(Circulation. 1995;92:183-189.)
© 1995 American Heart Association, Inc.
Articles |
From the Research Institute of Angiocardiology and Cardiovascular Clinic, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Correspondence to Takeshi Kuga, MD, Research Institute of Angiocardiology and Cardiovascular Clinic, Faculty of Medicine, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812, Japan.
| Abstract |
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Methods and Results The effect of bradykinin on vasomotion of epicardial coronary arteries was evaluated in 8 patients with normal coronary arteries (control group), 14 patients with organic coronary stenosis (coronary artery disease [CAD] group), and 8 patients with vasospastic angina (VSA group). Changes in the diameter of epicardial coronary artery were assessed by quantitative coronary arteriography. Intracoronary administration of bradykinin at graded doses (60, 200, and 600 ng) dilated epicardial coronary arteries without altering arterial pressure or heart rate in all patients of either group. In the control group, vasomotor responses of the site where acetylcholine caused dilation were compared with the responses of the site where acetylcholine caused constriction. The magnitudes of bradykinin-induced dilation at the site with acetylcholine-induced dilation (mean±SD: 6±6%, 11±9%, and 15±9%) were comparable to that (3±6%, 8±8%, and 13±9%) at the site with acetylcholine-induced constriction. In the CAD group, vasomotor responses of the stenotic site (% diameter stenosis, 15% to 50%) and nonstenotic site were examined. The bradykinin-induced dilation at the stenotic site (0±4%, 3±8%, and 5±9%) was significantly less (P<.01) than at the nonstenotic site (3±4%, 8±6%, and 16±11%) and in the control group. Coronary vasodilation with nitrate at the stenotic site (20±11%) was comparable to that at the nonstenotic site (22±16%) and in the control group (21±10%). In the VSA group, vasomotor responses of the site with acetylcholine-induced spasm and the site without spasm were examined. The bradykinin-induced vasodilation at the spastic site (5±5%, 16±15%, and 33±17%) was comparable to that at the nonspastic site (4±8%, 12±14%, and 21±9%). Nitrate-induced dilation was comparable at the spastic site (51±19%) and the nonspastic site (32±13%). The ratio of bradykinin-induced vasodilation to nitrate-induced vasodilation at the spastic site was comparable to the control group.
Conclusions These results suggest that bradykinin causes vasodilation of human epicardial coronary arteries in vivo and that bradykinin-induced endothelium-dependent vasodilation is impaired at the stenotic site but is preserved at the angiographically normal site where endothelium-dependent vasodilation by acetylcholine is impaired and at the spastic site.
Key Words: bradykinin vasospasm atherosclerosis arteries
| Introduction |
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It has been shown that bradykinin, an endogenous vasoactive substance, induces endothelium-dependent relaxation of isolated human coronary artery in vitro.15 16 17 18 However, the effects of bradykinin on vasomotion of epicardial coronary arteries in patients with coronary atherosclerosis or spasm have not been studied in vivo. The aim of this study was first, to determine whether bradykinin dilates epicardial human coronary arteries in vivo, and second, to examine whether endothelium-dependent vasodilation with bradykinin is altered at the atherosclerotic site in patients with coronary artery disease and at the spastic site in those with vasospastic angina.
| Methods |
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The number of coronary risk factors (hyperlipidemia, diabetes mellitus, arterial hypertension, smoking habit, and family history of coronary artery disease) was significantly greater in the CAD group (1.9±0.9) than in the control group (0.9±0.6) (P<.05). That in the VSA group was 1.4±0.7.
Study Protocol
Written informed consent was obtained from
each patient after
approval by the Institutional Review Board. Cardiac catheterization was
performed in the fasting state after oral premedication of diazepam (5
mg). Antianginal and antihypertensive medications were discontinued at
least 24 hours before the study (Table 1
).
After control arteriography of the left coronary artery was performed, the following studies were performed. First, bradykinin was administered into the left coronary artery by hand. Each dose of bradykinin was diluted with 3 mL of physiological saline, which was infused into the coronary artery through the Judkins catheter in 10 seconds. The catheter was then flushed by infusing 3 mL of saline in 20 seconds. Coronary arteriography was performed 1 minute after the end of the infusion. We evaluated the effects of three doses of bradykinin (60, 200, and 600 ng). We waited for 2 minutes before administration of the next dose of bradykinin. We found in the preliminary studies that bradykinin at doses >600 ng significantly decreased arterial pressure, which is consistent with the previous study by Bonner et al.19 Moreover, we found that bradykinin at 600 ng did not increase coronary blood flow velocity 1 minute after bradykinin infusion using a Doppler flow guide wire (Advanced Cardiovascular Systems Inc), which is consistent with the results by Pelc et al.20
Second, acetylcholine at 100 µg was administered into the left coronary artery. This dose of acetylcholine was diluted with 2 mL of physiological saline and was infused into the left coronary artery through the Judkins catheter in 10 seconds. The catheter was then flushed by infusing 3 mL of saline in 20 seconds. Coronary angiograms were recorded 1 minute after the beginning of the acetylcholine infusion to evaluate coronary spasm. The additional coronary angiograms were recorded 2 minutes after the beginning of the infusion to evaluate endothelium-dependent vasodilation by acetylcholine. In 5 patients of the CAD group, acetylcholine was not infused because they had severe organic stenosis.
Third and finally, ISDN (2 mg/4 mL) was administered into the left coronary artery, and coronary angiograms were recorded 2 minutes after the beginning of the ISDN infusion. Our previous study confirmed that intracoronary infusion of saline had no significant effects on the coronary diameter, arterial pressure, or heart rate.7
Phasic and mean aortic blood pressures, heart rate, and 12-lead ECGs were continuously monitored using a Nihon-Koden polygraph system and were recorded on a multichannel recorder.
Quantitative Coronary Arteriography and Its Analysis
Coronary
cineangiograms were recorded using a Siemens
cineangiographic system (Siemens Bicor & Hicor). Nonionic contrast
media (Ioversol, Yamanouchi Pharmaceutical Co) was used. An appropriate
view that permitted clear visualization of the coronary segment under
study without overlapping branches was selected. An angle of the view,
the distance from x-ray focus to the object, and that from the object
to the image intensifier were carefully kept constant during the study.
An end-diastolic frame of the angiogram was selected, and
the luminal diameter was determined quantitatively by a
cinevideodensitometric analysis system (Kontron
Instruments).21 The readily identifiable branch points
were used as a reference marker of the measurement to allow assessment
serial changes in the diameter of the same site. The diameters were
measured three times, and the mean value was used for the analysis.
The size of the Judkins catheter was used for calibrating the arterial
diameter in millimeters. The accuracy and precision of quantitative
angiographic measurements were determined from the analysis of
cinefilms of the phantom with the precision-drilled models of coronary
arteries with diameters of 1.5, 2.0, and 3.0 mm (Kyoto Kagaku Hyouhon
Co) filled with contrast medium and filmed under 5 cm of
water.22 The accuracy was 0.7±0.2%, and the precision
was 2.6±0.6% (mean±SD, n=165 measurements). Measurements
with this
system for interobserver and intraobserver reproducibility were high
(r=.96 and r=.98, respectively). The changes
in
the coronary diameter in response to vasoactive drugs (bradykinin,
acetylcholine, and ISDN) were expressed as percent changes from the
baseline value. The degrees of organic stenosis were expressed as %
diameter stenosis in angiograms after administration of ISDN.
In the control group, we measured changes in the luminal diameter at 25 sites where acetylcholine caused dilation (proximal [n=5], middle [n=8], and distal [n=12] segments of the left coronary artery) and those at 19 sites where acetylcholine caused vasoconstriction 2 minutes after acetylcholine. These measurements were designed because 6 of the 8 patients in the control group had at least one risk factor that has been shown to impair endothelium-dependent coronary dilation in response to acetylcholine.8 12 It is reported that responses of angiographically normal coronary artery segments to acetylcholine may be segmental rather than diffuse.23 Thus, we assumed that the angiographically normal segment with acetylcholine-induced dilation is functionally normal.
In the CAD
group, we determined changes in the luminal diameter at 20
paired organic stenotic (15% to 50% stenosis) (Table 1
) and
adjacent
nonstenotic sites. The adjacent nonstenotic site was defined as the
angiographically normal, smooth segment.
In the VSA group, we determined changes in the luminal diameter at eight paired spastic and nonspastic sites, none of which showed organic stenosis. The nonspastic site was defined as an adjacent segment proximal or distal to the spastic site when focal spasm was provoked or as a segment of another nonspastic vessel with the baseline diameter similar to that at the spastic site when diffuse coronary vasospasm was provoked.
Preparation of Bradykinin and Acetylcholine
Bradykinin (Sigma
Chemical Co) was diluted with physiological
saline at a concentration of 0.2 mg/mL and was sterilized at the
Department of Pharmacy, Kyushu University Hospital. Acetylcholine
chloride (Dai-ichi Pharmaceutical Co) was freeze-dried and stored at
room temperature. Further dilution was made with physiological saline
immediately before use.
Statistical Analysis
Data are expressed as mean±SD.
When serial changes in %
increase in luminal diameter or hemodynamic variables in response to
bradykinin were compared, ANOVA for repeated measures followed by
Bonferroni's multiple comparison test was used. The relation between
nitrate-induced vasodilation and bradykinin-induced vasodilation was
analyzed by a single linear regression. Probability of less than .05
was considered statistically significant.
| Results |
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Bradykinin-Induced Coronary Vasodilation
In the control
group, bradykinin dilated (P<.01
by one-way ANOVA) the site with acetylcholine-induced dilation
(11±7%) in a dose-dependent manner (6±8%, 11±9%, and
15±9%)
(Fig 1
). The bradykinin-induced vasodilation was
comparable among the proximal, middle, and distal segments of the left
coronary arteries (Table 3
). The bradykinin-induced
vasodilation (3±6%, 7±8%, and 13±9%) at the site with
acetylcholine-induced constriction (-15±12%) was comparable to
that
at the site with acetylcholine-induced dilation (Fig 1
).
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In the CAD group, bradykinin at graded doses significantly increased
the diameter at the nonstenotic site (P<.01 by one-way
ANOVA) but not at the stenotic site (NS by one-way ANOVA) (Fig
2
). The % increases in the diameter evoked with
bradykinin at the stenotic site (0±4%, 3±8%, and 5±9%)
were
significantly less (P<.01 by two-way ANOVA) than those at
the nonstenotic site (3±4%, 8±6%, and 16±11%) and in the
control
group. There was no significant difference between bradykinin-induced
coronary vasodilation at the nonstenotic site in the CAD group and in
the control group (Fig 2
).
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In the VSA group, coronary
vasodilation evoked with bradykinin was
comparable between the spastic site (5±5%, 16±15%, and
33±17%)
and nonspastic site (4±8%, 12±14%, and 21±9%) (Fig
3
). Bradykinin-induced coronary vasodilation at the
spastic site in the VSA group was significantly greater than in the
control group (P<.01 by two-way ANOVA).
|
Nitrate-Induced Coronary Vasodilation
The % increases in the
diameter evoked with nitrate were 21±10%
in the control group, 20±11% and 22±16% (NS) at the stenotic and
nonstenotic sites in the CAD group, and 51±19% and 32±13% (NS)
at
the spastic and nonspastic sites in the VSA group. Nitrate-induced
vasodilation at the spastic site in the VSA group was significantly
greater (P<.01) than in the control group. There was a
significant positive correlation between nitrate-induced dilation and
bradykinin-induced dilation in the control group (P<.01,
r=.79). Thus, the ratio of bradykinin-induced vasodilation
to nitrate-induced vasodilation was calculated. The ratio at the
spastic site was comparable to that at the nonspastic site and in the
control group (Fig 4B
). The ratio at the stenotic site
in the CAD group was significantly less (P<.01 by two-way
ANOVA) than at the nonstenotic site and in the control group (Fig
4A
).
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| Discussion |
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Bradykinin-Induced Vasodilation of Human Coronary Arteries In
Vivo
In the present study, we administered bradykinin selectively
at graded doses into the left coronary arteries to examine the local
effect of bradykinin on vasomotion of human epicardial coronary
arteries in vivo. Since preliminary studies had shown that bradykinin
at doses exceeding 600 ng decreased systemic arterial pressure and that
bradykinin at 600 ng did not change coronary blood flow velocity, we
selected doses of bradykinin not exceeding 600 ng. The present
study showed that bradykinin at these doses increased the diameters of
epicardial coronary arteries without altering arterial pressure or
heart rate. These results suggest that bradykinin-induced dilation
resulted from the direct action of bradykinin on the epicardial
coronary artery but not from the indirect action such as flow-mediated
dilation. In vitro studies confirmed that bradykinin did not constrict
isolated human coronary smooth muscle15 16 and that
bradykinin-induced dilation of isolated human coronary artery was
totally endothelium
dependent.15 16 17 18 Thus,
it appears
reasonable to assume that bradykinin-induced dilation observed in the
present study resulted from the release of
endothelium-derived relaxing factor(s). It has been
shown that bradykinin stimulates the release of
endothelium-derived nitric oxide,15 16 17
hyperpolarizing factor,18 and prostacyclin24 ;
however, we did not examine the relative contribution of these three
factors in mediating bradykinin-induced coronary vasodilation in
vivo.
Effect of Bradykinin at the Atherosclerotic Site
Previous
studies have reported that
endothelium-dependent vasodilation is impaired in
atherosclerotic human epicardial coronary
arteries.5 6 7 8 25 26
Endothelium-dependent coronary
vasodilation evoked with acetylcholine is impaired not only at the
atherosclerotic sites6 7 8 but also at
the angiographically
normal segments of coronary arteries in patients with coronary artery
disease9 10 11 or with coronary risk
factors,8 12 indicating that altered
endothelium-dependent dilation with acetylcholine may
precede the structural changes of arterial wall assessed by
arteriography. On the other hand, substance Pinduced vasodilation is
not impaired at the angiographically normal segments in patients with
coronary artery disease.13 These results suggest that
endothelium-dependent vasodilation evoked with
substance P may be preserved at the early stage of atherosclerotic
process.5
In the present study, we demonstrated that bradykinin-induced coronary vasodilation at the stenotic site was significantly less than that at the nonstenotic site in the CAD group and in the control group. These results indicate that endothelium-dependent vasodilation evoked with bradykinin was impaired at the atherosclerotic site. We also demonstrated that bradykinin-induced vasodilation was preserved not only at the angiographically normal sites with acetylcholine-induced vasoconstriction in the control group but also at the nonstenotic site in the CAD group. The results of the present study and of the previous study suggest that endothelium-dependent vasodilation with bradykinin and substance P is preserved but that vasodilation with acetylcholine is impaired at the early stage of the atherosclerotic process.5 27
Effect of Bradykinin at the Spastic Site
Recent clinical
studies have demonstrated that
endothelium-dependent vasodilation with substance
P,7 14 histamine,25 and the low dose of
acetylcholine7 is preserved at the spastic site in
patients with vasospastic angina. However, the effects of bradykinin on
vasomotion at the spastic site have not been studied. The present
study demonstrated that bradykinin-induced coronary vasodilation at the
spastic site was comparable to that at the nonspastic site in the VSA
group. There was no significant difference in nitrate-induced
vasodilation between the spastic site and the nonspastic site. The
ratio of bradykinin-induced vasodilation to nitrate-induced
vasodilation in the VSA group was comparable to that in the control
group. These results suggested that
endothelium-dependent coronary vasodilation evoked with
bradykinin was preserved at the spastic site and that augmented
vasodilation evoked with bradykinin in the VSA group may be due to
elevated basal coronary artery tone.28 Our results are in
agreement with the suggestion that coronary spasm is caused by
augmented reactivity of vascular smooth muscle but not by defective
endothelial function alone.7 29
Limitations of the Study
The first limitation was that a
small number of patients was
studied. The second limitation was that most of our patients were
taking various antianginal and antihypertensive drugs before the study
(Table 1
). Since these drugs were discontinued 24 hours before
the
study, it is unlikely that the drugs have significant effects on
coronary vasomotor tone.
Summary
The results of this study suggest that bradykinin
causes
vasodilation of human epicardial coronary arteries in vivo and that
endothelium-dependent coronary vasodilation with
bradykinin is impaired at the atherosclerotic site but is preserved at
the angiographically normal site where
endothelium-dependent coronary vasodilation by
acetylcholine is impaired, at the angiographically normal site in
patients with coronary atherosclerosis, and at the spastic site in
patients with vasospastic angina. Our results may provide further
information for understanding the pathophysiology of endothelial
dysfunction in coronary atherosclerosis and vasospasm in humans.
| Acknowledgments |
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Received November 14, 1994; revision received January 3, 1995; accepted January 10, 1995.
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