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(Circulation. 1998;98:2911-2918.)
© 1998 American Heart Association, Inc.
Basic Science Reports |
From the Institut National de la Santé et de la Recherche Médicale (INSERM), Unité 400, Faculté de Médecine, Créteil, and Unité 367, Paris (T.T.G.), France.
Correspondence to Jin Bo Su, PhD, INSERM U400, Hôpital Emile Roux, 94456 Limeil-Brevannes, France. E-mail jbsu{at}im3.inserm.fr
| Abstract |
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Methods and ResultsFourteen chronically instrumented dogs were studied in the control state and in pacing-induced HF (250 bpm for 3 weeks). The dose-dependent decrease in mean aortic pressure (MAP) induced by acetylcholine was significantly blunted in HF. In contrast, in both control and HF, bradykinin infusion caused similar dose-dependent decreases in MAP and increases in cardiac output (CO). This vasodilator effect of exogenous bradykinin was potentiated similarly in both states by enalaprilat, which blocks both angiotensin conversion and bradykinin degradation. For evaluating the role of endogenous bradykinin, the effects of enalaprilat were compared with those of ciprokiren, a pure renin inhibitor. In control, ciprokiren did not produce any effect. Enalaprilat, however, produced a significant decrease in MAP and a significant increase in CO, which were attributed to the inhibition of bradykinin degradation, because these effects were absent after pretreatment with Hoe 140 (a bradykinin B2 receptor antagonist). In contrast, in HF, vasodilator effects of ciprokiren were observed, but enalaprilat produced larger changes in MAP and CO, and after Hoe 140, the hemodynamic effects of enalaprilat were significantly decreased, showing the effects of endogenous bradykinin, which were similar to those measured in control.
ConclusionsIn this model of HF with a blunted endothelium-derived vasodilation, the vasodilator effects of exogenous and endogenous bradykinin are preserved. These results suggest that bradykinin may play an important role in HF, in which vasoconstriction is present and endothelium-dependent vasodilation is blunted.
Key Words: bradykinin heart failure renin angiotensin enzymes
| Introduction |
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Bradykinin is a potent endogenous vasodilator that participates, in human coronary vessels, in the regulation of NO production7 and vasomotor control8 and is involved in the effects of ACE inhibitors, as demonstrated in isolated vessels and hearts from normal animals,9 10 11 in normal conscious dogs,12 in normotensive humans,13 and in animals with HF.14 Bradykinin may thus be an important vasodilator factor in HF, but there is no study that examines whether the vasodilator effects of bradykinin are altered in HF. Therefore, the present study was designed to answer this question in the pacing-induced HF model. First, the endothelial function was determined by dose-response curves of acetylcholine in both the control state (CS) and HF. Second, the hemodynamic effects of exogenous bradykinin and the influence of enalaprilat on hemodynamic effects of exogenous bradykinin were compared in both states. Finally, to assess the function of endogenous bradykinin, the effects of enalaprilat, which blocks angiotensin conversion and bradykinin degradation, were compared with and without Hoe 140 (a bradykinin B2 receptor antagonist) and with those of ciprokiren, a pure renin inhibitor.
| Methods |
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Experimental Protocol
All experiments were performed with the dogs in the conscious
state.
In CS, experiments were performed when the dogs had fully recovered. To
determine vascular endothelial function, in 5 dogs,
acetylcholine was injected intravenously at doses of 0.3,
1, and 3 µg/kg. In a group of 8 dogs, after baseline data had been
recorded, stepwise bradykinin infusions were performed (3, 10, and
30 µg/min, 2 minutes each, via the left atrial catheter). After a
rest period of
15 minutes, when the hemodynamic
parameters had returned to their baseline levels,
enalaprilat 1 mg/kg was injected intravenously. When a new
steady state was reached, bradykinin infusions were repeated to
determine the influence of enalaprilat on the
hemodynamic effects of bradykinin. To examine the role
of endogenous bradykinin, in 6 dogs, enalaprilat 1 mg/kg or
ciprokiren 3 mg/kg was injected intravenously in random
order on different days separated by 48 hours.
Hemodynamic parameters were monitored for
20 minutes. The chosen dose of ciprokiren was based on a study in
sodium-depleted dogs.15 In the same dogs, on a
different day, 5 minutes after a pretreatment with Hoe 140 (10 µg/kg
IV), the hemodynamic effects of enalaprilat 1 mg/kg IV
were studied again.
After completion of the studies in CS, continuous right ventricular pacing was initiated (250 bpm) with a programmable miniature pacemaker placed in a pocket of a jacket on the back of the animal. Dogs were examined daily to confirm the continuous pacing and to evaluate cardiac function. After 3 weeks of right ventricular pacing, the same protocol as in CS was carried out. Experiments were performed after a 15-minute period of stabilization after the pacemaker interruption. Hemodynamic responses to acetylcholine were studied in 4 dogs. Bradykinin infusions were performed in 8 dogs in the absence and presence of enalaprilat. To analyze whether the effects of bradykinin were dependent on vascular tone, on a different day, bradykinin perfusions were performed in 5 dogs in which total peripheral resistance (TPR) was reduced by an injection of ciprokiren 1 mg/kg IV. Ciprokiren and enalaprilat were studied in 7 dogs. In these dogs, on a different day, the effects of enalaprilat were also examined in the presence of Hoe 140 10 µg/kg IV.
Data Collection and Analysis
Absolute values of LV pressure were obtained by calibrating the
micromanometer in 37°C water against a Statham
P23ID transducer (Gould Inc) before implantation. All signals were
recorded on a microcomputer and analyzed with Hem v1.5
software (NOTOCORD Systems) and on a graphic recorder. TPR was
calculated as (MAP-MRAP)/CO, where MAP is mean aortic pressure, MRAP
is mean right atrial pressure, and CO is cardiac output. LV stroke
volume was calculated as CO/heart rate.
Plasma Renin Activity, Angiotensin I, and
Angiotensin II Measurements
To measure baseline plasma renin activity (PRA),
angiotensin (Ang) I, and Ang II, blood samples were
withdrawn from the aortic catheter before any drug injection in CS and
in HF. In the subgroup in which hemodynamic effects of
enalaprilat and ciprokiren were monitored for 20 minutes, blood samples
were also collected 15 minutes after each drug injection. For plasma
Ang I and Ang II measurements, 10 mL of blood was stored in iced
EGTA-K3 tubes containing 0.5 mL of a mixture of
inhibitors and centrifuged at 4000 rpm at 4°C for
10 minutes, and plasma samples were stored at -80°C until assay. PRA
and plasma Ang I and Ang II were measured as described
previously.14
Drugs
Bradykinin was purchased from Sigma Chemical Co.
Enalaprilat was a generous gift of Dr Sweet (Merck Sharp & Dohme Ltd,
West Point, Pa), and ciprokiren (chemical formula:
(S)-2-benzyl-N-[(S)-1-[(1S,2R,3S)-1-cyclohexylmethyl-3-cyclopropyl-2,
3-dihydroxy-propylcarbamoyl]-2-(imidazol-4-yl)-ethyl]-3-[1-methyl-1-(morpholin-4-ylcarbonyl)-ethylsulfonyl-methyl]-propionamide)
was a generous gift of Dr Clozel (F. HoffmannLa Roche Ltd,
Basel, Switzerland).
Statistical Analysis
ANOVA was performed with SuperANOVA software (V1.11, Abacus
Concepts Inc). Values are presented as mean±SEM. A 1-way ANOVA
was used for intragroup interactions. When a significant trend was
found by ANOVA, comparisons with baseline were performed using the
contrasts. A 2-way ANOVA of repeated measurements for the same
parameters over time was used to study intergroup
interactions. When a significant trend was found by ANOVA, comparisons
between means were performed by the Student-Newman-Keuls method. When
only 2 means were compared, an appropriate t test was used.
A value of P<0.05 was considered statistically
significant.
| Results |
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In HF, baseline PRA and Ang I and Ang II concentrations were increased from 0.7±0.1 ng · mL-1 · h-1, 4.9±0.8 pg/mL, and 2.7±0.4 pg/mL in CS to 4.4±1.3 ng · mL-1 · h-1, 40.7±10.3 pg/mL, and 17.7±3.2 pg/mL, respectively (all P<0.02).
Hemodynamic Effects of Acetylcholine in CS and
in HF
In HF, the vasodilator effects of acetylcholine were significantly
blunted with regard to the measured parameters (Figure 2
), indicating an impaired vascular
endothelial function.
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Hemodynamic Effects of Bradykinin in CS and
in HF
In both CS and HF, bradykinin infusion produced a dose-dependent
decrease in MAP and a dose-dependent increase in CO (Table 1
). The reduction in MAP was
similar in both states (Figure 3
). During
bradykinin infusion, heart rate increased significantly in both states,
but the magnitude was smaller in HF than in CS. Bradykinin did not
produce significant changes in stroke volume in CS, whereas it
increased stroke volume significantly in HF (Table 1
). When changes in
TPR induced by bradykinin (30 µg/min) were plotted against
corresponding baseline TPR, there was a linear correlation between
these parameters. Changes in TPR induced by bradykinin in
CS, HF, and HF with reduced TPR after ciprokiren fell on the same line.
A significant linear correlation was also found between changes in MAP
induced by bradykinin and baseline TPR
(y=-0.25x-0.02, r=0.54,
P<0.02). This indicates that the effect of bradykinin is
dependent on vasomotor tone and that the response to bradykinin is
preserved in HF (Figure 4
).
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Influences of Enalaprilat on Hemodynamic Effects of
Bradykinin in CS and in HF
After pretreatment with enalaprilat, the pressure-lowering effect
of bradykinin was significantly enhanced in both CS and HF (Table 2
, Figure 3
). For example, 3 µg/min of
bradykinin after pretreatment with enalaprilat produced a decrease in
MAP equal to that induced by 30 µg/min of bradykinin in the absence
of enalaprilat (Figure 3
). The magnitude of the potentiation was
similar in both CS and HF.
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Functional Role of Endogenous Bradykinin
To evaluate the functional role of endogenous
bradykinin, the effects of enalaprilat, which blocks both
angiotensin conversion and bradykinin degradation, were
compared with those of ciprokiren, a renin inhibitor.
In CS, ciprokiren did not produce any significant changes in
hemodynamic parameters (Figure 5
, left), despite significant inhibition
of PRA and plasma Ang I and Ang II concentrations (Table 3
), suggesting that the RAS plays a
minimal role in the regulation of vascular tone in this state. In HF,
ciprokiren significantly decreased MAP and significantly increased CO
(Figure 5
, left), showing the activation of the RAS. In both states,
PRA was nearly completely inhibited by ciprokiren, and plasma Ang I and
Ang II concentrations were reduced (Table 3
).
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In contrast with ciprokiren, in CS, enalaprilat produced a significant
decrease in MAP and a significant increase in heart rate, CO, and LV
dP/dtmax, with an unchanged stroke volume (Figure 5
, right). In HF, the pressure-lowering effect of enalaprilat was
significantly larger than in CS (P<0.05) and larger than
that induced by ciprokiren in the same state (P<0.05). In
both states, enalaprilat increased PRA and plasma Ang I but decreased
plasma Ang II to levels similar to those produced by ciprokiren (Table 3
). The difference between the effects of enalaprilat and ciprokiren on
MAP and on CO, which is probably related to endogenous
bradykinin, was similar in CS and in HF (Figure 6
).
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Hemodynamic Effects of Enalaprilat in the Presence
of Hoe 140 in CS and in HF
To verify that the difference between the effect of ciprokiren and
enalaprilat was due to endogenous bradykinin, Hoe 140 was
injected intravenously. In both CS and HF, injection of Hoe
140 10 µg/kg did not produce any significant
hemodynamic change (Table 4
), suggesting an unchanged baseline
endogenous bradykinin.
|
In CS, in the presence of Hoe 140, enalaprilat did not produce any
significant change in hemodynamics (Figure 7
, left). In HF, after pretreatment with
Hoe 140, the hemodynamic effects of enalaprilat were
significantly smaller than those in the absence of Hoe 140, with a
smaller reduction in MAP and smaller increase in CO and stroke volume
(Figure 7
, right). The effects of endogenous bradykinin
were apparent, as indicated by the difference between the effects of
enalaprilat in the absence and presence of Hoe 140 (Figure 8
). These effects were not only preserved
but even increased in HF when MAP was considered (P<0.05;
Figure 8
, top) but were similar for CO in both CS and HF (Figure 8
, bottom).
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| Discussion |
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Characterization of the Model
Chronic ventricular tachycardiainduced
HF is a well-established HF model that shares many of the
characteristics of human dilated
cardiomyopathy.16 17 18 19 20 In the
present study, most of these characteristics were observed.
In our preparation, in CS, there was no apparent activation of the RAS, as shown by the absence of vasodilator effect of the renin inhibitor ciprokiren, which is in accordance with a previous study in normotensive subjects.13 After induction of HF, an increased contribution of the RAS in the control of arterial vascular tone was apparent, as suggested by increased levels of PRA, Ang I, and Ang II and by increased vasodilator effects of ciprokiren.
In agreement with previous studies in patients with HF,2 4 7 an impaired endothelium-mediated vasodilation with an impaired response to acetylcholine stimulation1 5 21 and reduced endothelial NO production6 has been described in dogs with pacing-induced HF. In agreement with these studies, our study also showed significantly decreased vasodilator effects of acetylcholine in dogs with HF, suggesting that in this model, in addition to increased RAS activity, endothelium-mediated vasodilation is blunted.
Role of Exogenous and Endogenous Bradykinin in
HF
A major new finding of the present study is that, in contrast
with acetylcholine, vasodilator effects of exogenous bradykinin were
preserved in HF and that these effects were dependent on the vasomotor
tone (Figure 3
and 4
). It is worth noting that, in association with
similar decreases in MAP, exogenous bradykinin increased CO similarly
in both CS and HF. However, the increased CO induced by bradykinin in
CS was due in large part to the increased heart rate, because
calculated stroke volume was not modified. In contrast, stroke volume
increased significantly during bradykinin infusion in HF, suggesting an
improved cardiac function. The small increase in LV
dP/dtmax after bradykinin infusion (Table 1
) may
have been due to the increased heart rate and/or to an increased
sympathetic stimulation secondary to bradykinin-induced vasodilation.
This increase in sympathetic tone may have modified CO and thus TPR.
However, the fall in aortic pressure induced by bradykinin in the
failing dogs demonstrates a preserved response to this agent.
The preserved response to bradykinin suggests that, in addition to the NO pathway, the vasodilator action of bradykinin may be also mediated by other substances, such as prostaglandins and a nonidentified endothelium-dependent hyperpolarizing factor,10 22 or substances that are not endothelium dependent, such as nonendothelial vasodilator prostanoids.23 24 Hyperpolarizing factor may not be an important primary mediator of endothelium-dependent relaxation in most normal blood vessels, but it appears to back up or enhance the relaxing action of NO. When NO synthesis is inhibited and in this case only, high potassium concentration can affect the cGMP-independent hyperpolarizing and relaxing effect of bradykinin.25 This suggests that hyperpolarizing factor may take over when the NO pathway is impaired. Another possibility is that NO could inhibit the formation or action of hyperpolarizing factor, and the blunted NO production in HF may suppress this inhibition.26 However, these hypotheses remain to be demonstrated.
Another important finding of the present study is that in HF and in
CS, enalaprilat potentiated the vasodilator effect of bradykinin to a
similar extent. Although the potentiation of the vasodilator effect of
bradykinin has been observed in HF,14 the
present study shows for the first time that the potentiation of the
vasodilator effect of bradykinin induced by enalaprilat is unchanged
after induction of HF (Figure 3
). The vasodilator role of
endogenous bradykinin was confirmed by comparing the
effects of ciprokiren, which affects only the RAS, with those of
enalaprilat, which affects both the RAS and bradykinin
degradation27 28 (Figure 6
). The local
accumulation of bradykinin contributes to the vasodilator effect of
enalaprilat, because our data also show that a specific bradykinin
B2 receptor antagonist, Hoe 140,
markedly reduced the effects of enalaprilat in both CS and HF (Figure 7
). In addition, enalaprilat increased CO and stroke volume in HF, but
the increased CO and stroke volume were prevented by Hoe 140,
demonstrating the role of endogenous bradykinin in the
improvement of cardiac function in this setting. The preserved effect
of Hoe 140 on the effect of enalaprilat in HF also suggests a preserved
role of endogenous bradykinin.
The preserved hemodynamic effects of bradykinin in HF may be explained by a preserved response of bradykinin B2 receptors to bradykinin in HF, and the similar potentiation of the vasodilator effect of bradykinin by enalaprilat in both CS and HF suggests a preserved function of ACE in the degradation of bradykinin in this model. However, our preparation did not allow us to examine the cellular mechanisms, but whatever the underlying mechanisms are, the present study shows a preserved vasodilator effect of exogenous bradykinin in HF, despite an impaired vascular endothelial function, and a beneficial role of endogenous bradykinin.
Clinical Implications
In HF, enhanced vasoconstriction due to the activation of
vasoconstrictor systems increases the workload of the failing heart.
The presence of a blunted production or release of NO, a major
endothelium-derived relaxing factor, may worsen the
vasoconstriction and thus HF. The preserved vasodilator effect of
exogenous and endogenous bradykinin suggests that
bradykinin remains a potent vasodilator agent in HF. However, because
in the phase of HF that we studied, the response to
endothelium-independent dilators, such as nitroprusside
and nitroglycerin, is normal, as shown by previous
studies,5 16 the results may be different in the
late phase of HF, in which the response of smooth muscle cells to
endothelium-independent dilators is also abnormal.
Also, because the present study examined the effects of short-term
exogenous bradykinin and the effects of endogenous
bradykinin through short-term enalaprilat and Hoe 140, these results
may not be directly extended to the situation of the chronic
stimulation of the bradykinin system. In addition, in some cases, an
excessive production of bradykinin may not be well tolerated
and may induce an excessive hypotension in patients during therapy with
ACE inhibitors. Conversely, improved cardiac function in
response to exogenous bradykinin and to enalaprilat suggests that, in
addition to the inhibition of the vasoconstrictor systems, adequate
stimulation of an endogenous vasodilator, such as
bradykinin, may be useful in the management of HF.
| Acknowledgments |
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Received April 22, 1998; revision received August 10, 1998; accepted August 12, 1998.
| References |
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