Download Canine Right and Left Ventricular Cell and Sarcomere Lengths after

Canine Right and Left Ventricular Cell
and Sarcomere Lengths after Banding
the Pulmonary Artery
By Michael M. Laks, M.D., Fred Morady, and H. J. C. Swan, M.B., Ph.D.
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ABSTRACT
Canine hearts were fixed with glutaraldehyde at zero transmural pressure 17
to 48 weeks after main pulmonary arterial banding. Tissues were taken from
the trabeculae carneae at the ventricular right base, right apex, left base, and
left apex. They were placed in osmium tetroxide, embedded in Epon 812,
stained with Azure II methylene blue, and sectioned at M fi. The mean cell
lengths of the hearts with main pulmonary arterial banding were greatest at the
right base, 105 ±5 fj, and left base, 103 ± 5.7 fx. (The means ± SE are given.)
The mean cell length at the left apex was 95 ± 4 //, and that at the right apex
was 92 ± 5 p. All were greater ( P < 0.001) than the cell lengths of normal
hearts, 71 ± 1.5 ft. The mean sarcomere lengths of the right ventricle with
main pulmonary arterial banding (right base, 2.04 ± 0.006 fj.; right apex,
2.18 ±0.004 fi) were less than those of normal hearts (right base,
2.41 ±0.006 fi; right apex, 2.46± 0.003 fj,). The mean sarcomere length of
the left base with main pulmonary arterial banding (2.10 ±0.01 p) was less
than the normal (2.16 ± 0.002 fji); however, the mean sarcomere length of the
left apex with main pulmonary arterial banding (2.28 ±0.005 fi) was the
same as the normal.
With main pulmonary arterial banding, both the right and left ventricular
cell lengths increased more at the bases than at the apexes, and the sarcomere
• lengths decreased in the right base, right apex, and left base.
ADDITIONAL KEY WORDS
right ventricular base
right ventricular apex
• Previously reported quantitative determinations of cellular myocardial hypertrophy
have been based solely on the estimation of
the cross-sectional area of myocardial cells (13). No quantitative knowledge is available as
to whether the length of the myocardial cell
changes when the heart is stimulated to
hypertrophy. We described a technique for
stretching the myocardial fiber under constant
conditions in the normal heart and for fixing
this tissue with minimal shrinkage and distorFrom the Department of Cardiology and the
Division of Medicine, Cedars-Sinai Medical Research
Institute, Cedars-Sinai Medical Center, Los Angeles,
California 90029.
This work was supported in part by U. S. Public
Health Service Grant HE-10382 from the National
Heart Institute, Los Angeles County Heart Association
Research Award 412 IC, and Ives Laboratories,
Division of American Home Products.
Received December 4, 1968. Accepted for publication March 19, 1969.
Circulation Research, Vol. XXIV, May 1969
ventricular hypertrophy
left ventricular muscle
tion (4, 5). In addition, we described an
increase in glycogen at the base as compared
with the apex of the hypertrophied right
ventricle (6). As an extension of these studies,
we are reporting the changes in the cell and
sarcomere lengths at the bases and apexes of
the canine right and left ventricles produced
by banding the pulmonary artery.
Methods
In five mongrel dogs weighing between 16 and
22 kg, right ventricular systolic pressures of 50
mm Hg or greater were produced by banding the
main pulmonary artery. This technique has been
described in detail previously (4, 5). Seventeen
to forty-eight weeks after banding the pulmonary
artery, the dogs were anesthetized with sodium
pentobarbital, 27 mg/kg iv, and killed. The
hearts were rapidly removed and fixed with
glutaraldehyde at zero transmural pressure.
Tissues were then taken from the trabeculae
carnae at the bases and apexes of the right and
left ventricles, placed in osmium tetroxide,
705
LAKS, MORADY, SWAN
706
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Vol. XXIV, Ma> I5
Ctf.uUiton Rutir.b,
707
HYPERTROPHIED CELL AND SARCOMERE LENGTHS
TABLE 1
Effect of Pulmonary Arterial Banding on Ventricular Weight
Dog
no.
Right
ventricle
weight*
(g/m=)
Left
ventricle
weight*
(g/m=)
Right ventricular
pressure
(mm Hg)
Normal
1
2
3
4
37.0
48.0
46.0
44.2
60.2
71.5
66.2
54.7
Pulmonary artery
banding
5
6
7
8
9
78.7
50.2
70.5
60.1
82.3
69.9
55.5
88.5
94.2
65.8
20/2
25/4
22/3
20/2
72/4
50/3
55/3
58/3
80/4
'Expressed as grams per square meter of body surface area.
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embedded in Epon 812, sectioned at )i ft, stained
with Azure II methylene blue, and then photomicrographed with a 4 by 5 camera fixed on a
Zeiss Universal Light Microscope (Fig. 1). All
measurements were made from high-contrast
prints with a l,000x magnification for cell
lengths and 4,000 X magnification for sarcomere
lengths. The variability in the measurement of
cell length due to stepwise configuration of
intercalated discs was 2.3%. Statistical analysis
was performed using both the standard f-test (7)
and the rank sum method (8). A presentation of
this method and a discussion of measurements of
cell and sarcomere lengths in the normal canine
heart have been reported (5). These animals
were not considered to be in heart failure because
there was no liver and lung congestion, pleural
effusion, or ascites, and the end-diastolic pressure
in the right ventricle was normal.
All values are the means ± SEM.
Results
Ventricular Weights.—After banding the main
pulmonary artery for 17 to 48 weeks, all of the
right ventricular weights (Table 1) were
greater than in the normal hearts (P < 0.01),
and two of the five left ventricular weights
were greater than in the control group.
Cell Lengths.—After banding the main
pulmonary artery, the mean cell lengths at
zero transmural pressure were greatest at the
right base, 105 ± 5 (i, and the left base,
103 ±5.7 (i, followed in length by the left
apex, 95 ± 4 /x, and the right apex, 92 ± 5 /i.
All were greater than those of normal hearts
(right base, 67 ±2.5 fi; left base, 67±3.3 fi;
left apex, 70 ±2,8 (i; right apex, 70 ±3.4 fi)
Circulation Research, Vol. XXIV, May 1969
(P<0.01) (Table 2). Furthermore, in the
hearts with pulmonary arterial banding, the
cell lengths ranged from low normal to greater
than normal; the percentages of cell lengths
greater than 100 /A were 54% at the right base,
35% at the right apex, 45% at the left base, and
33% at the left apex, and all were significantly
greater than the percentage in the normal
hearts (right base, 16%; left base, 18%; right
apex, 15%; left apex, 18%).
Sarcomere Lengths.—After banding the
main pulmonary artery, the mean sarcomere
lengths at zero transmural pressure were
2.04 ±0.006 ft at the right base and 2.16 ±
0.004 fi at the right apex (Table 2) and were
less than those of normal hearts (right base,
2.41 ±0.006 fi; right apex, 2.46±0.003 ft).
However, after banding the main pulmonary
artery, the mean sarcomere lengths were
2.10 ± 0.01 yu, at the left base and 2.22 ± 0.005
ix at the left apex, and were moderately,
although significantly, less than the mean left
ventricular sarcomere lengths of normal hearts
(left base, 2.16 + 0.002 fi; left apex, 2.28±
0.005 ft) (P<0.001).
Number of Sarcomeres Per Cell Length.—
As previously described, the number of sarcomeres per cell length was computed by dividing each cell length by the mean sarcomere
length in that region. After banding the main
pulmonary artery, the mean number of sarcomeres per cell length (Table 2) was greatest
at the right base, 53, followed by the left base,
LAKS, MORADY, SWAN
708
TABLE 2
Statistical Data for Five Dog Hearts with Pulmonary Arterial Banding and Four Normal Hearts
Sarcomere length
Region
Dog
no.
N
Mean
Cell length (ji)
±SEM
N
Mean
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Right apex
5
6
7
8
9
Five Dogs With Pulmonary Arterial Banding
2.18
109.1
159
22
0.003
64
2.40
71.3
0.010
19
85.6
2.20
145
0.003
18
131
2.06
0.003
97
2.15
97.5
0.005
27
Right base
5
6
7
8
9
114
52
174
67
140
1.84
1.96
2.16
2.02
2.12
0.004
0.005
0.004
0.005
0.003
30
26
27
20
26
117.7
102.9
98.4
101.4
103.0
Left apex
5
6
7
8
9
200
120
153
78
96
2.24
2.39
2.20
2.29
2.25
0.003
0.002
0.002
0.010
0.007
19
18
24
17
33
Left base
5
6
7
8
9
125
89
177
116
53
2.11
2.26
1.93
2.00
2.14
0.004
0.009
0.003
0.007
0.006
25
14
26
15
18
±SEM
Sarcomeres per
cell length
12.7
7.8
10.8
50.0
29.7
38.9
8.8
45.4
7.8
8.8
8.7
7.0
9.7
64.0
52.5
45.5
50.2
48.6
93.7
108.1
76.3
95.7
95.6
7.6
13.6
7.8
9.8
6.4
41.8
45.2
34.7
41.8
42.5
92.4
94.9
104.0
108.9
110.9
8.3
11.6
10.9
9.1
7.2
43.6
42.0
53.9
54.5
52.1
Comparison Between Pooled Data
Right apex
Normal
PAB
P
P
390
596
2.46
2.18
0.003
0.004
66
86
70.0
92.0
3.4
5.0
29.0
43.0
Right base
Normal
PAB
P
P
480
547
2.41
2.04
0.006
0.006
94
129
67.0
105.0
2.5
5.0
29.0
53.0
Left apex
Normal
PAB
P
P
464
647
2.28
2.22
0.005
0.005
92
111
70.0
95.0
2.8
4.0
31.0
43.0
Left base
Normal
PAB
P
P
411
560
2.16
2.10
0.002
0.01
68
98
67.0
103.0
3.3
5.7
31.0
47.0
PAB = pulmonary arterial banding. P = pooled data.
47, left apex, 43, and right apex, 43; and all were
greater than the normal (right base, 29; left
base, 31; left apex, 31; right apex, 29). In the
hearts with pulmonary arterial banding, the
percentage of sarcomeres per cell greater than
45 was 63% at the right base, 41% at the right
apex, 41% at the left base, and 43% at the left
apex. These percentages were significantly
greater than in the normal hearts (right base,
7%; right apex, 1%; left base, 13%; left apex,
9%).
Discussion
Cell Lengths.—In dogs with banded pulmonary arteries, the discovery that the longest
cell lengths were at the right base might be
predicted by the law of Laplace: Tension or
strain is equal to the product of pressure and
radius. Therefore, with a pressure overload,
Circulation Research, Vol. XXIV, May 1969
709
HYPERTROPHIED CELL AND SARCOMERE LENGTHS
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the greater strain or stimulus to hypertrophy
would occur at the ventricular base which has
a larger diameter than the apex.
The calculated increase in the number of
sarcomeres per cell length indicates that the
increase in cell length is the result of adding
more sarcomeres to the cell and not merely
due to a stretching of the sarcomeres. We
previously reported (6) an increase of glycogen adjacent to the intercalated disc, and this
raises the question whether the locus for the
addition of more sarcomeres may be at the
intercalated discs. Since hypertrophy is a
process by which the heart compensates, a
study of the area of the intercalated disc in the
failing heart may reveal a clue to the
biochemical alterations in heart failure.
The left ventricular cell lengths of dogs with
pulmonary arterial banding were significantly
longer than those of normal hearts; although
this increase was less than that in the right
ventricle. The participation of the left ventricle in the hypertrophy process cannot be
attributed to the interventricular stimulus of
pressure overload. The left ventricular volume
appears to be increased after pulmonary
arterial banding (9). Spann et al. (10)
reported a moderate decrease in left ventricular norepinephrine content in cats with
banded pulmonary arteries. Although we have
no knowledge of the mechanism by which the
left ventricular cells hypertrophy, the right
and left ventricular myocardium may behave
as a single structure in that a stress to one
results in a hypertrophy of both. It is possible
that a substance which has the property of
producing hypertrophy may be released from
the overloaded right ventricle and transported
to the left ventricle.
In the hearts with pulmonary arterial
banding, the frequency distribution of cell
lengths ranged from low normal to significantly greater than normal. Because of this
extreme variability, we may deduce that the
stimulus to hypertrophy is either nonuniform
or the individual cells have a different
capability of adding more sarcomeres. At
present, it is not known whether myocardial
Circulation Research, Vol. XXIV, May 1969
cells differ metabolically or anatomically from
the cells with a normal length.
Sarcomere Lengths.—The striking decrease
in right ventricular sarcomere lengths after
banding the pulmonary artery may be considered a reflection of a decrease in right
ventricular compliance. This decrease in compliance may be simply the results of an
increase in muscle mass. On the other hand,
the study of Buccino et al. (11) pointed to an
alteration in the myocardium per se. They
demonstrated an increase in connective tissue
as indicated by an increase in hydroxyproline
in the right ventricles of cats with banded
pulmonary arteries. The slight decrease in left
ventricular sarcomere lengths may be explained by an increase in left ventricular
connective tissue as reported by Buccino et
al. (11) in cats with banded pulmonary arteries.
References
1. KABSNEB, H. T., SAPHIB, O., AND TOPP, T. W.:
State of the cardiac muscle in hypertrophy and
atrophy. Am. J. Pathol. 1: 351, 1925.
2.
LOWE, T. E., AND BATE, E. W.: Diameter of
cardiac muscle fibers in the left ventricle in
normal hearts and in the left ventricular
enlargement of simple hypertension. Med. J.
Australia 1: 467, 1948.
3. HARBISON, T. R., ASHMAN, R., AND LARSON, R.
M.: Congestive heart failure: The relation
between the thickness of the cardiac muscle
fiber and the optimum rate of the heart. Arch.
Internal Med. 99: 151, 1932.
4. LAKS, M. M., GARNER, D., AND SWAN, H. J. C :
Volumes and compliances measured simultaneously in the right and left ventricles of the
dog. Circulation Res. 20: 565, 1967.
5. LAKS, M. M., NISENSON, B. A., AND SWAN, H. J.
C : Myocardial cell and sarcomere lengths in
the normal dog heart. Circulation Res. 2 1 :
671, 1967.
6. LAKS, M. M., VAN D E VELDE, S., AND SWAN, H.
J. C : Presence and location of glycogen in the
hypertrophied right ventricle of the canine
heart (absrr.). Clin. Res. 15: 211, 1967.
7. DIXONT, W., AND MASSEY, F.: Introduction
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Statistical Analysis. New York, McGraw-Hill
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8. WILCOXON, F.: Individual comparison by ranking
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9. LAKS, M. M., GOLDBERG, D., AND SWAN, H. J. C :
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LAKS, MORADY, SWAN
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hypertrophied canine ventricle (abstr.). Federation Proc. 25: 1966.
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SPANN, J. F., JR., BUCCINO, R. A., SONTNENBLICK,
E. H., AND BRAUNWALD, E.: Contractile state
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11. BUCCINO, R. A., HARMS, R., SPANN, J. R., JR.,
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Circulation Research, Vol. XXIV, May 1969
Canine Right and Left Ventricular Cell and Sarcomere Lengths after Banding the
Pulmonary Artery
MICHAEL M. LAKS, FRED MORADY and H.J.C. SWAN
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Circ Res. 1969;24:705-710
doi: 10.1161/01.RES.24.5.705
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Copyright © 1969 American Heart Association, Inc. All rights reserved.
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