摘要:

The pH has marked effects on the blood flow in several vascular beds but the underlying mechanisms remain incompletely understood. It is still not agreed, for example, whether it is the fall in extracellular pH or intracellular pH that is responsible for changes in tone resulting from hypercapnic acidosis. The issue has been further complicated by the recent discovery that nitric oxide (NO) may also be involved in vasodilator responses to hypercapnia with the result that, in some laboratories, attention has been focused away from vascular smooth muscle. The recent availability of fluorescent dyes sensitive to pH has enabled some of the uncertainties in this field to be addressed. In light of these new observations, we have attempted to put older viewpoints in perspective. We conclude that, whilst a fall in smooth muscle intracellular pH is likely to be responsible for immediate responses to acidosis, the extracellular pH probably plays the predominant role in the steady state. The role of NO is best investigated in the cerebral circulation where it plays an important modulating role in the response to acidosis, and is probably of extravascular origin.

ISSN:1018-1172    

DOI:10.1159/000159163

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

The influence of flow-imposed shear stress on the intracellular calcium concentration ([Ca2+]i) of cultured endothelial cells (ECs) remains incompletely understood. In the present study, we measured [Ca2+]i in single bovine aortic ECs, using fluorescence ratiometric image analysis. The effects of several flow patterns were analysed: steady shear stress (5–70 dyn/cm2), 1-Hz pulsatile shear stress (nonreversing 40 ± 20 dyn/cm2, reversing 20 ± 40 dyn/cm2, or purely oscillatory 0 ± 20 dyn/cm2), or changing shear stress levels. Under all flow conditions, single-cell analyses revealed flow-induced asynchronous [Ca2+]i oscillations, which occurred randomly over the monolayer and which were not seen in the average [Ca2+]i signal corresponding to the monolayer response. The number of single-cell [Ca2+]i oscillations and the corresponding oscillation frequency rose as the shear stress associated with the steady flow increased: 0.06 ± 0.02 min–1 at 5 dyn/cm2, 0.19 ± 0.03 min–1 at 20 dyn/cm2, and 0.28 ± 0.02 min–1 at 70 dyn/cm2 (means ± SD). Also, the number of oscillations was greater for any type of pulsatile flow (0.53 ± 0.07 min–1 at 40 ± 20 dyn/cm2,0.54 ± 0.08 min–1 at 20 ± 40 dyn/cm2, and 0.39 ± 0.07 min–1 at 0 ± 20 dyn/cm2), as compared to any level of steady flow. The most dramatic finding was that purely oscillatory flow induced numerous single-cell [Ca2+]i oscillations, yet the average [Ca2+]i response for the monolayer did not change. Furthermore, an EC monolayer switched from low to high (or from high to low) steady flow consistently showed an increase (or a decrease) in the number of single-cell [Ca2+]i oscillations. These experiments show that ECs respond to different flow conditions by varying single-cell [Ca2+]i oscillatory activity. This may have important implications in the endothelium-dependent control of vascular physiology, such as the releas

ISSN:1018-1172    

DOI:10.1159/000159164

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

This study was designed to evaluate the effects of lipopolysaccharide (LPS)-activated macrophages in the perfused mesenteric circulation of the rat. The mesenteric network of anesthetized rats was perfused in situ under constant flow conditions and the diameter and pressure of the mesenteric artery were continuously recorded. For the first 30 min the mesenteric network was perfused with an RPMI solution (control condition); thereafter it was perfused for 60 min with the same solution containing either (1) LPS (1 µg/ml), (2) elicited macrophages (106 cells/ml), (3) LPS-activated macrophages or (4) superna-tants derived from LPS-activated macrophages (SPN). The changes in arterial diameter induced by topical application of phenylephrine (PE, 10 µmol/l) were measured under control conditions and then 30 and 60 min after the onset of perfusions. The intravascular pressure was similarly increased (51 ± 6%, p < 0.001) by the perfusion of activated macrophages or elicited macrophages but was not affected by perfusion of LPS or SPN. Despite the same level of transmural mesenteric pressure in rats perfused with activated and elicited macrophages, the mesenteric diameter was significantly larger with activated than with elicited macrophages (p < 0.05). Under control conditions, PE induced a marked decrease in arterial diameter from 495 ± 15 to 265 ± 13 µm (p < 0.001). Perfusion of LPS, elicited macrophages or SPN did not modify the vascular reactivity to PE. Perfusion of activated macrophages reduced the PE-induced contraction by 77 ± 6% (p < 0.001). Perfusion of elicited macrophages with a nitric oxide (NO) donor (SIN-1,10 µmol/l) reproduced the effect of LPS-activated macrophages while addition of an NO scavenger (oxyhemoglobin, 10 µmol/l) prevented the depression of the vascular reactivity to PE by activated macrophages. Finally, activated macrophages preincubated with an inhibitor of NO synthesis (NG-monomethyl-L-arginine; L-NMMA), and then perfused in RPMI solution without L-NMMA had no effect on the PE reactivity of the mesenteric artery suggesting that NO released by activated macrophages directly and rapidly inhibited the contractility of the mesenteric artery. The results of this study demonstrate the opposing effects of macrophages in the mesenteric circulation to increase microvascular resistance by a rheological effect while decreasing the reactivity of the mesenteric artery as a result of NO released by mac

ISSN:1018-1172    

DOI:10.1159/000159165

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

The kinins, substance P and bradykinin, cause endothelium-dependent hyperpolarizations in smooth muscles of the pig coronary artery. We tested whether the propagation, in the media, of these hyperpolarizations is passive or whether the hyperpolarizations are regenerated in the smooth muscle cells. The space constants measured in response to the kinin endothelium-dependent stimulations were compared to those obtained by electrical field stimulation. The space constant is 2.6 ± 0.2 mm (n = 13) measured for substance P and 2.2 ± 0.2 mm (n = 12) for bradykinin. The space constants established by electrical field stimulation-induced hyperpolarization are 3 ± 0.2 mm (n = 7) for strips with intact endothelium and 2.7 ± 0.3 mm (n = 7) for strips with removed endothelium. These results show that the space constants obtained for the kinin stimulations are not larger than those caused by electrical field stimulation. This suggests that the kinin-induced hyperpolarizations propagate, in the media, in a passive, electronic manner, therefore the hypothesis of regenerated kinin hyperpolarizations is unlik

ISSN:1018-1172    

DOI:10.1159/000159166

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

The role of endothelium-derived nitric oxide (NO) in the vascular contractile response to angiotensin II (Ang II) has been investigated in isolated small mesenteric resistance arteries of the rat. Both contraction and intracellular Ca2+ ion concentration ([Ca2+]i) were monitored in vessels, with and without functional endothelium, which were exposed to physiological salt solution containing 25 mM KC1. Ang II induced concentration-dependent contractile responses and increases in [Ca2+]i which, at the concentration giving the maximal response (10 nM), were not sustained in arteries with functional endothelium; however, the presence of a functional endothelium did not modify the peak responses. Ang II did not increase the cyclic guanosine 3’,5’-monophos-phate content of the tissue nor did it induce relaxation in arteries precontracted with 3 µM noradrenaline. The decline of the Ang II responses was suppressed by removal of the endothelium or by exposure of arteries with endothelium to either the NO synthase inhibitor, Nω-nitro-L-arginine methyl ester (300 µM), or the cyclic GMP-dependent protein kinase inhibitor, Rp-8-bro moguanosine 3’, 5’-cyclic monophosphorothioate (30 µM). On the other hand, the NO donor SIN-1 (3-morpholino-sydnonimine, 10 µM) accelerated the decline in [Ca2+]i and contraction. These results show that endothelium-derived NO does not affect the magnitude of the phasic element of the response to Ang II, but is involved in the rapid attenuation of the tonic component. Activation of cyclic GMP-dependent protein kinase accounts for this effect of endotheliu

ISSN:1018-1172    

DOI:10.1159/000159167

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

Studies have provided evidence for the role of gap junctional intercellular communication in syncytial tissue function. This study tested the hypothesis that the vasodilating effects of nitric oxide (NO) rely on gap junctions. The effects of the gap junction inhibitors octanol (10-4 mol/l) and heptanol (10-3 mol/l) were examined on acetylcholine-, the NO-donor S-nitroso-N-acetyl-penicillamine (SNAP)-, and guanosine-3’, 5’-cyclic monophosphate (cGMP)-induced relaxation. In addition, we tested varying concentrations of the gap junction inhibitor sucrose on SNAP-induced relaxation in the presence and absence of methylene blue, an inhibitor of guanylate cyclase. Helical strips of rat thoracic aorta were placed in muscle baths for isometric force measurements. Tissues treated with SNAP and cGMP were denuded of endothelium. Tissues incubated in octanol and heptanol exhibited 4- to 7-fold rightward shifts in acetylcholine-induced and 6- to 15-fold rightward shifts in SNAP-induced relaxation. Both octanol and heptanol produced 2-fold rightward shifts in cGMP-induced relaxation, comparably less in magnitude than shifts produced in acetylcholine- and SNAP-induced relaxation. Sucrose (10-2 to 10-1 mol/l) produced a concentration-dependent rightward shift of up to 30-fold in relaxation to SNAP. Incubation with methylene blue (10-6 mol/l) altered this rightward shift only slightly, indicating a possible cGMP-indepen-dent mechanism for NO. These findings support the hypothesis that NO-induced vasodilation, through both cGMP-dependent and -independent pathways, relies on gap junctional communicat

ISSN:1018-1172    

DOI:10.1159/000159168

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

The proliferation of intimal smooth muscle cells (SMCs) in large muscular arteries and veins often occurs after surgical interventions such as angioplasty and bypass grafting, and may lead to restenosis and graft failure. Clinical observations suggest that increased pulsatile deformation of veins grafted into an arterial position may play a role in intimal hyperplasia. Since intimal hyperplasia occurs at the vein/arterial interface of the graft, SMC hyperplasia could be due to the proliferation of either aortic or venous SMCs. Therefore, we compared the effects of in vitro mechanical deformation on the proliferation of aortic SMCs with venous SMCs. Using the FlexercellR apparatus (Flex-cell Corp., McKeesport, Pa., USA), aortic SMCs, stretched at 3 and 60 cpm did not lead to a significant increase in growth as compared to the non-stretched controls. In contrast, stretch of venous SMCs at 3 and 60 cpm led to a significant increase in growth as compared to the nonstretched controls. These results suggest that the SMC proliferation, as occurs in vein interposition grafts in vivo, may be partially due to a stimulatory response by venous SMCs to increased mechanical stimulation.

ISSN:1018-1172    

DOI:10.1159/000159169

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

Acetylcholine (ACh)-induced membrane hyperpolarization was studied in freshly isolated endothelial cells from rabbit aorta. Ten µM ACh induced transient hyperpolarization due to the opening of Ca2+-sensitive K+ channels, sensitive to TEA and charybdotoxin (CTX). The membrane potential response was accompanied by an increase in intracellular Ca2+ [Ca2+]i. Pretreatment of endothelial cells with 20 µM ATP, 0.2 µM bradykinin or 0.1 µM platelet-aggregating factor, which induced either a transient hyperpolarization or no response, changed the subsequent ACh-induced response to a large maintained hyperpolarization. This sustained membrane hyperpolarization was also due to the opening of Ca2+-activated K+ channels as confirmed by CTX and TEA blockade, and was related to elevated [Ca2+]i measured by fura-2 fluorescence. Pertussis toxin blocked potentiation, indicating involvement of a G protein. The linkage to receptor-operated Ca2+ (ROC)-entry was suggested by observations that the maintained hyperpolarization during potentiation was dependent on extracellular Ca2+ and was abolished by the ROC blockers SKF-96365 and Ni2+. Inhibition of the Ca2+ pump of the endoplasmic reticulum mimicked the potentiating effect of the agonists. The results suggest that crosstalk between the agonists in endothelial cells involves Ca2+ movements and that this crosstalk is important for the generation of endothelial secreti

ISSN:1018-1172    

DOI:10.1159/000159170

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

The aortic expression of endothelin-1 (ET-1) was examined in three species of rat using a novel en face immunohistochemical technique. A genetically hypertensive strain was compared to two normotensive strains, one of which is known to develop spontaneous lesions within the abdominal aorta. ET-1-positive staining was increased about the major aortic branch ostia and over the dorsal abdominal aortic wall in all three species indicating a flow-related expression pattern. Mitotic and hyperchromatic endothelial cells stained strongly for ET-1 as did occasional multi-nucleated endothelial cells. The aortic-lesion-prone normotensive strain developed transverse tears of the internal elastic lamina with a corresponding endothelial cell response. Endothelium at the edge of these lesions was strongly stained for ET-1 and appeared to be associated with increased leucocyte adhesion as did other strongly ET-1-stained areas in all three species. This study indicates that increased ET-1 expression is anatomically localised within the rat aorta, possibly by haemodynamic stress. This may have implications for maintaining endothelial cell confluence, aortic smooth muscle cell reparative processes and possibly eventual pathophysiological conditions such as atherosclerosis.

ISSN:1018-1172    

DOI:10.1159/000159171

出版商:S. Karger AG    

年代:1996

数据来源: Karger

ISSN:1018-1172    

DOI:10.1159/000159172

出版商:S. Karger AG    

年代:1996

数据来源: Karger