Vol. 273, Issue 4, H1824-H1831, October 1997
Dose-dependent effect of ANG II-receptor antagonist on myocyte
remodeling in rat cardiac hypertrophy
Masakazu
Obayashi,
Masafumi
Yano,
Michihiro
Kohno,
Shigeki
Kobayashi,
Taketo
Tanigawa,
Katsumi
Hironaka,
Tsutomu
Ryouke, and
Masunori
Matsuzaki
Second Department of Internal Medicine, Yamaguchi University School
of Medicine, Ube, Yamaguchi 755, Japan
 |
ABSTRACT |
The goal of this study was to examine the
effect of an angiotensin II type 1 (AT1)-receptor antagonist
(TCV-116) on left ventricular (LV) geometry and function during the
development of pressure-overload LV hypertrophy. A low (LD; 0.3 mg · kg
1 · day1) or a high (HD; 3.0 mg · kg1 · day1)
dose of TCV-116 was administered to abdominal aortic-banded rats over 4 wk, and hemodynamics and morphology were then evaluated. In both LD and
HD groups, peak LV pressures were decreased to a similar extent
compared with the vehicle-treated group but stayed at higher levels
than in the sham-operated group. In the LD group, both end-diastolic
wall thickness (3.08 ± 0.14 mm) and myocyte width (13.3 ± 0.1 µm) decreased compared with those in the vehicle-treated group (3.67 ± 0.19 mm and 15.3 ± 0.1 µm, respectively; both
P < 0.05). In the HD group, myocyte
length was further decreased (HD: 82.6 ± 2.6, LD: 94.1 ± 2.9 µm; P < 0.05) in association with a reduction in LV midwall radius (HD: 3.36 ± 0.12, LD: 3.60 ± 0.14 mm; P < 0.05) and peak midwall
fiber stress (HD: 69 ± 8, LD: 83 ± 10 × 103
dyn/cm2;
P < 0.05). There was no significant
difference in cardiac output among all groups. The
AT1-receptor antagonist TCV-116
induced an inhibition of the development of pressure-overload
hypertrophy. Morphologically, not only the width but also the length of
myocytes was attenuated with TCV-116, leading to a reduction of midwall radius and hence wall stress, which in turn may contribute to a
preservation of cardiac output.
pressure overload; TCV-116; pressure-volume relation
| |
INTRODUCTION |
LEFT VENTRICULAR (LV) hypertrophy is
regarded as an adaptive response to increased workload. During the
development of compensated LV hypertrophy, wall stress initially
increases, reflecting an elevation in blood pressure and acute
dilatation of the LV, followed by its normalization due to an increase
in wall thickness and a reduction in cavity size (28). At a late phase,
LV dilatation occurs with impaired cardiac function, resulting in
cardiac failure.
Clinical and experimental observations suggest that the degree of
cardiac hypertrophy is not proportional to workload (21). Therefore,
other factors such as neuroendocrine activation have been implicated to
modulate the cardiac growth response. In particular, angiotensin II
(ANG II) contributes to development and maintenance of cardiac
hypertrophy via its growth-promoting effect on cardiac myocytes (2,
29).
TCV-116 is a benzimidazole derivative that has noncompetitive
antagonistic properties highly specific to ANG II type 1 (AT1) receptors. In this regard,
several studies have focused on the effect of
AT1-receptor antagonists on the
development of pressure-overload hypertrophy. These drugs induce
prevention or regression of in vivo LV pressure-overload hypertrophy
and reduce the stretch-induced hypertrophic response in cardiac
myocytes (4, 14, 26). Morphologically, myocyte width decreases with ANG
II inhibition by either angiotensin-converting enzyme inhibitor (4, 27) or AT1-receptor antagonist (4,
14). However, there is no report evaluating a change in hypertrophied
myocyte length with ANG II inhibition. Because the change in myocyte
length may also directly affect LV cavity size and wall stress (8), it
is important to investigate how the width and also the length of the
hypertrophied myocyte are influenced by ANG II inhibition and how such
a structural change in myocytes is related to LV wall stress and
cardiac function. In the present study, we assessed the chronic effect
of two different doses of TCV-116 on LV geometry and function and
demonstrated that this
AT1-receptor antagonist induced
inhibition of the development of pressure-overload hypertrophy. In
particular, not only the width but also the length of the myocytes was
significantly attenuated with TCV-116, accompanied by a reduction of
the midwall radius and hence the wall stress. This inhibitory effect of
TCV-116 on the hypertrophic responses may contribute to preservation of
cardiac output.
| |
METHODS |
Animals and drug treatment.
Male Wistar rats weighing 140-170 g were obtained from
laboratories (Japan SLC). Rats were given food and water ad libitum and
were kept on a 12:12-h light-dark cycle. After an acclimatization period of at least 5 days, they were randomly divided into four main
groups: sham-operated rats (Sham) and three groups of rats with aortic
banding [vehicle-treated (AC); 0.3 mg/kg body wt of TCV-116 (low
dose; LD); and 3.0 mg/kg body wt of TCV-116 (high dose; HD)].
TCV-116 administration (0.3 or 3.0 mg · kg1 · day1 by gastric gavage) was
started 1 day before the surgery and continued for 4 wk after the
surgery. TCV-116 was suspended in 2% gum arabic solution. The same
volume of gum arabic solution was given in vehicle-treated
aortic-banded rats and vehicle-treated sham controls. TCV-116 was
provided by Takeda Chemical Industries.
Abdominal aortic constriction.
Pressure-overload LV hypertrophy was produced by constriction of the
abdominal aorta (12). Rats were anesthetized, and the aorta was exposed
through a midline abdominal incision. A blunted needle 0.8 mm in
diameter was placed alongside the abdominal aorta below the diaphragm
but proximal to renal bifurcations and was tightly fixed with surgical
silk. The needle was then removed, leaving the aorta constricted to an
outer diameter equivalent to the diameter of the needle. In the Sham
animals, the suture was not tightened.
Hemodynamic measurements.
To investigate the effect of TCV-116 on the time course of development
of pressure-overload LV hypertrophy, peak systolic pressure and LV
weight were measured at 4 days, 10 days, and 4 wk after the surgery.
Also, 2 wk after the chronic administration of TCV-116, the changes in
daily blood pressure were measured. Other hemodynamic measurements
including LV wall thickness and aortic flow were also performed 4 wk
after the surgery.
Twenty-four hours after the last administration, rats were anesthetized
with an intraperitoneal injection of pentobarbital sodium (50 mg/kg)
and hemodynamic parameters were obtained. After the rats were fully
sedated, a tracheal tube was inserted, and the LV was catheterized with
an ultraminiature catheter pressure transducer (PR 249, Millar
Instruments) via the right common carotid artery. Peak LV pressure, LV
end-diastolic pressure, and maximal value of the first derivative of LV
pressure (+dP/dt) were measured. The
ascending aorta was isolated, and the ultrasonic transit-time flow
probe (T-106, Transonic Systems) was placed for measurement of phasic
instantaneous aortic blood flow. The frequency response of the
pressure-recording channel was flat from 0 to 100 Hz. Pressure was
low-pass filtered with a corner frequency at 100 Hz. Flow velocity
signal was recorded at a 100-Hz filter setting (frequency response
6 dB at 100 Hz). After left sternal thoracotomy, LV anterior
wall thickness was measured by a 20-MHz wall tracking module (WT-20,
Crystal Biotech) attached to the midportion of the epicardium of the LV
anterior wall with triggering peak
+dP/dt of LV pressure (12). After the
hemodynamic measurements, the heart was arrested by intravenous
injection of potassium chloride (2 meq/ml), and rapidly excised. The
right ventricular free wall was trimmed away, and the LV was weighed.
The analog signals were digitized at 1-ms intervals and stored on disk.
Ten consecutive cardiac cycles were sampled at each stage and averaged
to provide the hemodynamic values.
To calculate LV internal diameter and wall stress, we made the
following assumptions: 1) the shape
of the LV is spherical, 2) LV wall
thickness is uniform at all portions of the LV, and 3) the specific gravity of the
myocardial tissue is 1.06 (10). Midwall fiber stress (
), the
circumferential stress at midwall for a sphere, was calculated using
the following equation (25)
where
D is internal diameter of the LV
cavity and WT is LV wall thickness.
Ex vivo LV pressure-volume relations, chamber stiffness, and LV
cavity and wall volume.
The heart was arrested by intravenous injection of potassium chloride
(2 meq/ml) and quickly removed along with the ascending aorta. One
catheter was attached to a pressure transducer (Statham 23 ID), and the
other was attached to an infusion pump (model 680, Harvard Apparatus).
After gentle aspiration of the LV cavity to remove residual blood,
normal saline was infused into the LV at 0.70 ml/min while pressure was
recorded. Saline was infused until the pressure increased to 30 mmHg.
The procedure was performed either two or three times within 10 min of
cardiac arrest before the onset of rigor mortis. The overall chamber
stiffness constant Kc was calculated
from the pressure (P)-volume (V) relation (P = P0 · eKcV
where P0 is modeling constant;
Refs. 7, 19). LV cavity volume at a distending pressure of 10 mmHg was
determined from the pressure-volume relation. LV wall volume
(Vw) was determined from the
mass of the LV (19).
Myocardial stiffness.
The myocardial stiffness constant
(Km) was
obtained from the incremental modulus-stress
(Einc-)
relation by a spherical model applied for the LV (7)
where
V is cavity volume and a and
b are inner and outer radii,
respectively.
where
R = (a + b)/2 is the midwall radius and P is
the LV cavity pressure. To determine 
, the stress-radius
(-R) relations were curve fitted
in the form of = BR
, where
B and are curve-fitting
parameters. This study was approved by the Animal Care Committee of the
School of Medicine, Yamaguchi University.
Fixation and cell size data.
Using an additional 16 rats, we obtained morphological data using the
method reported by Oh et al. (23). After the heart was arrested by
injection of potassium chloride (2 meq/ml), the thorax was opened, and
polyethylene catheters (PE-200) were introduced into the LV via the
left atrial appendage. After the right atrium was opened, the aorta was
perfused with heparinized saline for 2-3 min to wash out blood.
The myocardium was perfused at a pressure of 50 mmHg for 20 min
retrogradely from the aorta with 95% ethanol and 1% acetic acid using
an infusion pump (model 680, Harvard Apparatus). On fixation, LV
pressure was maintained at 2.5 mmHg to minimize the effect of the
fixation pressure on the dilatation of the LV chamber. After hardening,
the heart was excised, and the atria and right ventricle were carefully
dissected away. The LV was weighed and immersed into cold mixed
solution containing 95% ethanol and 1% acetic acid.
The fixed LV was embedded with paraffin. Transmural myocardial sections
were cut in a transverse plane perpendicular to the apex-to-base axis
and in 4-µm sections. After deparaffinization and dehydration, the
immunohistochemical study was performed using the DAKO LSAB kit based
on the labeled streptavidin-biotin method. In brief, the sections were
frequently washed in tris(hydroxymethyl)aminomethane-buffered saline
(TBS, pH 7.4) buffer and then incubated with an appropriate dilution of
the primary antibody (directed against connexin 43; Ref. 17) at 4°C
overnight. Rinsing with TBS buffer was followed by incubation with
biotinylated goat anti-rabbit immunoglobulin G (Zymed Lab, San
Francisco, CA) for 2-3 h. After the sections were rinsed in TBS
buffer, they were treated with peroxidase-labeled streptavidin. The
staining was visualized by incubation with 3% 3-amino-9-ethylcarbazole
in
N,N-dimethylformamide,
followed by counterstaining with 0.1% hematoxylin for 5 min. A
negative-control study was performed by replacing the primary
antibodies with nonimmune serum or TBS, which resulted in negative
staining.
After immunohistochemical staining of connexin 43, we obtained optimal
contrast between intercalated disks and myocytes in the sections. The
morphometric measurement was performed with a magnification of
×400. Using the method of Vliegen et al. (30) with some
modifications, we selected 30 myocytes in one section that showed the
proper longitudinal orientation and did not branch in the circular
midwall muscle bundles of the LV free wall. Only myocytes in which
intercalated disk was located on both sides and a nucleus was in the
center of the myocyte were measured. Myocyte width was determined as
the transnuclear width of the myocyte. Myocyte length was determined as
the distance between the middle points of intercalated disks on both
sides of the myocyte.
Interstitial percent fibrosis.
The LV was fixed in 20% buffered formaldehyde. After 2-3 days,
the preparations were dehydrated and embedded in paraffin. Sections
were cut at 6 µm. Tissue sections were stained with picrosirius red
staining [Sirius Red F3BA (Chroma-Gesellschaft) in aqueous picric
acid], which is specific for collagen. The protocol for picrosirius red staining was adopted from Volders et al. (31). Interstitial percent fibrosis in which perivascular collagen was excluded was determined with NIH Image (National Institutes of Health)
image-analysis software. Tissue sections stained with picrosirius red
were analyzed with polarization microscopy (×100). In each
section taken from the middle portion of the LV free wall, 10-12
fields were randomly selected to measure percent fibrosis and the
average of percent fibrosis was obtained.
Statistical analysis.
Statistical analysis was performed using analysis of variance (ANOVA).
P values <0.05 were accepted as
statistically significant. Fisher's protected least significant
difference was used to make individual comparisons between groups when
a significant change was observed with ANOVA. Correlation coefficients
were calculated using linear regression analysis.
| |
RESULTS |
Hemodynamics and LV geometry.
Both peak systolic pressure and the LV weight-to-body weight ratio
increased significantly in the AC group as early as 4 days after the
operation, and this increase was maintained over 4 wk. Treatment with
TCV-116 reduced the LV weight-to-body weight ratio in a dose-dependent
manner, whereas peak systolic pressure was decreased to a similar
extent regardless of the dose of TCV-116 (Fig.
1; Table 1).
Figure 2 shows the change in daily blood pressure 2 wk
after the chronic administration of TCV-116. A low dose (0.3 mg · kg1 · day1)
of TCV-116 significantly reduced peak systolic pressure to a similar
extent as a high dose (3.0 mg · kg1 · day1)
of TCV-116 at 8, 16, and 24 h after the last administration of the
drug. There was no significant difference in blood pressure between
low- and high-dose administration of TCV-116 at any time studied.
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Fig. 1.
Effect of TCV-116 on time course of peak systolic pressure and
development of left ventricular (LV) hypertrophy in abdominal
aortic-banded rats. Results are expressed as means ± SD; nos. in
parentheses, no. of animals. Open bars, sham-operated rats (Sham);
solid bars, untreated rats with aortic constriction (AC); hatched bars,
rats with aortic constriction + 0.3 mg · kg1 · day1
of TCV-116 (LD); crosshatched bars, rats with aortic constriction + 3.0 mg · kg1 · day1
TCV-116 (HD). * P < 0.05 vs.
Sham;  P < 0.05 vs. AC;
 P < 0.05 vs. LD.
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Fig. 2.
Change in daily blood pressure after last administration of TCV-116.
TCV-116 was administered for 2 wk and then peak systolic pressure was
measured with ultraminiature catheter pressure transducer via right
common carotid artery. Results are means ± SD; nos. in
parentheses, no. of animals. Open bars, Sham; solid bars, AC; hatched
bars, LD; crosshatched bars, HD. * P < 0.05 vs. Sham; P < 0.05 vs. AC.
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The parameters of hemodynamics and LV geometry 4 wk after the surgery
are summarized in Table 2. Peak LV
pressures were elevated in all three banded groups compared with the
Sham group. Peak LV pressures in the TCV-116-treated groups were lower
than in the AC group, but no significant difference was observed
between the TCV-116 treated groups. Heart rate and LV end-diastolic
pressure did not differ among all groups. Peak
+dP/dt of LV pressure in the AC group
was higher than in the HD and Sham groups. There was no significant
difference in cardiac output among all groups including the Sham group.
LV end-diastolic wall thickness was increased in the AC group, whereas
the increment of end-diastolic wall thickness was severely attenuated
in both TCV-116 treated groups (LD and HD). In the HD group, the
increment in either LV internal diameter or LV midwall radius was also
suppressed compared with the LD group.
Although end-diastolic wall stress was not significantly different
among all groups, peak wall stress was increased in the AC group,
reflecting the elevation of peak LV pressure, whereas it was normalized
in the HD group. In the LD group, peak wall stress remained at a high
level despite the reduction in LV pressure.
Ex vivo LV pressure-volume relations, chamber stiffness, cavity and
wall volume, and myocardial stiffness.
Figure 3 shows the ex vivo pressure-volume
relations, and Table 3 summarizes various
parameters derived from the pressure-volume relations. In the AC group,
the pressure-volume relations tended to shift toward the left
associated with a smaller V/Vw
compared with the Sham group, indicating concentric hypertrophy. The LD group had a rightward shift in the pressure-volume relations compared with the AC group, reflecting an increase in LV cavity volume, whereas
the pressure-volume relations in the HD group became close to those in
the Sham group. Although there was no difference in myocardial
stiffness constant among all groups, the chamber stiffness constant was
decreased in the LD group although unchanged in the HD group.
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Fig. 3.
Ex vivo LV pressure-volume relation in Sham ( ), AC ( ), LD ( ),
and HD ( ) rats. * P < 0.05 vs. Sham; P < 0.05 vs.
AC; P < 0.05 vs. LD.
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Morphological data.
Figure 4 shows the immunohistochemical
staining of connexin 43. Both intercalated disks and myocytes were
clearly detected in the sections. Figure 5
shows the histograms of myocyte width and myocyte length in a total of
120 myocytes from 4 rats in each group. The mean value of myocyte size
was obtained from 30 myocytes in each rat, and these data are
summarized in Table 4. In the AC group, the
histograms of myocyte width and length were shifted toward a higher
value compared with those in the Sham group. In the TCV-116-treated
groups, the increases in myocyte width were significantly inhibited to
similar extents. Myocyte length in the LD group was smaller than in the
AC group but still larger than in the Sham group. In the HD group,
myocyte length was further decreased and became close to that of the
Sham group. There was no significant difference in interstitial percent
fibrosis among all groups (Table 4).
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Fig. 4.
Longitudinal orientation of myocytes in circular midwall muscle bundles
of LV free wall by immunohistochemical staining of connexin 43. Note
clearly visible intercalated disks (arrows). Bar, 30 µm.
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Fig. 5.
Distribution of myocyte width (left)
and length (right) in circular
midwall muscle bundles of LV free wall in Sham
(A), AC
(B), LD
(C), and HD
(D) rats. For each group, a total of
120 myocytes from 4 rats were available for measurement.
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Figure 6 shows the relation between LV
weight and myocyte volume in aortic-banded groups based on the
assumption of a cylindrical configuration {myocyte volume = 
× [(average myocyte
width)/2]2 × (average
myocyte length)}. There was a good correction
(r = 0.87, P < 0.001) between these two
parameters.
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Fig. 6.
Relation between LV weight and myocyte volume in all aortic-banded
groups. Note that there was a good correlation between these 2 parameters. Myocyte volume was calculated by assuming a cylindrical
configuration (see METHODS).
n, No. of animals.
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| |
DISCUSSION |
The major finding of this study is that chronic administration of the
AT1-receptor antagonist TCV-116 to
rats with abdominal aortic constriction induced a decrease not only in
myocyte width but also length of hypertrophied myocardium induced by
pressure overload.
Treatment with a low dose (0.3 mg · kg1 · day1)
of TCV-116 inhibited the increase in LV wall thickness and,
morphologically, myocyte size (width and length), whereas peak wall
stress still remained at a high level. Interestingly, with a high dose
(3.0 mg · kg1 · day1)
of TCV-116, additional reduction of myocyte length was observed accompanied by a decrease in both midwall radius and peak wall stress
without a further reduction in blood pressure. Although LV
contractility was decreased with the high dose of TCV-116, cardiac
output was not significantly changed. These results suggest that in the
effect of AT1-receptor antagonist
on the development of pressure-overload hypertrophy, the reduction of
myocyte length might be an important factor of reducing LV wall stress
and preventing a decrease in cardiac output.
LV hypertrophy and renin-angiotensin system.
Afterload reduction might be involved in the mechanism by which LV
hypertrophy is regressed by various antihypertensive drugs (3, 13).
Indeed, in aortic-banded rats, we observed a decrease in LV weight in
association with a significant reduction in systolic pressure after
treatment with a low dose of TCV-116. However, Linz et al. (18)
reported that the angiotensin-converting enzyme (ACE) inhibitor
ramipril, at a dose that did not decrease blood pressure, reversed LV
hypertrophy in aortic-banded rats, whereas the calcium antagonist
nifedipine and the vasodilator hydralazine did not reverse LV
hypertrophy despite a reduction of blood pressure. Kromer
et al. (16) also reported that the ACE inhibitor quinapril induced a
regression of pressure-overload LV hypertrophy despite a persistent
elevation of blood pressure. These data indicate that factors other
than hemodynamic changes play a role in the pathogenesis of pressure
overload-induced LV hypertrophy.
In this regard, the renin-angiotensin system (RAS) is now regarded as
another important factor in the development of cardiac hypertrophy. ANG
II has been shown to cause proliferation of cardiac myocytes (2, 29).
Khairallah et al. (11) reported that ANG II induced cardiac hypertrophy
without increasing blood pressure. Rockman et al. (26)
reported that the AT1-receptor
antagonist losartan prevented an increase in the heart weight-to-body
weight ratio without a significant reduction in hemodynamic load in
mice with aortic arch constriction. In the present study, we also found a further suppression of LV hypertrophy by an increase in TCV-116 from
0.3 to 3.0 mg · kg1 · day1
without a further reduction in blood pressure, indicating the involvement of RAS in the development of LV hypertrophy.
Myocyte remodeling by TCV-116. In most prior studies, the
prevention or regression of LV hypertrophy by ANG II inhibition was
demonstrated based on the finding that LV weight or morphological myocyte width was decreased. However, to our knowledge, there is no
report evaluating the change in myocyte length with ANG II inhibition
during the development of LV hypertrophy. Using morphometry of whole
tissue sections (1) or the isolation technique for myocytes (5, 15),
previous investigations showed that abdominal aorta banding induced
cellular hypertrophy in which both the width and the length of myocytes
were increased. We also observed substantial increases in both the
width and the length of myocytes with LV pressure overload. However,
consistent with the report by Korecky and Rakusan (15), the
length-to-width ratios were not significantly altered in
pressure-overload LV hypertrophy.
In the present study, treatment with TCV-116 did not induce a
proportional reduction of myocyte size. The increase in myocyte width
was substantially inhibited with a low dose of TCV-116, and no further
inhibition was observed with a high dose of TCV-116. On the other hand,
the increase in myocyte length was only slightly inhibited with a low
dose of TCV-116 and was inhibited to a greater extent by a high dose of
TCV-116. Because AT1 blockade or
ACE inhibition induces a regression of LV hypertrophy with a
proportional decrease in cardiac tissue ANG II (20, 22), it is
suggested that the mode of arrangement of myofibrils or sarcomeres
(parallel or series addition, respectively; Ref. 8), which is
responsible for the change in myocyte size, might be dependent on the
extent of endogenous ANG II content of cardiac tissue during the
development of pressure-overload hypertrophy.
Effect of TCV-116 on cardiac function.
In pressure-overload LV hypertrophy, systolic function is usually
preserved at a compensatory state (24). In the present study, systolic
function was preserved or even enhanced in the untreated aortic-banded
group, as evidenced by the increase in peak LV
+dP/dt and normal cardiac output. With
an AT1-receptor antagonist, LV
contractility might be reduced as evidenced by a decrease in peak
+dP/dt, probably due to inhibition of
the positive inotropic effect of local ANG II in cardiac tissue (6).
However, because cardiac output did not decrease with the
AT1-receptor antagonist, LV pump
function may be preserved in part because of a concomitant reduction of
LV wall stress. Thus, although TCV-116 has a negative inotropic effect
on the heart, RAS inhibition by TCV-116 decreases myocyte length, which
directly reduces LV radius and LV wall stress followed by preservation
of LV pump function.
Study limitations.
First, the reliability of the measurement of myocyte size should be
addressed. Previous reports using the isolation technique for cardiac
myocytes indicated that transverse diameter of myocytes increases with
pressure-overload hypertrophy (5, 15). In morphometric data from whole
tissue sections, most of these findings were based on measurement using
hematoxylin-eosin staining (14, 27), whereas in the present study we
used immunohistochemical staining with connexin 43 because we needed to
detect clearly intercalated disks for the measurement of myocyte
length. Therefore, we also measured myocyte width using
hematoxylin-eosin staining and obtained a finding compatible with
immunohistochemical staining with connexin 43 (not shown). There are
few reports in which hypertrophied myocyte length is measured using
morphometry of whole tissue sections (1, 9, 30), because myocyte length
is difficult to estimate for at least two reasons: true longitudinal
sections are rare, and distances between intercalated disk vary within
the same myocyte (9, 30). Immunohistochemical staining with connexin 43 allowed us to detect clearly intercalated disks so that we could select myocytes in which intercalated disk was located on both sides and a
nucleus was in the center of the myocyte. Campbell et al. (5) reported
that there was good agreement between changes in heart weight and
average myocyte volume in aortic-constricted rats. We also obtained a
good correlation between LV weight and average myocyte volume that was
determined on the assumption of a cylindrical configuration
(r = 0.87, P < 0.001), suggesting a reasonable
estimation of myocyte size in our study. Moreover, by showing the
histogram of the myocyte size, we confirmed the reasonable application
of statistical analysis.
Second, we calculated LV internal diameter and midwall radius by
applying several assumptions (see Hemodynamic
measurements). Therefore, the accuracy
of the calculation, particularly for LV internal diameter, should be
addressed. In this regard, the LV internal volume derived from ex vivo
pressure-volume relations showed a change compatible with the
calculated LV internal diameter on chronic administration of TCV-116.
In conclusion, the AT1-receptor
antagonist TCV-116 induced an inhibition of the development of
pressure-overload hypertrophy: decrease in LV weight, wall thickness,
and midwall radius. Morphologically, not only the width but also the
length of myocytes was decreased with TCV-116, leading to a reduction
of LV wall stress and a preservation of cardiac output.
| |
ACKNOWLEDGEMENTS |
We thank Dr. Dale W. Laird (Dept. of Anatomy and Cell Biology,
McGill University) and Dr. Y. Fujikura (1st Dept. of Anatomy, Yamaguchi
University School of Medicine) for the gift of the antibody directed
against connexin 43.
| |
FOOTNOTES |
Address for reprint requests: M. Matsuzaki, 2nd Dept. of Internal
Medicine, Yamaguchi Univ. School of Medicine, 1144 Kogushi, Ube,
Yamaguchi 755, Japan.
Received 30 January 1997; accepted in final form 27 May 1997.
| |
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AJP Heart Circ Physiol 273(4):H1824-H1831
0363-6135/97 $5.00
Copyright © 1997 the American Physiological Society
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Abstract
Introduction
![<IT>D</IT> = [LV weight/(1.06 × &pgr; × WT) − (WT)<SUP>2</SUP>/3]<SUP>½</SUP> − (WT)](/content/vol273/issue4/fulltext/H1824/img002.gif)
