Influence of acetaminophen consumption and exercise on Achilles tendon structural properties in male Wistar rats

Chronic consumption of acetaminophen (APAP) during exercise training leads to a reduction in tendon stiffness and modulus compared with a placebo. We explored whether this effect could be due to a reduction in tendon collagen content or cross-linking. Ten-week-old male Wistar rats (n = 50) were divided into placebo or APAP groups and into sedentary or treadmill-exercised groups. APAP (200 mg/kg) or saline was administered once daily by oral gavage. Rats in the exercise groups ran on a treadmill 5 days per week for 8 wk with progression to 60 min per day, 20 m/min, and 8° incline. After 8 wk, lyophilized Achilles tendon samples were assayed for the collagen-specific amino acid hydroxyproline and cross-linking [hydroxylyslpyridinoline (HP)] content by high-performance liquid chromatrography. Collagen content was not influenced by exercise or APAP (P > 0.05). Compared with placebo, tendon water content was 7% (P = 0.006, main effect) lower in animals consuming APAP (placebo: 54.79 ± 0.8%, APAP: 50.89 ± 1.2%). HP in the Achilles tendon was 36% greater (sedentary: 141 ± 15, exercise: 204 ± 26 mmol/mol collagen) in the exercise-trained rats independent of drug treatment (P = 0.020, main effect). Independent of exercise, HP content was 33% lower (P = 0.032, main effect) in the animals consuming APAP (placebo: 195 ± 21, APAP: 140 ± 19 mmol/mol collagen). Our data suggests that chronic consumption of APAP results in a reduction in collagen cross-linking and a loss of tissue water independent of chronic exercise. This reduction in cross-linking and water content could contribute to the decrease in tendon stiffness noted in humans chronically consuming APAP.     

Patellar tendon matrix changes associated with aging and voluntary exercise

Male rats maintained under constant environmental conditions were randomly assigned to nonrunner (NR) and voluntary exercise (R) groups. At 9 mo, voluntary exercise significantly increased muscle cytochrome c concentration and citrate synthase activity. Also, at the same age, R animals had significantly greater glycosaminoglycan concentration than NR, but no changes in dry weight and collagen concentration were significant. By age 28 mo, the R groups had reduced daily running by 70%, and elevation of tendon glycosaminoglycans relative to NR animals was no longer statistically significant. A similar trend was noted for muscle mitochondrial markers. Aging significantly decreased tendon glycosaminoglycans and increased collagen concentration. Although aging reduced the total amount of voluntary exercise, the concentration of tendon glycosaminoglycans in 28-mo-old runners was equivalent to levels in 9-mo-old sedentary rats, suggesting that voluntary exercise slowed the decline in galactosamine-containing glycosaminoglycans with aging.     

Relative systolic dysfunction in female spontaneously hypertensive rat myocardium.

Hypertension and exercise independently induce left ventricular (LV) remodeling and alter LV function. The purpose of this study was to determine systolic and diastolic LV pressure-volume relationships (LV-PV) in spontaneously hypertensive rats (SHR) with and without LV hypertrophy, and to determine whether 6 mo of exercise training modified the LV-PV in SHR. Four-month-old female SHR (n = 20), were assigned to a sedentary (SHR-SED) or treadmill-trained (SHR-TRD) group (approximately 60% peak O2 consumption, 5 days/wk, 6 mo), while age-matched female Wistar-Kyoto rats (WKY; n = 13) served as normotensive controls. The LV-PV was determined using a Langendorff isolated heart preparation at 4 (no hypertrophy: WKY, n = 5; SHR, n = 5) and 10 mo of age (hypertrophy: WKY, n = 8; SHR-SED, n = 8; SHR-TRD, n = 7). At 4 mo, the LV-PV in SHR was similar to that observed in WKY controls. However, at 10 mo of age, a rightward shift in the LV-PV occurred in SHR. Exercise training did not alter the extent of the shift in the LV-PV relative to SHR-SED. Relative systolic function, i.e., relative systolic elastance, was approximately 50% lower in SHR than WKY at 10 mo of age (P < 0.05). Doppler-derived LV filling parameters [early wave (E), atrial wave (A), and the E/A ratio] were similar between groups. LV capacitance was increased in SHR at 10 mo (P < 0.05), whereas LV diastolic chamber stiffness was similar between groups at 10 mo. Hypertrophic remodeling at 10 mo of age in female SHR is manifest with relative systolic decompensation and normal LV diastolic function. Exercise training did not alter the LV-PV in SHR.     

Low-intensity exercise training delays onset of decompensated heart failure in spontaneously hypertensive heart failure rats

Data regarding the effectiveness of chronic exercise training in improving survival in patients with congestive heart failure (CHF) are inconclusive. Therefore, we conducted a study to determine the effect of exercise training on survival in a well-defined animal model of heart failure (HF), using the lean male spontaneously hypertensive HF (SHHF) rat. In this model, animals typically present with decompensated, dilated HF between approximately 18 and 23 mo of age. SHHF rats were assigned to sedentary or exercise-trained groups at 9 and 16 mo of age. Exercise training consisted of 6 mo of low-intensity treadmill running. Exercise training delayed the onset of overt HF and improved survival (P < 0.01), independent of any effects on the hypertensive status of the rats. Training delayed the myosin heavy chain (MyHC) isoform shift from alpha- to beta-MyHC that was seen in sedentary animals that developed HF. Exercise was associated with a concurrent increase in cardiomyocyte length (approximately 6%), width, and area and prevented the increase in the length-to-width ratio seen in sedentary animals in HF. The increases in proteinuria, plasma atrial natriuretic peptide, and serum leptin levels observed in rats with HF were suppressed by low-intensity exercise training. No significant alterations in sarco(endo)plasmic reticulum Ca2+ ATPase, phospholamban, or Na+/Ca2+ exchanger protein expression were found in response to training. Our results indicate that 6 mo of low-intensity exercise training delays the onset of decompensated HF and improves survival in the male SHHF rat. Similarly, exercise intervention prevented or suppressed alterations in several key variables that normally occur with the development of overt CHF. These data support the idea that exercise may be a useful and inexpensive intervention in the treatment of HF.     

Skeletal muscle lipid peroxidation in exercised and food-restricted rats during aging

The effects of chronic endurance exercise and food restriction on nonenzymatic lipid peroxidation (LP) of gastrocnemius muscle during aging were studied in male, Fischer 344 rats. One set of rats aged 6 and 18 mo were assigned to an exercise group (treadmill running) or an age-matched sedentary control group. After 6 mo (at the ages of 12 and 24 mo), LP and levels of alpha-tocopherol and its oxidized form, alpha-tocopheryl quinone, were measured. The extent of LP was determined in homogenates by measuring the content of thiobarbituric acid-reactive substances. After homogenization, the muscles were immediately evaluated for basal LP and also incubated in the presence of oxidant stressors for 2 h to assess antioxidant capacity (AOC) and for 24 h to estimate total peroxidizable lipid (TPL). Basal LP was not affected by age or exercise. AOC was not affected by exercise at either age. However aging significantly decreased AOC and increased alpha-tocopheryl quinone in both sedentary and exercised groups. TPL was not affected by age, but was increased by exercise training (P less than 0.05). Another set of rats was divided into the following three groups at 3 mo of age: sedentary, fed ad libitum (S); sedentary, caloric restricted by alternate day feeding (R); and exercised by forced treadmill running (E). Two years later, when the rats were 27 mo of age, the extent of LP was assessed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Attenuation of age-related declines in glucagon-mediated signal transduction in rat liver by exercise training

This study investigated alterations in glucagon receptor-mediated signal transduction in rat livers from 7- to 25-mo-old animals and examined the effects of exercise training on ameliorating these changes. Sixty-six young (4 mo), middle-aged (12 mo), and old (22 mo) male Fischer 344 rats were divided into sedentary and trained (treadmill running) groups. Isolated hepatic membranes were combined with [(125)I-Tyr(10)]monoiodoglucagon and nine concentrations of glucagon to determine maximal binding capacity (B(max)) and dissociation constant (K(d)). No alterations were found in B(max) among groups; however, middle-aged trained animals had significantly higher glucagon affinity (lower K(d); 21.1 +/- 1.8 nM) than did their untrained counterparts (50.2 +/- 7.1 nM). Second messenger studies were performed by measuring adenylyl cyclase (AC) specific activity under basal conditions and with four pharmacological stimulations to assess changes in receptor-dependent, G protein-dependent, and AC catalyst-dependent cAMP production. Age-related declines were observed in the old animals under all five conditions. Training resulted in increased cAMP production in the old animals when AC was directly stimulated by forskolin. Stimulatory G protein (G(s)) content was reduced with age in the sedentary group; however, training offset this decline. We conclude that age-related declines in glucagon signaling capacity and responsiveness may be attributed, in part, to declines in intrinsic AC activity and changes in G protein [inhibitory G protein (G(i))/G(s)] ratios. These age-related changes occur in the absence of alterations in glucagon receptor content and appear to involve both G protein- and AC-related changes. Endurance training was able to significantly offset these declines through restoration of the G(i)/G(s) ratio and AC activity.     

Time course of collagen and decorin changes in rat cardiac and skeletal muscle post-MI

We examined the temporal relationship between messages (type I and type III mRNAs) for the principal fibrillar procollagens and subsequent collagen accretion, cross-linking, and decorin expression in the left ventricle (LV) postmyocardial infarction (post-MI). We sought to determine 1) what role the proteoglycan decorin plays in extracellular matrix (ECM) remodeling known to take place as a consequence of MI and 2) the extent skeletal muscle ECM is altered early post-MI. Therefore, after surgically induced production of small- to moderate-sized infarcts (approximately 20% of LV mass), extent and time course of ECM remodeling was evaluated in remaining viable LV free wall and in slow- [soleus (SOL)] and fast-twitch [gastrocnemius (GAST)] skeletal muscles. Decorin, collagen, and hydroxylysylpyridinium cross-link concentrations and alpha1(I) (type I) and alpha1(III) (type III) procollagen mRNAs were measured in LVs from noninfarcted controls and at 72 h, 1, 2, 5, and 13 wk post-MI. These same data were collected in SOL and GAST muscles at all time points except 13 wk. Type I procollagen mRNA increased at both 72-h and 1-wk time points in LVs. Type III procollagen mRNA was elevated at 1 wk, returning to baseline by 2 wk post-MI. Collagen concentration was significantly increased by 1 wk, more than doubled by 5 wk, and was elevated 129% by 13 wk in the remaining viable LV. LV decorin expression was unaltered at early time points, but increased 38% at 5 wk post-MI and doubled by 13 wk post-MI. In skeletal muscle, procollagen mRNAs were transiently altered in SOL and GAST muscles without any demonstrable effect on the measured ECM parameters. This study reports, for the first time, the upregulation time course of decorin and its relationship to increased HP cross-linking and accumulation of collagen in viable myocardium post-MI.     

Exercise training and beta-blocker treatment ameliorate age-dependent impairment of beta-adrenergic receptor signaling and enhance cardiac responsiveness to adrenergic stimulation

Cardiac beta-adrenergic receptor (beta-AR) signaling and left ventricular (LV) responses to beta-AR stimulation are impaired with aging. It is shown that exercise and beta-AR blockade have a favorable effect on cardiac and vascular beta-AR signaling in several cardiovascular diseases. In the present study, we examined the effects of these two different strategies on beta-AR dysregulation and LV inotropic reserve in the aging heart. Forty male Wistar-Kyoto aged rats were randomized to sedentary, exercise (12 wk treadmill training), metoprolol (250 mg.kg(-1).day(-1) for 4 wk), and exercise plus metoprolol treatment protocols. Ten male Wistar-Kyoto sedentary young rats were also used as a control group. Old trained, old metoprolol-treated, and old trained plus metoprolol-treated rats showed significantly improved LV maximal and minimal first derivative of the pressure rise responses to beta-AR stimulation (isoproterenol) compared with old untrained animals. We found a significant reduction in cardiac sarcolemmal membrane beta-AR density and adenylyl cyclase activity in old untrained animals compared with young controls. Exercise training and metoprolol, alone or combined, restored cardiac beta-AR density and G-protein-dependent adenylyl cyclase activation in old rats. Although cardiac membrane G-protein-receptor kinase 2 levels were not upregulated in untrained old compared with young control rats, both exercise and metoprolol treatment resulted in a dramatic reduction of G-protein-receptor kinase 2 protein levels, which is a further indication of beta-AR signaling amelioration in the aged heart induced by these treatment modalities. In conclusion, we demonstrate for the first time that exercise and beta-AR blockade can similarly ameliorate beta-AR signaling in the aged heart, leading to improved beta-AR responsiveness and corresponding LV inotropic reserve.     

Cardiac dysfunction in aging conscious rats: altered cardiac cytoskeletal proteins as a potential mechanism

The objective of this study was to test the hypothesis that the mechanism mediating left ventricular (LV) dysfunction in the aging rat heart involves, in part, changes in cardiac cytoskeletal components. Our results show that there were no significant differences in heart rate, LV pressure, or LV diameter between conscious, instrumented young [5.9 +/- 0.3 mo (n = 9)] and old rats [30.6 +/- 0.1 mo (n = 10)]. However, the first derivative of LV pressure (LV dP/dt) was reduced (8,309 +/- 790 vs. 11,106 +/- 555 mmHg/s, P < 0.05) and isovolumic relaxation time (tau) was increased (8.7 +/- 0.7 vs. 6.3 +/- 0.6 ms, P < 0.05) in old vs. young rats, respectively. The differences in baseline LV function in young and old rats, which were modest, were accentuated after beta-adrenergic receptor stimulation with dobutamine (20 mug/kg), which increased LV dP/dt by 170 +/- 9% in young rats, significantly more (P < 0.05) than observed in old rats (115 +/- 5%). Volume loading in anesthetized rats demonstrated significantly impaired LV compliance in old rats, as measured by the LV end-diastolic pressure and dimension relationship. In old rat hearts, there was a significant (P < 0.05) increase in the percentage of LV collagen (2.4 +/- 0.2 vs. 1.3 +/- 0.2%), alpha-tubulin (92%), and beta-tubulin (2.3-fold), whereas intact desmin decreased by 51%. Thus the cardiomyopathy of aging in old, conscious rats may be due not only to increases in collagen but also to alterations in cytoskeletal proteins.     

Age-related changes in conducted vasodilation: effects of exercise training and role in functional hyperemia

Conducted vasodilation may coordinate blood flow in microvascular networks during skeletal muscle contraction. We tested the hypotheses that 1) exercise training enhances conducted vasodilation and 2) age-related changes in the capacity for conduction affect muscle perfusion during contractions. To address hypothesis 1, young (4-5 mo), adult (12-14 mo), and old (19-21 mo) C57BL6 male mice were sedentary or given access to running wheels for 8 wk. Voluntary running distances were significantly different (in km/day): young = 5.8 +/- 0.1, adult = 3.9 +/- 0.1, old = 2.2 +/- 0.1 (P < 0.05). In gluteus maximus muscles, conducted vasodilation was greater in adult than in young or old mice (P < 0.05) and greater in young sedentary than in old sedentary mice but was not affected by exercise training. Citrate synthase activity was greater with exercise training at all ages (P < 0.05). mRNA for endothelial nitric oxide synthase did not differ among ages, but endothelial nitric oxide synthase protein expression was greater in adult and old mice with exercise training (P < 0.05). Connexin 37, connexin 40, and connexin 43 mRNA were not affected by exercise training and did not differ by age. To address hypothesis 2, perfusion of the gluteus maximus muscle during light to severe workloads was assessed by Doppler microprobe at 3-26 mo of age. Maximum perfusion decreased linearly across the lifespan. Perfusion at the highest workload, absolute and relative to maximum, decreased across the lifespan, with a steeper decline beyond approximately 20 mo of age. In this model, 1) exercise training does not alter conducted vasodilation and 2) muscle perfusion is maintained up to near maximum workloads despite age-related changes in conducted vasodilation.     

Alterations in myocardial signal transduction due to aging and chronic dynamic exercise

Roth, David A., Cynthia D. White, Deborah A. Podolin, andRobert S. Mazzeo. Alterations in myocardial signal transduction due to aging and chronic dynamic exercise. J. Appl. Physiol.84(1): 177-184, 1998.Normal aging without disease leads todiminished chronotropic and inotropic responses to catecholaminestimulation, resulting in depressed cardiac function with stress. Thepurpose of this study was to determine molecular mechanisms fordecrements in adrenergic responsiveness of the left ventricle (LV) dueto aging and to study the effects of chronic dynamic exercise on signaltransduction. We measured -adrenergic receptor (-AR) density,adenylyl cyclase (AC) activity, and G-protein content and distributionin LV from 66 male Fischer 344 rats from three age groups that wereeither sedentary or treadmill trained (60 min/day, 5 days/wk, 10 wk at75% of the maximal capacity). Final ages were 7 mo(young), 15 mo (middle-age), and 25 mo (old). There was no significantdifference in -AR density among groups as a function of age ortraining. AC production of adenosine 3,5-cyclic monophosphate (cAMP)with the use of five pharmacological stimulations revealed that oldsedentary myocardium had depressed basal, receptor-dependent, G-protein-dependent, and AC catalyst stimulation (30-43%)compared with hearts from young and middle-age sedentary rats. Training did not alter AC activity in either middle-age or old groups but didincrease G-protein-dependent cAMP production in young myocardium (12-34%). Immunodetectable concentrations of stimulatory andinhibitory G proteins (G_s and G_i, respectively)showed 43% less total G_s with similar G_icontent in hearts from old sedentary compared with middle-age sedentaryrats. When compared with young sedentary animals, G_icontent was 39 and 50% higher in middle-age sedentary and oldsedentary myocardium, respectively. With age, there was a significantshift in the -subunit of G_s distribution from cytosolic fractions of LV homogenates to membrane-bound fractions (8-12% redistribution in middle-age sedentary vs. old sedentary). The mostsignificant training effect was a decrease in G_i content inhearts from old trained rats (23%), which resulted in values comparable with young sedentary rats and reduced theG_i/G_s ratio by 27% in old-rat LV. We reportthat age-associated reductions in cardiovascular -adrenergicresponsiveness correspond with alterations in postreceptor adrenergicsignaling rather than with a decrease in receptor number. Chronicdynamic exercise partially attenuates these reductions throughalterations in postreceptor elements of cardiac signal transduction.

     

Influence of exercise on the immune function of rats of various ages

The purpose of this study was to determine whether exercise could prevent the age-related decline in mitogenesis, which has been well documented in rats, mice, and humans. At 1, 6, 12, and 18 mo of age, male Fischer F344 rats were subjected daily to swimming exercise for 6 mo. At the end of the 6-mo training period, spleen lymphocytes were isolated from the exercised rats and from age-matched sedentary controls. The induction of lymphocyte proliferation was measured with the mitogens concanavalin A (ConA) and lipopolysaccharide (LPS). In addition, the ability of the lymphocytes to produce interleukin 2 (IL 2) in response to ConA induction was measured. ConA- and LPS-induced proliferation decreased 41-63% between 7 and 25 mo of age in both exercised and sedentary control rats. ConA-induced IL 2 production decreased 42 and 62% between 7 and 25 mo of age for exercised and sedentary control rats, respectively. Although the age-related decline in mitogen-induced proliferation and IL 2 production was smaller in exercised rats, this was due to a lower level of mitogenesis and IL 2 production in lymphocytes from young exercised rats. Exercise resulted in a significant decrease (23-32%) in mitogen-induced lymphocyte proliferation and IL-2 production in 7-mo-old exercised rats compared with 7-mo-old sedentary rats. However, in the 18- and 24-mo-old rats, mitogen-induced lymphocyte proliferation and IL 2 production was not significantly different between exercised and sedentary control rats.     

Exercise training alters the effect of chronic hypoxia on myocardial adrenergic and muscarinic receptor number.

Chronic hypoxic exposure results in elevated sympathetic activity leading to downregulation of myocardial alpha(1)- and beta-adrenoceptors (alpha(1)-AR, beta-AR). On the other hand, it has been shown that sympathetic activity is reduced by exercise training. The objective of this study was to determine whether exercise training could modify the changes in receptor expression associated with acclimatization. Four groups of rats were studied: normoxic sedentary rats (NS), rats living and training in normoxia (NTN), sedentary rats living in hypoxia (HS, inspired PO(2) = 110 Torr), and rats living and training in hypoxia (HTH, inspired PO(2) = 110 Torr). Training consisted of running in a treadmill at 80% of maximal O(2) uptake during 10 wk. Myocardial receptor density was measured by radioactive ligand binding. Right ventricular (RV) hypertrophy occurred in HS but not in HTH. No effect of exercise was detected in RV weight of normoxic rats. Acclimatization to hypoxia (HS vs. NS) resulted in a decrease in both alpha(1)- and beta-AR density, whereas muscarinic receptor (M-Ach) expression increased. Hypoxic exercise training (HS vs. HTH) moderated beta-AR downregulation and M-Ach upregulation and prevented the fall in alpha(1)-AR density. Normoxic training (NS vs. NTN) did not change beta-AR density. On the other hand, densities of alpha(1)-AR in both ventricles as well as RV M-Ach increased in NTN vs. NS. The data show that exercise training in hypoxia 1) prevents RV hypertrophy, 2) suppresses the downregulation of alpha(1)-AR in the left ventricle (LV) and RV, and 3) attenuates the changes in both beta-AR and M-Ach receptor density in LV and RV. Exercise training in normoxia increases M-Ach receptor expression in the RV.     

Muscle atrophy and hypoplasia with aging: impact of training and food restriction

The purpose of this work is to study the influence of aging, training, and food restriction on skeletal muscle mass and fiber number. Male Fischer 344 rats (n = 49) at 3 mo postpartum were assigned to three groups: 1) sedentary control (confined to cage), 2) exercise trained (18 m/min, 8 degrees grade, 20 min/day, 5 days/wk), or 3) food restricted (alternate days of free access and no access to food). At 12 and 27 mo postpartum the soleus and extensor digitorum longus (EDL) muscles were excised, weighed, and fiber number was quantified after HNO3 digestion. At 27 mo the masses of soleus and EDL muscles of sedentary control rats were 83 and 70%, respectively, of 12-mo values (138 +/- 5 and 151 +/- 4 mg). At 27 mo, soleus muscle mass of trained rats was 113% of sedentary control values, whereas EDL muscle mass was unaffected by training. At 27 mo, food restriction had no effect on the mass of both muscles compared with 27-mo sedentary control values. Fiber number was not affected by training or food restriction in both muscles. Fiber number for soleus and EDL muscles of combined groups declined with age by 5.6 and 4.2%, respectively. With aging, the small loss of muscle fibers can account at most for approximately 25% of the observed skeletal muscle atrophy.     

Peak exercise stroke volume: associations with cardiac structure and diastolic function.

One of the most debilitating effects of primary aging is the decline in aerobic exercise capacity. One of its causes is an age-related decline in peak exercise stroke volume. This study's main purpose was to determine the cardiovascular adaptations to aging that most influence peak exercise stroke volume in the elderly. We hypothesized that increased left ventricular (LV) filling and mild concentric LV remodeling would be associated with an increase in peak exercise stroke volume corrected for lean body mass (LBM) and that an increased augmentation index (AI), which is a marker of arterial stiffness, would be associated with a decrease. A second aim was to determine the adaptations to aging that most influence LV concentric remodeling in the elderly. We hypothesized that AI would be a predictor of LV mass/LBM and the LV posterior wall thickness-to-LV radius ratio (h/r). We performed a cross-sectional study of cardiac and vascular adaptations to aging in 52 sedentary, elderly subjects. LV filling [as measured by the early-to-late transmitral flow velocity ratio (E/A)] was inversely correlated with and was an independent predictor of peak exercise stroke volume/LBM and was also a predictor of LV remodeling. AI was a predictor of LV remodeling (LV mass/LBM) but not of peak exercise stroke volume/LBM. We conclude that 1) maintenance of LV filling (E/A <1) is associated with a higher peak exercise stroke volume/LBM in very elderly subjects and thus may be a useful adaptation that enhances stroke volume during peak exercise, 2) LV remodeling and AI are less influential on peak exercise stroke volume/LBM, and 3) AI was the most important predictor of LV remodeling.     

Aging, exercise, and endothelial progenitor cell clonogenic and migratory capacity in men.

Numerical and functional impairment of circulating endothelial progenitor cells (EPCs) is thought to contribute to vascular aging and the associated increase in cardiovascular risk. We tested the following hypotheses: 1) EPC clonogenic and migratory capacity decrease progressively with age in healthy, sedentary adult men; and 2) regular aerobic exercise will improve EPC clonogenic and migratory capacity in previously sedentary middle-aged and older men. Peripheral blood samples were collected from 46 healthy sedentary men: 10 young (26 +/- 1 yr), 15 middle-aged (47 +/- 1 yr), and 21 older (63 +/- 1 yr). Mononuclear cells were isolated and preplated for 2 days, and nonadherent cells were further cultured for 7 days to determine EPC colony-forming units. Migratory activity of EPCs was determined using a modified Boyden chamber. Ten sedentary middle-aged and older men (59 +/- 3 yr) were studied before and after a 3-mo aerobic exercise intervention. The number of EPC colony-forming units was approximately 75% lower (P < 0.01) in middle-aged (12 +/- 3) and older (8 +/- 2) compared with young (40 +/- 7) men. There was no difference in colony count between middle-aged and older men. EPC migration (fluorescent units) was significantly reduced in older (453 +/- 72) compared with young (813 +/- 114) and middle-aged (760 +/- 114) men. The exercise intervention increased (P < 0.05) both EPC colony-forming units (10 +/- 3 to 22 +/- 5) and migratory activity (683 +/- 96 to 1,022 +/- 123) in previously sedentary middle-aged and older men. These results provide further evidence that aging adversely affects EPC function. Regular aerobic-endurance exercise, however, is an effective lifestyle intervention strategy for improving EPC clonogenic and migratory capacity in middle-aged and older healthy men.     

Effect of exercise training on passive stiffness in locomotor skeletal muscle: role of extracellular matrix

The purpose ofthis study was to evaluate the effect of endurance exercise training onboth locomotor skeletal muscle collagen characteristics and passivestiffness properties in the young adult and old rat. Young(3-mo-old) and senescent (23-mo-old) male Fischer 344 rats wererandomly assigned to either a control or exercise training group[young control (YC), old control (OC), young trained (YT), oldtrained (OT)]. Exercise training consisted of treadmill runningat ~70% of maximal oxygen consumption (45 min/day, 5 days/wk, for 10 wk). Passive stiffness (stress/strain) of the soleus (Sol) muscle fromall four groups was subsequently measured in vitro at 26°C.Stiffness was significantly greater for Sol muscles in OC rats comparedwith YC rats, but in OT rats exercise training resulted in muscles withstiffness characteristics not different from those in YC rats. Solmuscle collagen concentration and the level of the nonreduciblecollagen cross-link hydroxylysylpyridinoline (HP) significantlyincreased from young adulthood to senescence. Although training had noeffect on Sol muscle collagen concentration in either age group, itresulted in a significant reduction in the level of Sol muscle HP in OTrats. In contrast, exercise had no effect on HP in the YT animals.These findings indicate that 10 wk of endurance exercise significantlyalter the passive viscoelastic properties of Sol muscle in old but notin young adult rats. The coincidental reduction in the principalcollagen cross-link HP also observed in response to training in OTmuscle highlights the potential role of collagen in influencing passivemuscle viscoelastic properties.

     

Effect of exercise training on aortic collagen content in spontaneously hypertensive rats (SHR)

We investigated the effects of exercise training on the amount of aortic collagen and systolic blood pressure in spontaneously hypertensive rats (SHR). Ten-week old SHR were trained either by forced treadmill running (26.8 m X min-1 -1 h X day-1, five times a week, 0% incline) or by voluntary running in revolving wheels (7,800 m X day-1 at peak) for 8 weeks. Succinate dehydrogenase (SDH) activity measured as a marker of an endurance training effect was 13% higher (P less than 0.01) in the soleus of forced-exercised animals than in that of sedentary ones. (6.56 +/- 0.17 mumol X g-1 X min-1; mean +/- SEM), whereas SDH activity in that of voluntarily-exercised group was found to be at the same level as in sedentary animals. The systolic blood pressure after training increased by 26.4 in sedentary, 21.1 in voluntarily-exercised, and 33.9 mm Hg in forced-exercised rats, when compared with the value of each group at the beginning of the training program. A significant difference was observed in the increment of blood pressure only between the voluntarily- and forced-exercised groups (P less than 0.05). The amount of aortic collagen in voluntarily-trained rats (96.5 +/- 2.0 mg X g tissue-1, 39.8 +/- 0.7 mg X 100 mg protein-1) was significantly less than that in forced-trained rats (P less than 0.05). These results suggest that voluntary, mild exercise training may be more effective in the reduction of collagen accumulation in the aorta associated with the suppression of blood pressure increase than forced, vigorous exercise training in SHR.     

Exercise training improves aging-induced downregulation of VEGF angiogenic signaling cascade in hearts

Exercise training improves aging-induced deterioration of angiogenesis in the heart. However, the mechanisms underlying exercise-induced improvement of capillary density in the aged heart are unclear. Vascular endothelial growth factor (VEGF) is implicated in angiogenesis, which activated angiogenic signaling cascade through Akt and endothelial nitric oxide synthase (eNOS)-related pathway. We hypothesized that VEGF angiogenic signaling cascade in the heart contributes to a molecular mechanism of exercise training-induced improvement of capillary density in old age. With the use of hearts of sedentary young rats (4 mo old), sedentary aged rats (23 mo old), and exercise-trained aged rats (23 mo old, swim training for 8 wk), the present study investigated whether VEGF and VEGF-related angiogenic molecular expression in the aged heart is affected by exercise training. Total capillary density in the heart was significantly lower in the sedentary aged rats compared with the sedentary young rats, whereas that in the exercise-trained rat was significantly higher than the sedentary aged rats. The mRNA and protein expressions of VEGF and of fms-like tyrosine kinase-1 (Flt-1) and fetal liver kinase-1 (Flk-1), which are main VEGF receptors, in the heart were significantly lower in the sedentary aged rats compared with the sedentary young rats, whereas those in the exercise-trained rats were significantly higher than those in the sedentary aged rats. The phosphorylation of Akt protein and eNOS protein in the heart corresponded to the changes in the VEGF protein levels. These findings suggest that exercise training improves aging-induced downregulation of cardiac VEGF angiogenic signaling cascade, thereby contributing to the exercise training-induced improvement of angiogenesis in old age.