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H4120002994pAm J Physiol Heart Circ Physiol279: H2994–H3002, 2000.
Effects of exercise training on cardiac function,gene expression, and apoptosis in rats HONGKUI JIN,1 RENHUI YANG,1 WEI LI,1 HSIENWIE LU,1 ANNE M. RYAN,2ANNIE K. OGASAWARA,1 JOHN VAN PEBORGH,1 AND NICHOLAS F. PAONI11Department of Cardiovascular Research and 2Department of Pathology,Genentech Incorporated, South San Francisco, California 94080 Received 1 December 1999; accepted in final form 21 June 2000 Jin, Hongkui, Renhui Yang, Wei Li, Hsienwie Lu,
thermore, systematic studies on the effects of exercise Anne M. Ryan, Annie K. Ogasawara, John Van Pe-
on hemodynamics and cardiac function assessed in borgh, and Nicholas F. Paoni. Effects of exercise training
conscious rats are limited. In this study, the effects of on cardiac function, gene expression, and apoptosis in rats.
treadmill training (for 13 wk) on cardiac function and Am J Physiol Heart Circ Physiol 279: H2994–H3002, hemodynamics were assessed by comparison of two 2000.—This study determined the effects of exercise training sets of control animals: sedentary rats of the same age on cardiac function, gene expression, and apoptosis. Rats and others of the same BW as the exercised cohort.
exposed to a regimen of treadmill exercise for 13 wk had asignificant increase in cardiac index and stroke volume index Hemodynamic and cardiac function measurements and a concomitant decrease in systemic vascular resistance were made while the animals were conscious and un- compared with both age-matched and body weight-matched sedentary controls in the conscious state at rest. In exercise- Second, to evaluate the molecular effects of exercise trained animals, there was no change in the expression of on the heart, real-time RT-PCR was used to study several marker genes known to be associated with patholog- the relative expression of several cardiac muscle ical cardiac adaptation, including atrial natriuretic factor, and extracellular matrix genes in the left ventricle ␤-myosin heavy chain, ␣-skeletal and smooth muscle actins, (LV) of the exercised rats compared with sedentary and collagens I and III. Exercise training, however, produced controls. These results were compared and contrasted a significant induction of ␣-myosin heavy chain, which was to changes in gene expression induced by adapta- not observed in rats with myocardial infarction. No histolog- tion to the pathological stimulus of myocardial infarc- ical features of cardiac apoptosis were observed in the tread- mill-trained rats. In contrast, apoptotic myocytes were de- Finally, exercise has been reported to produce apo- tected in animals with myocardial infarction. In summary,exercise training improves cardiac function without evidence ptosis in the thymocytes of rats (12) and in the skeletal of cardiac apoptosis and produces a pattern of cardiac gene muscle of mice (40). It is also known that cardiac expression distinct from pathological cardiac adaptation.
adaptation to myocardial infarction and chronic pres-sure overload is accompanied by programmed cell treadmill; hemodynamics; physiological loads; pathological death (27, 50). The effect of exercise training on cardiac loads; myocardial infarction apoptosis, however, has not been investigated. Thehearts of exercised-trained rats were examined forevidence of apoptotic cell death at 4 days, 10 days, and THE LABORATORY RAT has been used by many investiga- 13 wk after exercise training was initiated, and the tors to study the adaptation of cardiac function to results were compared with what was observed at chronic exercise (3, 4, 6, 8, 14, 15, 17, 21, 24, 25, 29 –31, similar time points after myocardial infarction.
33, 41, 45, 47, 52, 57, 61, 62), and much useful infor-mation has emerged from these studies. The purpose of MATERIALS AND METHODS
this investigation was to extend previous findings inseveral important ways. First, exercise training in this All experimental procedures conformed to the guiding principles of the American Physiology Society and were ap- model system can have a significant impact on rodent proved by the Institutional Animal Care and Use Committee body weight (BW), and there is a direct relationship of Genentech. The animals used in this study were male between BW and hemodynamic parameters, including Sprague-Dawley rats (6–8 wk of age, Charles River Breeding blood volume, cardiac output, stroke volume, and pe- Laboratories). The animals were acclimated to the facility for ripheral vascular resistance in rats (10). There are no at least 1 wk before the initiation of the study, fed a pelleted observations of cardiac function, however, where exer- rat chow and water ad libitum, and housed in a light- and cise-trained rats were compared with both BW- matched and age-matched sedentary controls. Fur- The costs of publication of this article were defrayed in part by the Address for reprint requests and other correspondence: H. Jin, payment of page charges. The article must therefore be hereby Dept. of Cardiovascular Research, Genentech, Inc., 1 DNA Way, S.
marked ‘‘advertisement'' in accordance with 18 U.S.C. Section 1734 San Francisco, CA 94080.
solely to indicate this fact.
0363-6135/00 $5.00 Copyright 2000 the American Physiological Society CARDIAC EFFECTS OF EXERCISE TRAINING Exercise Training diac index. Hemodynamic measurements were performed in11 exercise-trained, 10 age-matched, and 6 BW-matched Rats of approximately the same age were randomly di- rats, and cardiac output was not successfully measured in 2 vided into two groups: the exercise group (n ⫽ 31) and the rats (1 in the exercise group and 1 in the age-matched group) age-matched sedentary controls (n ⫽ 19). These groups were because the thermodilution curve was not reliable.
age-matched in the sense that the average ages of the two At the conclusion of the experiments, the rats were anes- groups were almost identical. The rats in the exercise group thetized with pentobarbital sodium (60 mg/kg). The hearts trained on a rodent treadmill (model CT-2, Columbus Instru- were removed, dissected, and weighed in 14 exercise-trained, ments International) according to the training protocol de- 14 age-matched, and 12 BW-matched rats.
scribed previously (32, 39). An electric grid at the rear of thebelt was used as the running stimulus. The animals trained 5 days/wk for 13 wk, with speed, grade, and duration pro-gressively increased. The rats began training at 10 m/min Echocardiograms were performed in eight exercise-trained and 5% grade for 15 min/day. The speed and grade were rats and eight age-matched controls before catheterization.
gradually increased such that by the end of the second week, The rats were anesthetized with ketamine and xylazine as the animals ran at 15 m/min, 15% grade, for 60 min/day.
described above and examined in the lateral decubitus posi- Thereafter, the grade and duration were maintained but tion. An annular array echocardiographic system (Apogee speed was increased 2–3 m/min each wk. By 10 wk, the rats CX, ATR Interspec, Bothell, WA) with a 7.5-MHz transducer ran at 36 m/min and 15% grade for 60 min/day, and this was used for two-dimensional and M-mode imaging. With the exercise program was maintained until the end of the study.
use of the two-dimensional parasternal short-axis imaging Because the exercise training significantly decreased the plane as a guide to the level of the papillary muscles, a poststudy BW, the age-matched sedentary controls could not M-mode tracing of the LV was obtained. The LV anterior and serve as BW controls. Thus a younger group of sedentary rats posterior wall thickness at end diastole, LV end-diastolic (n ⫽ 12) was established to serve as BW controls. With the internal diameter, and LV end-systolic internal diameter use of the knowledge of the BW-versus-age relationship for were measured according to standard procedures. The LV both sedentary and exercise-trained rats, we determined that mass was calculated with the standard cube formula as rats ⬃2.5 wk younger than the exercise group should emerge follows: LVM ⫽ 1.04[(AWT ⫹ PWT ⫹ EDD)3 ⫺ EDD3], where from the study with average BW roughly the same as that of LVM is LV mass, AWT and PWT are anterior and posterior the exercise group. Note that the average initial BW will wall thickness, respectively, and EDD is LV end-diastolic necessarily be smaller in this BW-matched group than in the internal diameter. Relative wall thickness was calculated as older, exercise group.
the ratio of 2PWT to 1EDD.
Assessments of Cardiac Growth and Cardiac Function Studies on Cardiac Gene Expression Catheterization. At the end of 13 wk of exercise training, Animal model and sample preparation. The hearts from rats in the three experimental groups were anesthetized with the exercise-trained rats (n ⫽ 5) and age-matched controls ketamine hydrochloride (100 mg/kg ip) and xylazine (10 (n ⫽ 5) were removed and dissected, and the LV were fast- mg/kg ip). A catheter [polyethylene (PE)-10 fused with PE- frozen in liquid nitrogen and stored at ⫺70°C for subsequent 50] filled with heparin-saline solution (50 U/ml) was im- RNA analysis. Cardiac gene expression analysis was also planted into the abdominal aorta through the left femoral performed in four rats 13 wk after myocardial infarction artery. This catheter was used to measure arterial pressure induced by ligation of the left coronary artery and four and heart rate. A second catheter (PE-50) was implanted into sham-operated control rats to allow comparison with cardiac the right atrium, through the right jugular vein, for measure- adaptation to a pathological load. The procedure used for left ment of left atrial pressure and for saline injection. A ther- coronary ligation has been described in detail elsewhere (18, mistor catheter (Lyons Medical Instrument, Sylmar, CA) was 26, 38, 63). In brief, the rats were anesthetized with ket- inserted into the aortic arch from the right femoral artery for amine hydrochloride and xylazine as described above, intu- measurement of cardiac output by the thermodilution bated via tracheotomy, and ventilated by a respirator (model method (10, 13, 26, 63). The catheters were exteriorized at 683, Harvard Apparatus). After a left-sided thoracotomy, we the back of the neck with the aid of a stainless steel wire.
ligated the left coronary artery ⬃2 mm from its origin with a After the catheters were implanted, all rats were housed 7–0 silk suture. Electrocardiograms were obtained under light metofane anesthesia 1 wk after surgery to document the Hemodynamic measurements. Mean arterial pressure and development of infarcts (26, 63). The rats without evident heart rate were measured in conscious, unrestrained rats pathological Q waves across the precardial leads were ex- 1 day after catheterization by connecting the catheters to cluded. Our previous studies (26, 63) have shown that rats a pressure transducer (model P23 XL, Viggo-Spectramed, selected by electrocardiogram have myocardial infarcts aver- Oxnard, CA) coupled to a polygraph (model 7, Grass In- aging 32–35% of the LV, which led to ventricular hypertro- struments, West Warwick, RI). For measurement of cardiac phy and cardiac dysfunction 6–14 wk after ligation.
output, the thermistor catheter was connected to a microcom- Cardiac RNA analysis. Total RNA was isolated from the puter system (Lyons Medical Instrument) (26, 63). Isotonic ventricular samples using the RNeasy Maxi Kit (Qiagen) saline (0.1 ml) at room temperature was injected as a bolus according to the manufacturer's instructions. Gene expres- via the jugular vein catheter. The thermodilution curve was sion analysis was performed using real-time RT-PCR (Taq- monitored by VR-16 Simultrace recorders (Honeywell, NY), Man) technology. RT-PCR was performed on 1 ng of total and cardiac output was digitally obtained by the microcom- RNA per reaction using the TaqMan sequence detector puter. Cardiac indexes were calculated as follows: stroke (model 7700, ABI-Perkin Elmer) (19). Amplification reaction volume ⫽ cardiac output/heart rate; cardiac index ⫽ cardiac conditions (for 50 l) were 1⫻ TaqMan buffer A, 300 M output/BW; stroke volume index ⫽ stroke volume/BW; and dATP, 300 M dCTP, 300 M dGTP, 600 M dUTP, 10% systemic vascular resistance ⫽ mean arterial pressure/car- glycerol, 5.5 mM MgCl , 50 U murine leukemia virus reverse CARDIAC EFFECTS OF EXERCISE TRAINING transcriptase, 20 U RNase Inhibitor, 1.25 U AmpliTaq Gold, 100 nM forward and reverse primers, and 100 nM fluorogenicprobe. RT-PCR reagents and glycerol were purchased from Effects of Exercise on BW and Cardiac Growth Perkin Elmer and Sigma, respectively. Reactions were per- Because chronic exercise generally induces a signif- formed in MicroAmp optical tubes and caps (ABI-Perkin icant reduction in BW, we compared the exercised Elmer). TaqMan primers and probes were designed accord- animals to not only age-matched but also BW-matched ing to guidelines determined by Perkin Elmer and synthe-sized at Genentech except for those for rodent GAPDH, which sedentary controls. After 13 wk of treadmill training, were a generous gift from Perkin Elmer. Reverse transcrip- the BW of the exercised group was ⬃17% lower than tion was performed at 48°C for 30 min followed by heat the age-matched sedentary controls (P ⬍ 0.01) and the activation of AmpliTaq Gold at 95°C for 10 min. Thermal same as the BW-matched group, which contained ani- cycling was at 95°C for 30 s and 60°C for 1.5 min for 40 cycles.
mals that were ⬃2.5 wk younger (Table 1). The ratios Quantitation of the TaqMan results was performed as of heart and ventricular weights to BW were the same described by Heid et al. (23) with modifications. Briefly, in the two sedentary groups despite the difference in standard curves (1:5 serial dilution) for each target gene of BW and age, indicating that the heart and body grew interest were run in duplicate. The threshold cycle (C ) was proportionally in these animals. The BW-normalized plotted on the y-axis versus the log of the total RNA concen- heart and ventricular weights of the exercised group tration (x-axis), and the equation describing the line was were significantly greater than the two sedentary con- determined. Experimental samples were analyzed using 3–5 trol groups, however (Table 1).
replicates each, and the quantity of the mRNA for each targetgene was determined from the appropriate standard curve by LV Geometry Measured by Echocardiography entering the C (y value) and solving for the input mRNA (x value). The value for the target gene was then normalized to There was a close correlation between echocardio- GAPDH by solving the following equation: 10x1/10x2, where x gram-derived LV mass and actual LV wet weight in a is the target gene and x is GAPDH.
combined group of exercise-trained rats and age- matched controls (r ⫽ 0.84, P ⬍ 0.0001, n ⫽ 16) indi- Studies on Cardiac Myocyte Apoptosis cating the accuracy of echocardiographic measurements.
Programmed cell death in the heart has been demon- strated during the first 1–2 wk, with a peak at several days, Table 1. Effects of exercise training on BW, HW, after the onset of pressure overload or myocardial infarction MAP, and HR in rats (27, 50). Cardiac apoptosis was evaluated by exami-nation of morphological features under light microscopy and by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling reaction (TUNEL) labeling of the 3⬘ 307.8 ⫾ 4.6 (14) 306.2 ⫾ 5.8 (14) 252.7 ⫾ 4.7† (12) 508.8 ⫾ 11.1 (14) 612.6 ⫾ 15.1† (14) 502.3 ⫾ 7.6 (12) OH ends of DNA in myocardial tissue sections after 4 days, 1.351 ⫾ 0.041 (14) 1.374 ⫾ 0.043 (14) 1.082 ⫾ 0.086† (12) 10 days, or 13 wk of exercise training (n ⫽ 4 for each time 1.281 ⫾ 0.040 (14) 1.277 ⫾ 0.039 (14) 1.015 ⫾ 0.086† (12) point) or after myocardial infarction induced by coronary 1.019 ⫾ 0.034 (11) 1.001 ⫾ 0.037 (11) 0.803 ⫾ 0.013† (12) ligation (n ⫽ 3 for each time point) as described above.
0.241 ⫾ 0.012 (11) 0.244 ⫾ 0.010 (11) 0.213 ⫾ 0.008* (12) The hearts were removed from the rats under anesthesia, fixed in 10% neutral-buffered Formalin, processed routinely, 2.668 ⫾ 0.096† (14) 2.247 ⫾ 0.056 (14) 2.151 ⫾ 0.167 (12) embedded in paraffin, and sectioned at 5 m. Replicate 2.531 ⫾ 0.095† (14) 2.107 ⫾ 0.055 (14) 2.017 ⫾ 0.166 (12) sections were stained with hematoxylin and eosin for light microscopic analysis; apoptotic cells were identified by posi- 2.037 ⫾ 0.079† (11) 1.636 ⫾ 0.050 (11) 1.601 ⫾ 0.021 (12) tive staining with the digoxigenin-dUTP terminal de- oxytransferase method (ApoTag kit, Oncor, Gaithersburg, 0.482 ⫾ 0.024† (11) 0.400 ⫾ 0.014 (11) 0.408 ⫾ 0.014 (12) MD). Twelve sections were evaluated on each heart. Forma- 1.69 ⫾ 0.07 (8) 1.68 ⫾ 0.08 (8) lin-fixed thymus from 4-wk-old C57BL/6 mice treated with 50 1.74 ⫾ 0.07 (8) 1.67 ⫾ 0.07 (8) 3.84 ⫾ 0.20 (8) 4.40 ⫾ 0.22 (8) g of cortisone acetate for 12 h (to induce thymic involution) 7.85 ⫾ 0.18 (8) 8.45 ⫾ 0.27 (8) and embryonic day 14 (E14) mouse embryos were used as 0.445 ⫾ 0.016‡ (8) 0.396 ⫾ 0.016 (8) positive controls for apoptotic staining. With this method, apoptotic cells were identified in the thymic cortex and in the 112.6 ⫾ 1.9 (11) 109.9 ⫾ 3.8 (10) 117.1 ⫾ 4.0 (6) embryonic heart of the control tissues.
360.0 ⫾ 7.1 (11) 370.1 ⫾ 9.2 (10) 368.3 ⫾ 12.5 (6) Data are expressed as means ⫾ SE; the number in parentheses Results are expressed as means ⫾ SE. One-way analysis of represents the number of rats. BW , body weight before the initiation variance (ANOVA) was performed to assess differences in of exercise training; BW, body weight 13 weeks after exercise train- parameters between groups. Significant differences were ing; HW, heart weight; VW, ventricular weight; LVW, left ventricu- then subjected to post hoc analysis using the Newman-Keuls lar (LV) weight; RVW, right ventricular weight; AWT, anterior wallthickness; PWT, posterior wall thickness; ESD, LV end-systolic in- method. For analysis of gene expression, parameters be- ternal diameter; EDD, LV end-diastolic internal diameter; RWT, tween the exercise or infarct group and the respective control relative wall thickness; MAP, mean arterial pressure; HR, heart group were compared by an unpaired Student's t-test. P ⬍ rate. * P ⬍ 0.05 and † P ⬍ 0.01 compared to other two groups. ‡ P ⬍ 0.05 was considered significant.
0.05 compared with the age-matched group.
CARDIAC EFFECTS OF EXERCISE TRAINING No significant difference in LV anterior and posteriorwall thickness was observed between the exercisegroup and age-matched group (Table 1). LV end-sys-tolic and end-diastolic internal diameters tended to bedecreased in the exercise-trained animals comparedwith the age-matched sedentary controls, but the dif-ference was not statistically significant. However,there was a significant increase in relative wall thick-ness, an index of cardiac geometry, in the exercisegroup compared with the age-matched sedentary con-trols (Table 1), indicating that treadmill running wasassociated with alterations in cardiac morphology.
Effects of Exercise on Cardiac Function Mean arterial pressure and heart rate at rest were similar in the three experimental groups (Table 1). Thecardiac index and stroke volume index of the treadmill-trained rats were significantly higher (P ⬍ 0.01) thanthose of either sedentary control group (Fig. 1). Exer-cise also significantly reduced systemic vascular resis-tance (P ⬍ 0.01). No differences in cardiac index, strokevolume index, and systemic vascular resistance werefound between the two sedentary control groups.
Effects of Exercise and Myocardial Infarction onCardiac Gene Expression LV expression levels of 11 genes were used to com- pare the molecular phenotypes of cardiac adaptation tostress induced by exercise training versus myocardialinfarction (Table 2). Treadmill training for 13 wk re-sulted in a significant increase in the expression of onlyone measured gene, ␣-myosin heavy chain (P ⬍ 0.05),which was unchanged in animals after myocardial in-farction. In contrast, the mRNA abundance of six geneswere significantly increased 13 wk after myocardialinfarction. mRNA levels of atrial natriuretic factor, ␣-skeletal actin, and ␣-smooth muscle actin were in-creased by 5.7-, 2.9-, and 2.2-fold, respectively (Fig. 2).
The ␤-myosin heavy chain isoform was induced, andmRNA levels of the extracellular matrix proteins col-lagen I and III increased by 2.3- and 2.6-fold, respec-tively (Fig. 3).
Effects of Exercise and Myocardial Infarction on Fig. 1. Effects of exercise training on cardiac index (CI), stroke Cardiac Myocyte Apoptosis volume index (SVI), and systemic vascular resistance (SVR) in con-scious rats. BW, body weight. Data expressed as means ⫾ SE. **P ⬍ Apoptotic myocytes, ⬃3–5 apoptotic cells/high-power 0.01 compared with the exercise group.
field, were detected adjacent to the myocardial infarct4 days after left coronary artery ligation (Fig. 4). In stroke volume index at rest in the conscious state contrast, no apoptotic cells were detected in the hearts compared with both age-matched and BW-matched of exercise-trained animals. No histological features of sedentary controls, indicating that exercise training apoptosis (nuclear pyknosis and karyorrhexis) were enhances cardiac function. Second, mRNA levels for observed in either hematoxylin and eosin-stained or atrial natriuretic factor, ␤-myosin heavy chain, ␣-skel- ApoTag-stained myocardial sections after 4 days, 10 etal actin, ␣-smooth muscle actin, collagen I, and col- days, or 13 wk of treadmill training.
lagen III in the LV were significantly elevated in rats13 wk after myocardial infarction but not in the exer- cise-trained animals. In contrast, there was a signifi- There are three major findings in the present study.
cant induction of ␣-myosin heavy chain in the exercise First, rats subjected to chronic treadmill exercise for 13 group but not in the infarct group. This suggests a wk exhibited a significant increase in cardiac index and distinct pattern of cardiac gene expression induced by
CARDIAC EFFECTS OF EXERCISE TRAINING Table 2. Effects of exercise training vs. MI on cardiac stroke volume in healthy humans and pigs (7, 48, 59).
gene expression However, our finding of increased resting cardiac indexin exercise-trained rats is not in agreement with the observation that there is no significant increase in Natriuretic factors resting cardiac index after exercise training in humans Atrial natriuretic factor and pigs. This discrepancy may be due mainly to the change in resting heart rate after exercise training.
␣-Cardiac actin Humans receiving exercise training exhibit bradycar- ␣-Skeletal actin dia at rest that offsets the increase in resting stroke ␣-Smooth muscle actin volume, leading to an insignificant change in cardiac ␣-Myosin heavy chain output or cardiac index at rest (7, 48). In pigs, exercise ␤-Myosin heavy chain training tends to reduce resting heart rate, which is Myosin light chain 2 associated with a tendency to increase resting cardiac Sarco(endo)plasmic reticulum Ca2⫹-ATPase output (59). In the present study, however, resting heart rate did not change after exercise training in Extracellular matrix conscious rats, which is consistent with previous re- ports (8, 11, 24, 31, 33–35, 62) by the majority of other investigators who observed little or no change in rest- n ⫽ 5 rats in each exercise and age-matched group, and n ⫽ 4 rats in each myocardial infarction (MI) and sham group. Results areas compared with the respective control: NS, no significant change; 1, significant increase (P ⬍ 0.05); and 11, very significant increase(P ⬍ 0.01).
the physiological load versus pathological load. Third,myocardial apoptosis was detected in rats 4 days aftermyocardial infarction but not in the exercise-trainedanimals at 4 days, 10 days, and 13 wk. This is the firstdemonstration that myocardial adaptation to exercisetraining was not associated with cardiac apoptosis.
In the present study, animals receiving exercise training exhibited a significant enhancement in car-diac index and stroke volume index at rest in theconscious state compared with both age-matched andBW-matched sedentary controls. The improvement incardiac function was associated with a reduction insystemic vascular resistance. The decrease in afterloadmay contribute to the enhanced cardiac function byreducing the impedance of LV ejection. Recent studies(46, 54) in dogs suggest that exercise training is asso-ciated with an increase in nitric oxide formation thatmay mediate endothelium-dependent peripheral vaso-dilation. In addition, another mechanism for enhancedcardiac function observed in exercise-trained ratsmight relate to an increase in myocardial contractility.
It has been reported that exercise training increasescontractile performance of rat hearts in vitro (5, 20, 42,43, 51). A study (51) on the effect of exercise training onexcitation-contraction coupling in the rat myocardiumdemonstrated that treadmill exercise enhances myo-cardial performance by increasing Ca2⫹ availability tothe contractile element. A further study is needed todetermine the effect of exercise training on myocardialcontractility in conscious rats, because it was not fea- Fig. 2. Effects of exercise training versus myocardial infarction (MI) sible for us to use a high-fidelity Millar catheter with a on cardiac gene expression of atrial natriuretic factor (ANF), ␣-skel- pressure transducer at the tip to obtain these measure- etal actin (SKA), and ␣-smooth muscle actin (SMA). Expression data ments in the conscious state.
were first normalized by dividing all values in a particular compar- The present study demonstrated a significant in- ison by the average expression in the corresponding control group, crease in stroke volume index at rest in conscious rats thus forcing the control average to be 1. Means ⫾ SE of thesenormalized data are displayed. *P ⬍ 0.05 and **P ⬍ 0.01 compared by exercise training. This is consistent with the finding with the respective control; n ⫽ 5 rats in each exercise and age- that exercise training significantly augments resting matched group, and n ⫽ 4 rats in each MI and sham group.
CARDIAC EFFECTS OF EXERCISE TRAINING ing heart in conscious and anesthetized normal ratsafter exercise training. With unchanged heart rate, theincreased stroke volume index would elevate cardiacindex in exercise-trained rats.
The incremental load on the heart after myocardial infarction reflects a blend of pressure and volume over-loading. The adaptation to this pathological load hasbeen shown to be associated with a unique molecularphenotype of altered myocardial gene expression. Thepresent study showed that LV expression of severalgenes, including atrial natriuretic factor, ␤-myosinheavy chain, ␣-skeletal actin, and ␣-smooth muscleactin, were increased 13 wk after myocardial infarc-tion. This is consistent with recent studies (22, 36, 64,65) that demonstrate the increased ventricular expres-sion of these genes coding for the fetal phenotypeduring ventricular remodeling after myocardial infarc-tion in rats. Less is known, however, about ventricularexpression of the fetal genes after chronic physiologicalloads. It has been reported that atrial natriuretic factorgene expression in the rat ventricle is unchanged aftertreadmill training (2) and minimally increased afterswimming training compared with a profound increaseafter chronic pathological loads in rats (9). The presentstudy is the first to demonstrate that cardiac adapta-tion to exercise training was not associated with the LVinduction of mRNA encoding the fetal contractile pro-teins (␤-myosin heavy chain, ␣-skeletal actin, and ␣-smooth muscle actin) in addition to atrial natriureticfactor.
In the present study, the LV mRNA level of ␣-myosin heavy chain was significantly increased after exercisetraining but not after myocardial infarction, whereasthere was an induction of LV ␤-myosin heavy chaingene in the infarct group but not in the exercise group.
It is known that the mature adult rat expresses mainly ␣-myosin heavy chain as the major contractile proteinin the LV. Our findings are consistent with the previ- Fig. 3. Effects of exercise training versus MI on cardiac gene expres- ous observations that a physiological load (exercise sion of ␣-myosin heavy chain (aMHC), ␤-myosin heavy chain(bMHC), collagen I (Col I), and collagen III (Col III). Expression data training) results in a further increase in the V myosin were first normalized by dividing all values in a particular compar- isoenzyme (␣-myosin heavy chain) and a pathological ison by the average expression in the corresponding control group, load induces a shift in the isoenzyme pattern from the thus forcing the control average to be 1. Means ⫾ SE of these V to V isoenzyme (␤-myosin heavy chain) in rats (37, normalized data are displayed. *P ⬍ 0.05 and **P ⬍ 0.01 compared with the respective control; n ⫽ 5 rats in each exercise and age- ␣-Myosin heavy chain is associated with high matched group, and n ⫽ 4 rats in each MI and sham group.
ATPase activity and increased contractility, whichmight contribute, in part, to the enhanced cardiacindex and stroke volume index observed in the exer-cise-trained rats. In contrast, ␤-myosin heavy chain Fig. 4. Hematoxylin and eosin-stained(a) and ApoTag-stained (b) sections ofmyocardial adjacent to the infarct atthe 4-day time point after MI. Individ-ual apoptotic cells exhibiting nuclearpyknosis and karryorhexis or labeledvia ApoTag are indicated (arrows).
CARDIAC EFFECTS OF EXERCISE TRAINING has a fivefold lower ATPase activity, conferring de- In contrast, there was no evidence of myocardial apo- creased velocity of shortening, and its expression in the ptosis 4 days, 10 days, and 13 wk after chronic running heart after myocardial infarction may be teleologically exercise. These data suggest that cardiomyocyte apo- attributable to the more efficient utilization of de- ptosis may play an important role in the early stage of creased energy reserves (37, 44).
cardiac adaptation to pathological loads but not to Experimental and clinical studies have demon- physiological loads. Accordingly, myocardial apoptosis strated an increase in interstitial collagens of the LV or appears to be a new index for distinction between nonischemic myocardium at a chronic or late stage cardiac adaptation to physiological loads and patholog- after myocardial infarction, which may enhance car- ical loads at the early period.
diac stiffness and result in diastolic dysfunction, finally It is known that the effect of exercise training on leading to heart failure (16, 22, 53, 55, 56). In contrast heart and body growth varies because of differences in to myocardial infarction, we found exercise training did species, age, sex, the mode or regimen of exercise not affect the cardiac mRNA of collagen I and III.
training, the disease model, etc. In rats, for example, Consistent with this finding, Burgess et al. (8) showed treadmill running is often associated with "relative that total collagen content in the LV is not altered in hypertrophy" (an increase in heart-to-BW ratio with exercise-trained rats compared with control rats but is unchanged absolute heart weight), whereas swimming significantly greater in the heart subjected to chronic training may cause "true cardiac hypertrophy" (an hypertension. In addition, we show that the LV gene increase in both heart-to-BW ratio and absolute heart expression of ␣-smooth muscle actin is substantially weight). The data on rats that have been exercise increased after myocardial infarction but is unchanged trained by swimming are confounded, however, by ex- after exercise training. Recent studies (1, 16) suggest perimental evidence that swimming produces addi- that ␣-smooth muscle actin expression by fibroblasts tional stress in the animals that may also contribute to and myofibroblasts contributes to collagen remodeling the induction of cardiac hypertrophy independent of and may play a role in mediating wound healing in the the exercise (38). Furthermore, a recent study (66) in heart after myocardial infarction.
rats after myocardial infarction showed that high-in- The pathological adaptation to pressure overload has tensity sprint training improved cardiac function and also been shown to be associated with an increase in increased cardiac expression of ␣-myosin heavy chain the expression of several marker genes, including but was associated with reduced myocyte hypertrophy.
atrial natriuretic factor, ␤-myosin heavy chain, ␣-skel- Perrault and Turcotte (38) reviewed animal and hu- etal actin, and collagens (28, 49, 58, 60), whereas car- man studies on exercise training over the past three diac expression of these marker genes were not decades and found that using cardiac hypertrophy as changed in exercise-trained animals in the present an expected adaptation to regular exercise may not be study. In addition, cardiac expression of ␣-myosin totally warranted. Although we did not find true car- heavy chain is decreased in pressure overload (49). In diac hypertrophy in the treadmill-trained rats com- contrast, this gene expression was upregulated after pared with age-matched sedentary controls, it is clear exercise training. Furthermore, mRNA levels of sarco- from our data that myocardial adaptation to treadmill (endo)plasmic reticulum Ca2⫹-ATPase and phospho- training is characterized by improved function (cardiac lamban have been reported to be depressed in rats with index and stroke volume index) and altered cardiac pressure overload (28, 49, 58, 60), but exercise training gene expression (induction of ␣-myosin heavy chain) did not alter cardiac expression of these two calcium and geometry (increased relative wall thickness).
handling genes. Thus compared with pathological ad- In summary, treadmill-trained rats displayed im- aptation to pressure overload, physiological adaptation proved cardiac function in association with a profile of to exercise training is also associated with distinct cardiac gene expression distinct from pathological car- alterations in cardiac molecular phenotype.
diac adaptation. The cardiac adaptation to exercise Recent studies have shown that apoptosis may be training was not associated with myocyte apoptosis, involved in the pathogenesis of heart remodeling after which also contrasted to cardiac remodeling in the pathological loads. With the use of an in situ assay, early phase after pathological loads.
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