preconstricted segments of the basilar artery, with either acetylcholine or carbachol, was followed by endothelium-dependent smooth muscle relaxation and membrane hyperpolarization. 2. Smooth muscle relaxation to acetylcholine was stimulated in the presence of lower concentrations than the associated hyperpolarization (EC50 values 3.2 microM and 31.6 microM, respectively), and was sustained during agonist application, while the hyperpolarization was relatively transient. 3. Repeated exposure to acetylcholine was associated with loss of membrane hyperpolarization, while smooth muscle relaxation was unaltered. Following a second exposure to 100 microM acetylcholine, mean hyperpolarization was markedly depressed from 8.5 to 2 mV, and subsequent exposures failed to induce any hyperpolarization. Relaxations with a similar amplitude and rate of development, were recorded with each subsequent addition of acetylcholine. 4. The competitive substrate inhibitors for nitric oxide synthase, L-NG-monomethyl arginine (100 microM L-NMMA) or L-NG-nitro arginine methyl ester (100 microM L-NAME), modified the form and amplitude of both the relaxation and the hyperpolarization to acetylcholine. In the majority of experiments, both the hyperpolarization and the relaxation were almost totally abolished. 5. Neither nitric oxide, applied directly in physiological salt solution, nor sodium nitroprusside, produced smooth muscle hyperpolarization except in high concentrations. Reproducible, small amplitude (around 2 mV) hyperpolarization followed the application of either NO gas (15 microM) or sodium nitroprusside (100 microM), both of which induced almost maximal smooth muscle relaxation. 6. These data show that muscarinic stimulation of endothelial cells in the rabbit basilar artery is followed by both smooth muscle hyperpolarization and relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of Panax notoginseng saponins on vascular endothelial cells in vitro

AIM: To investigate the inhibition of endothelium-de-pendent in vitro vascular relaxation induced by the total saponins (gensenosides) from Panax notoginseng (PNS) and the effect of PNS on the cytosolic Ca2 concentration on cultured bovine pulmonary artery endothelial cells. METHODS: The endothelial-dependent vascular relaxation was assessed using acetylcholine (ACh) or cyclopi-azonic acid (CPA) induced relaxation in endothelium-intact rat aorta. Cytosolic Ca2 level was assessed in real time using dynamic digital fluorescence ratio imaging. RESULTS: In addition to its direct relaxation of the smooth muscle cells at high concentrations, PNS, at 100 mg/L having little effect on smooth muscle, caused a marked inhibition of endothelium-dependent relaxation brought about by PNS. This inhibitory effect was due to its inhibition of elevation of cytosolic Ca2 , which is required for the activation of NO generation and release from the vascular endothelial cells. Nifedipine has no effect on either the endothe     

Endothelium-dependent hyperpolarization of canine coronary smooth muscle.

1. Experiments were designed to determine whether endothelium-dependent relaxing factor(s) released by acetylcholine from the canine femoral artery influences the membrane potential of coronary arterial smooth muscle. 2. The membrane potential was recorded in small canine coronary arteries (internal diameter less than or equal to 500 micron; without endothelium) by means of intracellular microelectrodes. The organ bath also contained a strip of left descending coronary artery without endothelium in which isometric force was measured to bioassay relaxing factor(s) as well as segments of femoral artery with endothelium, which served as the source of endothelium-derived relaxing factor(s). 3. Acetylcholine induced endothelium-dependent, transient hyperpolarizations and relaxations that were not affected by indomethacin. 4. Inhibition of the sodium-potassium pump by ouabain or potassium-free solution did not inhibit the relaxation to acetylcholine but prevented the corresponding hyperpolarization. 5. Activation of the sodium-potassium pump of the smooth muscle cells by readmission of potassium ions after incubation in potassium-free solution caused relaxation and marked hyperpolarization. 6. These results suggest that endothelium-derived relaxing factor(s) induces hyperpolarization of vascular smooth muscle of the canine coronary artery, possibly by activation of sodium-potassium pumping, but that this effect on the cell membrane may only partially explain endothelium-dependent relaxations evoked by acetylcholine.     

单硝酸异山梨酯对小鼠损伤血管修复的影响

目的研究单硝酸异山梨酯对小鼠损伤血管修复的影响。方法采用电刺激小鼠颈总动脉制备血管损伤模型,再应用伊文思蓝染色研究损伤血管内皮修复过程。通过测定血管收缩、内皮依赖性舒张和非内皮依赖性舒张来评估NO对损伤血管功能恢复的影响。结果经单硝酸异山梨酯预处理一周（7 d）和一个月（30 d）的损伤血管,跟生理盐水对照组相比,在内皮修复过程中没有显著性差异,同时血管平滑肌细胞没有显著性改变。经过单硝酸异山梨酯预处理的小鼠损伤血管的功能也没有改善。结论血管平滑肌的修复并不是再生,平滑肌的修复主要靠已有平滑肌细胞的迁移,短期应用单硝酸异山梨酯可一定程度上抑制损伤后血管内膜增厚和血管重构。     

Effect of hypothyroidism on beta-adrenoceptor-mediated relaxation in the rat thoracic aortae. A time-dependent study

We investigated the time dependency of hypothyroid-induced changes in beta-adrenoceptor-mediated relaxation of vascular smooth muscle. Methimazole (0.03%) was administered to male Wistar-Imamichi rats for 3 days, 1, 2 or 6 weeks. This treatment led to significant increases in thyroid weight while inhibiting growth rate. Tension in isolated rings of thoracic aortae from control and hypothyroid rats was measured isometrically. Responses of aortic rings to cumulative doses of acetylcholine (ACh) and sodium nitroprusside (SNP) were not significantly different between control and hypothyroid groups. After 3 days and 1 week of treatment, isoprenaline (ISO)-induced relaxation was unchanged, but after 2 and 6 weeks, a marked increase was observed as compared to controls. Removal of the endothelium and pretreatment with NG-nitro-L-arginine (L-NOARG) inhibited the ISO-induced relaxation in both groups; but whereas this degree of inhibition was the same for both groups after 3 days and 1 week, it was significantly less pronounced in hypothyroid rats after 2 and 6 weeks as compared to their controls. These results suggest that hypothyroidism has a time-dependent influence on beta-adrenoceptor-mediated relaxation in the rat thoracic aortae and that the enhancement after 2 and 6 weeks of methimazole treatment may be due to a hypothyroid-induced alteration in arterial smooth muscle function.     

Chronic treatment with fluvastatin improves smooth muscle dilatory function in genetically determined hyperlipoproteinemia

We hypothesized that the HMG-CoA reductase inhibitor fluvastatin, does not only improve endothelium-dependent vasorelaxation, but that it also increases vascular smooth muscle reactivity in hyperlipoproteinemia. New Zealand White (NZW) rabbits aged 37 weeks (control), Watanabe Heritable Hyperlipidemic rabbits (WHHL) aged 37 weeks, and WHHL aged 35 weeks with fluvastatin treatment of 17 weeks (10 mg/kg/d) were examined. Aortas were isolated for isometric tension recording. Both endothelium-dependent and independent relaxation were impaired in WHHL. Fluvastatin significantly restored impaired endothelium-independent relaxation (WHHL: 57 +/- 12 versus WHHL+ fluvastatin: 150 +/- 22%; P < 0.05) and in tendency endothelium-dependent relaxation (WHHL: 26 +/- 5 versus WHHL+ fluvastatin: 83 +/- 29%; (P = 0.07)). In parallel, fluvastatin restored nitrite plasma level in hyperlipoproteinemic animals (WHHL: 480 (13-3821) versus WHHL+ fluvastatin: 808 (467-1595) nmol; P < 0.05). Thus, chronic treatment with fluvastatin not only improves endothelial but also vascular smooth muscle function in hyperlipoproteinemia, which may contribute to the beneficial clinical effects of statins.     

Endothelium-dependent relaxation and hyperpolarization of canine coronary artery smooth muscles in relation to the electrogenic Na-K pump.

1 In the smooth muscle cells of canine coronary artery, acetylcholine (ACh) produced a transient, endothelium-dependent hyperpolarization of the membrane. A similar hyperpolarization was also elicited by exposure to Krebs solution after incubation of the artery in K-free solution for 30 min. 2 A hyperpolarization of reproducible amplitude was generated when ACh was applied at intervals greater than 30 min. Repetitive application of ACh at 15 min intervals caused a successive reduction in the amplitude of hyperpolarization. 3 The reduction in the amplitude of relaxation during five successive applications of ACh at 15 min intervals was less than 10% of the first relaxation. 4 The ACh-induced hyperpolarization was blocked by atropine but not by ouabain, whereas the K-free induced hyperpolarization was blocked by ouabain. In low Na (Li-substituted) solution, ACh still induced a hyperpolarization but the K-free induced hyperpolarization was absent. 5 In coronary artery precontracted by high-K solution, ACh produced an endothelium-dependent relaxation, without membrane hyperpolarization. The associated relaxation was resistant to ouabain but sensitive to atropine. 6 It is concluded that in the canine coronary artery, the electrogenic Na-K pump does not contribute to the endothelium-dependent hyperpolarization or relaxation. The results are consistent with the release of two different inhibitory factors from the vascular endothelium.     

The neuroprotective effect of the antioxidant flavonoid derivate di-tert-butylhydroxyphenyl is parallel to the preventive effect on post-ischemic Kir2.x impairment but not to post-ischemic endothelial dysfunction

In the rat model of transient cerebral ischemia induced by intraluminal occlusion of the middle cerebral artery, we investigated the respective roles of ischemia and reperfusion in endothelium-dependent relaxation and smooth muscle relaxation related to the inward rectifier potassium current (Kir2.x), using the Halpern arteriography technique and/or patch-clamp technique. We first demonstrated that reperfusion is necessary to induce a significant impairment of smooth muscle Kir2.x, since ischemia alone has no effect on Kir2.x current density and function. In addition, we demonstrated that both ischemia and reperfusion are necessary for the occurrence of maximal post-ischemic endothelial dysfunction. The crucial role of reperfusion in post-ischemic vascular impairment prompted us to characterize the effect of a new antioxidant synthetic flavonoid derivate, 35di-tert-butylhydroxyphenyl (dt-BC), on both neuronal and vascular injuries. Dt-BC (10 mg/kg) induced a neuroprotective effect as demonstrated by a significant decrease in infarct size, while there was no protective effect with the doses of 3 mg/kg and 30 mg/kg. Parallel to neuroprotection, dt-BC at a dose of 10 mg/kg, but not with doses of 3 mg/kg and 30 mg/kg, prevented post-ischemic impairment of smooth muscle Kir2.x current density and function, while dt-BC had no effect on the post-ischemic alteration of endothelial function whatever doses are used. These data demonstrate the potential of a new synthetic flavonoid derivate to induce neurovascular protection and support a possible relationship between vascular and neuronal protection via pharmacological modulation of oxidative stress. All experiments were performed in strict accordance with guidelines of the National Institutes of Health and the French Department of Agriculture.     

Gender differences in the regulation of vascular tone

1. The greater incidence of hypertension and coronary artery disease in men and post-menopausal women compared with premenopausal women has suggested vascular protective effects of the female sex hormone oestrogen. However, vascular effects of the female sex hormone progesterone and the male sex hormone testosterone have also been suggested. 2. Oestrogen, progesterone and testosterone receptors have been identified in the plasmalemma, cytosol and nuclear compartments of vascular cells. The interaction of sex hormones with their specific receptors triggers not only long-term genomic vascular effects, but also acute non-genomic vascular responses. 3. Sex hormones may activate endothelium-dependent vascular relaxation pathways, including the nitric oxide-cGMP and prostacyclin-cAMP pathways and a hyperpolarizing factor pathway. 4. Sex hormones may also inhibit the mechanisms of vascular smooth muscle contraction, such as [Ca2+]i, protein kinase C and other protein kinases. 5. The sex hormone-induced stimulation of endothelium-dependent vascular relaxation and inhibition of vascular smooth muscle contraction may contribute to the gender differences in vascular tone and may represent potential beneficial vascular effects of hormone-replacement therapy during natural and surgically induced deficiencies of gonadal hormones.     

Cholesterol feeding attenuates endothelium-dependent relaxation response to acetylcholine in the main pulmonary artery of chickens

The endothelium-dependent relaxation in response to acetylcholine was significantly less in pulmonary artery strips from chickens fed 5% cholesterol for 4 weeks than in strips from animals fed an 'ordinary' diet. No relaxation was observed in the strips from either group when the endothelium was disrupted or the strips were pretreated with hydroquinone. These results indicate that the relaxing effect of acetylcholine is endothelium-dependent and that hypercholesterolemia leads to an impairment of the endothelium-mediated relaxation response of the pulmonary artery strips to acetylcholine.     

Differential Efficacy of Vasodilators in Hypercholesterolaemic Rabbits

The effects of hypercholesterolaemia on the endothelium-dependent and -independent vascular reactivity of the superior mesenteric artery has been examined in anaesthetized rabbits in-vivo. Rabbits were fed with either standard or cholesterol-enriched diet for 24 weeks. Plasma lipids and changes in the endothelin content of plasma and vascular tissue were measured in the superior mesenteric artery and in the thoracic aorta. The functional severity of atherosclerosis was determined by examining vascular responses in the isolated thoracic aorta. The blood flow in the superior mesenteric artery was measured by transit-time flowmetry and drugs were injected through an intra-abdominal aortic catheter. Acetylcholine (5, 10, 20 μg kg^?1) elicited dose-dependent, mesenteric vasodilation in normocholesterolaemic rabbits. In hypercholesterolaemic animals the response to acetylcholine was completely abolished and even became a vasoconstriction. Endothelin levels in plasma and in the vascular tissue were significantly elevated in hypercholesterolaemic animals compared with controls. Cromakalim at a dose of 3 μg kg^?1, elicited similar mesenteric vasodilation in hypercholesterolaemic and normocholesterolaemic animals. These experiments show that the endothelium-dependent responses of the superior mesenteric artery to acetylcholine are functionally impaired by prolonged hypercholesterolaemia, that this altered vascular reactivity is associated with the elevation of endothelin levels in the circulation and in vascular tissues, and that in hypercholesterolaemia the mesenteric vasodilator effect of the K+-channel opener cromakalim is entirely preserved, suggesting that severe hypercholesterolaemia does not depress the function of ATP-sensitive potassium channels in mesenteric vascular smooth muscle.     

The mechanism of bradykinin-induced endothelium-dependent contraction and relaxation in the porcine interlobar renal artery

The mechanism of endothelium-dependent regulation of vascular tone of bradykinin was investigated by simultaneously monitoring the changes in the cytosolic Ca(2+) concentration and the force of smooth muscle in fura-2-loaded strips of the porcine renal artery with endothelium. During phenylephrine-induced sustained contraction, bradykinin (>3x10(-9) M) caused endothelium-dependent triphasic changes in the force of the strips, composed of an initial relaxation, a subsequent transient contraction and a late sustained relaxation. At low concentrations (10(-10) - 10(-9) M), bradykinin caused an endothelium-dependent biphasic relaxation with no contraction. A thromboxane A(2) (TXA(2))/prostaglandin H(2) (PGH(2)) receptor antagonist (10(-5) M ONO-3708) completely inhibited, while a TXA(2) synthase inhibitor (10(-5) M OKY-046) only partially inhibited, the transient contraction induced by bradykinin. Under conditions where the bradykinin-induced contraction was inhibited by ONO-3708 during the phenylephrine-induced contraction, bradykinin induced only a transient relaxation in the presence of N(Omega)-nitro-L-arginine methyl ester (L-NAME). This transient relaxation was inhibited when the precontraction was initiated by phenylephrine plus 40 mM extracellular K(+). The removal of L-NAME from this condition caused a partial reappearance of the initial relaxation and a complete reappearance of the sustained relaxation. In conclusion, bradykinin caused the endothelium-dependent triphasic regulation of vascular tone in the porcine renal artery. The concentrations of bradykinin required to induce a contraction was higher than that required to induce relaxation. Both TXA(2) and PGH(2) were involved in the bradykinin-induced contraction. The initial relaxation was mediated by nitric oxide and hyperpolarizing factors while the sustained relaxation depended on nitric oxide.     

Up-regulation of proteinase-activated receptor 1 and increased contractile responses to thrombin after subarachnoid haemorrhage

BACKGROUND AND PURPOSE: The mechanism for the development of post-haemorrhagic cerebral vasospasm after subarachnoid haemorrhage (SAH) still remains unknown. EXPERIMENTAL APPROACH: We investigated the role of thrombin and its receptor PAR1 in the development of hyper-contractility of the basilar artery in a rabbit double haemorrhage model, which received two injections of autologous blood into the cisterna magna. KEY RESULTS: In the basilar artery isolated from the control rabbits, thrombin, only at 10 units ml(-1), induced a transient endothelium-dependent relaxation and a slight smooth muscle contraction. In SAH, the contractile response to thrombin was markedly enhanced, while the endothelium-dependent relaxant effect of thrombin remained unchanged. The enhancement of the contractile responses was also observed in the absence of endothelium and thrombin induced an enhanced contraction at concentrations higher than 0.3 units ml(-1). The contractile response to PAR1-activating peptide was also enhanced after SAH. However, the contractile responses to high K+ and endothelin-1, and the myofilament Ca2+-sensitivity remained unchanged after SAH. An immunoblot analysis suggested the up-regulation of PAR1 in the smooth muscle of the basilar artery. The heparinization of blood before injection prevented the enhancement of the contractile responses to thrombin and PAR1-activating peptide. CONCLUSIONS AND IMPLICATIONS: The present study demonstrated, for the first time, that the contractile response of the basilar artery to thrombin was markedly enhanced after SAH. Mechanistically, our findings suggested that the activation of thrombin following hemorrhage up-regulated the expression of PAR1, thereby inducing the hyper-responsiveness to thrombin.     

Prevention of intimal thickening after endothelial removal by a nonpeptide angiotensin II receptor antagonist, losartan.

1. The present experiments were designed to investigate the role of local angiotensin II receptors in the myointimal proliferative response of the vascular wall after endothelial removal, by use of a novel, nonpeptide, angiotensin II receptor antagonist, losartan. 2. When administered 1 week before endothelial removal from the rabbit carotid artery and then continuously until animals were killed 6 weeks later, losartan in a dose of 10 mg kg-1 daily, p.o. had no significant effects on the carotid blood flow (CBF), mean arterial blood pressure (MBP) and heart rate (HR). 3. A full endothelial lining with increased density of regenerated endothelial cells was observed 6 weeks after the endothelial removal. These changes were unaffected by treatment with losartan. 4. Six weeks after endothelial removal, acetylcholine (ACh)- and adenosine diphosphate (ADP)-induced relaxations were greatly reduced though endothelial cells had regenerated. The reduction of the relaxations to these agonists were significantly restored by chronic treatment with losartan. The endothelial-independent, sodium nitroprusside (SNP)-induced relaxation remained unaffected in all groups. 5. There were no differences in the noradrenaline (NA)- and endothelin-1 (ET-1)-induced contractions of the carotid artery strips between vehicle and losartan-treated groups. In contrast, the contractile response of the strips to angiotensin II was significantly decreased in the losartan group, indicating the specific antagonism by chronic losartan against the angiotensin II receptor. 6. Six weeks after endothelial removal, marked myointimal proliferation resulting from new accumulation of proliferating smooth muscle cells and connective tissue was observed in the vehicle group. Losartan treatment greatly suppressed the myointimal proliferative response.(ABSTRACT TRUNCATED AT 250 WORDS)     

Altered vasodilator and endothelium-dependent responses in hypertension

A compromised ability to relax has been described as a characteristic of vascular smooth muscle from animal models of hypertension. Since the discovery that many vasodilators act via the release of an endothelium-derived relaxant factor (EDRF), studies have been designed to assess whether endothelium-dependent vs. -independent relaxations are impaired in the hypertensive state. A decreased maximal relaxation for such endothelium-dependent vasodilators as acetylcholine, A23187, and histamine exists in both large conduit and resistance vessels from hypertensive animals compared to their normotensive counterparts. Endothelium-independent vasodilators (i.e., sodium nitroprusside) typically achieve similar maximal percent relaxations in hypertensive vs. normotensive vascular preparations. This defect for endothelium-dependent vasodilators has been described in vessels from genetic, renal, mineralocorticoid, and coarctation models of hypertension. An altered endothelium-dependent relaxation could be a corollary of the documented structural changes which occur in hypertension although it remains to be determined if there exists an abnormal coupling between EDRF and its putative receptor in vascular smooth muscle. Several complexities hamper interpretation of altered endothelium-dependent responses in hypertersion such as regional vascular differences, suitability of reference endothelium-independent vasodilators, and endothelium-dependent contractile responses elicited by acetylcholine.     

Hyperpolarization caused by serotonin contributes to endothelium-dependent relaxations in the porcine coronary artery.

AIM: The present study was designed to investigate the contribution of membrane hyperpolarization to endothelium-dependent relaxations induced by serotonin in the porcine coronary artery. METHODS: Rings with and without endothelium of porcine coronary arteries were suspended in conventional organ chambers for the measurement of isometric force. The cell membrane potential of the vascular smooth muscle cells was measured using glass microelectrodes, in the presence of indometacin, ketanserin, and/or N omega-nitro-L-arginine. RESULTS: Serotonin induced a transient endothelium-, and concentration-dependent relaxation in rings contracted with prostaglandin F2 alpha in the presence of N omega-nitro-L-arginine (maximal relaxation: 19%). The N omega-nitro-L-arginine resistant relaxation was abolished by high K+ and tetrabutylammonium chloride. Serotonin also caused an endothelium-, concentration-dependent membrane hyperpolarizations with a maximal amplitude of -8.8 mV. The nitro-L-arginine resistant relaxations and hyperpolarizations were abolished by methiothepin, but not by glibenclamide. The time course of the endothelium-dependent relaxations and hyperpolarizations was similar. CONCLUSION: These results suggest a contribution of cell membrane hyperpolarization to the endothelium-dependent relaxations induced by serotonin in the porcine coronary artery.     

Hydrogen peroxide and endothelium-dependent hyperpolarization in the guinea-pig carotid artery

This study was designed to determine whether or not endothelium-dependent hyperpolarizations evoked by acetylcholine in the isolated guinea-pig carotid artery involve hydrogen peroxide. Membrane potential was recorded in the vascular smooth muscle cells of that artery. Under control conditions, acetylcholine induced endothelium-dependent hyperpolarization of the vascular smooth muscle cells which was not affected by the presence of catalase, superoxide dismutase or their combination. Neither the superoxide dismutase mimetic, tiron nor the thiol-reducing agent N-acetyl-l-cysteine modified the hyperpolarization evoked by 0.1 μM acetylcholine but each produced a partial and significant inhibition of the hyperpolarization induced by 1 μM acetylcholine. Neither 10 nor 100 μM hydrogen peroxide influenced the resting membrane potential of the smooth muscle cells and the higher concentration did not significantly influence the hyperpolarization elicited by acetylcholine. These data indicate that, in the guinea-pig isolated carotid artery, hydrogen peroxide is unlikely to contribute to the endothelium-dependent hyperpolarization evoked by acetylcholine.