© 1997 American Heart Association, Inc.
Articles |
Repeated Balloon Injury of Rat Aorta
A Model of Neointima With Attenuated Inhibition by Heparin
From the Laboratoire de Recherches sur les Maladies Vasculaires Périphériques, Association Claude Bernard (L.C., J.J.), and Institut National de la Santé et de la Recherche Médicale (INSERM), Unité 430, Immunopathologie Humaine (D.H., D.J.-M., P.B.), Hôpital Broussais, Paris France.
Correspondence to Loïc Capron, MD, Service de Médecine Interne, l'Hôtel-Dieu, 1, Place du Parvis Notre-Dame, 75181 Paris Cedex 04, France.
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Abstract Repeated arterial injury, because it challenges already activated cells, may elicit a reaction that differs from that provoked by a single injury. We compared the response of rat aorta to single and double balloon injury and tested the inhibitory effect of heparin in both situations. For repeated injury, the first and second lesions were induced 3 weeks apart. Two weeks after repeated injury, the neointima that existed from the first lesion had expanded, with significant increases in intima-media wet weight and its DNA and elastin content and in the intima-to-media (I/M) thickness ratio. Two days after repeated injury, the expression of proliferating cell nuclear antigen (PCNA) was enhanced in both the media and the intima, indicating that cells from both layers are involved in the aortic response to a second lesion. As established previously, treatment with heparin (continuous intravenous administration, 50 IU/kg · h-1) almost totally suppressed the response to single injury. However, heparin only attenuated the response to repeated injury, with a partial decrease in intima-media wet weight and its DNA and elastin content and in I/M thickness ratio. PCNA labeling showed that heparin inhibited the proliferative activity in medial cells much more strongly than in intimal cells. In conclusion, repeated aortic injury elicits a reaction of both the media and preexisting neointima. In this mixed response, neointimal smooth muscle cells are less sensitive than medial cells to inhibition by heparin, which results in a weakened effect of the drug on the fibromuscular reaction.
Key Words: heparin • balloon injury • restenosis • rat aorta • neointima • PCNA
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The fibromuscular response of arteries to experimental injury in various animal species has been studied extensively to understand the mechanism of restenosis after angioplasty and to find treatments to prevent restenosis.1 So far, although several drugs, such as angiotensin-converting enzyme inhibitors, heparin, and corticosteroids, have proved efficient in the experimental setting, none have been demonstrated in the clinical setting to have consistent efficacy in preventing restenosis in patients with coronary artery disease. The reasons for this discrepancy are unclear. One explanation could be that our experimental models are inadequate.2 Indeed, experimental injury occurs in a healthy artery, whereas in humans, angioplasty is performed in a severely diseased artery. An atherosclerotic stenosis, the usual indication for angioplasty, is a complex inflammatory thickening of the intima with a mixed population of cells (eg, arterial smooth muscle cells, monocytes, and lymphocytes) that are in variable states of activation.3 In sharp contrast, immediately after endothelial denudation by experimental injury, a normal inner arterial wall consists of multiple layers of mostly quiescent medial smooth muscle cells. It is conceivable that a pharmacological intervention that is inhibitory in the latter setting may become inefficient in the former setting because the cellular reactions and interactions in the two settings can be quite different.1 4
To explore this possibility, models of repeated injury are a logical proposition: a first (preparative) injury modifies the arterial wall by establishing an intimal thickening with activated cells; later on, a second (inductive) injury provokes an additive response that is used as the model to study restenosis experimentally. So far, the most widely exploited of these two-step protocols has been performed in rabbits with endothelial denudation accompanied by cholesterol feeding as the preparative injury and conventional dilatation using a balloon catheter as the inductive injury.1 2 5 6 7 8 9 In the investigation reported here, we adapted this experimental strategy to the rat aorta. Because rats do not respond to cholesterol feeding by developing arterial lipid deposits, we used dilatation with a balloon catheter for both the first and second injuries. A similar model of double injury was recently used by Gerdes et al10 in rabbit carotid artery. Heparin is a well-established inhibitor of the fibromuscular reaction to a single injury.11 12 Our working hypothesis was that heparin may exert a different degree of inhibition on the responses to single and double injuries, which would result from aortic cells being in a resting state and in an activated state, respectively, when the injury is induced.
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Animals
We used male Wistar rats (Iffa Credo, l'Arbresle, France) weighing 360 to 380 g (12 to 14 weeks old) at the outset of experiments. All aggressive procedures (catheterization of the aorta, implantation of osmotic pumps, and killing by severance of the lower abdominal aorta) were performed with the rats under anesthesia with ketamine hydrochloride (150 mg/kg body weight IP). Animals had free access to water and regular chow. They were killed by bleeding the abdominal aorta with a large-bore needle; blood was collected in EDTA (final concentration, 7.5 mmol/L) for determination of hematocrit and plasma anti-Xa activity with a chromogenic substrate (CBS31-39, Stago, Asnières, France).13 The experiments were conducted in accordance with the guidelines of our institution and recommendations for the care and use of laboratory animals of the French Ministry of Agriculture (authorization 004814).
Aortic Injuries, Study Design, and Treatment
The aorta was submitted to two types of mechanical lesions that
were either isolated or combined. Although the same balloon catheter
(2F) was used to induce the lesions, lesions differed in both timing
and route of catheter insertion: the first lesion was created on the
first day (day 0) of the experiment by introducing the catheter via the
left external carotid artery, and the second lesion was created on day
21 via the left common carotid artery. In each instance, the catheter
was pushed into the aorta down to the level of the renal arteries, the
balloon was inflated with fixed volumes of distilled water (50 µL,
followed by an additional 50 µL after the passage of the diaphragm)
to prevent any bias related to variations in the intensity of the
stress applied to the aorta,14 and the catheter was pulled
up until it was blocked at the origin of the left common carotid
artery. This sequence was completed three times. The catheter was then
removed, the artery used for inserting it was ligated, and the skin
incision was closed with surgical staples. Sham operations consisted of
ligating the corresponding artery without any catheter introduction. We
used various combinations of actual catheterization and
sham intervention to form four experimental groups of rats: L0,
uninjured control rats (both operations were sham operations); L1,
first injury only (second operation was a sham); L2, second injury only
(first operation was a sham); and L1L2, both first and second injuries
(Fig 1
).
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After preliminary tests to establish the model (results not shown), the study comprised two experiments. The main experiment assessed the late fibromuscular response of the aorta 2 weeks after the second operation by measuring the wet weight of intima-media; its content in DNA, collagen, and elastin (using biochemical methods); and the thickness of the intima and media (using histomorphometry). In an auxiliary experiment, we explored the early mitotic response of the intima and media 2 days after the second operation by measuring the expression of PCNA using immunohistochemistry, a sensitive method for detecting proliferating cells in injured rat aorta.15
On day 21, ie, 3 weeks after the first carotid operation and immediately after the second one, an osmotic minipump was inserted into the peritoneal cavity of all animals except those in group L0; a 14-day pump was used for the main experiment (2-week treatment), and a 7-day pump was used for the auxiliary experiment (2-day treatment). A catheter connected to the pump was inserted into the left jugular vein for continuous intravenous delivery. The pump was loaded with either normal saline (control groups, indicated by a C after the group number) or heparin (treated groups, indicated by an H; sodium heparinate). To ensure immediate delivery of the contents, loaded pumps were primed by incubation in normal saline at 37°C for 24 hours before implantation. The concentration of heparin in the pump was adjusted to ensure an infusion rate of 50 IU/kg body weight · h-1. Treatment was assigned randomly so that the second lesion, when actually induced (groups L2 and L1L2), was inflicted without knowing to which group the animal would eventually belong.
Main Experiment
All animals were killed on day 35, ie, 5 weeks after the first
carotid operation and 2 weeks after the second carotid operation and
the beginning of treatment (Fig 1
).
Biochemical Analysis of Intima-Media
The segment of thoracic aorta between the left subclavian and
subcostal arteries was removed, and the intima-media was separated from
the adventitia by dissection.16 The strips of intima-media
from each aorta were blotted on filter paper, weighed (wet weight to
assess the whole intima-media mass), then homogenized in 2
mL of Tris-EDTA (10 and 2 mmol/L, respectively). Analytical
techniques were described previously.12 Briefly, the DNA
content of each intima-media was determined using 1.5 mL of
homogenate; the remaining 0.5 mL of homogenate
was used to estimate two protein fractions of intima-media. After
hydrolysis in 0.1 N NaOH for 50 minutes at 95°C, soluble and
insoluble fractions were obtained and separated. Each fraction was then
hydrolyzed in 6 N HCl for 48 hours at 105 to 110°C, and its
hydroxyproline content was measured. Collagen and elastin contents of
intima-media were estimated from the soluble and insoluble fractions,
respectively, assuming a hydroxyproline content of 92 residues per 1000
for collagen and of 23 residues per 1000 for elastin.
Histomorphometry of Aorta
The segment including the first 4 to 5 mm of the abdominal
aorta (between the subcostal and celiac arteries) was fixed in 10%
formaldehyde for at least 48 hours, treated with graded alcohol
solutions and xylene, and embedded in paraffin. From each segment, two
nonadjacent 5-µm-thick cross sections were cut, and the slides were
stained with orcein (elastic stain). Computer-assisted morphometry was
performed using a Nachet 15000 analyzer working with 256 levels
of gray on an image of 512x512 pixels and connected to a microcomputer
with an image-analysis program. For each aortic section, eight
random, noncontiguous microscopic fields (final magnification on video
screen, x250; actual area, ~300 000 µm2; final
calibration, 1.14 µm2 per pixel) were examined. An
algorithm computed the mean thickness (in µm) of
neointima and media in each field, from which the I/M
thickness ratio was derived. To compute the mean thickness values
(intima, media, and I/M) of an aorta, all measurements performed on the
two sections of this aorta were averaged.
Auxiliary Experiment
All animals were killed 23 days after the beginning of the
experiment (first carotid operation), ie, 2 days after the second
carotid operation and the beginning of treatment (Fig 1). The whole
aorta was fixed in 4% formaldehyde for 24 hours and processed for
immunohistoenzymatic detection of PCNA. For each aorta, five
nonadjacent 5-µm-thick paraffin sections were harvested on
polylysine-coated slides at room temperature. Sections were stained
using the following steps: pretreatment with 1 mmol/L EDTA
buffer, pH 8, in a microwave oven, three times for 5 minutes each time;
incubation with normal sheep serum to decrease background; rinsing;
incubation with monoclonal antibody against recombinant rat PCNA (PC10
clone, Dako, Trappes, France) diluted 1/200 for 30 minutes; rinsing;
detection of fixed antibodies using a biotinylated goat antibody
against mouse IgG diluted 1/50 for 30 minutes, then
streptavidin-peroxidase diluted 1/400 for 15 minutes with 1
mg/mL diaminobenzidine and 0.3% H2O2;
and counterstaining with hematoxylin. The percentage of PCNA-positive
(ie, proliferating) cells out of the total number of cells was
determined by visual counting. For neointima, all
microscopic fields with neointima formation were assessed
in the five aortic sections; for media, all consecutive fields were
counted in three randomly selected sections out of the five aortic
sections available. A total of about 2500 medial cells and 1500
neointimal cells (when present) were examined in each
aorta, and the average percentage of PCNA-expressing cells was computed
for each layer.
Statistic Analyses
Group values are summarized as the mean±SEM. We used one-way
ANOVA followed by Bonferroni's modified t tests to compare
heparin-treated animals with the saline-treated control animals and to
compare both these groups with the corresponding uninjured group, which
gave the baseline status of the aorta (ie, how the aorta would be if
heparin had completely inhibited the response to injury). Therefore,
for single injury, ANOVA included groups L2C, L2H, and L0, and for
repeated injury, ANOVA included groups L1L2C, L1L2H, and L1C. We used
an unpaired Student's t test to compare animal
characteristics (body weight and hematocrit) between the control and
heparin-treated groups in the same protocols of injury (L1, L2, and
L1L2). Calculations were performed using SigmaStat for Windows, version
2.0. In all instances, two-sided P values are considered
significant when<.05.
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Main Experiment
The animal groups are described in Table 1
. Intraperitoneal
insertion of an osmotic pump for the last 2 weeks of the experiment
resulted in a significant stagnation of body weight
(P<.002, Student's t test): mean final body
weight decreased from 435±13 g in group L0 (in which rats were
operated on twice for carotid ligation but did not receive an osmotic
pump, n=5) to 401±3 g in all other groups combined (n=47).
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Repeated Versus Single Injury
Compared with the response in the uninjured state (L0), the
fibromuscular response of aorta 2 weeks after balloon injury (L2C) was
characterized by the formation of a neointima (increase of
mean I/M thickness ratio, from 0 to 19±4%) with a parallel increase
in the wet weight of intima-media and its DNA, collagen, and elastin
contents. All these differences were statistically significant (Table 2 and Fig 2). The L1C group, in which the aorta was
studied 5 weeks after a single injury, when compared with the L2C
group, studied 2 weeks after a single injury, provided information on
how the neointima spontaneously evolves between 2 and 5
weeks: there was a modest expansion of the neointima during
this 3-week interval, with the mean I/M thickness ratio increasing from
19±4% to 24±5% and the intima-media components and wet weight
following a similar trend. A second injury applied 3 weeks after the
first injury resulted in further expansion of neointima: in
aortas from group L1L2C, all variables except collagen content of
intima-media were significantly higher than in aortas from group L1C
(injured once); and mean I/M thickness ratio reached 56±8%. In all
types of injury, media thickness remained fairly constant (Table 2).
The main point here is that an injured aorta retains its ability to
react to a second mechanical stimulation by increasing its amount of
fibromuscular tissue. As shown in Fig 3, a major mechanism in the second response is the addition of a second
layer of neointima over the preexisting one.
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Effect of Heparin Treatment
Continuous intravenous treatment with heparin (50
IU/kg · h-1) resulted in highly variable levels
of plasma heparin (anti-Xa activity, 0.05 to 1.0 U/mL) because at the
time of death, when blood was sampled, osmotic pumps were nearing the
end of their delivery capacity, 2 weeks after their implantation.
Heparin treatment induced minor bleeding with moderate anemia, as shown
by significant lowering of the hematocrit (C versus H) in groups L2 and
L1L2 (Table 1).
Heparin had a powerful inhibitory effect on the response to
a single injury. In aortas from group L2H, all studied
variables were significantly lower than in aortas from group L2C
and remained quite close to the values found in uninjured aortas from
group L0. The mean I/M thickness ratio in group L2H was 3±1%. Heparin
treatment did not influence media thickness in this type of injury (as
in any other; Table 2). Heparin administered between 3 and 5 weeks
after a single injury (L1 groups) did not modify the composition of
aortic intima-media (Table 2): the mean I/M thickness ratio was 24±2%
in group L1H and 24±5% in group L1C. Because heparin did not
influence the late (and modest) progression of the fibromuscular
response, aortas from group L1C provided a suitable reference for
assessing the influence of heparin on aortas from L1L2 groups (where
this progression and the response to a second injury are assumed to be
combined). Here, the influence of heparin, in contrast with that
exerted on the reaction to a single injury, was attenuated. All
variables except collagen were consistently lower in aortas
from group L1L2H than in aortas from group L1L2C, but the decrease was
significant only for intima-media wet weight. Means for aortas from
group L1L2H were intermediate between those found in aortas from groups
L1L2C and L1C; intima-media wet weight and DNA content were
significantly higher in group L1L2H than in group L1C aortas; and the
mean I/M thickness ratio was 56±8% in group L1L2C, 39±4% in group
L1L2H, and 24±5% in group L1C.
Auxiliary Experiment
To explore further the contrasting influence of heparin on the
response to single and double injury (complete versus partial
inhibition), we assessed the early mitotic response of the aortic
layers to a first and second injury with and without heparin treatment
by counting the proportion of cells expressing PCNA (Figs 4 and 5).
The number of animals studied was five for group L0, five for group
L2C, five for group L2H, four for group L1C, five for group L1L2C, and
seven for group L1L2H; there was no L1H group.
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Repeated Versus Single Injury
In the uninjured aorta, the mean percentage of PCNA-positive media
cells was very low: 0.09±0.08%. Two days after a single injury (L2C),
this ratio increased to 1.9±0.2%. Twenty-three days after a single
injury (L1C), when a neointima had formed, the proportion
of PCNA-positive cells in the media had fallen to 0.40±0.02%,
although substantial proliferative activity persisted in the intima
(8.1±1.1%). Two days after a second injury (group L1L2C), as compared
with group L1C, there was a significant increase (P<.05) in
PCNA-positive cells, both in the media (from 0.40±0.02% to
1.3±0.3%) and the neointima (from 8.1±1.1% to
16.1±2.6%). Clearly, the response to repeated injury elicits a
proliferative reaction involving both the medial and intimal cells.
Effect of Heparin Treatment
In this experiment, intravenous heparin (50 IU/kg
· h-1) induced higher and less dispersed levels of
plasma anti-Xa activity than in the main experiment (1.5±0.2 and
1.3±0.1 U/mL in groups L2H and L1L2H, respectively) because blood was
collected 2 days after implantation of the pump, while the device had
its full delivery capacity. Two days after a single injury, the mean
percentage of PCNA-positive media cells was lower (P<.05)
in heparin-treated animals (group L2H, 0.95±0.10%) than in
saline-treated animals (group L2C, 1.9±0.2%). Two days after a second
injury, the same inhibition was observed under heparin treatment for
medial cells (0.42±0.09% in aortas from group L1L2H versus
1.3±0.28% in aortas from group L1L2C, P<.05); however,
heparin did not significantly decrease the expression of PCNA by
intimal cells (14.5±1.4% in aortas from group L1L2H versus
16.1±2.6% in aortas from group L1L2C) (Fig 5).
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Repeated arterial injury with a balloon catheter has been used previously in rabbits, leading to the uniform conclusion that a second lesion enhances intimal thickening as compared with a single one.10 17 18 19 Our results in the aortas of untreated rats confirm and extend these earlier findings: compared with a single injury (L1C group), a second injury inflicted 3 weeks after a first injury (L1L2C) significantly increases the whole mass (wet weight) of intima-media, its DNA and elastin content, and the I/M thickness ratio; however, the collagen content of intima-media remained unaffected by reinjury. Immunohistoenzymatic staining for PCNA 2 days after the second injury further indicates that cells from both the media and neointima participate in the additional proliferative response: the mean percentage of PCNA-positive cells was about three times higher in the media and two times higher in the neointima from twice-injured aortas from the L1L2C group than in once-injured aortas from the L1C group. Cells from a neointima formed 3 weeks after a first injury are still able to proliferate in response to a second injury. Neointimal cells remain in a state of activation for several weeks after balloon injury, with enhanced expression of intercellular adhesion molecule-1, class II major histocompatibility antigen,20 or basic fibroblast growth factor21 ; other distinct biological features of cells from rat neointima, such as increased migratory22 and proliferative23 activity, the expression of platelet-derived growth factor-B chain,24 or altered responses to platelet-derived growth factor and other stimuli,25 have been reported in vitro. Most smooth muscle cells cultivated from rat aortic neointima (15 days after balloon injury) exhibit an epithelioid phenotype characterized by serum-independent growth and enhanced migration.26
The principal aim of our study was to test whether, given their state of sustained activation, cells from a previously injured artery remain sensitive to pharmacological inhibition when challenged by a second injury. For that purpose we selected heparin because, like many other groups since the pioneering study by Guyton et al,11 we have found it to be among the most powerful inhibitors of the arterial response to a single injury.12 Our results in the L2 groups confirm this eloquently: continuous intravenous treatment with heparin (50 IU/kg · h-1) suppressed the reaction; 2 weeks after a single injury, aortas from group L2H were indistinguishable from uninjured aortas from group L0 except for a tenuous intimal thickening; 2 days after injury, PCNA expression by medial cells was significantly lowered (by 50%) in aortas from group L2H as compared with aortas from group L2C. In contrast, the inhibitory effect of heparin on the fibromuscular response to repeated injury was less clear-cut: 2 weeks after the second lesion was induced, the intima-media wet weight in aortas from group L1L2H was significantly lower than in aortas from group L1L2C but remained significantly higher than in the reference group (once-injured aortas, group L1C); except for the collagen content of intima-media (which did not vary significantly in response to a second injury), all variables displayed the same trend, with values in group L1L2H intermediate between those in groups L1L2C and L1C. PCNA labeling 2 days after the second injury indicated that heparin did not significantly reduce (by 10%) the mean proliferative activity of neointima cells, although it did significantly inhibit (by 68%) proliferation in the media. The nonsignificant inhibition of intimal cells by heparin after reinjury cannot be interpreted as complete heparin resistance, yet intima cells are clearly less inhibited by heparin than media cells.
The incapacity of heparin to inhibit neointimal cells as strongly as medial cells can explain why the drug loses a substantial part of its power against the aortic response to repeated injury, a reaction that elicits both medial and neointimal cells. This difference suggests that, contrary to medial cells that are in (or have regained) a quiescent state, activated neointimal cells tend to become insensitive to heparin. Previous in vitro studies support this conclusion by showing that arterial smooth muscle cells can be or become resistant to the antiproliferative effect of heparin. Such is the case for cells cultured from the aorta of spontaneously hypertensive rats27 and for selected cell lines from normal rat aorta that have been subjected to continuous passage in media containing heparin.28 In eight patients with coronary artery disease who underwent reoperation for venous graft stenosis, cells cultured from restenotic lesions displayed a much lower sensitivity to growth inhibition by heparin than cells harvested in normal arteries or veins from patients without restenosis.29 Caplice et al30 examined the outgrowth of smooth muscle cells from cultured coronary artery explants of primary atherosclerotic plaques and of undiseased regions. For undiseased tissue, heparin significantly delayed the time required for reaching the half-maximum percentage of outgrowth from the explant. For plaque tissue, heparin had no such effect, suggesting that heparin acts differently depending on the phenotype and proliferative state of the cells involved in outgrowth (a phenomenon that combines cell proliferation and migration). This conclusion, although reached in a very different setting, agrees well with our own observations in vivo. However, in closer relation with our model, heparin did inhibit the growth of smooth muscle cells cultured (fifth passage) from the neointima of rat thoracic aorta (2 weeks after balloon injury).31
Heparinoids have been tested in other types of combined arterial aggressions with variable results: unfractionated heparin and low-molecular-weight heparin decreased cellular proliferation but had no significant effect on neointima thickness in rabbit carotid artery submitted to electrical stimulation and cholesterol-rich diet followed by balloon angioplasty;7 low-molecular-weight heparin decreased neointima formation in minipig coronary artery submitted to cholesterol-rich diet and balloon injury followed by stent implantation,8 as well as in rabbit iliac artery challenged with combined cholesterol diet and balloon angioplasty;5 and heparin (delivered either locally or subcutaneously) failed to reduce plaque formation and luminal narrowing in rabbit femoral artery submitted to cholesterol-rich diet and air desiccation injury followed by balloon angioplasty.2 Overall, these observations in rabbit and pig arteries partially support those we report here in rat aorta, ie, heparin can be less potent in inhibiting neointima formation after repeated arterial injury than after a single injury. Interestingly, in the rabbit carotid artery, Gerdes et al10 found that treatment with the thrombin inhibitor hirudin is slightly more effective in decreasing neointima formation after a single injury (59% inhibition) than after a double injury (44% inhibition).
This study has several limitations. Repeated balloon injury to rat aorta is a highly simplified model for the study of restenosis after angioplasty in humans. The target lesion (fibromuscular neointima formed 3 weeks after a first injury) lacks several capital features of an atherosclerotic plaque, such as extracellular and intracellular lipid deposition, infiltration by monocytes and T lymphocytes, and neovascularization. Aside from proliferation and migration of smooth muscle cells and from extracellular matrix synthesis, many aspects likely to be implied in the arterial reaction to angioplasty are absent, such as plaque rupture, intraplaque hemorrhage, mural thrombus formation, elastic recoil, and remodeling. Sensitivity of smooth muscle cells to inhibition by heparin varies between species, as documented recently by Geary et al.32 In that study, conducted in baboons, a species more closely related to humans than rats, low-molecular-weight heparin failed to inhibit intimal thickening and smooth muscle cell proliferation after a single arterial injury. Culture studies have identified heparin-sensitive and -insensitive pathways in the stimulation of baboon smooth muscle cell migration and proliferation. In our model, the exact mechanisms involved in the relative resistance of intimal cells to heparin remain to be determined.
Our results, along with those of some previous studies,2 7 30 could help to explain why heparin is inefficient in preventing restenosis after angioplasty in patients with coronary heart disease.33 Activated smooth muscle cells, like those present in experimental neointima and atherosclerotic plaques, may become less sensitive to inhibition by heparin. Although the cellular composition of a rat aortic neointima is much less complex than that of an atherosclerotic plaque (where, besides smooth muscle cells, activated leukocytes are present in large numbers),3 repeated arterial injury brings us one small step closer to the real situation of restenosis. In rats, this experimental model, which is simpler than rabbit models of combined arterial aggressions, might prove more useful than single arterial injury for testing drugs to prevent the most common complication of angioplasty, which has thus far almost invariably resisted pharmacological prevention.
Note Added in Proof
H. Koyama and M.A. Reidy (Circ Res. 1997;80:408–417.)
recently published a study on the response of rat carotid artery to
repeated injury with a balloon catheter. An intravenous injection of
heparin (888 u/kg body weight) 10 minutes before injury failed to
decrease the replicative activity of smooth muscle cells in the
neointima, measured 2 days after reinjury, but strongly inhibited the
mitotic response of the media to single injury.
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Selected Abbreviations and Acronyms |
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Acknowledgments |
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This study was supported in part by a grant from the Fondation pour la Recherche Médicale.
Received September 20, 1996; accepted December 6, 1996.
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