(Hypertension. 2000;35:985.)
© 2000 American Heart Association, Inc.
Scientific Contributions |
Increased Cardiac Angiotensin II Levels Induce Right and Left Ventricular Hypertrophy in Normotensive Mice
Presented in part at the 1998 American Blood Pressure Council Meeting; September 15–18, 1998; Philadelphia, Pa.
From the Division of Hypertension and Vascular Medicine (L.M., T.P., F.N., H.-R.B., J.N.), University Hospital of Lausanne, Lausanne, Switzerland, and the Department of Pathology (G.G.), University Hospital of Geneva, Geneva, Switzerland.
Correspondence to Dr J. Nussberger, Division of Hypertension and Vascular Medicine, CHUV, 1011 Lausanne, Switzerland. E-mail Juerg.Nussberger{at}chuv.hospvd.ch
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Abstract |
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Abstract—Angiotensin II is a potent arterial vasoconstrictor and induces hypertension. Angiotensin II also exerts a trophic effect on cardiomyocytes in vitro. The goals of the present study were to document an in vivo increase in cardiac angiotensins in the absence of elevated plasma levels or hypertension and to investigate prevention or regression of ventricular hypertrophy by renin-angiotensin system blockade. We demonstrate that high cardiac angiotensin II is directly responsible for right and left ventricular hypertrophy. We used transgenic mice overexpressing angiotensinogen in cardiomyocytes characterized by cardiac hypertrophy without fibrosis and normal blood pressure. Angiotensin-converting enzyme inhibition and angiotensin II type 1 receptor blockade prevent or normalize ventricular hypertrophy. Surprisingly, in control mice, receptor blockade decreases tissue angiotensin II despite increased plasma levels. This suggests that angiotensin II may be protected from metabolization by binding to its receptor. Blocking of the angiotensin II type 1 receptor rather than enhanced stimulation of the angiotensin II type 2 receptor may prevent remodeling and account for the beneficial effects of angiotensin antagonists.
Key Words: angiotensin II • angiotensin-converting enzyme inhibitors • blood pressure • fibrosis • receptors, angiotensin II • angiotensin I • renin
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Introduction |
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Among the regulators of cardiac growth, the renin-angiotensin system (RAS) appears to play a prominent role. It is well known that an activated RAS with increased circulating angiotensin II (Ang II) levels can induce hypertension and that the increased pressure load provokes cardiac hypertrophy.1 2 However, for a long time, it has been debated whether Ang II, besides its effect on blood pressure, could also act directly on cardiomyocytes to trigger the hypertrophic response. With transgenic (TG) mice overexpressing angiotensinogen (Ang-N) exclusively in the heart, we have recently shown that a locally activated RAS can induce cardiac hypertrophy in the absence of blood pressure changes.3 Ang II itself may indeed directly stimulate myocardial growth independent of the mechanical stress caused by its blood pressure–raising effect. This hypothesis is supported by indirect evidence. In vitro studies have shown that the addition of Ang II to cultured cardiomyocytes induces hypertrophy.4 5 In animal models of hypertension/cardiac hypertrophy, treatment with blockers of the RAS induced regression of hypertrophy that was not evident when blood pressure was equally reduced by other classes of antihypertensive drugs.6 7 8 However, so far, no direct proof in vivo of the growth factor effect of Ang II in cardiac hypertrophy has been obtained. There are 2 main reasons for this shortcoming. First, it was almost impossible to generate an animal model in which manipulation of the RAS would not induce a concomitant change in blood pressure. Second, reliable methods to measure plasma and tissue Ang II and angiotensin I (Ang I) levels in mice were not available.
The present study tackles these shortcomings by specific measurement of Ang II and Ang I concentrations in plasma and tissue of TG mice that are characterized by cardiac hypertrophy in the presence of normal blood pressure. Right ventricular hypertrophy would exclude any undetected systemic blood pressure effect, and administration of an angiotensin-converting enzyme (ACE) inhibitor or an antagonist of the Ang II type 1 (AT1) receptor was hypothesized to prevent or reduce any Ang II–mediated cardiac hypertrophy.
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Methods |
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Animals
TG mice used for the experiments were the recently produced TG1306 line (Transgenic mice should be requested directly from Dr T. Pedrazzini, Division of Hypertension and Vascular Medicine, CHUV, 1011 Lausanne, Switzerland. E-mail Thierry.Pedrazzini@ chuv.hospvd.ch).3 These are 1 renin gene C57BL/6 male TG mice with cardiac Ang-N gene overexpression. Mice were used at 8 and 12 weeks of age. Animals were handled in accordance with institutional guidelines.
Study Design
Untreated mice were studied at 8 and 12 weeks of age. No cardiac
hypertrophy was found in the TG1306 mice at 4 weeks of age.
For the prevention study, TG and control mice were treated at 4 weeks
of age with either the Ang II receptor antagonist
losartan (1 mg per milliliter of drinking water9 )
or the ACE inhibitor ramipril (0.05 mg per milliliter of
drinking water10 ) for 4 weeks. In the regression study,
mice were treated at 8 weeks of age for 4 weeks with either
losartan or ramipril administered in drinking water at the same
dosages as for the prevention group. In all mice, mean blood pressure,
heart rate, and cardiac weight index (CWI) were obtained (n=30). Among
these mice, subgroups were used for angiotensin
measurements, determination of right ventricular index
(RVI) and left ventricular index (LVI), and histology (n=5
to 10).
Blood Pressure and Heart Rate Measurements
Mean blood pressure and heart rate were measured as previously
described3 via an intra-arterial catheter
connected to a pressure transducer in conscious mice.
Cardiac Indices
To evaluate cardiac mass, LVI, RVI, and CWI were measured. From
harvested hearts, the atria were removed, and the ventricles were
separated. The interventricular septum remained as part of
the left ventricle. Ventricles were weighed, and indices were
calculated as the ratio of ventricular wet weight
(milligrams) to body weight (grams).
Blood and Tissue Sampling
After hemodynamic measurements, 300 µL
blood was collected from conscious mice, through the
arterial catheter, into chilled tubes containing 20 µL
enzyme inhibitor cocktail (EDTA,
o-phenanthroline, and renin inhibitor R-Pep156).
Plasma was snap-frozen immediately, and samples were stored at
-80°C. Mice were euthanized by neck dislocation under halothane
anesthesia, and liver, kidney, and heart tissues were
harvested and fixed in formalin and subsequently paraffin-embedded for
histological analysis. For
angiotensin measurements, tissue (10 to 100 mg) was rinsed
with saline, blotted, and stored in ethanol at -80°C.
Angiotensin Measurements
Angiotensin concentrations were measured by
radioimmunoassay after solid-phase extraction on
phenylsilylsilica and subsequent separation by reversed-phase
isocratic high-performance liquid
chromatography (HPLC).11 Samples from each
mouse were analyzed individually. Tissue was immediately
snap-frozen and homogenized in pure ethanol with a Polytron
homogenizer (Kinematica), and the liquid phase after
evaporation and reconstitution in Tris buffer was subjected to
solid-phase extraction, HPLC, and radioimmunoassay in the same manner
as that of the plasma samples. The detection limits were 2 fmol/mL for
plasma and 2 fmol/mg for wet tissue. Within- and between-assay
precision was consistently <15% for both plasma and tissue
assays.
Histological Analysis
Tissue samples were fixed in 4% buffered formaldehyde and
embedded in paraffin. Sections (5 µm thick) were stained by the
following different histological methods: hematoxylin
and eosin, Masson’s trichrome, and the Miller technique.
Sections adjacent to the sections stained
histologically were incubated with a mouse monoclonal
IgG2a recognizing 
-smooth muscle actin12 for 1 hour at
room temperature. This was followed by incubation with goat anti-mouse
biotinylated antibody (Jackson ImmunoResearch) for 1 hour at room
temperature and treatment with streptavidin-biotin-peroxidase complex
(Dako). The development of peroxidase activity was performed with
diaminobenzidine (Serva). Slides were counterstained with
hemalum and mounted in Aquatex (Dako). Samples were observed by
use of a Zeiss Axiophot photomicroscope (Carl Zeiss) with an oil
immersion Plan-Neofluar 40x1.3 objective. Images were acquired by use
of a high-sensitivity Photonic Science Coolview camera (Carl Zeiss)
with the software package Image Access 2.04 (Imagic). Images were
processed with Adobe Photoshop 5.0 (Adobe System) and printed with a
digital Fujifilm Pictography 4000 printer.
Statistical Analysis
Results are expressed as mean±SEM. Statistical analysis
was performed by 2-way ANOVA followed by the Newman-Keuls multiple
comparison test. Hormonal data were not normally distributed;
therefore, a logarithmic transformation was performed before testing,
and geometric means are reported in the tables. Significance was set at
P<0.05.
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Results |
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Cardiac Hypertrophy in Normotensive Untreated TG Mice (Tap Water)
At 8 weeks of age and in the absence of any drug treatment (tap water was used), control and TG mice had normal blood pressures, but CWI was 20% higher in TG mice; RVI and LVI tended to be increased in TG mice (Table 1). Plasma angiotensin concentrations did not differ significantly between TG and control mice, but tissue levels in the hearts of TG mice were increased 4-fold for Ang I and nearly doubled for Ang II (Table 2). In the livers of TG mice, Ang II and Ang I were unchanged, and in the kidneys of TG mice compared with control mice, Ang II was unchanged, and Ang I was decreased (Table 3).
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At 12 weeks of age, the findings were similar to those at 8 weeks, but the changes induced by the transgene were more marked: in TG mice, CWI was now increased by 33% (RVI 33% and LVI 31%, Table 1), and cardiac levels were increased 8-fold for Ang I and by 55% for Ang II (Table 2, Figure 1). Again, blood pressure, heart rate, and plasma angiotensin levels remained unchanged and so did liver and kidney angiotensin levels, with the exception of the again decreased kidney Ang I level in TG mice (Table 3).
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Histological analysis of cardiac tissue,
after staining with hematoxylin and eosin, revealed enlarged
cardiomyocytes in TG mice compared with control mice (data
not shown). Masson’s trichrome and Miller staining showed an absence
of fibrotic changes in the myocardium of TG mice (Figure 2). When the myocardial sections were
immunostained for -smooth muscle actin, the staining
appeared exclusively located in vessel walls, and no myofibroblasts
were noted (data not shown).
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Prevention of Cardiac Hypertrophy by RAS Blockade
(Ramipril and Losartan)
At 8 weeks of age and after 4 weeks of ramipril administration,
blood pressure was similarly lowered in TG and control mice. In
contrast to untreated mice, no increase in cardiac indices was found in
TG mice (Table 1). In both TG and control mice, plasma Ang II
was decreased and plasma Ang I was increased (Table 2). Cardiac
tissue Ang II was decreased by 82% in TG and by 75% in control mice,
respectively, compared with untreated mice. Cardiac Ang I was
unchanged. Also, in liver and kidney, Ang II was similarly decreased by
the ACE inhibitor in TG and control mice, and levels of Ang
I were similar in both groups of mice and not significantly increased;
the decrease in renal Ang I of TG mice was not found with preventive
ramipril administration.
Losartan also prevented cardiac hypertrophy in TG mice: as with ramipril, in TG and control mice, blood pressure decreased slightly, and cardiac indices became normal (Table 1). Increases in plasma Ang II and Ang I did not reach significance in control mice, but in TG mice, these plasma peptides were increased (Table 2). In losartan-treated hearts of TG mice, Ang II levels were not increased, whereas Ang I concentration was 4-fold higher than in control mice. In the liver, the same unchanged Ang II and Ang I levels were found for TG and control mice. In TG mice, renal Ang II tended to be decreased, and like ramipril, losartan abolished the decrease in renal Ang I concentration found in TG mice.
Regression of Cardiac Hypertrophy by RAS Blockade
(Ramipril and Losartan)
At 12 weeks of age and after 4 weeks of ramipril treatment, blood
pressure was decreased, particularly in control mice but also in TG
mice. This decrease in blood pressure did not reduce cardiac indices in
control mice. In contrast to untreated TG mice, ramipril-treated TG
mice no longer exhibited increased cardiac indices (Table 1).
Plasma angiotensin levels were similarly affected by
ramipril treatment in TG and control mice: compared with levels in
untreated mice, Ang II levels were decreased by 40% to 50%, and Ang I
levels tended to be increased. In the heart, Ang I was still increased
in TG mice, but cardiac Ang II was not significantly different in TG
and control mice. In the liver and kidney of TG compared with control
mice, Ang I was reduced by half, whereas Ang II was unchanged.
Losartan, much like ramipril, slightly reduced blood pressure in control and TG mice and completely abolished cardiac hypertrophy in TG mice (Table 1). Plasma angiotensin levels were the same in control and TG mice, but both were more than doubled compared with levels in untreated mice (Table 2). Cardiac Ang I was not changed by losartan treatment in control mice, whereas in TG mice, cardiac Ang I was increased 3-fold. In TG mice, in contrast to plasma Ang II, cardiac Ang II was not significantly increased by losartan; surprisingly, losartan treatment reduced cardiac Ang II levels in control mice by 86%. As a consequence of the losartan treatment, renal tissue of control mice contained only 1/10 of normal Ang I concentrations and 1/5 of normal Ang II concentrations (Table 3). In TG mice, renal Ang II was comparably reduced by 75%, but Ang I levels remained unchanged. In TG and control mice, losartan reduced liver Ang II concentration by 95%, but liver Ang I remained unchanged at very low levels.
Only in 12-week-old animals did losartan treatment reduce heart rate. Heart rate did not change in any other experimental condition (Table 1).
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Discussion |
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TG mice overexpressing Ang-N in cardiomyocytes develop cardiac hypertrophy even in the absence of hypertension. The present study demonstrates that cardiac, but not plasma, angiotensin levels are increased in these TG mice. Left and right ventricles are hypertrophic, reflecting the trophic effect of Ang II independent of an enhanced load. Left and right ventricular hypertrophy can be prevented/reversed by ACE inhibition or by Ang II receptor antagonism.
Angiotensin Concentrations and Cardiac
Hypertrophy
Sensitive micromethods for the specific measurement of plasma and
tissue Ang II and Ang I concentrations allowed us to demonstrate for
the first time in the living organism that enhancement of local
angiotensin production in the heart induces
myocardial hypertrophy. Angiotensin levels were
not increased in plasma, liver, and kidneys; thus, enhancement of
angiotensin generation was successfully limited to cardiac
tissue. Blood pressure and heart rate changes did not account for the
cardiac hypertrophy. The enhanced RVI, particularly in
12-week-old mice, could hardly be explained by an Ang II–mediated
increased pressure load. Furthermore, 12-week-old control mice treated
with the Ang II antagonist losartan showed more of
a blood pressure decrease (-24 mm Hg) than did the TG peers
(-21 mm Hg), but only the TG mice showed reductions in cardiac
mass; the control mice did not. That Ang II indeed caused the cardiac
hypertrophy was demonstrated by the administration of the
Ang II receptor antagonist losartan and the ACE
inhibitor ramipril, both of which prevented or fully
reversed cardiac hypertrophy. The TG animals never became
hypertensive, and the drug-induced decrease in blood pressure from
normal to low-normal values was comparable in control and TG mice. Drug
treatment changed cardiac weight indices only in TG mice; the hearts of
control animals remained unchanged.
The hormonal measurement of Ang I and Ang II in plasma and tissues of mice has been achieved by combining highly specific HPLC and very sensitive radioimmunoassay. This allowed specific quantification of angiotensin peptides in 100 µL plasma and 100 mg tissue with detection limits of 2 fmol/mL and 2 fmol/g, respectively. We have previously shown that Ang-N from TG hearts spills over in the circulation and tends to increase circulating Ang-N levels.3 Consequently, plasma Ang II would be expected to rise unless renal renin secretion is successfully reduced by the Ang II–mediated negative feedback. The success of this feedback control can be seen by the almost unchanged plasma Ang II levels in our TG mice (Table 2). Circulating renin concentrations in TG mice were actually 95% to 98% lower than those in control mice (data not shown). Indeed, in the kidney, where Ang-N levels usually limit the production of Ang I by the abundant renal renin, our untreated TG mice exhibit, despite the increased circulating Ang-N, suppressed Ang I levels (but unchanged Ang II levels), reflecting reduced renal active renin. Thus, the kidneys have shut down renin secretion and have succeeded in preventing renal Ang II levels from rising.
As anticipated, cardiac angiotensin production was increased in TG mice: the genetically induced overproduction of cardiac Ang-N could not be offset by reduced circulating renin. Cardiac angiotensin levels rose. In the presence of high cardiac Ang-N concentrations in TG mice, the actual plasma renin concentration is not sufficiently suppressed to avoid enhanced production of angiotensin in the heart, although this suppression of renin appears to sufficiently compensate increased Ang-N levels in the kidneys, liver, and plasma, as can be seen from unchanged Ang I and Ang II levels in these organs of TG mice. In the liver (the ordinary factory of mouse Ang-N), Ang I and Ang II concentrations are unaffected by the cardiac TG production of (rat) Ang-N.
Cardiac tissue Ang I levels are normally lower than Ang II levels, probably because Ang I is rapidly metabolized, whereas Ang II is partially protected from metabolization by binding to receptors. Generation of Ang I in the heart of untreated TG mice is increased 5- to 8-fold; Ang II levels at the same time are almost doubled in TG mice. The absolute increase in Ang II of 80 to 100 fmol/g in TG mice is greater than the increase in Ang I and may reflect stimulated production as well as more receptor-bound peptide (Table 2).
RAS Blockade by ACE Inhibition
The administered dose of ramipril of 200 µg/d is higher than the
dose used by other investigators,10 but full blockade of
Ang II production was not obtained. In the heavier 12-week-old
mice, plasma Ang II levels were decreased by 50%, and plasma Ang I
levels were not significantly increased. Cardiac tissue Ang II was
decreased by 82% in TG and by 75% in control mice when compared with
untreated mice. Whether a relatively higher dose of ramipril or
eventually smaller Ang-N production in the younger mice
accounts for the enhanced effects of ramipril cannot be decided from
the present data. Also, the blood pressure–lowering effect of
ramipril was more marked in the prevention than in the regression study
(-20/-25 mm Hg versus -15/-8 mm Hg, respectively). In
contrast, the losartan dose of 4 mg/d appeared to be equally
effective in all mice.
Ramipril reduced renal Ang II production in the prevention study by 82% in control mice and by 86% in TG mice. At the same time, the limited supply of Ang-N in control mice does not allow higher renal Ang I production by the stimulated renin secretion in response to the decrease in Ang II. In contrast, in TG mice, the increased Ang-N supply from the heart allows us to visualize, by the 3-fold increase in renal Ang I, the effort of the RAS to overcome the shortage of renal Ang II. During tap water administration, renin secretion is turned off in TG kidneys (decreased Ang I) because much Ang II is generated from increased plasma Ang-N and reaches the receptors. In the kidneys of the regression study, very similar, though less striking, results were obtained with ramipril: Ang II levels were decreased by half, and renal Ang I levels in TG mice treated with ramipril were twice those found in tap water–fed TG mice (not significant). In both studies, mean liver Ang II levels were decreased with ramipril, and mean liver Ang I levels were increased in TG and control mice, but these changes were only partially significant (Table 3).
In the heart, efficient ACE inhibition as seen in the prevention study brings Ang I and Ang II concentrations to equivalent levels. The low cardiac Ang II levels after preventive ramipril treatment may well explain the perfectly normal cardiac weight indices, whereas high cardiac Ang II levels in untreated TG mice caused significant hypertrophy. In the regression study, cardiac hypertrophy was established at 8 weeks of age in TG mice, and a 4-week subsequent treatment with ramipril completely abolished the hypertrophy. Untreated mice at 12 weeks of age had virtually the same cardiac Ang II levels as they had at 8 weeks of age; also, Ang I levels were comparable at the 2 ages. At 12 weeks, cardiac Ang II levels were again reflected in the CWI. At the same time, in the ramipril-treated TG mice, a 20% decrease in mean cardiac Ang II was accompanied by a 20% decrease in CWI. Cardiac Ang I levels of these older (and heavier) ramipril-treated mice were below Ang II levels, which were no longer suppressed as they had been at 8 weeks after preventive ramipril treatment. This may indicate that these 12-week-old "regression" mice successfully counterbalance ACE inhibition to achieve normal cardiac Ang II receptor occupancy. Interestingly, in these TG mice at 12 weeks, the slightly higher (than control mice) though normalized (by ramipril) cardiac indices occurred concurrently with slightly higher, though normalized, cardiac Ang II levels. The observations made in the present study with ramipril in control and TG mice would be compatible with an Ang II–mediated pathogenesis of cardiac hypertrophy on the basis of 2 assumptions: (1) hypertrophic response requires stimulation of myocardial Ang II receptors by >140 fmol/g receptor-bound Ang II, and (2) cardiac tissue levels of free (ie, not receptor-bound) Ang I and Ang II are approximately equal, and receptor bound Ang II can therefore be calculated by subtraction of Ang I from total Ang II concentrations.
RAS Blockade by Ang II Receptor Antagonism
The clear abolishment of cardiac hypertrophy by
losartan treatment in the prevention and in the regression
studies also demonstrates that Ang II most likely caused the myocardial
hypertrophy in our TG mice. As expected, Ang II receptor
blockade by losartan increased plasma Ang I and Ang II levels,
because Ang II no longer restrained renal renin secretion. High renin
levels in plasma and kidneys necessarily reduce circulating Ang-N
concentrations (substrate consumption). In the kidneys, in the presence
of efficient angiotensinases and with
losartan-blocked protecting receptors, Ang I levels may fall as
soon as the shortage in Ang-N no longer allows for the
maintenance of Ang II levels at a set point of 
100 fmol/g at
8 weeks and 230 fmol/g at 12 weeks. All our results suggest that the
RAS primarily regulates renal Ang II concentration. In the heart,
preventive losartan did not change angiotensin
levels in control mice, but in TG mice, losartan normalized Ang
II levels together with the normalization of the
hypertrophy. Losartan may have prevented excessive
Ang II from being protected against angiotensinases. The
most striking finding of the regression study is the very low cardiac
level of Ang II in the losartan-treated control mice, whereas
the very high corresponding levels in the TG mice are easily explained
by the high cardiac Ang-N and the high renal renin secretion (these
"free" angiotensin concentrations are not trophic, in
view of the fact that the corresponding Ang II receptor is blocked by
losartan). The low cardiac angiotensin
concentrations of the control mice are most likely the consequence of
considerable renal consumption of the only available hepatogenic Ang-N.
Indeed, in the kidney, high renin output cannot successfully overcome
the Ang II receptor blockade, as suggested from decreased renal
angiotensin levels: very little Ang-N may reach the
heart, and virtually no angiotensin is formed or protected
from degradation because protecting receptors are blocked by
losartan. Losartan, like all commercially available Ang
II antagonists, blocks only the subtype
AT1 of the Ang II receptors and leaves subtype
AT2 receptors unopposed. Because
AT1 blockade induces high circulating Ang II
levels, it has been postulated that enhanced AT2
stimulation mediates the antigrowth effect of AT1
antagonists.13 Indeed, Campbell et
al14 have reported increased cardiac Ang II levels with
losartan, but experimental conditions were different
(Sprague-Dawley rats, 8 days, and intraperitoneal
administration). In our TG mice, losartan tended to increase
cardiac Ang II (17%), but in control mice, losartan decreased
it by 86%. This points to the importance of the availability of Ang-N.
Consistent with the importance of Ang-N is a previous
observation involving the Langendorff rat heart, in which
losartan abolished tissue Ang II when angiotensin
but not when Ang-N/renin was perfused.15 Low cardiac Ang
II levels that we actually measured under AT1
blockade provide a rationale for an antigrowth effect of
AT1 antagonists in the absence of
enhanced AT2. The explanation for the decreased
Ang II in the liver after losartan treatment may be similar to
the explanation for the decreased Ang II in the heart. Therefore, it
would be expected that liver Ang II, unlike cardiac Ang II, is low also
in TG mice, in view of the fact that only cardiac but not liver Ang-N
is increased by the transgene. The substrate production of the
liver does not appear to be enhanced in this situation. It remains to
be seen whether the intermediate liver Ang II concentrations in
losartan-treated 8-week-old mice can be explained by less Ang-N
consumption by renal renin or by less efficient
angiotensinases.
Histology
Histological examinations confirmed the previous
observation that no fibrosis occurs in the hypertrophic heart of our TG
mice.3 This could be of interest, because circulating Ang
II concentrations are not increased, and aldosterone levels
may also remain normal. Aldosterone has been postulated to
be involved in the pathogenesis of cardiac fibrosis.16 17
The absence of increased aldosterone levels could explain
the absence of fibrosis in our TG mice. Our results are in agreement
with those of others,18 19 who reported no fibrosis in
hypertrophied hearts of hypertensive rats without signs of heart
failure. On the other hand, cardiac fibrosis was shown to be
present in mouse and rats models in which concomitant heart failure
developed.20 21 Therefore, fibrosis may characterize a
failing heart, and no fibrosis may be found in compensated cardiac
hypertrophy.
In conclusion, the local increase in angiotensin concentrations in the hearts of normotensive TG mice induces left and right ventricular myocardial hypertrophy without fibrosis. A causal relation between Ang II levels and myocardial hypertrophy is suggested because hypertrophy can be prevented by early treatment or reversed by late treatment with ramipril, which decreases the generation of Ang II, and with losartan, which antagonizes Ang II at its receptor. Low tissue concentrations of Ang II during AT1 receptor blockade challenge the concept of enhanced AT2-mediated growth inhibition in vivo.
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Acknowledgments |
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This study was supported by the Cardiovascular Research Foundation Lausanne, the Swiss National Science Foundation, and the Leenards Foundation. The authors thank Irene Keller for excellent technical assistance and the pharmaceutical companies Astra (for providing ramipril) and Merck (for providing losartan).
Received September 21, 1999; first decision October 14, 1999; accepted November 15, 1999.
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References |
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|---|
1. Reid IA, Morris BJ, Ganong WJ. The renin-angiotensin system. Ann Rev Physiol. 1978;40:377–410.[Medline] [Order article via Infotrieve]
2. Gunning ME, Ingelfinger JR, King AJ, Brenner BM. Vasoactive peptide and the kidney. In: Brenner BM, ed. The Kidney. Philadelphia, Pa: WB Saunders Co; 1996:627–712.
3.
Mazzolai L, Nussberger J, Aubert J, Brunner D,
Brunner H, Pedrazzini T. Blood pressure independent cardiac
hypertrophy induced by locally activated
renin-angiotensin system. Hypertension. 1998;31:1324–1330.
4.
Schunkert H, Sadoshima JI, Cornelius T, Kagaya
Y, Weinberg EO, Izumo S, Riegger G, Lorell BH. Angiotensin
II–induced growth responses in isolated adult rat hearts: evidence for
load-independent induction of cardiac protein synthesis by
angiotensin II. Circ Res. 1995;76:489–497.
5.
Baker KM, Aceto JF. Angiotensin II
stimulation of protein synthesis and cell growth in chick heart cells.
Am J Physiol. 1990;259:H610–H618.
6. Oparil S, Erinoff L, Cutilletta A. Catecholamines, blood pressure, renin and myocardial function in the spontaneously hypertensive rat. Clin Sci Mol Med. 1976;3:445s–459s.
7.
Sen S, Tarazi RC, Khairallah PA, Bumpus FM.
Cardiac hypertrophy in spontaneously hypertensive rats.
Circ Res. 1974;35:775–781.
8.
Pfeffer JM, Pfeffer MA, Mirsky I, Braunwald E.
Progression of left ventricular hypertrophy and
prevention of left ventricular dysfunction by captopril in
the spontaneously hypertensive rat. Proc Natl Acad Sci
U S A. 1982;79:3310–3314.
9.
Rockman HA, Wachhorst SP, Mao L, Ross J Jr. Ang
II receptor blockade prevents ventricular
hypertrophy and ANF gene expression with pressure overload
in mice. Am J Physiol. 1994;266:H2468–H2475.
10. Grimm D, Kromer EP, Bocker W, Bruckschlegel G, Holmer S, Riegger GAJ, Schunkert H. Regulation of extracellular matrix proteins in pressure-overload cardiac hypertrophy: effects of angiotensin converting enzyme inhibition. J Hypertens. 1998;16:1345–1355.[Medline] [Order article via Infotrieve]
11. Nussberger J, Brunner DB, Waeber B, Brunner HR. True versus immunoreactive angiotensin II in human plasma. Hypertension. 1985;7(suppl I):I-1–I-7.
12.
Skalli O, Ropraz P, Trzeciak A, Benzonana G,
Gillessen D, Gabbiani G. A monoclonal antibody against -smooth
muscle actin: a new probe for smooth muscle differentiation.
J Cell Biol. 1986;103:2787–2796.
13. Unger T, Culman J, Gohlke P. Angiotensin II receptor blockade and end-organ protection: pharmacological rationale and evidence. J Hypertens. 1999;16:S3–S9.
14. Campbell DJ, Kladis A, Valentijn AJ. Effects of losartan on angiotensin and bradykinin peptides and angiotensin-converting enzyme. J Cardiovasc Pharmacol. 1995;26:233–240.[Medline] [Order article via Infotrieve]
15.
de Lannoy LM, Danser AHJ, Bouhuizen AMB, Saxena
PR, Schalekamp MADH. Localization and production of
angiotensin II in the isolated perfused rat heart.
Hypertension. 1998;31:1111–1117.
16. Weber KT, Brilla CG. Myocardial fibrosis and the renin-angiotensin-aldosterone system. J Cardiovasc Pharmacol. 1992;20(suppl I):48–54.
17. Zhou G, Kandala JC, Tyagi SC, Katwa LC, Weber KT. Effects of angiotensin II and aldosterone on collagen gene expression and protein turnover in cardiac fibroblasts. Mol Cell Biochem. 1996;154:171–178.[Medline] [Order article via Infotrieve]
18.
Flesch M, Schiffer F, Zolk O, Pinto YM,
Rosenkranz S, Hirth-Dietrich C, Arnold G, Paul M, Böhm M.
Contractile systolic and diastolic dysfunction in
renin-induced hypertensive cardiomyopathy.
Hypertension. 1997;30:383–391.
19.
Bohlender J, Fukamizu A, Lippoldt A, Nomura T,
Dietz R, Menard J, Murakami K, Luft FC, Ganten D. High human renin
hypertension in transgenic rats. Hypertension. 1997;29:428–434.
20. Geisterfer AAT, Christe M, Conner DA, Ingwall JS, Schoen FJ, Seidman CE, Seidman JG. A mouse model of familial hypertrophic cardiomyopathy. Science. 1996;272:731–734.[Abstract]
21.
Bryant D, Becker L, Richardson J, Shelton
J, Franco F, Peshock R, Thompson M, Giroir B. Cardiac failure in
transgenic mice with myocardial expression of tumor necrosis
factor-alpha. Circulation. 1998;97:1375–1381.
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 J. Nussberger, J.-F. Aubert, K. Bouzourene, M. Pellegrin, D. Hayoz, and L. Mazzolai Renin Inhibition by Aliskiren Prevents Atherosclerosis Progression: Comparison With Irbesartan, Atenolol, and Amlodipine Hypertension, May 1, 2008; 51(5): 1306 - 1311. [Abstract] [Full Text] [PDF]
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 O. W. van den Brink, L. M D. Delbridge, T. Pedrazzini, F. L Rosenfeldt, and S. Pepe Augmented myocardial methionine-enkephalin in a murine model of cardiac angiotensin II-overexpression Journal of Renin-Angiotensin-Aldosterone System, December 1, 2007; 8(4): 153 - 159. [Abstract] [PDF]
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 M. Burnier, O. Phan, and Q. Wang High salt intake: a cause of blood pressure-independent left ventricular hypertrophy? Nephrol. Dial. Transplant., September 1, 2007; 22(9): 2426 - 2429. [Full Text] [PDF]
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 J. Xu, O. A. Carretero, C.-X. Lin, M. A. Cavasin, E. G. Shesely, J. J. Yang, T. L. Reudelhuber, and X.-P. Yang Role of cardiac overexpression of ANG II in the regulation of cardiac function and remodeling postmyocardial infarction Am J Physiol Heart Circ Physiol, September 1, 2007; 293(3): H1900 - H1907. [Abstract] [Full Text] [PDF]
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 S. D. Crowley, S. B. Gurley, M. J. Herrera, P. Ruiz, R. Griffiths, A. P. Kumar, H.-S. Kim, O. Smithies, T. H. Le, and T. M. Coffman Angiotensin II causes hypertension and cardiac hypertrophy through its receptors in the kidney PNAS, November 21, 2006; 103(47): 17985 - 17990. [Abstract] [Full Text] [PDF]
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B. Pilz, E. Shagdarsuren, M. Wellner, A. Fiebeler, R. Dechend, P. Gratze, S. Meiners, D. L. Feldman, R. L. Webb, I. M. Garrelds, et al. Aliskiren, a Human Renin Inhibitor, Ameliorates Cardiac and Renal Damage in Double-Transgenic Rats Hypertension, September 1, 2005; 46(3): 569 - 576. [Abstract] [Full Text] [PDF]
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A. A. Domenighetti, Q. Wang, M. Egger, S. M. Richards, T. Pedrazzini, and L. M.D. Delbridge Angiotensin II-Mediated Phenotypic Cardiomyocyte Remodeling Leads to Age-Dependent Cardiac Dysfunction and Failure Hypertension, August 1, 2005; 46(2): 426 - 432. [Abstract] [Full Text] [PDF]
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 B. C Cholewa and D. L Mattson Influence of elevated renin substrate on angiotensin II and arterial blood pressure in conscious mice Exp Physiol, July 1, 2005; 90(4): 607 - 612. [Abstract] [Full Text] [PDF]
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E. R Porrello, C. E Huggins, C. L Curl, A. A Domenighetti, T. Pedrazzini, L. M. Delbridge, and T. O Morgan Elevated dietary sodium intake exacerbates myocardial hypertrophy associated with cardiac-specific overproduction of angiotensin II Journal of Renin-Angiotensin-Aldosterone System, December 1, 2004; 5(4): 169 - 175. [Abstract] [PDF]
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W. C. De Mello and J. Monterrubio Intracellular and Extracellular Angiotensin II Enhance the L-Type Calcium Current in the Failing Heart Hypertension, September 1, 2004; 44(3): 360 - 364. [Abstract] [Full Text] [PDF]
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L. Mazzolai, M. A. Duchosal, M. Korber, K. Bouzourene, J. F. Aubert, H. Hao, V. Vallet, H. R. Brunner, J. Nussberger, G. Gabbiani, et al. Endogenous Angiotensin II Induces Atherosclerotic Plaque Vulnerability and Elicits a Th1 Response in ApoE-/- Mice Hypertension, September 1, 2004; 44(3): 277 - 282. [Abstract] [Full Text] [PDF]
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D. J. Campbell, T. Alexiou, H. D. Xiao, S. Fuchs, M. J. McKinley, P. Corvol, and K. E. Bernstein Effect of Reduced Angiotensin-Converting Enzyme Gene Expression and Angiotensin-Converting Enzyme Inhibition on Angiotensin and Bradykinin Peptide Levels in Mice Hypertension, April 1, 2004; 43(4): 854 - 859. [Abstract] [Full Text] [PDF]
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 L. Bahi, N. Koulmann, H. Sanchez, I. Momken, V. Veksler, A. X. Bigard, and R. Ventura-Clapier Does ACE inhibition enhance endurance performance and muscle energy metabolism in rats? J Appl Physiol, January 1, 2004; 96(1): 59 - 64. [Abstract] [Full Text] [PDF]
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A. Stanton, C. Jensen, J. Nussberger, and E. O'Brien Blood Pressure Lowering in Essential Hypertension With an Oral Renin Inhibitor, Aliskiren Hypertension, December 1, 2003; 42(6): 1137 - 1143. [Abstract] [Full Text] [PDF]
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 M. Nahrendorf, K. Hu, K.-H. Hiller, P. Galuppo, D. Fraccarollo, G. Schweizer, A. Haase, G. Ertl, W. R. Bauer, and J. Bauersachs Impact of hydroxymethylglutaryl coenzyme a reductase inhibition on left ventricular remodeling after myocardial infarction: An experimental serial cardiac magnetic resonance imaging study J. Am. Coll. Cardiol., November 6, 2002; 40(9): 1695 - 1700. [Abstract] [Full Text] [PDF]
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S. Sanada, K. Node, H. Asanuma, H. Ogita, S. Takashima, T. Minamino, M. Asakura, Y. Liao, A. Ogai, J. Kim, et al. Opening of the adenosine triphosphate-sensitive potassium channel attenuates cardiac remodeling induced by long-term inhibition of nitric oxide synthesis: Role of 70-kDa S6 kinase and extracellular signal-regulated kinase J. Am. Coll. Cardiol., September 4, 2002; 40(5): 991 - 997. [Abstract] [Full Text] [PDF]
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G. P. Rossi, V. Di Bello, C. Ganzaroli, A. Sacchetto, M. Cesari, A. Bertini, D. Giorgi, R. Scognamiglio, M. Mariani, and A. C. Pessina Excess ldosterone Is Associated With Alterations of Myocardial Texture in Primary Aldosteronism Hypertension, July 1, 2002; 40(1): 23 - 27. [Abstract] [Full Text] [PDF]
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 Q. Wang, E. Hummler, J. Nussberger, S. Clement, G. Gabbiani, H. R. Brunner, and M. Burnier Blood Pressure, Cardiac, and Renal Responses to Salt and Deoxycorticosterone Acetate in Mice: Role of Renin Genes J. Am. Soc. Nephrol., June 1, 2002; 13(6): 1509 - 1516. [Abstract] [Full Text] [PDF]
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C. M Filipeanu, R. H Henning, S A. Nelemans, and D. de Zeeuw Review: Intracellular angiotensin II: from myth to reality? Journal of Renin-Angiotensin-Aldosterone System, December 1, 2001; 2(4): 219 - 226. [PDF]
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 B. C. Cholewa and D. L. Mattson Role of the renin-angiotensin system during alterations of sodium intake in conscious mice Am J Physiol Regulatory Integrative Comp Physiol, September 1, 2001; 281(3): R987 - R993. [Abstract] [Full Text] [PDF]
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S. Sanada, M. Kitakaze, K. Node, S. Takashima, A. Ogai, H. Asanuma, Y. Sakata, M. Asakura, H. Ogita, Y. Liao, et al. Differential Subcellular Actions of ACE Inhibitors and AT1 Receptor Antagonists on Cardiac Remodeling Induced by Chronic Inhibition of NO Synthesis in Rats Hypertension, September 1, 2001; 38(3): 404 - 411. [Abstract] [Full Text] [PDF]
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F. C. Barone, R. W. Coatney, S. Chandra, S. K. Sarkar, A. H. Nelson, L. C. Contino, D. P. Brooks, W. G. Campbell Jr., E. H. Ohlstein, and R. N. Willette Eprosartan reduces cardiac hypertrophy, protects heart and kidney, and prevents early mortality in severely hypertensive stroke-prone rats Cardiovasc Res, June 1, 2001; 50(3): 525 - 537. [Abstract] [Full Text] [PDF]
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L. H. Opie and M. N. Sack Enhanced Angiotensin II Activity in Heart Failure : Reevaluation of the Counterregulatory Hypothesis of Receptor Subtypes Circ. Res., April 13, 2001; 88(7): 654 - 658. [Abstract] [Full Text] [PDF]
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E. Abro, C. D Griffiths, T. O Morgan, and L. M. Delbridge Regression of cardiac hypertrophy in the SHR by combined renin-angiotensin system blockade and dietary sodium restriction Journal of Renin-Angiotensin-Aldosterone System, March 1, 2001; 2(1_suppl): S148 - S153. [Abstract] [PDF]
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