Intracoronary low-dose beta-irradiation inhibits neointima formation after coronary artery balloon injury in the swine restenosis model

BACKGROUND

Neointima formation contributing to recurrent stenosis remains a major limitation of percutaneous transluminal angioplasty. Endovascular low-dose gamma-irradiation has been shown to reduce intimal thickening (hyperplasia) after balloon overstretch injury in pig coronary arteries, a model of restenosis. The objective of this study was to determine whether the use of a beta-emitting radioisotope for this application would have similar effects and to examine the dose-response relations with this approach.

METHODS AND RESULTS

Normal domestic pigs underwent balloon overstretch injury in the left anterior descending and left circumflex and coronary arteries. A flexible catheter was introduced by random assignment into one of these arteries and was afterloaded with a 2.5-cm ribbon of encapsulated 90Strontium/90Yttrium sources (90Sr/Y, a pure beta-emitter). It was left in place for a period of time sufficient to deliver one of four doses: 7, 14, 28, or 56 Gy, to a depth of 2 mm. Animals were killed 14 days after balloon injury, the coronary vasculature was pressure-perfusion fixed, and histomorphometric analysis of arterial cross sections was performed. All arteries treated with radiation demonstrated significantly decreased neointima formation compared with control arteries. The ratio of intimal area to medial fracture length was inversely correlated with increasing radiation dose: control (no radiation), 0.47; 7 Gy, 0.34; 14 Gy, 0.20; 28 Gy, 0.08; and 56 Gy, 0.02 (r = -.78, P < .000001). Scanning electron microscopy demonstrated a confluent layer of endothelium-like cells both in control and in 14 Gy-irradiated arteries. There was neither evidence of significant necrosis nor excess fibrosis in the media, adventitia, or perivascular space of the coronary arteries or adjacent myocardium in the irradiated groups. Furthermore, the exposure to the staff and the total body exposure to the pig with the beta source was a small fraction of the dose previously measured and calculated with 192Ir, a gamma-emitting radioisotope.

CONCLUSIONS

Administration of endovascular beta-radiation to the site of coronary arterial overstretch balloon injury in pigs with 90Sr/Y is technically feasible and safe. Radiation doses between 7 and 56 Gy showed evidence of inhibition of neointima formation. A dose-response relation was demonstrated, but no further inhibitory effect was seen beyond 28 Gy. These data suggest that intracoronary beta-irradiation is practical and feasible and may aid in preventing clinical restenosis.

Calcified deposit formation in intimal thickenings of the human aorta

The formation of calcified deposits in intimal thickenings of human aorta was studied by electron microscopy. Microzones of calcification were detected in about 20% of fatty streaks and were located predominantly in the deep musculoelastic layer of the intima. Calcified deposits formed only on previously existing structures including extracellular vesicles and unesterified cholesterol. Calcified deposits in the musculoelastic layer of the intima localised inside altered elastin fibres, but initiating the calcification of of elastin required the prior accumulation of cholesterol esters inside elastin fibres. Co-localization of calcified deposits and elastin fibres was followed by destruction of elastin. The present study suggests that at an early stage of development is atherosclerotic lesions, calcified deposits are formed by a physicochemical process which is not strongly controlled by the intimal cells. The recognition of calcified deposits in intimal thickenings support the hypothesis that a subset of fatty streaks might progress to fibrous plaques in human atherosclerosis.

Complex structure of the common carotid artery of sheep

BACKGROUND

Mechanical properties of blood vessels are dictated by the vessel wall structure. In many large conduit vessels the tunica media is a sheath of circular musculature and the tunica adventitia a layer of fibrous connective tissue with limited longitudinal extensibility. In contrast, the carotid artery of the sheep displays in each tunica a more complex architecture of muscle and connective tissue.

METHODS

Vessels collected from ewes were measured and processed for light microscopy and for transmission electron microscopy.

RESULTS

Layers of histologically different materials are found within the tunica intima, media and adventitia. (1) The tunica media is made of circumferentially arranged muscle cells markedly different at different depths. In the innermost third of the media, muscle cells are small and with irregular profiles, the cells are widely separated, and the extracellular material is abundant and composed mainly of elastic fibres. In the outermost third, muscle cells are larger and with more regular profiles, the cells are relatively close to each other and the extracellular material is sparse and consists mainly of collagen fibrils. (2) A small number of fibroblasts is found in all parts of the media amongst the preponderant muscle cells. (3) The intima contains fibroblast-like cells and longitudinally arranged muscle cells. (4) The adventitia contains a thick layer of collagen and elastic fibres; external to this, it displays a conspicuous musculature, made of large bundles of longitudinal muscle.

CONCLUSIONS

The carotid artery of the sheep presents in all three coats of its wall features which are at variance from those in the better known vessels of small laboratory animals. The presence of many layers of material within the wall, the heterogeneity of the tissues found, and the occurrence of an extensive longitudinal musculature, have important effects on the mechanical properties of the vessel.

Extracellular mast cell granules carry apolipoprotein B-100-containing lipoproteins into phagocytes in human arterial intima. Functional coupling of exocytosis and phagodytosis in neighboring cells

In experimental studies in vitro, mast cells have induced uptake of apolipoprotein B-100 (apoB-100)-containing low-density lipoproteins by macrophages, with the subsequent formation of foam cells, the hallmarks of atherosclerosis. Recently, increased numbers of activated, ie, degranulated, mast cells were found to be present in human coronary fatty streaks and atheromas. We therefore sought evidence of a connection between mast cells and foam cell formation in vivo. In electron microscopic studies of human aortic and coronary fatty streaks and atheromas, exocytosed cytoplasmic secretory granules of mast cells were detected in the vicinity of their parent cells. These exocytosed granules had bound apoB-100-containing lipoproteins, as indicated by their positive staining with MB 47, a monoclonal antibody against apoB-100. A smooth muscle cell was observed to be in the process of phagocytosing one such exocytosed granule, and in the vicinity of a degranulated mast cell a foam cell contained an ingested mast cell granule. Therefore, the micrographs show that exocytosed granules of intimal mast cells may contribute to intimal foam cell formation and suggest a role for mast cells in human atherogenesis. More generally, the findings provide evidence that phagocytosis of apoB-100-carrying particles is one mechanism by which lipoproteins enter human arterial intimal cells.

Composite porosity of expanded polytetrafluoroethylene vascular prosthesis

Polytetrafluoroethylene (PTFE) prostheses were modified to produce two types of composite porosity PTFE grafts: type I--inner 60 microns/outer 20 microns and type II--inner 20 microns/outer 60 microns. These composite porosity PTFE designs were investigated for bleed through, graft healing and patency and compared with high porosity PTFE (60 microns) and standard PTFE (20 microns) grafts. The grafts were implanted into the carotid and femoral arteries of dogs and retrieved after 4, 12 and 18 weeks. Both composite porosity grafts showed significantly less bleed through than standard and high porosity grafts after reperfusion. In composite grafts, the 60-microns layer allowed fibrovascular tissue and histiocyte ingrowth from perigraft tissue, but the 20-microns layer did not. Neointima formation occurred earlier and endothelialization was more extensive in high porosity grafts, but seroma formation occurred in 25% of cases. In type I composite porosity grafts, smooth muscle cells of neointima migrated into the pores of the graft, providing a firmly anchored intima. Type II composite porosity grafts allowed better ingrowth of fibrovascular tissue at the outer layer from the perigraft tissue; however, endothelialization was not completed. Composite porosity grafts should be considered for evaluation in specific clinical situations.

The effects of acute norepinephrine-induced hypertension on the coronary arteries of newborn piglets

Newborn piglets were subjected to 45 min of sustained norepinephrine-induced hypertension and then monitored for 4 hr at baseline conditions. They were then sacrificed and the anterior descending coronary artery was serially sectioned for study by light and electron microscopy. Other groups were sacrificed after 72 and 168 hr of baseline conditions. Changes were limited to the endothelium and subendothelial intima of the most proximal segment of the anterior descending coronary artery. As similar changes are normally present in perinatal piglets, the experimental animals were compared with sham-operated controls to determine if there was a modification of the naturally occurring congenital lesions. Although the prevalence of coronary lesions in control and experimental animals was not significantly different, the experimental groups showed unique features. At 4 hr, there was marked intimal edema and disruption of the endothelium with fragmentation and dissolution of the internal elastic lamina. There was selective invasion of the intima by platelets and monocytemacrophages. After 72 and 168 hr, there was an increase and progression in preexisting modified smooth muscle cell plaques in which there developed prominent fibroplasia and collagenization. It is proposed that acute hypertension may be responsible for these changes. Such perinatal surges in blood pressure may be involved in the initiation of atherogenesis.

Isolation and cultivation of aortic endothelial cells from spontaneously hypertensive rat with a modified tissue explant technique

In the present study, we successfully established a "tissue explant technique" to obtain high yield and purity of endothelial cells from the aorta of hypertensive and normotensive rats (SHR and WKY). Small pieces of aorta were placed on fibronectin precoated petri dishes. The effects of oxygenation in the tissue preparation stage, tilting of the petri dish during the explanting period and timing of the removal of tissue blocks from petri dishes were evaluated. These procedures appeared to be critical for cell survival, tissue adhesion and minimizing of non-endothelial cell contamination. The cultured endothelial cells were characterized by morphological, immunohistochemical and biochemical examination. The cultured cells from both SHR and WKY rats showed similar endothelial cell character, positive immunofluorescence staining for the von Willebrand factor, and uptake of acetylated low-density lipoprotein (DiI-ac-LDL). The secretory function of prostacylcin I2 (PGI2), thromboxane A2 and endothelin of cultured endothelial cells was measured. The results showed that the secretion of both PGI2 and endothelin was greater in SHR than in WKY rats, but that there was no difference in thromboxane A2 secretion. Therefore, our "tissue explant technique" can provide high yield and purity of endothelial cells with their specific biological function in vitro. It will permit us to further study the role of endothelial cells in the development of hypertension.

VCL, an antagonist of the platelet GP1b receptor, markedly inhibits platelet adhesion and intimal thickening after balloon injury in the rat

BACKGROUND

Arterial injury is immediately followed by platelet adhesion at the site of injury, a process that requires the interaction of subendothelial von Willebrand factor with the platelet GP1b receptor. VCL, a recombinant von Willebrand factor GP1b binding domain, inhibits platelet binding to von Willebrand factor. The aim of this study was to determine whether VCL inhibits platelet adhesion at the site of arterial injury and affects neointimal thickening after injury in rats.

METHODS AND RESULTS

Sprague-Dawley rats were randomized to receive VCL, 4 mg/kg bolus followed by a continuous infusion of 2 mg.kg-1.h-1 for 72 hours, or an identical volume of saline. Balloon injury of the femoral artery was performed 15 minutes after the initial bolus injection of VCL. Scanning electron microscopy performed 1 and 3 days after injury indicated that VCL-treated rats had > 80% reduction in the number of platelets adherent to the vessel wall at the site of injury compared with controls (P < .003). Histological examination at day 14 showed that, compared with controls, VCL-treated rats had a 60% reduction in the intima-media ratio (0.21 +/- 0.03 versus 0.53 +/- 0.06, P = .001) and a reduced luminal area stenosis (12 +/- 3% versus 38 +/- 10%, P = .04). At 28 days after injury, there was no rebound of neointimal thickening in VCL-treated rats (intima-media ratio, 0.19 +/- 0.04; luminal stenosis, 17 +/- 5%). The difference between VCL-treated rats and control rats persisted but was attenuated (intima-media ratio, 0.19 +/- 0.04 versus 0.28 +/- 0.1, P = .162; luminal stenosis, 17 +/- 5% versus 31 +/- 5%, P = .058) as neointimal thickening regressed in untreated rats. With the use of proliferating cell nuclear antigen immunohistochemistry on day 3, VCL had no effect on smooth muscle cell (SMC) proliferation.

CONCLUSIONS

Antagonism of the platelet GP1b receptor by VCL profoundly decreased platelet deposition at the site of balloon injury in the rat femoral artery. This effect was associated with a persistent reduction in neointimal thickening. The lack of effect of VCL on SMC proliferation suggests that the decrease in neointimal thickening may have been mediated through inhibition of SMC migration and/or modulation of the extracellular matrix.

Assessment of cyclosporine A-induced ultrastructural changes in vascular wall using an experimental arterial autograft model

The objective of this ultrastructural study was to assess the effects of cyclosporine A (CsA) in an experimental model of arterial autograft. Fifty female Sprague-Dawley rats weighing 250-300 g were employed. Using a microsurgical technique, an arterial autograft measuring approximately 5 mm in length was placed in the right common iliac artery. Two groups were established: group I (control), consisting of 25 animals subjected only to arterial autograft; and group II (pre- and postoperative CsA), also consisting of 25 animals which received a daily subcutaneous dose of 5 mg/kg CsA (Sandimmun, Sandoz) on the four days preceding the surgery and thereafter, until sacrifice. The animals were sacrificed on postoperative day 7, 14, 21, 30 and 50. The specimens (autografts) obtained were studied under transmission and scanning electron microscopes. In the control group, the process of endothelialization of the graft was completed by day 14. In the CsA-treated group, restoration of the endothelium took 50 days. The development of intimal hyperplasia was delayed in the treated group. There were no morphological changes in its structure when compared to the control group. The tunica media had thinned in the treated grafts, with loss of smooth muscle cells, fragmentation and lysis of the elastic lamina, presence of lipid-filled macrophages, and muscle cells with cytoplasmic lipid vacuoles. In our opinion, these results suggest that the action of CsA mainly targets on the endothelium and smooth muscle cells, exerting a toxic effect in an in vivo arterial graft model.

Proteoglycan alterations in the aortic intima-media of alloxan-diabetic rabbits: an ultrastructural and biochemical study

Proteoglycans and glycosaminoglycans in the aortic intima of diabetic rabbits and age-matched controls were examined at 2 weeks and 3, 6, and 12 months after alloxan (or saline) treatment. Measurements were made by morphometric analysis of ruthenium red-stained large proteoglycan granules (LPG) in electron micrographs and by analysis of 35S-labeled glycosaminoglycans, extracted and purified from the intima-media of aortas of rabbits which had been injected with 35S-sulfate 18 hr before exsanguination. There was a progressive increase in the area of the aortic intima with time which was greater in diabetic than in control rabbits. The concentration of proteoglycan (LPG/microns 2) and the concentration of the 35S-glycosaminoglycans in diabetic intima-media were similar to respective values of control intima-media throughout the 12 months. However, the specific radioactivity of the [35S]glycosaminoglycan pool from intima-media of diabetic rabbits was significantly less than that from controls (P < 0.001) at 6 and 12 months. In addition, the staining intensity of LPG of the diabetic compared to control extracellular matrix was decreased at these times. The profile and electrophoretic mobility of the glycosaminoglycan types were similar in diabetic and control intima-media. We conclude that the onset of diabetes in the rabbit has altered the metabolic turnover but not the concentration, sulfate content or profile of aortic intima-media proteoglycan and glycosaminoglycans.

Endothelial cell seeding fails to attenuate intimal thickening in balloon-injured rabbit arteries

BACKGROUND

Restenosis of arteries or bypass grafts after vascular reconstruction is a common clinical entity that significantly limits long-term patency. This process, termed intimal hyperplasia (IH), is characterized by smooth muscle cell proliferation in the intima and subsequent accumulation of intercellular matrix. This study was designed to test the hypothesis that endothelial cell (EC) seeding of acutely injured arteries accelerates reendothelialization of the flow surface and limits the development of IH.

METHODS

ECs were harvested from jugular veins of New Zealand white rabbits (n = 13) and were amplified in tissue culture. Each animal subsequently underwent bilateral balloon catheter injury of the iliofemoral arteries; one side was immediately seeded with cultured autologous ECs at supraconfluent density, whereas the contralateral vessel served as a nonseeded control. Animals were killed 33 +/- 5 days after balloon injury. Intimal thickening was quantitated on histologic sections of vessels (three sections per vessel, total of 60 sections) and percent endothelialization was assessed by SEM; measurements were obtained by use of computer-aided morphometry performed by a blinded observer. Data were analyzed by use of a paired t test for comparison between seeded and control vessels.

RESULTS

Seeded vessels exhibited a greater degree of reendothelialization (93.9% +/- 7.6% of the surface) than their unseeded counterparts (65.1% +/- 22.5%, p < 0.01). Intimal cross-sectional area and the ratio of intimal area to medial area were not significantly different between seeded and control vessels (intima: 0.32 +/- 0.19 vs 0.37 +/- 0.11 mm2, p = 0.28; intimal area to medial area ratio: 0.84 +/- 0.35 vs 1.02 +/- 0.2, p = 0.24).

CONCLUSIONS

We conclude that seeding with autologous venous ECs accelerated restoration of the endothelial monolayer but failed to attenuate IH in balloon-injured rabbit arteries. Further studies are necessary to determine the functional properties of seeded endothelium and to examine the effect of EC seeding on intimal thickening in other clinically relevant models.

Thrombolytic therapy and balloon catheter thrombectomy in experimental femoral artery thrombosis: effect on arterial wall morphology

PURPOSE

To determine vessel wall architectural changes after lytic therapy and balloon catheter thrombectomy in experimentally thrombosed arteries.

MATERIALS AND METHODS

Bilateral 5-cm femoral artery occlusions were created by ligation in 14 dogs. Two dogs served as controls, and 12 animals underwent balloon catheter thrombectomy on the left and lytic therapy with urokinase on the right either 24 hours (group 1, n = 6) or 7 days (group 2, n = 6) after creation of the occlusion. After treatment, the area of thrombosis was subjected to light and scanning electron microscopy.

RESULTS

The IEL was intact in all lysed arteries. IEL fractures were present in 11 of 12 arteries treated with thrombectomy. For group 1 arteries, average luminal area after thrombectomy was 5.63 mm2 +/- 0.66 versus 1.94 mm2 +/- 0.7 after lytic therapy (P < .007). Mean control artery luminal area was 2.86 mm2 +/- 0.52. Similar differences were found in group 2 arteries. With lytic therapy, scanning electron microscopy grading revealed surfaces to be intact in group 1, but moderate injury was exhibited in group 2. All arteries treated with thrombectomy had severe injury.

CONCLUSIONS

Lysis of acute thrombi (group 1) preserved arterial wall architecture, with an intact IEL and no endothelial injury. Lysis of chronic thrombi (group 2) was associated with mild to moderate injury. Catheter thrombectomy caused severe injury regardless of the time of intervention. These results may help explain the poor long-term patency observed after these interventions.

Ultrastructural characteristics of cellular reaction after experimentally induced lesions in the arterial vessel

Restenosis after angioplasty occurs with an incidence of 20-50% and remains a major drawback. Certain randomized studies suggest that a bigger post-angioplasty lumen predicts a better long-term outcome. Conversely other studies showed a better outcome with limited injury. The present study aimed to investigate the depth of the lesion and relate this to cellular alterations after graded vascular injury.

METHOD

Vessel segments of 30 pigs underwent injury using a directional atherectomy catheter. Vessels were assigned according to the extent of injury to Group 1 (intima lesion) or Group 2 (media injury). 2 hours to 7 days after injury, 68 arteries showing 41 intimal and 27 media lacerations were excised and processed for histology and transmission electron microscopy.

RESULTS

Immediately after injury, thrombus formation was found at the site of the altered segment. A marked, transient infiltration of polymorphonuclear leukocytes (PMN) occurred only if the media was lacerated, starting within the first hours and increasing up until the 12 hours time point. The cellular infiltration was followed by a transformation of contractile myocytes to a synthetic subtype. The ratio of myofilaments to organelles decreased. A pronounced myoproliferative response was found in Group 2 after 7 days (p < 0.01), whereas only moderate tissue hyperplasia was seen in Group 1.

CONCLUSION

The data presented provide evidence that the cellular alteration of injured vessels begins immediately. Subsequent to an initial temporary PMN infiltration, an activation of local myocytes occurs at a very early stage. In particular, a myoproliferative response was found only after deep injury with rupture of the internal elastic lamina.

Experimental microvenous thrombosis following anastomosis with a knotted suture

An experimental model for producing venous thrombosis was developed in end-to-end anastomoses of femoral veins in rats. The anastomoses were performed using a suture (9-0 suture-70 microns needle) with a knot 1 cm from the needle. The knot was formed by making either six or eight half-hitches in one throw of the suture. Vessel patency was assessed through the direct "milking test" at 20 min and 24 hrs. The incidence of thrombosis when using one knot with six half-hitches ranged from 20% to 40% and with eight half-hitches, from 50% to 70%. The incidence of femoral vein thrombosis varied directly with the presence and size of the knot. In this model, thrombosis was induced by exaggerating vessel injuries that may occur when performing routine microvascular anastomoses. This study demonstrates a reproducible thrombogenic model which mimics clinical practice and may be used to study the effects of local and systemic antithrombogenic agents.

Neointima formation is promoted by surgical preparation and inhibited by cyclic nucleotides in human saphenous vein organ cultures

Intimal thickening is an important cause of late coronary vein graft occlusion, which no variation of surgical technique or pharmacologic intervention has been shown to reduce. We used a recently developed quantitative organ culture of human saphenous vein to investigate whether surgical preparative injury promotes neointima formation. We also investigated the effects on neointima formation of the lipid-soluble cyclic nucleotide analogs, 8-Br-cyclic adenosine monophosphate and 8-Br-cyclic guanosine monophosphate, and the phosphodiesterase inhibitor, isobutylmethylxanthine. These agents are pharmacologic mimetics of endothelium-derived prostacyclin and nitric oxide, which elevate vascular smooth muscle cyclic adenosine monophosphate and cyclic guanosine monophosphate concentrations, respectively, and may normally suppress neointima formation. Surgical preparation was found to promote intimal thickening and neointimal smooth muscle cell proliferation by 42% and 48%, respectively. 8-Br-cyclic adenosine monophosphate, 8-Br-cyclic guanosine monophosphate, or isobutylmethylxanthine (which elevated endogenous cyclic adenosine monophosphate concentrations) inhibited intimal thickening by 80%, 40%, and 72%, respectively, at a concentration of 0.1 mmol/L. The results imply that surgical techniques that avoid preparative injury and vasodilator drugs that act by elevating cyclic adenosine monophosphate or cyclic guanosine monophosphate concentrations may reduce neointima formation in vein grafts.

Effects of cold storage on the subsequent structure and function of microvenous autografts

A study was undertaken to evaluate the structure and patency of cold stored rabbit femoral veins following reinsertion as autografts for 3 weeks. The periods of cold ischaemic storage were 1, 2, 3 and 4 weeks (n = 10/gp) and 6 and 10 weeks (n = 6/gp). All rabbits were subject to 3 operations under general anaesthesia. In the first, a 4 cm segment of left femoral vein was harvested and stored at 4 degrees C for the specified ischaemic interval. Following storage the graft was microsurgically reinserted at a second operation into the right femoral artery of the donor rabbit. Three weeks later, graft patency was assessed by surgical exploration and the graft processed for light and electron microscopy. Patency rates remained over 80% after 3 weeks in all groups except the 10 week storage group where only 1 of 6 (17%) grafts was patent at 3 weeks. In all groups normal vein structure was absent, being replaced by thin walled necrotic areas or by neointimal ingrowth. The excellent patency rates achieved indicate it is possible to cold preserve extra lengths of vein grafts harvested at initial operation for reuse should regrafting be necessary.

A fiber matrix model for the growth of macromolecular leakage spots in the arterial intima

A new model is presented for the growth of cellular level macromolecular leakage spots in the arterial intima. The theoretical approach differs from the recent study by Yuan et al. [19] in that it directly models and calculates the intimal transport parameters based on Frank and Fogelman's [22] ultrastructural observations of the extracellular subendothelial proteoglycan matrix that their rapid freeze etching technique preserves (see Addendum). Using a heterogeneous fiber matrix theory, which includes proteoglycan and collagen components, the model predicts that the Darcy permeability Kp and macromolecular diffusivity D of the subendothelial intima is two orders of magnitude larger than the corresponding values measured in the media, and supports the observations in Lark et al. [24] that the proteoglycan structure of the intima differs greatly from that of the media. Numerical results show that convection parallel to the endothelium is a very significant transport mechanism for macromolecules in the intima in a large region of roughly 200 microns diameter surrounding the leaky cleft. The predictions of the new model for the early-time spread of the advancing convective-diffusive front from the leakage spots in the intima are in close agreement with our experimental measurements for the growth of HRP spots in [20]. The regions of high concentration surrounding the leaky cell, however, are much more limited and cover an area that is typically equivalent to 20 cells. This prediction is consistent with the recent measurements of Truskey et al. for LDL spot size in rabbit aorta [21] and the hypothesis advanced in [19] that there is a colocalization of subendothelial liposome growth and cellular level leakage. Finally, comparison of predicted and experimentally-measured average LDL concentration in leakage spots strongly suggests that there is significant local molecular sieving at the interface between the fenestral openings in the internal elastic lamina and the media.

Foam cell replication and smooth muscle cell apoptosis in human saphenous vein grafts

Occlusion of saphenous vein grafts is a major problem after coronary artery bypass grafting. Segments of occluded and suboccluded implanted aortocoronary grafts were obtained during re-intervention bypass grafting in 47 patients yielding a total of 80 vein grafts. The grafts were studied by immunohistochemistry for smooth muscle cells (alpha-SMC actin), macrophages (HAM56), cell replication (PCNA, Ki-67) and transmission and scanning electronmicroscopy (TEM, SEM). In 81% of the examined grafts the (sub)occlusion was due to a myo-intimal thickening and an associated luminal accumulation of foam cells and mural thrombi. The foam cells were constantly found at the luminal site of the myo-intimal thickening and within the luminal part of adherent thrombi. Transmission electronmicroscopy demonstrated phagocytosis of platelets and platelet fragments by the foam cells. A significant fraction of the foam cells demonstrated nuclear immunoreactivity for Ki-67 and PCNA. The myo-intimal thickening of the vein grafts was composed of smooth muscle cells lying in a fibrous tissue matrix. The smooth muscle cells were surrounded by prominent basal lamina and showed ultrastructural features of apoptosis. Our results support the hypothesis that phagocytosis of lipid rich platelets by monocytes set up a mechanism for foam cell formation and replication in human saphenous vein grafts. The transformation of a smooth muscle cell rich myointimal thickening towards a fibrous, cell poor intimal thickening could be induced by progressive smooth muscle cell loss through apoptosis.

Postoperative reduction of high serum cholesterol concentrations and experimental vein bypass grafts. Effect on the development of intimal hyperplasia and abnormal vasomotor function

Hypercholesterolemia is an important contributor to the development of intimal hyperplasia and superimposed accelerated atherosclerosis in vein bypass grafts. This study examines the effect of dietary modification of serum cholesterol on the development of intimal hyperplasia and vasomotor function of vein grafts. Thirty male New Zealand White rabbits had a right carotid vein bypass graft and were put to death 28 days after the operation. Twenty animals received a 1% cholesterol diet for 4 weeks before the operation. In 10 animals this diet was continued until harvest (hypercholesterolemia group). In another 10 animals the diet was changed to standard rabbit chow on the day of the surgical procedure and continued until harvest (cholesterol reduction group). The last 10 animals were control subjects. Vein grafts were harvested either for histologic study or for in vitro isometric tension studies. Cumulative dose response curves to norepinephrine, serotonin, bradykinin, and endothelin-1 were determined. After in situ pressure fixation, intimal thicknesses of the vein grafts were measured by videomorphometry. The change in diet produced a 74% reduction in serum cholesterol concentration within 28 days. There was a 26% reduction in the intimal thickness of vein graft intimal hyperplasia and the macroscopic disappearance of atheromatous lesions from the graft wall, which are always observed in vein grafts from the hypercholesterolemia group. Cholesterol reduction did not change hypercholesterolemia-induced agonist supersensitivity. Therefore, cholesterol reduction slows the formation of intimal hyperplasia in vein grafts but does not prevent the persistence of the hypercholesterolemia-associated smooth muscle phenotype.

Release of platelet-derived growth factor activity from pig venous arterial grafts

Intimal smooth muscle cell proliferation and superimposed atheroma are the main causes of late failure of saphenous vein bypass grafts. It has been suggested that these reactions are caused by the production of growth factors from the cells of the vessel wall. To test this hypothesis, we cultured segments of pig venous arterial grafts, removed 1 and 4 weeks after implantation, in serum-free medium for 24 hours. Tissue viability as assessed by adenosine triphosphate concentration was maintained throughout the 24-hour culture period (239 +/- 21 nmol/gm wet weight [standard error of the mean], n = 26, 0 hours; 240 +/- 24 nmol/gm wet weight, n = 17, 24 hours). Cell proliferation occurred and autoradiography showed proliferating cells to be located in the neointimal and medial layers. These cells were identified as smooth muscle cells by means of a monoclonal antibody to alpha-actin. Graft-conditioned media were tested for mitogenic activity by means of a fibroblast proliferation assay. Media conditioned for 24 hours produced significant stimulation of cell growth (284% +/- 30%, n = 17) above that obtained in culture medium alone (100%). This mitogenic activity was inhibited by 61% +/- 9%, n = 8, with a polyclonal-neutralizing antibody to platelet-derived growth factor. Reverse-transcription polymerase chain reaction analysis and Northern blots demonstrated platelet-derived growth factor B messenger ribonucleic acid (mRNA) in vein grafts but not in ungrafted vein. Analysis of graft tissue sections by in situ hybridization demonstrated an abundance of platelet-derived growth factor B mRNA positive cells in the endothelial and neointimal layers, as well as in the endothelial cells of the adventitial vessels. These data constitute direct evidence for active growth factor production within the cells of the vein graft. They also suggest that endogenously produced platelet-derived growth factor may play a role in regulating smooth muscle cell proliferation in this model.

Suramin inhibits intimal thickening following intimal injury in the rabbit aorta in vivo

OBJECTIVE

Proliferation of vascular smooth muscle cells is a major event in atherogenesis. Several growth factors have been well documented to control this proliferation. Inhibition by suramin of the binding of some growth factors to their receptors has recently been reported. The aim of this study was to examine the effects of this agent on neointimal thickening following intimal mechanical injury, as well as on platelet function.

METHODS

Intimal thickening was induced by indwelling of polyethylene tubing for 24 h in the rabbit aorta. Rabbits were killed 10 d after drawing out the tubing. Throughout the experiment, suramin (15 mg.kg-1) was injected intravenously every 24 h. Morphological and morphometrical studies were performed in the suramin treated group (n = 6) and in a control group (n = 6). Platelet-rich plasma was prepared from animals before and 3 h after injection of suramin. Platelet aggregation and ATP release induced by collagen were examined. Platelet adhesion on the de-endothelialised area of the rabbit aorta was also examined in the two groups.

RESULTS

The mean intimal thickening in the suramin treated group was significantly less than in the control group. Smooth muscle cell replication and cell density in the thickened intima of the suramin treated group were less than in control. Suramin did not affect collagen induced platelet aggregation, ATP release, or platelet adhesion.

CONCLUSIONS

Suramin has an inhibitory effect on the neointimal thickening and intimal smooth muscle cell proliferation after intimal injury in the rabbit aorta, but has no effect on platelet function.

Ultrastructural changes in arteries proximal to short-term experimental carotid-jugular arteriovenous fistulae in rabbits

The afferent arteries of 10 carotid-jugular arteriovenous fistulae in rabbits were examined by transmission electron microscopy to determine the early ultrastructural changes in the vicinity of haemodynamically induced tears of the internal elastic lamina. No significant changes appeared to precede the development of the tears but radially orientated partial fractures were observed adjacent to some major tears. The elastic tissue tears became more numerous, extended proximally along the artery and with time involved the innermost medial elastic laminae. Endothelial discontinuities were present over only a few early tears and the small size suggested repair was rapid. Endothelial cells overlying the elastic tissue tears increased in density and thickness. They were adherent to the underlying matrix and eventually to the thickened and multilaminated basal lamina. In the floor of the tears between the edges of the torn internal elastic lamina there were some smooth muscle cells of the synthetic type, degenerative and necrotic muscle cells and areas devoid of matrix with scarce proteoglycan material suggestive of oedema. Sixteen days post-operatively the smooth muscle cells in the floor of the tears were all of the contractile variety with thickened basal laminae overlaid by a relatively normal endothelial layer. There was no suggestion that inflammatory cells were responsible for the elastic tissue tears. The abrupt edges and the adjacent microfractures are consistent with the concept of mechanical failure of the elastic tissue.

Subendothelial layer of pseudointima of polytetrafluoroethylene graft is formed by transformation of fibroblasts migrated from extravascular space

A well organised pseudointima is formed in polytetrafluoroethylene (PTFE) grafts within 4 weeks after implantation into inferior vena cava (IVC) of rabbits. To investigate the process of the subendothelial organisation of pseudointima, an animal experiment was conducted. The outer wall of PTFE graft (30 microns fibril length, 3 mm inner diameter, 3 cm long) was coated with 10 um silicon film in the following ways to prevent cellular ingrowth from the extravascular space: non-coating; full-length coating; half-length coating; and full-length coating excluding 5 mm midportion. These grafts were implanted into rabbit IVC and were harvested 4 weeks later. All the grafts were patent but the lumen of the non-coated area was narrowed by pseudointimal hyperplasia. The degree of the hyperplasia estimated by dried tissue deposit was inversely proportional to the length of the coating. The coverage of the luminal surface with endothelial-like cells was noted at anastomotic areas and also at the surface corresponding to the non-coated area. Light microscopy and immunostaining studies on the non-coated midportion revealed the presence of fibroblasts in the interstices of PTFE and smooth muscle cells and myofibroblasts in the pseudointima. Transmission electron microscopy confirmed the presence of myofibroblasts in the midportion of the non-coated area. No transmural capillary ingrowth was observed in the midportion by histological and immunohistochemical analysis. These observations suggest that the subendothelial layer of pseudointima in PTFE grafts is formed by proliferation and transformation of fibroblasts migrating from the extravascular space and that endothelial-like cells may also be derived from such transformation.

Tantalum-Dacron coknit stent for endovascular treatment of aortic aneurysms: a preliminary experimental study

PURPOSE

The purpose of this study was to evaluate the efficiency of intraluminal tantalum-Dacron coknit stents for the treatment of artificial aortic aneurysms in minipigs.

METHODS

Replacement of the infrarenal abdominal aorta with Dacron artificial aneurysm graft was performed in eight minipigs. After 2 weeks, balloon-expandable coknit stents were inserted through the femoral artery to the site of the artificial aneurysm in seven minipigs. One animal was kept as a control. Coknit stent/artificial aneurysm complexes were explanted at various intervals from 24 hours to 12 weeks and underwent gross examination, followed by scanning electron and light microscopy studies.

RESULTS

Aortography performed at the time of stent placement displayed immediate exclusion of the aneurysm in every case. In follow-up studies, all coknit stents remained patent until the time of explant. Scanning electron microscopy studies revealed apparent endothelialization of the entire coknit stent lumen at and after 6 weeks.

CONCLUSION

Tantalum-Dacron coknit stents are efficient in the treatment of artificially created aneurysms in minipigs and facilitate the creation of an endothelialized new vascular wall. Clinical application of this coknit stent can be considered but necessitates retaining the same stent structure in diameters greater than 20 mm and the development of a suitable delivery system.

Photodynamic therapy inhibition of experimental intimal hyperplasia: acute and chronic effects

PURPOSE

Intimal hyperplasia (IH) is a focal arterial problem that still eludes successful therapy. We have previously demonstrated the feasibility of use of photodynamic therapy (PDT) for the acute treatment of experimental IH with light to activate an otherwise biologically inert photosensitizer. The purpose of this study was to determine the acute and long-term effects of PDT inhibition of IH on the artery wall.

METHODS

Segmental IH was induced by balloon injury localized to the cervical common carotid artery of 33 rats. The photosensitizer chloroaluminum sulfonated phthalocyanine (5 mg/kg) for the experimental group or saline solution for the control group was administered intravenously. Twenty-four hours later, all instrumented portions of arteries were irradiated at 675 nm to induce cytotoxic injury in the PDT-treated arteries as compared with laser only-treated arteries for controls. Animals were killed at 1, 2, 4, and 16 weeks.

RESULTS

There were no untoward side effects in either group. All PDT-treated arteries were devoid of smooth muscle or inflammatory cells in the treated media. There was no evidence of arterial degeneration of PDT-treated arteries. Only three arteries in the PDT group developed IH, whereas it was universal in all controls. In control arteries, immunocytochemistry with bromodeoxyuridine revealed maximal intimal and medial cell proliferation at 1 week, and morphometric analysis demonstrated a maximal IH at 2 weeks. Immunocytochemistry staining for smooth muscle cell actin was positive for the IH in control and when present in PDT-treated arteries, whereas the adventitia of PDT-treated arteries were positive after 2 weeks. Electron microscopy demonstrated early myofibroblast migration to the adventitia, and at 16 weeks occasional myofibroblasts were noted in the media of PDT-treated arteries. There was complete reendothelial cell covering of the intima by 4 weeks.

CONCLUSIONS

These in vivo data demonstrate that PDT is an effective local method for the treatment of experimental IH. There is no evidence of significant recurrence of IH or arterial degeneration. Further studies with PDT may provide novel approaches to the understanding and treatment of arterial IH.

Transitional features in human atherosclerosis. Intimal thickening, cholesterol clefts, and cell loss in human aortic fatty streaks

The possible transition from a subset of fatty streaks to fibrous plaques in human atherosclerosis has long been postulated, but transitional features in lesions have rarely been demonstrated. We examined human aortic fatty streaks to determine whether significant tendencies toward intimal thickening and toward deep extracellular lipid deposition might be found. To provide accurate ultrastructural assessment of lipid, tissues were processed by new electron microscopic cytochemical techniques. Unilateral fatty streaks exhibited a 60% increase in intimal thickness when compared to contralateral control tissue. Fat droplets in intimal cells accounted for approximately half of the increase; nonfat portions of cells and extracellular matrix accounted for the remainder. Six of 32 fatty streaks (19%) contained cholesterol clefts, which were found in the musculo-elastic (deep) layer of the intima or in the tunica media. Volume fractions occupied by cells in deep intima were reduced when cholesterol clefts were evident, suggesting loss of cells in early core regions. Light and electron microscopy showed structures consistent with lipid-rich core regions in lesions with cholesterol clefts and in a few lesions without cholesterol clefts. The findings of intimal thickening, core region formation, and disappearance of intimal cells constitute new evidence that some fatty streaks are progressive lesions and sites of eventual fibrous plaque development. The findings also suggest that the lipid-rich core region does not originate primarily from the debris of dead foam cells in the superficial intima, but instead arises from lipids accumulating gradually in the extracellular matrix of the deep intima.

Analysis of atherectomy specimens

Atherectomy specimens may be regarded as biopsy tissue excised from human vascular target lesions. Proceeding from contrary histologic findings that attribute focal hypercellularity to restenosis, and hypocellularity to chronic lesions, further analysis of atherectomy specimens was performed to study ultrastructural characteristics and functional aspects propagated by both lesion types. Transmission electron microscopy examination showed that intimal smooth muscle cells (SMCs) were the predominant cells in both primary and restenotic lesions. SMCs exhibited variable degrees of metabolic activation, typically higher in SMCs of restenotic lesions. This SMC phenotype was equally expressed when tissue samples were placed in a cell culture model. In an attempt to quantify SMC activity, proliferative as well as migratory activities of cultured cells were measured by growth curves and a computer-assisted motion analysis system, respectively. A 2- to 3-fold increase of both activity determinants was observed with SMCs cultivated from restenotic lesions compared with those from primary lesions, irrespective of their coronary or peripheral origin. Drug-induced interference of human SMC metabolic activation and antagonism to their proliferative and migratory activities may be helpful in evaluation of therapeutic concepts to prevent restenosis. The antitubulin colchicine was studied for its effect on the defined determinants. The data in vitro demonstrate that colchicine decreased proliferative and migratory activity of SMCs and caused disorganization of the cytoplasmic ultrastructure. In conclusion, electron microscopy and cell culture studies may help to shed more light on the structures and mechanisms underlying restenosis and plaque growth. Deliberate counteraction of any of the specific early events implicated in these complex pathobiologic processes may eventually become effective means to suppress restenosis and may thus result in a prophylactic as well as therapeutic treatment of the diseased vascular wall.

The functional and structural effects of hypothermic storage on ischaemic arterial grafts

The effects of hypothermic ischaemia on blood vessels are unknown. This study aimed to determine the 3 week patency rate and the pathology of 9 experimental groups of hypothermically stored ischaemic arteries and one control group in a rabbit femoral artery model. Ischaemia times were 0 h, 24 h, 1, 2, 4, 6, 8 and 10 weeks (Groups 1-8). Patency was over 80% in all groups after 3 weeks reinsertion. Following reinsertion control grafts maintained normal arterial structure, but cellular degeneration had occurred in all ischaemic grafts and appeared complete after 4 weeks ischaemia. The graft connective tissue framework frequently remained intact. Repair was evident in central graft regions after 2 weeks ischaemia and 3 weeks reinsertion, but occurred only adjacent to the anastomosis in 4-10 week ischaemic arteries. Four week ischaemic arteries (Groups 9 and 10) reinserted for 6 and 12 weeks respectively exhibited near complete repair but patency dropped to 60% in the 12 week group.

The importance of a substantial elastic lamina subjacent to the endothelium in limiting the progression of atherosclerotic changes

This study examines the hypothesis that progressive intimal thickening and atherosclerosis in the larger pulsatile arteries arise from failure to maintain, subjacent to the endothelial cells, a substantial elastin membrane, a component which has been shown to be of special structural significance. The internal thoracic arteries of 293 subjects of all ages up to 60 years were compared histologically with the anterior descending coronary arteries of the same individuals by light- and electronmicroscopy and immunoperoxidase staining for macromolecules. The internal thoracic arteries usually developed a new robust reduplicated internal elastic lamina at an early age, no further intimal thickening, and no significant entry of lipid or cells to the intima. The coronary arteries showed areas of rapid intimal thickening with poor and incomplete reduplicated internal elastic laminae, entry of lipid, macrophages, and other cells to the intima. The reduplicated internal elastic laminae appeared to be formed primarily by the endothelial cells themselves. An elastin membrane subjacent to the endothelial cells appears to be essential. It provides a secure attachment for the cells and a barrier to the entry of macromolecules and cells to the intima. Its absence is associated with progressive intimal thickening and atherosclerosis.

Recruitment and dynamics of leukocytes in the formation of arterial intimal thickening--a comparative study with normo- and hypercholesterolemic rabbits

Leukocyte involvement in intimal thickening was investigated as a function of time and diet. Fibromuscular or foam cell-rich thickings were induced by electrical stimulation (ES) of carotid arteries in rabbits either on a normal or a high (1%) cholesterol diet. Under both dietary conditions granulocytes (predominantly neutrophils), monocytes and lymphocytes migrated through and accumulated beneath a continuous, yet structurally altered endothelium already after 1 day of ES. This preceded the occurrence of smooth muscle cells (SMCs) in the intima. Under normocholesterolemia, leukocyte attachment to the endothelium decreased with continued ES, which coincided with the re-establishment of a normal endothelial cell pattern. Neutrophils ceased to invade the stimulated intima and disappeared from the lesion after 14 days. The proportion of mononuclear leukocytes was also reduced in the thickened intima, finally amounting to 5.5 +/- 5.9% in the 4-week-old fibromuscular lesion where SMCs prevailed. Hypercholesterolemia did not affect neutrophil involvement in response to ES. However, it provoked lipid deposition first in macrophages, then in SMCs and resulted in elevated amounts of mononuclear leukocytes both within the foam cell-rich thickening and in association with the overlying endothelium. These data indicate adaptive behavior of leukocytic infiltration in the development of fibromuscular thickening, and a shift to a chronic inflammatory response under additional hypercholesterolemia.

[The morphogenesis of the tunica elastica interna of the rat aorta in the early periods after birth]

The ultrastructural and three-dimensional spatial arrangement of the internal elastic membrane (IEM) of the rat's aorta was studied by transmissive electron microscopy, native and scanning electron microscopy of chemically extracted specimens. Changes in the passage of different levels of organization of IEM is shown in the process of its maturation in postnatal ontogenesis. The first--fibrillar--step of morphogenesis of IEM is characterized by the formation of microfibril fascicles in 10-day-old animals. Within 1 month after birth the elastic fiber of the lamellar shape was formed which consists of tightly packed fascicles of microfibrils. This fiber is a structural-functional unit of the elastic framework of the aorta. The last stage is characterized by the formation of the tissue system of the fibrous elastic framework consisting of elastic fibers which are structurally interconnected and are having functional interaction. The formation of openings (pores) in IEM is a regular stage of clastogenesis. Through the pores in EM a contact of endotheliocytes and smooth myocytes (SM) is realized, by means of which a system is formed responsible for the transmission of information from receptors on the surface of endotheliocytes to SM. A stereometric analysis has revealed the dynamics of pore distribution density in IEM in the process of its maturation.

[The application of a periarterial synthetic tube results in the formation of rhythmic structures in the intima]

Structure of rabbit carotid artery and aorta after their wrapping with synthetic tube was investigated using light and scanning electron microscopy. Periarterial manipulations lead to the development of myointimal thickening covered with endothelium. Surface of the thickening consisted of rhythmically intermitted elevations and pits situated across the long axis of the vessel. Polymorphism of the covering endothelium was observed. Non-random pattern of the subendothelial smooth muscle cells location (connected with hemodynamic changes) was the main cause of formation of rhythmic structures. Structure of intimal thickening in rabbit arteries is similar to that of human aortic intima at early stages of atherogenesis (before lipid accumulation). This model may be used for studying the mechanisms of atherogenesis as well as for pharmacological investigations.

Ultrastructural studies on the phenotypic modulation of human intimal smooth muscle cells

The present study was carried out to clarify the mechanism of intimal thickening at the ostia of celiac and superior mesenteric arteries. The cell components involved in the process were analyzed under electron microscope. Autopsy samples from cases without significant atherosclerotic diseases were examined and the percentages of smooth muscle cells in either synthetic or contractile state, macrophages, and foam cells in the intima of mesenteric and celiac arteries were calculated. Smooth muscle cells in the synthetic state were predominant in the proximal region and those in the contractile state were predominant in the distal region. Few macrophages were present in both regions. The intima in the proximal and distal regions of celiac arteries in autopsy samples was further divided into three layers and the percentages of various smooth muscle cell phenotypes in each layer were calculated and compared in patients at different ages. In the proximal region, the phenotype of the smooth muscle cells changed from the synthetic to the contractile state from the deeper to the superficial layers with the advance of age. In the distal region, the contractile state was dominant regardless of the age. These results suggest that the phenotypic modulation of human intimal smooth muscle cells is reversible dedifferentiation-redifferentiation process; this phenomenon plays an important role in the initiation of atherosclerosis.

[A comparative ultrastructural and morphometric analysis of the smooth myocytes in the tunicae intima and media of the human fetal aorta]

Transmission electron microscopy was used for studying the thoracic part of the aorta of 9 human fetuses of 20-28 weeks of development. In the medial tunic of the human fetus aorta there are smooth myocytes (SM) of the contractile and synthetic phenotypes. The latter are localized mainly in the inner part of the media. In the inner tunic there are also SM of the synthetic phenotype. With the help of processes they make contacts with endotheliocytes and processes of SM of the media. In the gaps between the subendothelial SM and endothelium there are particles of elastin which form the structure resembling an additional elastic membrane. It is reasonable to think that the migration of SM into the intima is a stage of normal development of the vessel associated with the adaptation to local hemodynamic conditions rather than an initial manifestation of atherosclerosis.

Intimal proliferation in an organ culture of human internal mammary artery

OBJECTIVE

Intimal smooth muscle cell proliferation is an early feature of atherosclerosis. Its progression is difficult to monitor in humans and previous studies have mostly relied on necropsy material. The aim of this study was therefore to establish whether intimal proliferation occurred in an organ culture of human internal mammary artery.

METHODS

Segments of freshly isolated internal mammary artery were maintained din standard tissue culture medium containing 30% calf serum for 14 d. Tissue viability (measured by ATP concentration) was maintained during processing and throughout the culture period [211(SEM 28) nmol ATP.g-1 wet weight on d 1 v 208(27) on d 14].

RESULTS

Histological transverse sections of cultured internal mammary artery showed the development of a neointima containing smooth muscle cells identified by immunocytochemistry for alpha actin. Pulse labelling of cultures with [3H]-thymidine showed proliferating cells predominantly in a neointimal layer with few dividing cells in the media. Cultured de-endothelialized vessels showed less neointimal thickening than cultured freshly isolated vessels [16(3) v 36(5) microns, p < 0.0025] as well as a reduced number of dividing cells per mm of neointimal length [3.1(0.6) v 5.5(1.1), p < 0.05].

CONCLUSIONS

Intimal proliferation occurred in organ culture of internal mammary artery. There is evidence for a factor derived from the endothelium, which may be important in the development of intimal proliferation.

Thrombogenicity and intimal hyperplasia after conventional and thermal balloon dilation in normal rabbit iliac arteries

Acute occlusion and restenosis are the major complications of percutaneous transluminal coronary balloon angioplasty. Application of heat during balloon dilation was postulated to reduce these complications. We evaluated thrombogenicity and intimal hyperplasia of normal rabbit iliac arteries after conventional (37 degrees C) and thermal balloon dilation. Thermal dilation was performed with a radio-frequency-heated balloon, provided with three thermocouples attached to the inside of the balloon skin. In a previous in vitro study, thrombogenicity of human subendothelium was increased at 55 degrees C and greatly decreased at temperatures over 70 degrees C. Thermal balloon dilation was therefore performed at 55 and 90 degrees C in vivo. Rabbits survived 2 h for evaluation of platelet adhesion or either 3 or 8 weeks for intimal hyperplasia. Angiograms revealed no occlusions or thrombi after any procedure. Platelet adhesion was quantified on 20 scanning electron microscopic pictures per balloon dilation site and was expressed as the percentage of the luminal surface covered by platelets. Platelet adhesion was similar in all groups, although large thrombi were present in the 90 degrees C group. Intimal hyperplasia was measured morphometrically at regular intervals over the balloon site. After 3 weeks, the average intimal hyperplasia was significantly reduced in the 90 degrees C balloon dilation group, which was mainly due to the absence of intimal hyperplasia in the midpart of these segments. After 8 weeks, intimal hyperplasia was equal in all groups. Thus, in the applied model, platelet coverage was equal after conventional balloon angioplasty and after 55 and 90 degrees C balloon angioplasty.(ABSTRACT TRUNCATED AT 250 WORDS)

[Localization of fibronectin in atherosclerotic lesions by immunohistochemistry and immunoelectron microscopy]

This paper reports the results of a study on the distribution of fibronectin (FN), its form, character and source in atherosclerotic lesions, using immunohistochemistry (PAP method) and immunoelectron microscopic technique. The results showed that large amounts of FN were localized in fatty streaks, gelatinous lesions and early atherosclerotic plaques. The intima smooth muscle cells in atherosclerotic lesions synthesized more FN, and it is likely that FN represents a new marker of smooth muscle cell modulated from "contractile" to "synthetic" state. With the maturation of atherosclerotic plaque, FN did not fill the whole plaque but was concentrated only in the fibrous cap surface and basocentral part of the atheroma. We also proved that procollagen III peptide (PIIIP) distribution in atherosclerotic plaque was similar to that of FN.

[The three-dimensional structure of the tunica intima and tunica media of the human fetal aorta studied by a new method]

A new method is developed for revealing the latent surfaces in the structure of organs by scanning electronic microscopy. The method is based on the treatment of specimens with potassium ethoxide until cells start to appear in the dissociating solution. Using this method, thoracic aorta of nine human fetuses at the stage of 20-28 weeks was studied. Subendothelial intima and media of human fetal aorta contain smooth muscle cells differing by their arrangement, shape and surface microrelief. The intima cells are arranged in a mosaic pattern formed of single cells or cell clusters. By means of cell processes they are connected with each other, as well as with endothelial and smooth muscle cells of the media. Smooth muscle cells in the inner part of the media also have processes and form an open network. Part of the cells penetrate the intima through pores of the inner elastic membrane. In the deeper layers of the media, laterally adjoining spindle-shaped smooth muscle cells are found. It is suggested that the observed cell polymorphism is due mostly to penetration of the media smooth muscle cells into subendothelium and modification of their shape under the effect of the microenvironment.

[The structure of the endothelialized and nonendothelialized areas of myointimal thickening of the rabbit aorta]

De-endothelialization of the abdominal aorta of the rabbit was performed with a balloon catheter. As a result, a partially endothelialized myointimal thickening was formed consisting of smooth myocytes and macrophages. As compared with the zone devoid of the endothelium the endothelialized zone was characterized by less thickness and by the presence of an additional elastic membrane. Great amount of leukocytes and solitary thrombocytes were adhesed just in the place of contact. In the center of nonendothelialized zone no adhesion was observed. In the zone covered by the endothelium smooth myocytes of the synthetic and contractile phenotype were seen with similar frequency. The nonendothelialized zone was presented mainly by smooth myocytes of the synthetic phenotype and macrophages. The myointimal thickening of the rabbit aorta might be considered as an informative model for analysis of myoendothelial interactions.

Stellate cells of aortic intima: I. Human and rabbit

Stellate cells hitherto accounted exclusively in the innermost elastic-hyperplastic layer were already reported to inhabit human aortic intima. The present paper shows that most of these cells are situated just beneath the endothelium. Stellate cells also appear in the deendothelialization-induced myointimal thickening of rabbit aorta. In the myointimal thickening these cells were revealed in the direct proximity to the endothelium. A conclusion is available that the previously demonstrated polymorphism of human aortic intimal cells may be reproduced in a simple experimental model, which gives new possibilities for the study of the cellular polymorphism in the vessel wall.