Arterial and venular endothelial cell costimulation of cytokine secretion by human T cell clones

Vascular endothelial cell (EC) costimulation of cytokine secretion by T lymphocytes may be important in inflammation and allograft rejection. Venous and arterial iliac endothelial cells (VIEC, AIEC) both costimulate interleukin-2 (IL-2) production by peripheral blood lymphocytes (PBL) or T cell clones stimulated with phytohemagglutinin (PHA). Interferon-gamma (IFN-gamma) production is costimulated in a subset of clones but IL-4 is not. Surprisingly, two T cell clones were reciprocally better costimulated by VIEC or AIEC. EC activation by pretreatment with tumor necrosis factor alpha (TNF-alpha) does not increase T cell costimulation despite large increases in EC cell adhesion molecule expression. Neither VIEC nor AIEC express CTLA4-binding molecules and costimulation is blocked by cyclosporin A, suggesting that CD28 is not involved in EC costimulation of T cells. These data suggest that adult vascular EC costimulate production of IL-2 and IFN-gamma but not IL-4 by mature T cells, that EC costimulation is not increased in inflamed tissues, and that different EC optimally costimulate particular T cells. These findings have implications for the nature of the costimulatory signal(s) provided by EC and may be important in understanding vasculitis or atherosclerosis.

Direct vascular effects of HMG-CoA reductase inhibitors

Several studies have demonstrated that any beneficial effect of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) on coronary events are linked to their hypocholesterolemic properties. However, since mevalonic acid (MVA), the product of the enzyme reaction, is the precursor of numerous metabolites, inhibition of HMG-CoA reductase has the potential to result in pleiotropic effects. MVA and other intermediates of cholesterol synthesis (isoprenoids) are necessary for cell proliferation and other important cell functions, hence effects other than cholesterol reduction may help to explain the antiatherosclerotic properties of statins. Recently, we provided in vitro evidence that fluvastatin, simvastatin, lovastatin, cerivastatin, but not pravastatin, dose-dependently decrease smooth muscle cells (SMC) migration and proliferation, independently of their ability to reduce plasma cholesterol. Moreover, statins are able to reduce the in vitro cholesterol accumulation in macrophages, by blocking cholesterol esterification and endocytosis of modified lipoproteins. This in vitro inhibition was completely prevented by the addition of mevalonate and partially by all-trans farnesol and all-trans geranylgeraniol, confirming the specific role of isoprenoid metabolites--probably through a prenylated protein(s)--in regulating these cellular events. The inhibitory effect of lipophilic statins on SMC proliferation has been recently shown in different models of proliferating cells such as cultured arterial myocytes and rapidly proliferating carotid and femoral intimal lesions in rabbits. Finally, ex vivo studies recently showed that sera from fluvastatin-treated patients interfere with smooth muscle cell proliferation. These results suggest that HMG-CoA reductase inhibitors exert a direct antiatherosclerotic effect in the arterial wall, beyond their effects on plasma lipids, that could translate into a more significant prevention of cardiovascular disease.

Effect of coacervated alpha-elastin on proliferation of vascular smooth muscle and endothelial cells

The arterial wall injury associated with arterial graft implantation causes smooth muscle cells (SMCs) in the media to migrate and proliferate in the intima at the graft-artery junction resulting in anastomotic intimal hyperplasia (AIH). An important step in developing a small-diameter prosthesis may be to stimulate endothelialization and thereby inhibit AIH. In this study, we investigated the effect of coacervated and crosslinked alpha-elastin on proliferation of SMCs and endothelial cells (ECs) in vitro. Coacervation is an important step in the conversion of proelastin to make an elastin fiber in vivo. SMCs and ECs were prepared from porcine aortic media and endothelium, respectively. SMCs and ECs (three to five passages, 4 x 10[4] cells/well) were seeded onto 12 well plates, coated and crosslinked with 0 or 10 mg/mL of coacervated alpha-elastin. After the 1st, 2nd, or 3rd day of cultivation, proliferation was assayed by scintillation counting of [3H]-thymidine incorporation. For the 4th day only, 0, 0.1, 1, 10 mg/mL concentration of coacervated alpha-elastin was coated and crosslinked. SMC proliferation (1st, 2nd day: p<0.005; 3rd, 4th day: p<0.0001) was significantly inhibited over time and dose dependently, eg, 0.1 mg/mL (45.7+/-2.3%: % of control p<0.005), 1 mg/mL (5.9+/-0.7%, p<0.0005), 10 mg/mL (2.8+/-0.4%, p<0.0005). EC proliferation was inhibited over time by 10 mg/mL of coacervated alpha-elastin (2nd, 3rd day: p<0.005; 4th day: p<0.0001), but proliferation (132.8+/-9.9%: % of control p=NS) was stimulated by 0.1 mg/mL of coacervated alpha-elastin. These results suggest that coating and crosslinking a coacervated alpha-elastin into the structure of arterial prosthesis may inhibit AIH and stimulate endothelialization.

Voltage-dependent Ca2+ channels in arterial smooth muscle cells

The past years have seen some significant advances in our understanding of the functional and molecular properties of voltage-dependent Ca2+ channels in arterial smooth muscle. Molecular cloning and expression studies together with experiments on native voltage-dependent Ca2+ channels revealed that these channels are built upon a molecular structure with properties appropriate to function as the main source for Ca2+ entry into arterial smooth muscle cells. This Ca2+ entry regulates intracellular free Ca2+, and thereby arterial tone. We summarize several avenues of recent research that should provide significant insights into the functioning of voltage-dependent Ca2+ channels under conditions that occur in arterial smooth muscle. These experiments have identified important features of voltage-dependent Ca2+ channels, including the steep steady-state voltage-dependence of the channel open probability at steady physiological membrane potentials between -60 and -30 mV, and a relatively high permeation rate at physiological Ca2+ concentrations, being about one million Ca2+ ions/s at -50 mV. This calcium permeation rate seems to be a feature of the pore-forming Ca2+ channel alpha1 subunit, since it was identical for native channels and the expressed alpha1 subunit alone. The channel activity is regulated by dihydropyridines, vasoactive hormones and intracellular signaling pathways. While the membrane potential of smooth muscle cells primarily regulates arterial muscle tone through alterations in Ca2+ influx through dihydropyridine-sensitive voltage-dependent ('L-type') Ca2+ channels, the role of these channels in the differentiation and proliferation of vascular smooth muscle cells is less clear. We discuss recent findings suggesting that other Ca2+ permeable ion channels might be important for the control of Ca2+ influx in dedifferentiated vascular smooth muscle cells.

Shear stress induces transforming growth factor-beta 1 release by arterial endothelial cells

BACKGROUND

Myointimal hyperplasia is a common complication after vascular reconstruction. Increasing shear stress has been shown to reduce formation of myointimal hyperplasia. The aims of our study were (1) to analyze the correlation between shear stress and release of transforming growth factor (TGF)-beta 1 by endothelial cells and (2) to determine the effect of TGF-beta 1 on smooth muscle cell proliferation.

METHODS

Bovine arterial endothelial cells were subjected to increasing shear stress in an in vitro serum-free system. The release of TGF-beta 1 by endothelial cells was assessed by enzyme-linked immunosorbent assay and Western blot analysis. The effect of TGF-beta 1 on the proliferation of the subconfluent monolayer of bovine smooth muscle cells was determined by tritiated thymidine uptake.

RESULTS

Shear stress induced a significant increase of the release of TGF-beta 1 by endothelial cells (p < 0.001). This phenomenon was proportional to the level of shear stress. The amount of TGF-beta 1 released by endothelial cells subjected to shear stress had a significant inhibitory effect on growth rate and tritiated thymidine uptake of smooth muscle cells.

CONCLUSIONS

On the basis of the results of our study, we conclude that increasing shear stress induces release of TGF-beta 1 by arterial endothelial cells in a concentration that has a clear inhibitory effect on smooth muscle cell proliferation. This phenomenon could explain the inhibitory effect of increasing shear stress on the formation of myointimal hyperplasia.

Continuous subendothelial network formed by pericyte-like cells in human vascular bed

The localization of pericyte-like cells in adult human vascular bed was studied immunocytochemically using anti-pericyte antibody--3G5. In large, medium- and small-size arteries, pericyte-like cells were identified in the inner intimal layer, predominantly in the subendothelium, in the outer layer of the media and in the adventitia in vasa vasora. In veins, pericytes were found in the subendothelial layer of the intima, in the media and in the adventitia where they were located in vasa vasora. These cells were revealed in the subendothelium of arterioles, venules and capillaries of the pia mater encephali. Examination of intimal en face preparations of various size blood vessels showed that subendothelial pericyte-like cells form a network contacting with their processes. Thus we found a continuous subendothelial network formed by pericyte-like cells in the human vascular bed.

Inhibitory action of insulin-sensitizing agents on calcium channels in smooth muscle cells from resistance arteries of guinea-pig

1. The actions of troglitazone, pioglitazone, metformin and bezafibrate, agents that improve insulin-resistance, on voltage-dependent Ca2+ channels in arterial smooth muscle cells were examined by use of the conventional and nystatin-perforated whole-cell clamp methods. Single cells were freshly isolated from resistance mesenteric arteries of guinea-pigs. The actions of these agents on 77 mM K+-induced contraction of the isolated arteries were also examined with the use of isometric tension recording. 2. The thiazolidinedione derivatives, troglitazone and pioglitazone, inhibited whole-cell Ca2+ currents in a dose-dependent manner with dissociation constants of 3.0 microM and 44.9 microM and Hill coefficients of 0.61 and 0.68, respectively. These two agents inhibited the 77 mM K+-induced contraction with similar potencies as those inhibiting the Ca2+ currents. Metformin and bezafibrate had no apparent effects on the Ca2+ current or high K+-induced contraction. 3. The inhibitory action of troglitazone on Ca2+ currents was not affected by the command potential, the holding potential, or the stimulation frequency, suggesting that its mode of the action differs from that of known organic Ca2+ channel antagonists. 4. The inhibitory action of troglitazone on Ca2+ currents was not affected by the addition of insulin to, or the removal of glucose from, the solutions. 5. In conclusion, the thiazolidinedione derivatives directly inhibited the voltage-dependent Ca2+ channels in a different manner from that of organic Ca2+ channel antagonists. This inhibitory action on Ca2+ channels was not a common feature of insulin-sensitizing agents.

Dynamics of endothelium-muscle cell contacts in the coronary artery of the dog in ontogeny

The myo-endothelial area in the coronary artery conduit was described in 3 developmental stages: in fetuses, newborns, and adult dogs. Transmission and scanning electron microscopy were used for the study, and morphometry was used for quantitative evaluation. In all three stages, the internal elastic lamina was found to be fenestrated. Endothelial cells and smooth muscle cells (SMC) approached the fenestrae, and protrusions of one or both cells entered into the fenestrae. In some places contacts between endothelial and SMC were found. The patterns of mutual approaches of smooth muscle and endothelial cells, as well as the entering into the fenestrae were similar in all three stages. The myo-endothelial contacts were counted per 100 microns inner circumference of the coronary artery and the numbers observed, i.e. 5.17 +/- 0.50 in fetuses, 1.94 +/- 0.17 in newborns and 0.33 +/- 0.09 in adult animals, proved clearly that the frequency of myo-endothelial contacts, highest in fetuses, decreases with age. With regard to the dual control of the coronary smooth muscle and/or diameter, it is noteworthy that an opposite trend can be observed in the development of innervation of the coronary artery: the autonomic nerve fibres with varicosities are missing in the coronary wall 1 week before birth, while after birth their number keeps increasing. Remarkable enough is also the difference in distances between the endothelium and SMC on the one hand and nerve varicosities and SMC on the other. The above facts indicate a prevalence of endothelial control of coronary diameter.

Proliferation and extracellular matrix production by human infragenicular smooth muscle cells in response to interleukin-1 beta

PURPOSE

Atherosclerotic peripheral vascular disease commonly involves the infragenicular arterial tree. Our study evaluated the effect of interleukin (IL)-1 beta on the proliferation of vascular smooth muscle cells (VSMCs) derived from atherosclerotic infragenicular arteries of human subjects who underwent below-knee amputation, as well as the role of IL-1 beta in VSMCs' production of extracellular matrix components, substances that are important in the transformation of VSMCs from the contractile to the synthetic phenotype. This transformation to the synthetic phenotype is an important step in the formation of the atherosclerotic lesion.

METHODS

Cultures were identified as being of smooth muscle origin through staining with the cytoskeletal marker, alpha-smooth muscle actin. Proliferation assays were performed by seeding confluent cultures of passages 4 to 7 into six-well plates at 10,000 cells per well. After serum starvation, samples were incubated with IL-1 beta (1 ng/ml). Cell number was determined on a daily basis. To study extracellular matrix production, cells were propagated in tissue culture chamber slides in the absence or presence of growth media containing IL-1 beta. After fixation with 100% methanol, each sample was stained with a primary antibody specific for an extracellular matrix component. After staining with the fluorescein-tagged secondary antibody, each sample was examined using immunofluorescent microscopic examination.

RESULTS

The results of our proliferation assays showed that IL-1 beta caused a significant increase in the proliferation of VSMCs at 24, 48, 72, and 96 hours (p < or = 0.003 when comparing IL-1 beta-treated samples with control specimens at each time period using unpaired t test). The number of IL-1 beta-treated cells at 96 hours was double the number present in the control samples (16,033 +/- 238 vs 8102 +/- 824). When compared with control samples, IL-1 beta was found to affect the production of extracellular matrix proteins by infragenicular VSMCs. IL-1 beta caused an increase in the production of fibronectin, a decrease in the production of laminin, and no change in the production of collagen type IV.

CONCLUSIONS

These results suggest that interleukin-1 beta acts as a potent stimulant of the proliferation of human infragenicular VSMCs. IL-1 beta also acts to augment the production of fibronectin by these cells. Fibronectin has been implicated in the phenotypic transformation of VSMCs from the contractile to the synthetic state. Therefore, IL-1 beta may serve as an important regulatory factor in the development of atherosclerosis by stimulating the proliferation of VSMCs and their transformation to the synthetic state, two important steps in the formation of the atherosclerotic lesion.

[Intramural blood vessels of the large intestine of the horse (Equus przewalskii f. caballus)]

The vascular system of the large intestine of 12 horses was examined by means of vascular corrosion casts, histology and transmission electron microscopy providing the following results. The Aa. et Vv. breves et longae leave the mesenteric vessels, respectively the subserously on the teniae lying cecal vessels to reach the tela subserosa at the mesenteric margin. The short vessels enter the deeper layers of the wall instantly, whereas the Aa. et Vv. longae move towards the submucosa by penetrating the muscular layers after a variable subserous course. The tela submucosa contains an arterial and a venous vascular plexus. In broader areas of the submucosa a three-dimensional vascular network can be found. This consists of a deep and a superficial vascular plexus, which are closely interconnected. The deep plexus is applied to the inner circular muscles, whereas the superficial plexus is adjacent to the muscularis mucosae. The (deep) arterial plexus receives its afflux from the Aa. breves et longae and supplies parts of the circular muscle layer with recurrent muscle branches. The vascularisation of the mucosa also originates from the submucosal (superficial) plexus. In the basal tunica mucosa, the ascending arteries form a transversal network from which arterioles branch into periglandular capillaries around each Lieberkühn crypt. Close to the lumen, a polygonal subepithelial capillary system is formed. The capillaries turn into postcapillary venules immediately below the epithelium of the mucosal surface. Veins move vertically through the submucosa to enter the submucosal plexus after few inflowing side branches. Branches of the subserous-submucosal connections form an intermuscular plexus between the circular and longitudinal muscular layer. This plexus supplies the capillaries of the tunica muscularis. The subepithelial capillaries are predominantly lined with a fenestrated endothelium, whereas the capillaries of the pericryptal mucosa mainly show a continuous endothelial lining. The latter contain multiple vesicles, which may fuse in order to form transcytoplasmic channels. Sphincter-like muscle bundles at the transition points from capillaries to venules may provide hemodynamic regulatory structures in the submucosa of the horse. Veins with circumferential cushions of smooth muscle fibres, so-called 'throttle veins', are also found.

Angiopeptin, a somatostatin analogue, inhibits rat coronary artery and aorta smooth muscle cell proliferation induced by the thromboxane A2 mimetic U46619

Thromboxane A2 (TXA2) is a potent mitogenic agent. Its synthesis is increased in transplant patients during rejection episodes, which is the suspected etiology of accelerated transplant arteriosclerosis. Angiopeptin, a stable analogue of somatostatin, inhibits arterial myointimal thickening in a number of vascular balloon injury models of angioplasty and in vivo models of transplant arteriosclerosis. In this study, we investigated whether TXA2-induced smooth muscle cell proliferation is inhibited by Angiopeptin in vitro. Primary rat coronary and aorta smooth muscle cells were cultured in the presence of U46619, a TXA2 mimetic. Proliferation induced by U46619, as determined by 3H-thymidine incorporation, was abrogated by two specific thromboxane receptor antagonists, SQ 30741 and SQ 29548, indicating that the effect of U46619 on smooth muscle cells is a specific receptor-mediated response. We found Angiopeptin to inhibit proliferation following exposure of both coronary and aorta smooth muscle cells to varying concentrations of U46619 for 3 and 6 days. This study demonstrates that U46619 exerts a specific receptor-mediated response stimulating the rat coronary and aorta smooth muscle cell proliferation. This mitogenic effect is obtained by increasing the G1 to S transition rate. Angiopeptin inhibits thromboxane-induced cell proliferation to the same extent as a thromboxane antagonist. This inhibition is obtained by maintaining the noncycling fraction in that Angiopeptin prevents a progression from G0-G1 to S phase.

Heterogeneity of L-type calcium current density in coronary smooth muscle

Heterogeneity of vascular responses to physiological and pharmacological stimuli has been demonstrated throughout the coronary circulation. Typically, this heterogeneity is based on vessel size. Although the cellular mechanisms for this heterogeneity are unknown, one plausible factor may be heterogeneous distribution of ion channels important in regulation of vascular tone. Because of the importance of voltage-gated Ca2+ channels in regulation of vascular tone, we hypothesized that these channels would be unequally distributed throughout the coronary arterial bed. To test this hypothesis, voltage-gated Ca2+ current was measured in smooth muscle from conduit arteries (>1.0 mm), small arteries (200-250 microm), and large arterioles (75-125 microm) of miniature swine using whole cell voltage-clamp techniques. With 2 mM Ca2+ or 10 mM Ba2+ as charge carrier, voltage-gated Ca2+ current density was inversely related to arterial diameter, i.e., large arterioles > small arteries > conduit. Peak inward currents (10 mM Ba2+) were increased approximately 2.5- and approximately 1.5-fold in large arterioles and small arteries, respectively, compared with conduit arteries (-5.58 +/- 0.53, -3.54 +/- 0.34, and -2.26 +/- 0.31 pA/pF, respectively). In physiological Ca2+ (2 mM), small arteries demonstrated increased inward current at membrane potentials within the physiological range for vascular smooth muscle (as negative as -40 mV) compared with conduit arteries. In addition, cells from large arterioles showed a negative shift in the membrane potential for half-maximal activation compared with small and conduit arteries (-13.23 +/- 0.88, -6.22 +/- 1.35, and -8.62 +/- 0.81 mV, respectively; P < 0.05). Voltage characteristics and dihydropyridine sensitivity identified this Ca2+ current as predominantly L-type current in all arterial sizes. We conclude that L-type Ca2+ current density is inversely related to arterial diameter within the coronary arterial vasculature. This heterogeneity of Ca2+ current density may provide, in part, the basis for functional heterogeneity within the coronary circulation.

Lipoprotein trafficking in vascular cells. Molecular Trojan horses and cellular saboteurs

During the pathogenesis of atherosclerosis, inflammatory cells such as the monocyte-derived macrophage accumulate in the vessel wall where they release cytokines. Initially, cytokines may assist in CE removal of lipoprotein-derived cholesterol/CE hydrolysis to clear intracellular lipid. When plasma levels of LDL become elevated, the vessel wall becomes lipid-engorged over time because it is unable to traffick the large amounts of endocytosed LDL-CE from the cell. In addition, lipoprotein entrapment by the extracellular matrix can lead to the progressive oxidation of LDL because of the action of lipoxygenases, reactive oxygen species, peroxynitrite, and/or myeloperoxidase. A range of oxidized LDL species is thus generated, ultimately resulting in their delivery to vascular cells through several families of scavenger receptors (Fig 1). These molecular Trojan horses and cellular saboteurs once formed or deposited in the cell can contribute to, and participate in, formation of macrophage- and smooth muscle-derived foam cells. A lipid-enriched fatty streak along the vessel wall can ensue. In addition to foam cell development, products of LDL peroxidation may activate endothelial cells, increase smooth muscle mitogenesis, or induce apoptosis because of the effects of oxysterols and products of lipid peroxidation (Fig 1). Because antioxidant defenses may be limited in the microenvironment of the cell or within LDL, the oxidation process continues to progress. Enzymes associated with HDL such as PAF acetylhydrolase and paraoxonase can participate in the elimination of biologically active lipids, but diminished cellular antioxidant activity coupled with low levels of HDL may allow acceleration of the clinical course of vascular disease. There is still much to be learned about how modified LDL initiate cellular signals that lead to inflammation, mitosis, or cholesterol accumulation. The present challenges include elucidation of the key signaling events that regulate lipoprotein-derived cholesterol trafficking in the vessel wall, which can impact on the pathogenesis of vascular disease.

Immunohistochemical examination of trophoblast populations in human first trimester and term placentae and of first trimester spiral arteries with the monoclonal antibody GZ 112

This paper presents an immunohistochemical study with a monoclonal mouse antibody GZ 112, an IgG1 kappa, which is directed against an antigen expressed in first trimester placenta by all proliferative and invasive extravillous trophoblast populations including a population of Langhans cells that represent extravillous stem cells. Additionally, the GZ 112 antigen is associated with morphological changes of spiral arteries preceding local trophoblast invasion. In term placentae, GZ 112 also strongly reacts with all extravillous trophoblast populations, but additionally recognizes partly villous cytotrophoblast and syncytiotrophoblast too, displaying a heterogeneous staining pattern. GZ 112 is directed against a 42-KDa antigen. Intracytoplasmic network-like staining and cross-reactivity with various human surface and glandular epithelia indicate a cytokeratin intermediate filament or a cytokeratin intermediate filament associated molecule as antigen.

Costimulatory molecules in human atherosclerotic plaques: an indication of antigen specific T lymphocyte activation

Atherosclerotic plaques contain inflammation, composed largely of macrophages and lymphocytes. A proportion of lymphocytes shows signs of activation, but the question arises whether they are activated in an antigen specific way. The expression of costimulatory molecules-receptors that provide accessory signals during antigen-specific activation is a prerequisite for such a condition. This aspect of inflammation in atherosclerotic lesions has not been investigated. Human arterial segments with diffuse intimal thickening, fatty streaks and atherosclerotic plaques were studied with immuno-single and double staining methods. Macrophages and T lymphocytes were stained with CD68 and CD3, respectively, and pan-B cell markers CD19 and CD22 were also used. Costimulatory molecules B7-1 and B7-2, together with their common ligand CD28, and CD27 with its ligand CD70, were stained with specific monoclonal antibodies. The results show that most T lymphocytes were CD27 positive and that only a subpopulation of these (5-15%) was positive also for B7-1, CD28 and CD70. Macrophages expressed B7-1, B7-2, CD28 and CD70, while macrophages positive for CD28 and CD70 have not been reported yet. The expression of costimulatory molecules was most pronounced in the superficial layers at the fibrous cap, but decreased towards the lipid core. This study shows, therefore, that atherosclerotic plaques provide costimulatory signals generally accepted as a prerequisite for adequate T cell stimulation. In addition, this study reveals that only approximately 5-15% of the lymphocytes appears actively involved in the inflammatory reaction.

Effects of acidosis or alkalosis on the actions of nifedipine on excitation-contraction coupling in the rat tail artery

1. The clinical success of calcium channel blockers in the management of organ ischaemia is less than theoretically anticipated. Blood gas/pH changes are associated with organ ischaemia; therefore, we studied the possibility that pH changes could alter the pharmacological effects of the calcium channel blocker nifedipine on rat tail artery contracted by either noradrenaline (NA) or potassium. 2. Segments (2-2.5 cm) of the proximal third of the male Sprague-Dawley rat tail ventral artery were initially bathed and perfused with a physiological salt solution (PSS; pH 7.48) for 25-30 min, after which time bathing/perfusion was continued with a nominally calcium-free PSS made acidotic (pH 7.20), alkalotic (pH 7.67) or unaltered (control). After equilibration, the perfusion pressure (PP) responses to increasing concentrations of calcium in the presence of NA (3.0 mumol/L) or potassium (100 mmol/L) with nifedipine or its vehicle were recorded. 3. The calcium sensitivity of potassium- or NA-stimulated rat tail arteries was reduced during acidosis, as was the maximum PP in potassium- but not NA-stimulated tissues. Alkalosis reduced the calcium sensitivity in potassium- but not NA-stimulated contraction and had no effect on maximum PP. 4. The inhibitory effect of nifedipine (0.6 mumol/L) on contraction was enhanced during acidosis in either NA- or potassium-stimulated arteries and also during alkalosis in NA-treated arteries, although it had little effect during normal conditions. 5. The results indicate that changes in pH alter the vascular contractility profile in a manner dependent on the excitation-contraction coupling mode. The calcium antagonistic effect of nifedipine is pH dependent and it is suggested that pH changes associated with ischaemic conditions may alter the therapeutic profile of nifedipine.

Progesterone inhibits arterial smooth muscle cell proliferation

Mortality from atherosclerotic cardiovascular disease is lower in premenopausal women than in age-matched men. It is also lower in postmenopausal women who take estrogens and progestins together rather than estrogens alone. Progesterone receptors were detected in human and rat aortic smooth muscle cells in vivo and in vitro (in subculture). We examined the effect of progesterone on proliferation of smooth muscle cells, important constituents of atherosclerotic plaques. Progesterone at physiologic levels inhibited DNA synthesis and proliferation in these cells in a dose-dependent manner, and pretreatment with the progesterone receptor antagonist RU486 blocked inhibition. Cyclin A and E messenger RNA levels decreased after progesterone treatment but those of cyclin B and D1 did not change. This cell cycle-dependent inhibition of arterial smooth muscle cell proliferation by progesterone may represent a mechanism for the hormone's protective effect against atherosclerosis.

Effect of intra-arterial environment on endothelialization and basement membrane organization in polytetrafluoroethylene grafts

PURPOSE

To determine if a complete intra-arterial environment affects endothelialization rate and basement membrane organization in polytetrafluoroethylene (PTFE) grafts.

METHOD

Thirty dogs underwent either infrarenal abdominal aorta PTFE interposition (12) or intraluminal stented (18) grafting. Grafts were explanted at 4 and 8 weeks and rate of endothelial ingrowth calculated. Endothelial cells were identified and basement membrane organization assessed using antibodies against endothelial cell-specific surface antigen CD31, type IV collagen, and laminin.

RESULTS

Endothelialization rates, expressed as percent graft surface area coverage per week, were 3.7% +/- 0.62% (4-week control), 12.9% +/- 0.58% (4-week stented), 4.2% +/- 0.62% (8-week control), and 10.0% +/- 0.54% per week (8-week stented grafts). Endothelial repaving rates were constant for control and increased in all stented grafts (P <0.01). At 4 weeks, laminin was identified in all control (6 of 6) and no stented grafts. Staining was confined to the 20% of the hyperplastic intimal area immediately below the endothelium. At 4 weeks, type IV collagen was present throughout the entire hyperplastic intima in control specimens but was confined to a discrete subendothelial zone in stented grafts. By 8 weeks, type IV collagen became concentrated in the luminal one third of the intima in control grafts.

CONCLUSION

Intra-arterial graft location is associated with early formation of an organized basement membrane and accelerated endothelialization in PTFE grafts.

Histological study of decidual spiral arteries and the presence of maternal erythrocytes in the intervillous space during the first trimester of normal human pregnancy

During the first trimester in normal human pregnancy, endovascular trophoblast migrate along the decidual spiral arteries and invade their walls to produce physiological change. There is controversy as to whether invading trophoblast plug the arteries and prevent blood flow into the intervillous space. Using light microscopy, placental bed sections from 25 first trimester gravid hysterectomy specimens were examined. From each specimen, one section was divided into equal central and peripheral compartments. Maternal red blood cells were present in the intervillous space in all specimens, in both central and peripheral areas. In total, 232 decidual spiral arteries were found, each of those represented by several cross sections, 136 in the central area and 96 in the periphery. Seventy-nine per cent had undergone physiological change (significantly more in the centre than in the periphery), 63 per cent contained scattered endovascular trophoblast, 20 per cent had plugs of trophoblast partially occluding the vessel and 17 per cent had plugs totally filling the vessel lumen. These data confirm that in the first trimester of normal pregnancy, maternal blood enters the intervillous space, total plugging of the arterial system by trophoblast is not common, and more spiral arteries undergo physiological change in the centre than in the periphery.

Human cytomegalovirus does not induce human leukocyte antigen class II expression on arterial endothelial cells

Human cytomegalovirus (CMV) has been associated with allograft rejection and, in particular, with transplant-associated arteriosclerosis. However, the role CMV plays in the development of transplant-associated arteriosclerosis remains unclear. CMV can infect the endothelium, the interface between allograft tissue and the host immune cells, but the direct induction of endothelial human leukocyte antigen (HLA) class II by CMV remains controversial. Our previous studies with venous endothelial cells (EC) have shown that CMV does not directly induce this antigen on infected EC and, furthermore, renders these cells refractory to interferon (IFN)-gamma induction. However, questions have arisen regarding the relevance of these findings to arterial endothelia. Thus, we have extended these studies to determine whether similar interactions occur in arterial EC. EC derived from human coronary artery, aorta, and umbilical artery were assayed by immunofluorescence flow cytometry and dual immunohistochemical staining following IFN-gamma treatment and/or inoculation with CMV. Data generated by these experiments demonstrate that regardless of vascular origin: (1) CMV does not directly induce endothelial surface or cytoplasmic HLA class II, and (2) although uninfected arterial EC are HLA class II inducible by IFN-gamma, infected cells are completely refractory to this effect. These results suggest that CMV-mediated inhibition of HLA class II expression is a phenomenon shared by human arterial and venous endothelia of both fetal and adult origin.

Acetylcholine-induced K+ currents in smooth muscle cells of intact rat small arteries

1. The mechanism of the sustained acetylcholine-induced endothelium-dependent hyperpolarization (EDH) in intact rat small mesenteric arteries prestimulated with noradrenaline (10(-6) M) was investigated by means of the single microelectrode voltage-clamp method. 2. The vascular smooth muscle cells (VSMCs) in this preparation are poorly or even not coupled for the reasons that: (1) the mean input resistance Rlnp of the clamped vascular smooth muscle increases from 120 M omega under control conditions to 440 M omega after application of K+ channel blocking drugs, (2) the voltage relaxation after injection of hyperpolarizing currents has a monoexponential time course and is linearly dependent on Rlnp, and (3) voltage steps induced by current-clamp steps are not transferred to locations in the vascular musculature 120 microns apart from the current injecting microelectrode. 3. Sustained (> 5 min) application of ACh (10(-5) M) hyperpolarized the VSMCs by induction of a hyperpolarizing current. This effect was completely blocked by the inhibitor of the nitric oxide (NO) synthase L-NAME (10(-3) M) but not by the inhibitor of the soluble guanylate cyclase (sGCl) Methylene Blue (MB, 10(-4) M). 4. Application of the NO donor sodium nitroprusside (SNP, 10(-6) M) for more than 5 min mimicked the induction of the endothelium-dependent hyperpolarizing current in vessels with destroyed endothelium. The reversal potential of this current is dependent on the extracellular K+ concentration. The effect of SNP could also not be blocked by MB. 5. The blockers of ATP-dependent and Ca(2+)-dependent K+ channels, glibenclamide (Glb, 10(-5) M) and charybdotoxin (CTX, 5 x 10(-8) M), respectively, blocked a hyperpolarizing current in the VSMCs similar to the ACh- or SNP-induced current. 6. The isolated application of either Glb or CTX did not block the activation of the hyperpolarizing current by SNP. Only the combined administration of Glb and CTX blocked the SNP-induced current completely. 7. Our results suggest that in rat small mesenteric artery, ACh hyperpolarizes the VSMCs tonically by activating both ATP- and Ca(2+)-dependent K+ currents, only via release of NO from the endothelium without need for activation of the sGCl.

Pregnancy stimulation of DNA synthesis and uterine blood flow in the guinea pig

Pregnancy stimulates DNA synthesis in uterine artery smooth muscle cells. Unknown is whether DNA synthesis increases in all layers of the vessel wall in uterine or nonuterine vessels, the distribution and time course of the proliferative response in relation to the rise in uterine blood flow, and the extent to which a pregnancy-induced rise in DNA synthesis can be mimicked by chronic estradiol treatment. To measure DNA synthesis, we implanted bromodeoxyuridine (BrdU, 400 mg) s.c. for 14-d periods in three nonpregnant, nine pregnant, three vehicle, and five estradiol (2.5 mg/14 d)-treated guinea pigs. Uterine blood flow was measured in four nonpregnant and 18 pregnant animals using radiolabeled microspheres. Pregnancy stimulated DNA synthesis in the adventitia, media, and intima of the uterine artery, radial artery (the vessels deriving from the main uterine artery and entering the uterine wall), and uterine vein but not in the aorta or mesenteric artery. Maximal uterine artery medial area and labeling indices in all layers of the uterine artery, uterine vein, and the radial artery adventitia were attained by mid-pregnancy (d 28-42 of the guinea pig's 63-day gestation), whereas DNA synthesis increased progressively until term in the radial artery media and intima. The greatest rise in uterine artery blood flow (y) occurred after peak proliferation in the uterine artery and in concert with radial artery medial and intimal proliferation (y = 1.99 x 10(0.023x) where x is day postconception). 17beta-Estradiol treatment for 14 d in ovariectomized guinea pigs increased DNA synthesis in the radial artery adventitia and tended (p = 0.08) to increase labeling indices in the media of all vessels examined but did not fully reproduce the effects of pregnancy. We concluded that pregnancy-related, possibly hormonal stimuli prompted growth in all layers of the uterine artery wall by mid-pregnancy and served to initiate a rise in uterine blood flow. The resultant increase in flow and shear stress likely stimulated DNA synthesis in the radial artery which helped sustain the rise in flow near term.

Adventitial stripping does not strip the adventitia

This study investigates the process of stripping the adventitia off a blood vessel, which is a normal procedure prior to performing a microvascular anastomosis. In five rats, the common carotid and the superficial femoral arteries of one side were stripped sharply, whereas the arteries of the other side were left unstripped to serve as controls. In a further set of five rats, the arteries were stripped bluntly. Immediately following stripping, experimental and control arterial segments were removed. Histology of cross sections of the segments was studied. In no case was there complete removal of the adventitia. When stripped and control arterial sections were compared, no significant difference between cross-sectional adventitial areas could be demonstrated. Morphologic study revealed that stripping mainly removes large collagen fibers from the adventitia. The small collagen fibrils that are still in place fan out in such a way that although considerable tissue is removed, the volume that the adventitia occupies remains the same. Stripping the adventitia does not cause complete removal of the adventitia, and in this study no significant reduction in the adventitial volume could be found. Stripping does, however, allow a better view of the cut edge of the vessel wall under an operating microscope. Since blunt stripping could cause damage to other vessel wall layers, sharp stripping is to be preferred.

Endothelial-derived superoxide anions in pig coronary arteries: evidence from lucigenin chemiluminescence and histochemical techniques

1. The generation of superoxide anions (O2-) by intact pig coronary artery rings was measured using a lucigenin-enhanced chemiluminescence technique and a histochemical technique with Nitroblue Tetrazolium (NBT) staining. 2. Isolated arteries with intact endothelium generated O2- at a rate of 9.0 +/- 0.8 pmol min-1 (mg dry weight)-1; this rate was diminished by about 24% when the endothelium was removed. The NBT staining of arterial ring preparations showed formazan precipitation mainly in the intima. Arterial rings were pretreated with diethylthiocarbamate in order to inhibit Cu-Zn superoxide dismutase (SOD) activity which increased the O2- generation by 184 +/- 55% (n = 10; P < 0.01). Stimulation of protein kinase C with phorbol 12-myristate 13-acetate (5 microM) enhanced endothelium-dependent O2- generation by 136 +/- 20% (n = 19; P < 0.01). Neither stimulation with bradykinin or substance P, nor inhibition with NG-nitro-L-arginine methyl ester of endothelial nitric oxide synthase had a significant effect on O2- generation. In contrast, the inhibition of flavoproteins with diphenyliodonium decreased concentration-dependent O2- generation (IC50, 1.85 +/- 5.33 microM). Inhibition of tetrahydrobiopterin synthesis with 2,4-diamino-6-hydroxy-pyrimidine resulted in a reduced generation of O2- by about 55%. 3. The addition of 100 microM NADH and 100 microM NADPH resulted in an excessive generation of O2- at a rate of 0.68 +/- 0.03 and 0.26 +/- 0.01 nmol O2- min-1 (mg protein)-1, respectively, in the membrane fraction, but not in the cytosolic fraction, of homogenates obtained from arteries. 4. The results suggest that intact coronary arteries do generate O2- under basal conditions and that the endothelial layer significantly contributes to this phenomenon. This generation of O2- is greatly influenced by intrinsic SOD activity. It is suggested that basal vascular O2- generation is mainly due to membrane-bound NAD(P)H oxidase activity and/or tetrahydrobiopterin-dependent processes.