Dexamethasone inhibits macrophage accumulation after balloon arterial injury in cholesterol fed rabbits.

Macrophages play a critical role in the development and progression of atherosclerosis. This study was designed to examine the effect of the glucocorticoid, dexamethasone, (Dex), on macrophage accumulation after acute arterial injury. Twenty New Zealand white rabbits were fed a 2% cholesterol, 6% peanut oil, rabbit chow diet for one month prior to bilateral balloon dilatation of the femoral arteries. Ten rabbits received Dex (1 mg/kg, im.) the day before and then daily for 7 days after arterial injury; control rabbits received vehicle only. Seven days after injury, Dex treatment resulted in a 96% and 77% reduction (P < 0.002) in the mean number of macrophages accumulating in the intima and media, respectively. This effect was apparently not due to a reduction in the number of circulating monocytes or to the ability of monocytes from Dex treated animals to adhere to endothelium or migrate in response to a chemotactic signal, determined in vitro under static conditions. It was associated with a 61% reduction in monocyte chemoattractant protein-1 (MCP-1) antigen (P < 0.004) in the injured arterial wall (media+intima). Glucocorticoids may be useful in attenuating the inflammatory response and subsequent foam-cell accumulation after arterial injury.

Induction of IG9 monocyte adhesion molecule expression in smooth muscle and endothelial cells after balloon arterial injury in cholesterol-fed rabbits.

The expression of monocyte-specific adhesion molecules and chemokines by cell types within the vessel wall plays an important role in foam cell accumulation during atherosclerotic plaque development. We previously identified IG9, a novel monocyte adhesion protein that is expressed on endothelial cells (ECs) overlying human and rabbit advanced atherosclerotic plaques. The present study was designed to determine the temporal and spatial expression of IG9 and the chemokine, monocyte chemoattractant protein-1 (MCP-1), after balloon injury with (double injury) or without (single injury) prior air desiccation EC injury in the femoral arteries of rabbits fed a high-cholesterol diet. By immunohistochemical analyses, intense reactivity with monoclonal antibodies to IG9 and MCP-1 was detected 24 hours after single injury in medial smooth muscle cells (SMCs) and in SMCs of adventitial microvessels. However, monocyte infiltration of the tunica media was minimal or not detected in these sections. IG9 and MCP-1 antibody reactivity in vessel sections 28 days after single injury and 24 hours, 7 days, and 28 days after double injury was localized to medial and neointimal SMCs, foam cells, and luminal ECs overlying the plaques. Uninjured rabbit (cholesterol or normal diet) vessel sections exhibited minimal IG9 and MCP-1 immunostaining. In vitro studies using human aortic SMCs demonstrated IG9 protein induction after 24 hours of treatment with platelet-derived growth factor-BB and interferon-gamma or epidermal growth factor. IG9 expression was further increased by pretreatment of SMCs with the proatherogenic lipid, minimally oxidized low density lipoprotein. After balloon injury (24 hours), IG9 is induced in vascular SMCs before the detectable accumulation of monocytes within the vessel wall. Thus, the expression of IG9 by SMCs as well as by ECs may be an important factor in the accumulation of foam cells in atherosclerotic plaque development after arterial injury.

Local delivery of platelet-derived growth factor receptor-specific tyrphostin inhibits neointimal formation in rats.

Signal transduction through the platelet-derived growth factor (PDGF)/PDGF receptor (PDGFR) system is involved in the process of postangioplasty restenosis. Tyrphostins are low molecular weight inhibitors of protein tyrosine kinases. We assessed the antiproliferative effects of PDGFRbeta-specific tyrphostin AG-1295 in vitro and in vivo. AG-1295 significantly inhibited rat smooth muscle cell growth stimulated by PDGF-BB or FCS. This antiproliferative effect was paralleled by reversible reduction of the total phosphotyrosine level and the degree of PDGFRbeta phosphorylation by the drug in vitro. Local sustained delivery of the drug from perivascularly implanted polymeric matrices resulted in focal AG-1295 levels of 711 and 29.1 ng/mg of dry arterial tissue 1 and 14 days after implantation in rats. AG-1295 delivered from polymeric matrices resulted in a 35% reduction of neointimal formation on day 14 after balloon injury in the rat carotid model. Tyrosine phosphorylation of certain transduction proteins in arterial tissue extracts was significantly upregulated by balloon injury on day 3 but was essentially returned to or below basal levels 14 days after injury. Tyrphostin treatment decreased tyrosine phosphorylation at both time points below the basal levels. Moreover, the enhancement of PDGFRbeta expression 3 and 14 days after arterial injury was strongly inhibited by AG-1295 treatment. It can be concluded that AG-1295 reduces neointimal formation by inhibiting PDGFbeta-triggered tyrosine phosphorylation.

Early plus delayed hirudin reduces restenosis in the atherosclerotic rabbit more than early administration alone: potential implications for dosing of antithrombin agents.

BACKGROUND: A 2-hour infusion of r-hirudin at the time of balloon angioplasty limits restenosis in atherosclerotic rabbits. Because thrombin activity in the vessel wall after angioplasty remains high for 48 to 72 hours, we hypothesized that a second infusion of hirudin at 24 hours would reduce restenosis more than early treatment alone. METHODS AND RESULTS: Femoral atherosclerosis was induced in 35 rabbits by air desiccation injury and a high-cholesterol diet. At the time of angioplasty, rabbits were randomly assigned to 1 of 4 groups: controls: heparin bolus, saline infusion at 24 hours; early hirudin: hirudin bolus+2 hours' infusion, saline infusion at 24 hours; delayed hirudin: heparin bolus, hirudin infusion+/-bolus at 24 hours; and early+delayed hirudin: hirudin bolus+2 hours' infusion, hirudin infusion+/-bolus at 24 hours. Rabbits were euthanized after 28 days. The early+delayed hirudin treatment group had less loss of minimal lumen diameter by angiography at 28 days. By histomorphometry, cross-sectional area narrowing by plaque was least in the early+delayed treatment group compared with controls (P=0.0001), early hirudin (P=0.01), or delayed hirudin (P=0.001). The early+delayed hirudin group also had a significant reduction in absolute plaque area and an improvement in lumen area compared with the other groups. No differences were observed between treatment groups with respect to the cross-sectional area encompassed by the internal or external elastic laminae. CONCLUSIONS: Combined early+delayed administration of hirudin significantly reduces angiographic restenosis and cross-sectional area narrowing by plaque compared with early or late treatment alone. These results suggest that restenosis after balloon angioplasty is markedly influenced by thrombin-mediated events not only occurring early but also extending beyond the first 24 hours in this model.

Hirudin reduces tissue factor expression in neointima after balloon injury in rabbit femoral and porcine coronary arteries.

BACKGROUND: Tissue factor (TF) is a transmembrane glycoprotein that, after binding to factor VII/VIIa, initiates the extrinsic coagulation pathway, resulting in thrombin generation and its sequelae. Thrombin has been shown to induce TF mRNA in endothelium, monocytes, and smooth muscle cells, further perpetuating the thrombogenic cycle. This study was designed to determine the effect of specific inhibition of thrombin by recombinant hirudin (r-hirudin) on TF distribution after balloon angioplasty in the cholesterol-fed rabbit femoral artery and porcine coronary artery models. METHODS AND RESULTS: Thirty-five femoral arteries from 32 cholesterol-fed New Zealand White rabbits and 84 coronary arteries from 55 Yorkshire-Albino swine were studied by use of a recently developed in situ method of TF localization based on digoxigenin labeling of recombinant factor VIIa (Dig-VIIa), with correlative studies of TF immunoreactivity by use of anti-rabbit (AP-1) or anti-human (sTF) antibodies. At sites of balloon angioplasty in rabbit femoral or pig coronary arteries (double or single injury), TF-antibody and Dig-VIIa staining were noted in association with endothelial cells, smooth muscle cells, and foam cells and within the fibrous tissue matrix primarily of the adventitia and neointima. Staining was significantly greater after balloon angioplasty than in vessels that had not undergone angioplasty but was similar after single and double balloon injury. Animals treated with r-hirudin (rabbits, 1 mg/kg bolus plus 2-hour infusion; pigs, 1 mg/kg bolus plus 0.7 mg x kg(-1) x d(-1) infusion for 14 days with implantable pump) had diminished TF-antibody and Dig-VIIa staining 28 days after balloon angioplasty compared with controls (bolus heparin only). This effect was more prominent on the neointima and was more striking in the porcine than the rabbit model. CONCLUSIONS: TF expression, persistent 1 month after balloon angioplasty in rabbit femoral arteries and porcine coronary arteries, is attenuated by specific thrombin inhibition with hirudin. These results suggest that thrombin inhibition, in addition to its effect on acute thrombus formation and its effect on luminal narrowing by plaque in experimental animals, may result in a prolonged reduction in thrombogenicity of the restenotic plaque through this effect on TF expression.

PDGF-receptor tyrosine kinase blocker AG1295 selectively attenuates smooth muscle cell growth in vitro and reduces neointimal formation after balloon angioplasty in swine.

BACKGROUND: Signaling through protein tyrosine kinases (PTKs) is a major contributor to the transmission of mitogenic stimuli to the interior of the cell and nucleus. The present study was designed to determine the effect of the tyrphostin AG1295, a selective blocker of PDGF-receptor PTK, on the growth of porcine and human smooth muscle cells (SMCs) in culture, on the outgrowth kinetics of SMCs from porcine and human arterial explants, and on neointimal formation after balloon injury in pigs. METHODS AND RESULTS: SMCs for culture were obtained from porcine abdominal aortas, human internal mammary arteries, and endarterectomy tissue from a single human carotid artery. Addition of AG1295 to SMCs before PDGF stimulation completely inhibited PDGF-beta-receptor tyrosine phosphorylation without affecting the level of PDGF-beta-receptor. AG1295 resulted in a selective, reversible inhibition of SMC proliferation in culture (76%) with only mild (13.5%) inhibition of endothelial cell proliferation. The number of SMCs accumulating around explants of porcine carotid arteries and human endarterectomy specimens 12, 15, 19, 22, and 24 days after plating was reduced by 82% to 92% in AG1295-treated compared with nontreated specimens, and initiation of SMC outgrowth was markedly delayed. The numbers of cells accumulated 10 days after initiation of outgrowth were significantly lower in treated versus control explants. Local intravascular delivery of AG1295-impregnated polylactic acid-based nanoparticles (130+/-25 nm) to the site of balloon injury to porcine femoral arteries resulted in significant reductions in intima/media area ratio and luminal cross-sectional area narrowing by neointima compared with contralateral control arteries to which empty nanoparticles were applied (0.15+/-0.07 versus 0.09+/-0.03, P=.046 and 20+/-4% versus 10+/-4%, P=.0009, n=6 for both). CONCLUSIONS: The tyrphostin AG1295, a selective blocker of PDGF-receptor kinase, exerts a marked inhibitory effect on the activation, migration, and proliferation of porcine and human SMCs in vitro and an approximately 50% inhibitory effect on neointimal formation after balloon injury in porcine femoral arteries when delivered via biodegradable nanoparticles. Further studies appear to be warranted to evaluate the applicability of this novel approach to the interventional setting.

A new single-injury model of balloon angioplasty in cholesterol-fed rabbits: beneficial effect of hirudin and comparison with double-injury model.

Air desiccation endothelial injury followed by cholesterol feeding is known to induce focal femoral atherosclerosis in rabbits. We previously demonstrated the effectiveness of hirudin in limiting restenosis after balloon angioplasty (BA) in this double instrumentation injury (DI) model. In the present study, we sought to determine whether BA without prior air desiccation endothelial injury (single instrumentation injury (SI)) would lead to similar femoral lesions, and whether the response to this injury might also be limited by hirudin. Accordingly, 38 femoral arteries of cholesterol-fed rabbits underwent BA with (n = 18, DI group) or without (n = 20, SI group) prior air desiccation endothelial injury. Animals were killed 24 hours or 28 days after BA. Twenty-four hours after BA, the SI group (n = 10) had a significantly smaller percentage of cross-sectional area narrowing by plaque than the DI group (n = 8) (0% versus 42% +/- 9%, p = 0.008). However, 28 days after BA, the percentages of cross-sectional area narrowing by plaque in the SI (n = 10) and DI (n = 10) groups were similar (59% +/- 6% versus 68% +/- 1%, p = NS). The percentages of intima (16% +/- 3% versus 16% +/- 3%, p = NS) and media occupied by foam cells were also similar in the two groups. To test whether hirudin administration would limit arterial narrowing after injury in the SI model, we randomly assigned cholesterol-fed rabbits that had not undergone air desiccation injury to either bolus hirudin followed by repeat dosing 24 hours after BA or bolus heparin (150 U/kg) at the time of BA. The hirudin-treated group showed significantly less angiographic and histologic restenosis 28 days after BA, despite no difference in early (0 to 72 hours) cumulative cellular proliferation between the two groups. Thus, in the cholesterol-fed rabbit, plaque formation and foam cell accumulation are similar after BA of a non-air-desiccated (SI) or focally atherosclerotic (DI) artery. Thrombin inhibition with hirudin limits arterial narrowing after SI, further emphasizing the role of thrombin in neointimal growth after injury.

Tissue factor modulates the thrombogenicity of human atherosclerotic plaques.

BACKGROUND: The thrombogenicity of a disrupted atherosclerotic lesion is dependent on the nature and extent of the plaque components exposed to flowing blood together with local rheology and a variety of systemic factors. We previously reported on the different thrombogenicity of the various types of human atherosclerotic lesions when exposed to flowing blood in a well-characterized perfusion system. This study examines the role of tissue factor in the thrombogenicity of different types of atherosclerotic plaques and their components. METHODS AND RESULTS: Fifty human arterial segments (5 foam cell-rich, 9 collagen-rich, and 10 lipid-rich atherosclerotic lesions and 26 normal, nonatherosclerotic segments) were exposed to heparinized blood at high shear rate conditions in the Badimon perfusion chamber. The thrombogenicity of the arterial specimens was assessed by 111In-labeled platelets. After perfusion, specimens were stained for tissue factor by use of an in situ binding assay for factor VIIa. Tissue factor in specimens was semiquantitatively assessed on a scale of 0 to 3. Platelet deposition on the lipid-rich atheromatous core was significantly higher than on all other substrates (P = .0002). The lipid-rich core also exhibited the most intense tissue factor staining (3 +/- 0.1 arbitrary units) compared with other arterial components. Comparison of all specimens showed a positive correlation between quantitative platelet deposition and tissue factor staining score (r = .35, P < .01). CONCLUSIONS: Our results show that tissue factor is present in lipid-rich human atherosclerotic plaques and suggest that it is an important determinant of the thrombogenicity of human atherosclerotic lesions after spontaneous or mechanical plaque disruption.

Predictors of luminal narrowing by neointima after angioplasty in atherosclerotic rabbits.

OBJECTIVE: The present study was designed to identify the predictors of cross-sectional area narrowing by neointima (%CSAN-N) after balloon angioplasty (BA) in the cholesterol fed rabbit model. METHODS: Angiographic, histomorphometric, and immunohistochemical data were analyzed from 91 femoral arteries of New Zealand white rabbits. Focal atherosclerosis was induced by air desiccation of the endothelium followed by a 2% cholesterol diet for 28 days. The rabbits received heparin (150 U/kg) at the time of BA (2.5 mm; three, 60-second, 10-atm inflations). Arteries were perfusion-fixed and excised 7 (n = 16), 14 (n = 11), 21 (n = 9), or 28 (n = 20) days after BA. Non-angioplastied arteries were de-endothelialized (cholesterol-fed [n = 12] or normal diet [n = 8]), non-injured but cholesterol-fed (n = 7), or normal (n = 8). RESULTS: Univariate regression across all groups showed that the absolute area of the lumen by histomorphometry (LA) correlated significantly with the area bounded by the external elastic lamina (EEL) (vessel size), but no correlation was found with the absolute area of neointima or media, the percentage disruption of the internal elastic lamina (IEL), or the percentage of neointima and media occupied by foam cells. However, %CSAN-N correlated significantly with the area bounded by the EEL, significantly with the absolute neointimal area, and negatively with the absolute LA (p < 0.0001). Significant correlations were also found between %CSAN-N and the % IEL disrupted, the area of neointima and media occupied by RAM-11 + foam cells, and the loss of alpha-actin positivity in the media (p < 0.0001). CONCLUSIONS: These studies show that neointimal formation contributes significantly to luminal narrowing 1 month after angioplasty in this model, that the degree of vascular injury and the extent of foam cell accumulation in the neointima and media are significant independent predictors of neointimal formation, and that the area of the neointima, and the percent narrowing by neointima, are important predictors of remodeling itself (EEL area). These predictors were not identifiable when the analysis was focused on the determinants of absolute luminal area alone.

Controlled delivery of a tyrphostin inhibits intimal hyperplasia in a rat carotid artery injury model.

We examined the inhibitory effect of AG-17, a potent inhibitor of protein tyrosine kinase activity on injury-induced vascular SMC proliferation by polymeric-based, periadventitial controlled release implant in the balloon catheter carotid injury model in rats. The AG-17 delivery system was formulated from ethylenevinyl acetate copolymer and the release kinetics as well as drug stability were determined. Polymeric matrices containing 2 or 10% AG-17 were implanted perivascularly in rats following balloon catheter injury. Western blot analysis of explanted arterial segments revealed enhanced tyrosine phosphorylation in injured arteries that was essentially reduced to normal levels in treated arteries. The mean neointima to media ratios were significantly reduced in both 2% (0.79 +/- 0.17, n = 9, P < 0.02) and 10% AG-17 (0.59 +/- 0.09, n = 12, P < 0.001) groups in comparison to the control group (1.38 +/- 0.18, n = 16). The mean areas of the media in the control and the 2% AG-17 group did not differ significantly but a significant reduction of the mean area of the media was observed in 10% AG-17 group. Embedding of the unstable tyrphostin compound, AG-17, in a hydrophobic matrix stabilizes the drug both in vitro and in vivo, and allows delivery-rate modulation as well as protracted site-specific therapy. Perivascular controlled release delivery of the tyrphostin AG-17 inhibits neointimal formation in the rat carotid injury model.

Effectiveness of hirulog in reducing restenosis after balloon angioplasty of atherosclerotic femoral arteries in rabbits.

BACKGROUND: Thrombin may play an important role in restenosis after balloon angioplasty (BA). Angiographic and pathologic restenosis have been shown to be reduced after BA in an atherosclerotic rabbit model using recombinant desulfatohirudin, a selective and direct thrombin inhibitor. We hypothesized that potent and specific thrombin inhibition with the synthetic peptide hirulog given intravenously at the time of angioplasty would reduce restenosis in rabbits, confirming a specific role of thrombin in restenosis. METHODS AND RESULTS: Focal femoral atherosclerosis was induced in 27 rabbits by air desiccation endothelial injury followed by a 2% cholesterol diet for 1 month. Rabbits received either heparin (150 units/kg bolus, n = 14) or hirulog (5 mg/kg bolus followed by 5 mg/kg/h for 2 h, n = 13) at the time of BA (2.5-mm balloon with three 60-second, 10-atm inflations 60 s apart). Angiograms performed before and after BA and before sacrifice were analyzed quantitatively. Rabbits were sacrificed 28 days after BA for quantitative histopathologic analysis. Minimum luminal diameter (mm) did not differ between treatment groups before (1.1 +/- 0.2 vs. 1.2 +/- 0.1 mm) or after (1.5 +/- 0.2 vs. 1.6 +/- 0.1) BA in arteries from heparin-versus hirulog-treated rabbits, respectively. At 28 days, however, minimum luminal diameter was significantly less (1.0 +/- 0.4 vs. 1.5 +/- 0.2, p = 0.0001) and percent stenosis was greater (0.46 +/- 0.25 vs. 0.22 +/- 0.08, p = 0.0002) in arteries from heparin- versus hirulog-treated rabbits, respectively. Similarly, quantitative histopathology showed less cross-sectional area narrowing by plaque in the hirulog group (56 +/- 24 vs. 42 +/- 21%, p = 0.04). CONCLUSION: A 2-hour infusion of hirulog at the time of angioplasty improved late angiographic luminal dimensions and reduced cross-sectional area narrowing by plaque in rabbits compared with heparin controls. Together with previous studies, this confirms a specific role for thrombin in restenosis after angioplasty.

Effect of thrombin inhibition with desulfatohirudin on early kinetics of cellular proliferation after balloon angioplasty in atherosclerotic rabbits.

BACKGROUND: Thrombin may have a pivotal role in restenosis after angioplasty. Hirudin, a potent thrombin inhibitor, reduces luminal narrowing by plaque after angioplasty in a rabbit model of atherosclerosis. Because cellular proliferation is believed to be an important mechanism for restenosis and thrombin has been shown to be a potent smooth muscle cell mitogen in vitro, we hypothesized that the mechanism of the effect of hirudin on limiting luminal narrowing by plaque occurs via inhibition of cellular proliferation. METHODS AND RESULTS: Femoral atherosclerosis was induced in 108 rabbits, and balloon angioplasty was performed. At angioplasty, group 1 rabbits (n=38) were treated with a 2-hour infusion of hirudin, and group 2 rabbits (n=41) were treated with heparin. Group 3 rabbits (n=29) were treated with hirudin (n=15) or heparin (n=14) and killed at 7 or 28 days to determine cross-sectional area narrowing by plaque and cellular proliferation with the use of bromodeoxyuridine labeling. At 29, 71, or 167 hours after angioplasty, group 1 and 2 rabbits were injected with 3H-thymidine and killed 1 hour later, and labeling indexes were determined. A significant increase in the index of 3H-thymidine-labeled nuclei was observed in the intima of "ballooned" arteries compared with "nonballooned" atherosclerotic arteries at both 30 hours (0.06+/-0.05 versus 0.01+/-0.01, P<.01) and 72 hours (0.10+/-0.06 versus 0.004+/-0.004, P<.01). By 7 days, the index of labeled cells was similar to baseline (0.04+/-0.03 versus 0.01+/-0.01, P=.12). Hirudin had no effect on the 3H-thymidine labeling indexes at any of the time points studied despite the fact that hirudin treatment in group 3 rabbits resulted in less cross-sectional area narrowing by plaque at both 7 and 28 days after angioplasty (41+/-16 versus 24+/-12 at 7 days and 60+/-21 versus 44+/-17 at 28 days, heparin versus hirudin; P<.03). CONCLUSIONS: Balloon angioplasty resulted in a marked increase in cellular proliferation that peaked at 72 hours. A 2-hour infusion of hirudin failed to reduce early 3H-thymidine labeling, suggesting that inhibition of cell proliferation within the first 7 days after angioplasty is not the predominant mechanism by which hirudin exerts its effect on limiting luminal narrowing by plaque 28 days after balloon angioplasty in this animal model.

Effect of midinfrared holmium: YAG laser angioplasty with and without balloon angioplasty on acute outcome and restenosis in atherosclerotic femoral arteries in rabbits.

BACKGROUND AND OBJECTIVE: Pulsed laser may lessen vascular damage and reduce restenosis. This study examined the acute and chronic effects of midinfrared laser angioplasty with and without balloon angioplasty in atherosclerotic femoral arteries in rabbits. STUDY DESIGN/MATERIALS AND METHODS: Atherosclerosis was induced in arteries by air desiccation and cholesterol feeding. Arteries were assigned to one of four groups: (1) laser angioplasty with a Thullium/Holmium/Chromium:YAG infrared laser (Eclipse), (2) balloon angioplasty, (3) laser followed by balloon angioplasty, and (4) no intervention. Arteries were examined angiographically and histologically at 2 hours and 28 days. RESULTS: Intervention groups had significant initial gain, but this gain was less with laser alone than after balloon or after laser plus balloon. At 2 hours, laser alone caused greater arterial damage and thrombosis compared to controls. At 28 days, arteries treated with laser plus balloon had greater narrowing compared with arteries treated with balloon angioplasty. By multivariate regression analysis, the severity of the pre-intervention stenosis (P = 0.001) and intervention with laser plus balloon (P = 0.01) correlated independently with the severity of luminal narrowing at 28 days. CONCLUSION: Midinfrared Ho:YAG laser angioplasty resulted in substantial acute damage with increased frequency of thrombus formation in this rabbit model. arteries treated with laser alone had suboptimal initial gain and more obstruction by plaque at 28 days compared to nonintervened arteries. The adjunctive use of balloon angioplasty improved initial gain, but correlated with smaller luminal diameters and more severe narrowing by plaque at 28 days.

Neointimal proliferation in canine coronary arteries. A model of restenosis permitting local and continuous drug delivery.

BACKGROUND: A number of experimental preparations have been used to elucidate the pathophysiology of restenosis after percutaneous transluminal coronary angioplasty; however, few models have been advanced that address restenosis in coronary arteries, and none provides an effective means of continuous local drug delivery. In this report, we describe a model of restenosis in coronary arteries with the provision for local, continuous delivery of cytotoxic and/or anti-proliferative agents. EXPERIMENTAL DESIGN: An ameroid constrictor was placed on the left circumflex coronary artery of 17 normocholesterolemic dogs. One month later, after substantial collateral development had ensued, a segment of the left circumflex coronary artery distal to the ameroid was mechanically compressed using surgical forceps for 10 (N = 4), 15 (N = 4), 20 (N = 2), or 30 minutes (N = 5). In two dogs, an indwelling left circumflex catheter and implanted pump maintained a continuous infusion of saline at the injury site. In addition, the pump side port provided transcutaneous access for serial, selective coronary arteriography. The animals were maintained on a normal diet, without cholesterol or fat supplementation. RESULTS: Three weeks after vascular injury, significant neointimal proliferation was observed in all dogs that was morphologically similar to the proliferation seen after percutaneous transluminal coronary angioplasty in human coronary arteries. The extent of neointimal formation was linearly related to the duration of injury: neointimal/medial area ratios were 0.35 +/- 0.10, 0.46 +/- 0.10, 0.58 +/- 0.03, and 1.16 +/- 0.26 (mean +/- SE) after 10, 15, 20, and 30 minutes of mechanical compression injury, respectively. CONCLUSIONS: This model produces striking neointimal proliferation in the coronary arteries of normocholesterolemic dogs, morphologically similar to that seen in human coronary restenosis specimens. The model appears suitable to test the efficacy of agents with the potential to inhibit neointimal formation, providing continuous intracoronary drug delivery, as well as transcutaneous access for serial, selective arteriography.

Geometric remodeling is not the principal pathogenetic process in restenosis after balloon angioplasty. Evidence from correlative angiographic-histomorphometric studies of atherosclerotic arteries in rabbits.

BACKGROUND: Restenosis after balloon angioplasty of coronary arteries is thought to be a proliferative response of the arterial wall to injury. Recently, it has been suggested that geometric remodeling of the arterial wall, rather than intimal fibromuscular hyperplasia, may be the major pathophysiological mechanism underlying restenosis. In this study, we evaluated the relative contribution of a geometric decrease in arterial size versus neointimal growth to luminal narrowing associated with restenosis after balloon angioplasty of atherosclerotic femoral arteries in rabbits. METHODS AND RESULTS: Focal femoral atherosclerosis was induced by endothelial desiccation injury followed by a 2% cholesterol diet. After 1 month on the high cholesterol diet, the animals were subjected to one of four strategies: (1) balloon angioplasty, (2) balloon angioplasty followed by treatment with the factor Xa inhibitor antistasin, (3) combined laser and balloon angioplasty, or (4) no angioplasty. Animals were killed 2 hours or 28 days after angioplasty, and excised femoral artery segments were prepared for histomorphometric analysis. Angiography was performed serially before and immediately after angioplasty and before the animals were killed. An initial postprocedural gain in luminal diameter at sites of angioplasty was followed by a significant reduction in diameter by angiography and a significant increase in luminal cross-sectional area narrowing by plaque by histomorphometry 28 days after angioplasty compared to adjacent nonangioplastied segments of the same arteries, to nonangioplastied control arteries, or to angioplastied segments of animals treated with the factor Xa inhibitor antistasin. By contrast, the overall arterial size (cross-sectional area bounded by the external elastic lamina) at sites of restenosis was not significantly different from adjacent nonangioplastied segments in the majority of arteries excised at 28 days, and the mean overall arterial size at sites of restenosis was not significantly different from corresponding segments of nonangioplastied control arteries or from angioplastied segments of animals treated with antistasin. In the minority of angioplastied arteries in which the arterial size did change, most got larger. CONCLUSIONS: Geometric remodeling resulting in a decrease in overall cross-sectional arterial size does not appear to be the principal pathogenetic mechanism for restenosis after balloon angioplasty with or without laser in this experimental model.