Changes in the Organization of the Smooth Muscle Cells in Rat Vein Grafts

Mechanical tensile stress in vein grafts increases suddenly under the influence of arterial blood pressure. In this study, we examined the influence of increased tensile stress on the organization of the smooth muscle cells (SMCs) in the neointima and media of the rat vein grafts. An autogenous jugular vein was grafted into the abdominal aorta of the rat, and changes in the organization of the vein graft SMCs were studied by observing the distribution of SMC actin filaments and nuclei at 3 min and 1, 5, 10, and 30 days after surgery. In a normal jugular vein, the average wall circumferential tensile stress was ~ 3 kPa at an internal pressure of 3 mm Hg. The SMCs, that contained long, slender actin filamentous bundles, were oriented mainly in the circumferential direction of the vessel, and constituted a 2- to 3-cell-thick medial layer underneath the endothelium. In a vein graft, the wall circumferential tensile stress suddenly increased by ~ 140 times compared with the control level. In response to this suddenly increased stress, the SMC layer was stretched into a structure with scattered pores and disrupted SMC actin filamentous bundles within 3 min. This initial change was followed by a rapid reduction in the density of the SMC nuclei and actin filaments within 1 day and progressive SMC proliferation, that was associated with medial thickening and a change in the SMC orientation from 5 to 30 days. Further studies showed that a local inflation of normal jugular veins to 120 mm Hg for 3 min induced a similar change as found in the vein grafts, whereas the organization of the SMCs was not significantly changed in vein-vein grafts, that did not experience a change in tensile stress. These results suggested that increased tensile stress contributed to the initial damage of the SMCs and played a role in the regulation of medial SMC remodeling in vein grafts. © 1998 Biomedical Engineering Society. PAC98: 8722-q, 8745-k     

Apoptosis, cell proliferation and modulation of cyclin-dependent kinase inhibitor p21cip1 in vascular remodelling during vein arterialization in the rat

Neo-intima development and atherosclerosis limit long-term vein graft use for revascularization of ischaemic tissues. Using a rat model, which is technically less challenging than smaller rodents, we provide evidence that the temporal morphological, cellular, and key molecular events during vein arterialization resemble the human vein graft adaptation. Right jugular vein was surgically connected to carotid artery and observed up to 90 days. Morphometry demonstrated gradual thickening of the medial layer and important formation of neo-intima with deposition of smooth muscle cells (SMC) in the subendothelial layer from day 7 onwards. Transmission electron microscopy showed that SMCs switch from the contractile to synthetic phenotype on day 3 and new elastic lamellae formation occurs from day 7 onwards. Apoptosis markedly increased on day 1, while α-actin immunostaining for SMC almost disappeared by day 3. On day 7, cell proliferation reached the highest level and cellular density gradually increased until day 90. The relative magnitude of cellular changes was higher in the intima vs . the media layer (100 vs . 2 times respectively). Cyclin-dependent kinase inhibitors (CDKIs) p27^Kip1 and p16^INKA remained unchanged, whereas p21^Cip1 was gradually downregulated, reaching the lowest levels by day 7 until day 90. Taken together, these data indicate for the first time that p21^Cip1 is the main CDKI protein modulated during the arterialization process the rat model of vein arterialization that may be useful to identify and validate new targets and interventions to improve the long-term patency of vein grafts.     

Proliferative activity in stenotic human aortocoronary bypass grafts.

BACKGROUND: Aortocoronary bypass graft disease is responsible for long-term failure of autologous vein grafts. The analyses of proliferation and cell type characterisation in human bypass grafts harvested during re-do surgery make it possible to investigate the cellular processes leading to bypass graft failure. METHODS: 30 stenotic vein grafts and 25 control veins were explantated during re-do heart surgery procedures. The total area and cell count of the neointima, media and adventitia were calculated computer-assisted. Actively proliferating cells were identified using antibody to Ki-67 and positive cells were determined by double-label immunocytochemistry with SMC alpha-actin, CD 31 (endothelial cells), CD 68 (macrophages) and CD 45 (T-lymphocytes). RESULTS: Active proliferation was detected in different cell types with an average proliferation index of 0.15%, 0.18% and 0.086% for neointima, media and adventitia. Only 9% of proliferating cells in the neointima were SMC (not identified cells 40%); correspondingly, 14% SMC (not identified cells 33%) were detected in the media. Endothelial cells turned out to be the predominant proliferating cell type in all sections of the vessel wall. CONCLUSION: Proliferation in our series of stenotic vein grafts occurred at a low level, but was significantly higher compared to native control veins. While proliferation may play an important role in early lesions, our data clearly show low proliferation activity in advanced graft lesions. The identification of proliferating macrophages and T-lymphocytes implicate an additional inflammatory component in the development of human bypass graft disease. SUMMARY: To clarify the role of cellular proliferation in human aortocoronary bypass grafts, we characterized the cellular composition and proliferation index in 30 stenotic saphenous vein grafts in comparison to 25 native veins. Proliferation in our series of stenotic vein grafts occurred at a low level, but was significantly higher compared to native control veins.     

Vascular tissue adaptations in end-to-end autologous arterial grafts in rats: a morphometric analysis

Autologous vein grafts are employed extensively to bypass stenoses in the arterial circulation. More recently arterial segments have been used for such bypass surgery. In this study the adaptation of regenerating vascular tissues in experimental autologous artery grafts (4 mm long and 1 mm in diameter) in 20 adult male Wistar rats was analysed. At 1, 2, 4, 8 and 16 wk after insertion, 4 grafts per time interval were removed, processed for high resolution light microscopy and the thicknesses of the media and neointima, as well as the area fractions of smooth muscle cells, were analysed morphometrically. All grafts were reendothelialised by 2 wk. Neointimal hyperplasia (a subendothelial layer of smooth muscle cells) developed in all grafts and reached its maximal thickness (40.4±4.7 μm) at 2 wk. The area fraction of smooth muscle cells in the neointima of the artery grafts did not change significantly at any time from 2 to 16 wk. The media underlying the neointima of the artery grafts remained relatively constant throughout the 16 wk duration of the experiment. Whilst the total wall thickness of the grafts reduced significantly between 2 and 4 wk after insertion, at all times the grafts were thicker than the host artery.     

Time course of the regression of intimal hyperplasia in experimental vein grafts.

A previous study in which vein grafts were removed from the arterial circulation and reimplanted into the venous circulation of the same animal demonstrated regression of vein graft intimal hyperplasia and medial thickening within 14 days. The present study was designed to characterize the kinetics of the morphological and ultrastructural changes over this 14-day period. Twenty-one male New Zealand White rabbits received a reversed vein interposition bypass graft of the right common carotid artery. Fourteen days after the procedure, 21 vein grafts were isolated, removed, and reimplanted into the contralateral external jugular venous system as veno-venous interposition bypass grafts (reversal grafts). The grafts were harvested at 60 minutes, 1 day, 3 days, 5 days, 7 days, and 14 days after reversal. Before insertion into the venous circulation, the vein graft had a confluent endothelial cell surface with multiple layers of smooth muscle cells representing intimal hyperplasia. After 1 hour, the reversal graft retained an intact endothelial cell layer with no evidence of tissue edema or cellular disruption. By 24 hours, there were a few blood cells on the endothelial cell surface. There was no inflammatory infiltrate seen in the subendothelium, and the smooth muscle cells were unaltered. At 3 days, the endothelial cell lining remained intact with no polymorphonucleocytes in the subendothelium or within the graft wall. Underlying smooth muscle cells at this time were noted to contain cytoplasmic vacuoles. At 5 days, there were no inflammatory cells seen on the surface or within the vein graft wall, but many of the underlying smooth muscle cells within the intimal hyperplasia were noted to be fragmented and to have clumping of chromatin. After 7 days, the endothelial cells remained intact and there was widespread evidence of apoptosis beneath the subendothelium with highly fragmented smooth muscle cells, some of which were histologically in the process of breaking up. At 14 days, the grafts retained uniform endothelial cell surfaces. Most of the smooth muscle cells that composed the intimal hyperplasia seen before implantation as a reversal graft were gone. Areas of newly laid down collagen could be observed. There were no acute inflammatory cells but for some mast cells seen in the graft wall. This study demonstrates that in this model, regression of intimal hyperplasia was associated with apoptosis of the smooth muscle cells and the deposition of collagen. There was no evidence that this process is mediated by an acute inflammatory response. Regression therefore appears to be due to induction of smooth muscle cell apoptosis by either a reduction in pressure or flow or a combination of both factors. The findings will enable a systematic cellular and molecular analysis of the biology of regression, which may afford clues to better understand the biology of the developing intimal hyperplasia.     

Histologic Fate of the Venous Coronary Artery Bypass in Dogs

The histologic fate of venous grafts used for coronary artery bypass has been observed with light and electron microscopy in dogs. Endothelial damage and thrombosis were chiefly limited to the first postoperative week. The muscular media uniformly suffered extensive necrosis and inflammatory cell infiltration during the first week. Its smooth muscle cells either hypertrophied, died or underwent apparent fibroblastic transformation, with eventual fibrous replacement, to a variable degree, of the vein wall. Vascular wall ischemia due to interruption of vasa vasorum during transplantation appears to initiate these medial changes. Much more slowly, intimal thickening by myointimal cells and collagen may reduce the graft lumen to a variable extent.     

Induction of smooth muscle cell-like phenotype in marrow-derived cells among regenerating urinary bladder smooth muscle cells

Tissue regeneration on acellular matrix grafts has great potential for therapeutic organ reconstruction. However, hollow organs such as the bladder require smooth muscle cell regeneration, the mechanisms of which are not well defined. We investigated the mechanisms by which bone marrow cells participate in smooth muscle formation during urinary bladder regeneration, using in vivo and in vitro model systems. In vivo bone marrow cells expressing green fluorescent protein were transplanted into lethally irradiated rats. Eight weeks following transplantation, bladder domes of the rats were replaced with bladder acellular matrix grafts. Two weeks after operation transplanted marrow cells repopulated the graft, as evidenced by detection of fluorescent staining. By 12 weeks they reconstituted the smooth muscle layer, with native smooth muscle cells (SMC) infiltrating the graft. In vitro, the differential effects of distinct growth factor environments created by either bladder urothelial cells or bladder SMC on phenotypic changes of marrow cells were examined. First, supernatants of cultured bladder cells were used as conditioned media for marrow cells. Second, these conditions were reconstituted with exogenous growth factors. In each case, a growth factor milieu characteristic of SMC induced an SMC-like phenotype in marrow cells, whereas that of urothelial cells failed. These findings suggest that marrow cells differentiate into smooth muscle on acellular matrix grafts in response to the environment created by SMC.     

原位静脉动脉化与静脉动脉间置后静脉的实验形态学研究

目的：探讨原位静脉动脉化与静脉动脉间置后，静脉的组织学和超微结构变化。在１８只犬后肢设计原位大隐静脉动脉化，静脉动脉间置实验模型，对原位大隐静脉动脉化和静脉动脉间置后不同时间（２、４、８、１６ｗ）静脉管壁的变化，进行了实验形态学观察。结果：①原位静脉动脉化后早期内皮细胞损伤较轻微，中、晚期主要表现为管腔内皮细胞损伤较轻微，管腔的扩张和中膜平滑肌的增生，肥厚；②静脉动脉间置早期内皮细胞有广泛脱落，中膜平滑肌细胞肿胀，细胞间积液，中晚期变化主要为内皮不规则增生，肥厚，中膜平滑肌不同程度的增生与纤维化，使血管腔呈现不同程度的狭窄。结论：原位静脉动脉化后静脉呈现结构上的“动脉化”倾向，并且较静脉动脉间置更有利于保持血管的通畅。     

Cytocontractile structures and proteins of smooth muscle cells during the formation of experimental lesions

The time course of structural changes in vascular smooth muscle cells (SMC) was investigated during the formation of an experimental lesion in response to balloon injury. We compared the filamentous organization, evaluated by quantitative electron microscopy, with the cellular content of two representative cytocontractile proteins (myosin and tropomyosin) as assessed by immunofluorescence. We found that the changes peak between 7 and 14 days after injury and that they are visible both in the neointima and to a lesser extent in the inner media. While virtually all SMC are of a filament-rich phenotype in the undisturbed media, after balloon injury SMC migrated into the intima and about 90% of these latter cells were either of a organelle-rich or an intermediate phenotype, with the remaining 10% being of the filament-rich phenotype. In the inner media about 40% of cells were either of organelle-rich or intermediate phenotype. In contrast to these profound organizational changes of responding SMC, histochemistry revealed only a slight and probably transient decrease of the cellular content of myosin and tropomyosin at that time point. Twenty-eight days after injury the discrepancies between the content and the organization of cytocontractile proteins became more apparent. While virtually all SMC showed a homogeneous intensive staining with both antibodies, indistinguishable from the media SMC, the organization of cytoplasmic filaments had not totally recovered. Even though this morphological study does not permit conclusions to be drawn on the contractile function of the cells, it shows that both the organization and the content of cytocontractile protein have to be analyzed and compared for SMC changes to be evaluated during the formation of an experimental lesion.     

Surgical sealant in the prevention of early vein graft injury in an ex vivo model.

BACKGROUND: The amelioration of the adaptation process (arterialisation) of the vein graft wall to the arterial circulation in coronary artery bypass surgery by using extravascular support is clearly established in animal models and in in vitro and ex vivo set-ups. This support consists of some form of external graft-supporting modality like a prosthetic graft of stent. The clinical application of perivenous support, however, is hampered due to the fact that no easy applicable external support is available. Considering that application in the form of a spray is the most convenient modality, we evaluated whether polyethylene glycol is capable of providing adequate perivenous support. Polyethylene glycol is a synthetic, biodegradable product, used in cardiac surgery as a sealant, and is commercially available in the form of a spray. METHODS: Segments of human saphenous vein graft obtained during coronary artery bypass graft (CABG) procedures were placed in an ex vivo model, a side loop of the extracorporeal perfusion circuit, and perfused with autologous blood, making the circumstances identical to the implanted saphenous vein grafts concerning pressure, temperature, level of complement and leukocyte activation and blood pressure. Alternately around every other study vein graft segment polyethylene glycol was applied. Unsupported grafts served as control. After 1 min of solidification, perfusion was started with a pressure of about 60 mmHg (nonpulsatile flow). Perfusion was maintained for 60 min, after which the grafts were collected for light microscopy and electron microscopy. RESULTS: Light microscopy and electron microscopy showed remarkable attenuation of endothelial cell loss and less injury of smooth muscle cells of the circular and longitudinal layer of the media in the supported group compared to the nonsupported vein graft segments. CONCLUSION: Polyethylene glycol is able to provide adequate external vein graft support, preventing overdistension, in an ex vivo model. This provides a basis for clinical application. Further investigation is warranted to evaluate long-term effects.     

The study of wall deformation and flow distribution with transmural pressure by three-dimensional model of thoracic aorta wall

The sensitivity of shear stress over smooth muscle cells (SMCs) to the deformability of media layer due to pressure is investigated in thoracic aorta wall using three-dimensional simulations. A biphasic, anisotropic model assuming the radius, thickness, and hydraulic conductivity of vessel wall as functions of transmural pressure is employed in numerical simulations. The leakage of interstitial fluid from intima to media layer is only possible through fenestral pores on the internal elastic lamina (IEL). The media layer is assumed a heterogeneous medium containing SMCs embedded in a porous extracellular matrix of elastin, proteoglycan, and collagen fibers. The applicable pressures for the deformation of media layer are varied from 0 to 180 mmHg. The SMCs are cylindrical objects of circular cross section at zero pressure. The cross sectional shape of SMCs changes from circle to ellipse as the media is compressed. The local shear stress over the nearest SMC to the IEL profoundly depends on pressure, SMCs configurations, and the corresponding distance to the IEL. The consideration of various SMC configurations, namely the staggered and square arrays, mimics various physiological conditions that can happen in positioning of an SMC. The results of our simulations show that even the second nearest SMCs to the IEL can significantly change their functions due to high shear stress levels. This is in contrast to earlier studies suggesting the highest vulnerability to shear stress for the innermost layer of SMCs at the intimal-medial interface.     

Rabbit ductus arteriosus during development: Anatomical structure and smooth muscle cell composition

The anatomical structure as well as the smooth muscle cell (SMC¹) composition of the ductus arteriosus (DA) were studied in rabbits ranging in age from 29 days of gestation to 20 days after birth. Computerassisted, three-dimensional reconstructions of hematoxylin-eosin stained serial cryosections from ductus arteriosus-aorta (DA-AO) junctures revealed that DA in animals near term is separated from the aorta by a “septumlike” structure that is continuous with the aortic wall. Two days after birth, obliteration of DA is almost complete, and a small “pocketlike” cavity appears in the pre-existing site in which DA merged into the aorta. This small cavity in the aortic arch was still evident in the large majority of animals examined even 20 days after birth, as also demonstrated by scanning electron microscopy. At this time period DA consisted of a central, fibrotic region surrounded by several layers of SMC (the ligamentum arteriosum, LA) and ended within the aortic media just above the small cavity, forming a round “scar.” Vascular SMC composition of DA during closure was examined by means of indirect and double immunofluorescence procedures, using a panel of monoclonal antibodies against some cytoskeletal and cytocontractile proteins (vimentin, desmin, smooth muscle (SM), and nonmuscle (NM) myosinisoforms). “Intimal cushions” were particularly evident from 5 hr after birth and were found to be desmin-negative, homogenously reactive for vimentin and NM myosin, and heterogeneously stained with anti-SM myosin antibody. In SMC subjacent to the “intimal cushions,” distribution of vimentin and SM myosin was homogeneous, whereas the one of desmin and NM myosin content was heterogeneous. The cytoskeletal and cytocontractile protein content displayed by SMC during the closure of DA is similar to that of “intimal thickening” found in some pathological conditions of the arterial wall in adult rabbits. Completation of DA closure (day 2) was accompanied by the disappearance of cellular heterogeneity in myosin isoform distribution in both the “intimal cushions” and the underlying media. These results give new insights into: (1) the structure of DA-AO juncture, which can be relevant to the physiology of blood circulation in the fetus, and (2) the phenotypic similarity of vascular SMC populations involved in the formation of “intimal cushions” and “intimal thickening”.     

Development of cardiac musculature in the cranial vena cava of rat embryos

Development of cardiac musculature in the rat cranial vena cava (common cardinal vein or duct of Cuvier) was examined by immunohistochemistry and transmission electron microscopy. Undifferentiated cardiac myocytes were detected in the cranial vena cava wall of rat embryos after 12.5 days post-coitum (dpc). The tunica media of the cranial vena cava was composed of cardiac myocytes after formation of the endothelium. Therefore, the cranial vena cava may be not only a part of the venous system but also of the heart. Myocytes in the cranial vena cava contained developing myofibrils, mitochondria and intercalated discs similar to those found in the myocytes in the heart. Striated myofibrils began to differentiate as soon as myocytes appeared in the vena cava wall, and myocytes with differentiating myofibrils occur in the wall as the first component of the tunica media at 12.5 dpc. We concluded that the cardiac musculature in the vena cava is not a secondary extension into the tunica media after birth only in the rat, but a basic structure formed in all mammals during early embryonic development.     

Distribution of shear stress over smooth muscle cells in deformable arterial wall

A biphasic, anisotropic model of the deformable aortic wall in combination with computational fluid dynamics is used to investigate the variation of shear stress over smooth muscle cells (SMCs) with transmural pressure. The media layer is modeled as a porous medium consisting of SMCs and a homogeneous porous medium of interstitial fluid and elastin, collagen and proteoglycans fibers. Interstitial fluid enters the media through fenestral pores, which are distributed over the internal elastic lamina (IEL). The IEL is considered as an impermeable barrier to fluid flow except at fenestral pores. The thickness and the radius of aortic wall vary with transmural pressure ranging from 10 to 180 mm Hg. It is assumed that SMCs are cylinders with a circular cross section at 0 mm Hg. As the transmural pressure increases, SMCs elongate with simultaneous change of cross sectional shape into ellipse according to the strain field in the media. Results demonstrate that the variation of shear stress within the media layer is significantly dependent on the configuration and cross sectional shape of SMCs. In the staggered array of SMCs, the shear stress over the first SMC nearest to the IEL is about 2.2 times lower than that of the square array. The shear stress even over the second nearest SMC to the IEL is considerably higher (about 15%) in the staggered array. In addition to configuration and cross sectional shape of SMCs, the variation of structural properties of the media layer with pressure and the sensitivity of the local shear stress to the minimum distance between SMCs and the IEL (reducing with transmural pressure) between SMCs and the IEL are studied. At 180 mm Hg, the ratio of the local shear stress of the nearest SMC to that of the second nearest SMC is 4.8 in the square array, whereas it reduces to about 1.8 in the staggered array. The importance of the fluid shear stress is associated with its role in the biomolecular state of smooth muscle cells bearing the shear stress.     

Prebypass histological and ultrastructural evaluation of the long saphenous vein as a predictor of early graft failure

BACKGROUND: Twenty percent of the long saphenous vein (LSV) grafts that are employed as coronary bypass conduits occlude during the first year after the operation. The aim of this study was to evaluate the morphological parameters of the LSV grafts before implantation as predictors for the early occlusion of the grafts. METHODS: Forty-two samples of LSV grafts were examined via light, transmission electron, and scanning electron microscopy and evaluated clinically and by angiography at 6 months and 2 years after the operation. Morphological parameters were statistically analyzed and examined for their significance on the viability of the vein grafts. RESULTS: Six (14.28%) of the examined grafts occluded within the first 6 months after the operation, and 11 grafts (26.19%) occluded within the first 2 years. The grafts that occluded at 6 months were characterized by thick intima (mean value, 206+/-32.29 vs. 67.44+/-10.17 in the group functioning normally and 98.42+/-34 in the group occluded within 2 years), low endothelial coverage (22.7+/-4.04 vs. 64.61+/-2.89 and 26.06+/-1.78 in the corresponding groups), and narrow lumen (46.73+/-9.69 vs. 527.18+/-45.78 and 204.26+/-16.5 in the corresponding groups). The presence of foam cells, edema, calcification, neovascularization, and thrombus in the lumen of the veins is frequently observed in the wall of the occluded vein grafts, whereas fibrosis does not seem to be related. CONCLUSIONS: LSV grafts with low endothelial cell coverage, stenosis of the lumen, and thick walls are at an increased risk of developing intrawall lesions that lead to early graft failure.     

Thrombospondin deposition in rat carotid artery injury.

The balloon catheter injury model was used to determine the relative contributions of vascular smooth muscle cells (SMC) and platelets to thrombospondin (TSP) antigen deposition in the artery wall. Rat carotid arteries were denuded of endothelium, exposing the thrombogenic subendothelial extracellular matrix (ECM) to the circulation. Rats were killed after 1 hour, or 5, 10, or 20 days. Thrombospondin antigen deposition in the injured arteries was assessed using a specific polyclonal antiserum raised in rabbit against rat platelet TSP and a sensitive silver-enhanced immunogold staining method. Faint immunostaining for TSP antigen was detected, associated mostly with cells, in the media of the carotid artery of the nonoperated controls. One hour after balloon catheter injury, however, prominent cell-associated immunostaining was evident in the media; extracellular matrix staining was negligible. At this time, large foci of immunostaining were present on the lumenal surface of the vessel. Intimal proliferation was evident on most stained sections of tissue taken 5 days after balloon injury. Thrombospondin antigen immunostaining was markedly increased compared to nonoperated controls in all sections, regardless of the degree of intimal thickening. Thrombospondin immunostaining remained associated with cells in the neointima and media; extracellular matrix staining remained negligible. Ten days after endothelial injury, immunostaining for TSP antigen was detected in all layers of the artery, but was greater in the neointima and media. Reaction product was still associated only with cells. Thrombospondin antigen levels, as detected by this procedure, remained high in the injured tissue through 10 days of observation but appeared less prominent 20 days after injury. At this time extracellular matrix staining was obvious and cell-associated staining was reduced. These data support the hypotheses that thrombospondin (TSP) expression by vascular smooth muscle cells is an early response to injury and that the primary source of TSP antigen in injured artery is the vascular smooth muscle cells (SMC). These results support data derived from in vitro studies of TSP secretion.     

不同原因诱导大鼠腹主动脉移植硬化的组织病理比较

目的：研究不同原因诱导的大鼠腹主动脉移植硬化的组织病理学改变。方法：140只大鼠随机分组：A组为非移植组,B组为同品系移植缺血小于30min组;C组为同品系移植缺血4h组;D组为异品系移植缺血小于30min组,术后7,15,30,60天切取植入的腹主动脉进行光镜,电镜检查。结果：移植7－15天时C组动脉内膜有多量多形粒细胞和单个核细胞粘附,浸润,电镜检查多形核粒细胞为中性粒细胞,而D组移植动脉各层均有大量的淋巴细胞浸润,移植30－60天时C组,D组移植动脉内膜均有显著增厚,增生的内膜均由单核／巨噬细胞和平滑肌细胞构成,但前者无中膜层平滑肌坏死及弹力膜断裂现象。结论：中性粒细胞在缺血／再灌注损伤诱导的同品系大鼠腹主动脉移植硬化发挥了重要作用,其机制值得进一步研究。     

Some properties of the smooth muscle of rabbit portal vein

1. The morphology of the smooth muscle of the rabbit portal vein and its innervation were studied with fluorescence and electron microscopy. Two layers of smooth muscle were observed in the tunica media: an inner layer of circularly arranged muscle cells and an outer layer consisting of bundles of smooth muscle cells arranged in a near longitudinal direction. The membranes of neighbouring smooth muscle cells were occasionally fused to form ;tight junctions'.2. Bundles of non-myelinated nerve fibres were observed in the adventitia, and between bundles and layers of smooth muscle cells in the media. Studies on longitudinal sections with fluorescence microscopy revealed a network of varicose noradrenergic axons.3. Electrical and mechanical activity was recorded from longitudinal strips of smooth muscle from the media of the vein with a sucrose-gap apparatus.4. The preparation was spontaneously active under minimal resting tension (less than 150 mg) and at temperatures above 28 degrees C. Slow depolarizations led to a burst of spikes (multi-spike complexes), which corresponded to rhythmic contractions. In 10% of preparations, the interval between multi-spike complexes showed a slower depolarization, suggesting the record was from a pace-maker region.5. The frequency of spontaneous activity (3-27 beats/min) was very sensitive to changes in temperature and tension.6. Noradrenaline in low doses (0.01 mug) caused an increase in frequency of the multi-spike complexes. Higher doses (0.1-0.3 mug) initiated continuous high-frequency spiking, while very high doses (0.6-2.0 mug) caused maintained depolarization.7. Responses to repetitive electrical stimulation of the vein were qualitatively similar to those in response to exogenous noradrenaline. The relation between the mechanical response and the various parameters of stimulation was consistent with the stimulation of sympathetic nerve fibres in the wall of the vein.8. The actions of isoprenaline, phentolamine and propranolol indicated the presence of alpha ;excitatory' and beta ;inhibitory' adrenotrophic receptors on the smooth muscle.     

Evaluation of electrostatically endothelial cell seeded expanded polytetrafluoroethylene grafts in a canine femoral artery model

(1) PURPOSE: The purpose of this study was to evaluate the extent (luminal coverage) of the endothelial cell (EC) lining/neointimal development and the thromboresistance of electrostatically EC seeded small diameter e-PTFE vascular grafts. (2) METHODS: This evaluation consisted of harvesting autologous, canine jugular vein ECs, electrostatically EC seeding the e-PTFE grafts (4 mm GORE-TEX, Length = 6 cm), implanting the grafts in a canine femoral artery model for six weeks, and excising the graft for histological and scanning electron microscopy evaluations. (3) RESULTS: The results of the histological evaluation (mid-graft region only) indicated that the electrostatic EC seeding significantly affected neointimal development (p < 0.01) and the degree of thrombus formation (p < 0.001) within the EC seeded grafts versus the untreated control grafts. Scanning electron microscopy examination demonstrated a mature, confluent endothelium with a "cobblestone" appearance on the EC seeded graft luminal surface. The control grafts demonstrated an equal distribution of SMCs through the graft wall while the electrostatically EC seeded graft sections exhibited an uneven SMC cellular distribution which was skewed toward the graft luminal surface. (4) CONCLUSIONS: The presence of electrostatic EC seeding significantly (p < 0.01) enhanced the development of a neointima and reduced the incidence of thrombosis in e-PTFE grafts implanted in a canine femoral artery model. Results of the mid-graft SMC migration measurements indicate that the electrostatic EC seeding had a significant (p < 0.001) impact on the acute healing of the standard wall e-PTFE vascular graft specimens.