Sedentary Hearts Research Articles

Ischemic Preconditioning Efficacy Following Anabolic Steroid Usage: A Clear Difference Between Sedentary and Exercise-Trained Rat Hearts.

Previous studies show that anabolic steroids impair innate cardioprotective mechanisms. Here, we investigated the effect of supraphysiological doses of nandrolone on ischemic preconditioning (IPC) as a potent cardioprotective tool against ischemia reperfusion (IR) injury in rat hearts. Male Wistar rats in two experimental settings of sedentary and exercise-trained (60min/day swimming, 5days/week, for 8weeks) were either pretreated with intramuscular injections of arachis oil (Arach, n = 16) as vehicle or nandrolone decanoate (ND, n = 8), 10mg/kg/week, for 8weeks. At the end, the hearts were excised and perfused in a Langendorff system. Then, the vehicle-treated hearts subdivided into the IR (30min of LAD coronary artery occlusion and 120min reperfusion, n = 8) and IPC (three cycles of 3-min ischemia and 3-min reperfusion before test ischemia, n = 8) groups and nandrolone-treated hearts served as ND + IPC (nandrolone pretreatment before IR and IPC protocols, n = 8) group. Post-ischemic cardiac function and infarct size were assessed. Reperfusion arrhythmias were analyzed using a standard scoring system. In sedentary hearts, ND slightly increased heart-to-body weight ratio and increased baseline cardiac contractile function. In trained hearts, ND markedly increased heart-to-body weight ratio which was also associated with enhanced baseline cardiac function. ND pretreatment enhanced protective effects of IPC in sedentary group; however, abolished these effects in exercise-trained group. The arrhythmia score was not significantly different between nandrolone-treated groups vs. respective preconditioned groups. Our findings show that ND impairs IPC-induced cardioprotection in exercise-trained rat hearts. Cardiac hypertrophy seems to play a crucial role in this response.

Untargeted metabolomics analysis of ischemia–reperfusion-injured hearts ex vivo from sedentary and exercise-trained rats

The effects of exercise on the heart and its resistance to disease are well-documented. Recent studies have identified that exercise-induced resistance to arrhythmia is due to the preservation of mitochondrial membrane potential. To identify novel metabolic changes that occur parallel to these mitochondrial alterations, we performed non-targeted metabolomics analysis on hearts from sedentary and exercise-trained rats challenged with isolated heart ischemia-reperfusion injury (I/R). Eight-week old Sprague-Dawley rats were treadmill trained 5 days/week for 6 weeks (exercise duration and intensity progressively increased to 1 h at 30 m/min up a 10.5% incline, 75-80% VO2max). The recovery of pre-ischemic function for sedentary rat hearts was 28.8 ± 5.4% (N = 12) compared to exercise trained hearts, which recovered 51.9% ± 5.7 (N = 14) (p < 0.001). Non-targeted GC-MS metabolomics analysis of (1) sedentary rat hearts; (2) exercise-trained rat hearts; (3) sedentary rat hearts challenged with global ischemia-reperfusion (I/R) injury; and (4) exercise-trained rat hearts challenged with global I/R (10/group) revealed 15 statistically significant metabolites between groups by ANOVA using Metaboanalyst (p < 0.001). Enrichment analysis of these metabolites for pathway-associated metabolic sets indicated a > 10-fold enrichment for ammonia recycling and protein biosynthesis. Subsequent comparison of the sedentary hearts post-I/R and exercise-trained hearts post-I/R further identified significant differences in three metabolites (oleic acid, pantothenic acid, and campesterol) related to pantothenate and CoA biosynthesis (p ≤ 1.24E-05, FDR ≤ 5.07E-4). These studies shed light on novel mechanisms in which exercise-induced cardioprotection occurs in I/R that complement both the mitochondrial stabilization and antioxidant mechanisms recently described. These findings also link protein synthesis and protein degradation (protein quality control mechanisms) with exercise-linked cardioprotection and mitochondrial susceptibility for the first time in cardiac I/R.

Abstract 335: Exercise Protects the Heart by Preserving Mitochondrial Membrane Potential During Early Reperfusion

Exercise evokes adaptations intrinsic to the myocardium that protect against ventricular arrhythmia, yet the underlying mechanisms are not completely understood. We have previously shown that the transition to arrhythmia occurs concomitant with a collapse in mitochondrial membrane potential (ΔΨm). As our previous studies indicated that exercise preserves intracellular redox homeostasis, which directly influences mitochondrial energetics, we hypothesized that rats exposed to exercise (Ex, 10 d of treadmill running) would be protected against reperfusion arrhythmia via better maintenance of ΔΨm. To fully understand the temporal relationship between ΔΨm and cardiac electrical activity, two-photon microscopy images (using the fluorescent probe TMRM) and volume-conducted electrocardiogram were simultaneously recorded. Langendorff-perfused hearts underwent 40/30 min of ischemia/reperfusion. Exercise lowered the incidence of arrhythmia, with 3 of 8 Ex hearts experiencing tachycardia or fibrillation compared to 7 of 8 sedentary (Sed) hearts. Ex prevented the collapse of ΔΨm during the first 10 min of reperfusion (74±6.4% v 57±1.5% of baseline fluorescence intensity; P&lt;0.05). To gain a more comprehensive understanding of energetics throughout the heterogeneous mitochondrial population, we then measured mean TMRM fluorescence intensity in isolated ventricular mitochondria harvested after reperfusion using flow cytometry (n=100,000 events per group). Interestingly, mean fluorescence intensity for ΔΨm was similar in Ex and Sed mitochondria (278±33 v 309 ±44 AU, respectively). Mitochondrial respiratory control ratios were also similar in Ex and Sed (9.03±0.70 v 9.00±0.92, respectively). Taken together, the isolated mitochondrial assessment did not reflect what was observed in vivo. This suggests that either intracellular factors influenced in vivo mitochondrial energetics, or our isolated mitochondria may have been enriched with predominantly healthy mitochondria. Our studies demonstrate for the first time that exercise prevents electrical dysfunction following an ischemic insult through better preservation of mitochondrial energetics, and that this preservation is only observed in the intact organ.

0012: Cardiac effects of a treatment with prolyl-hydroxylase inhibitors (PHI), used to improve exercise performance, in sedentary and trained rats

Stabilization of the Hypoxia Inducible Factor (HIF) using prolyl-hydroxylase inhibitors (PHI) leads to an EPO synthesis which is suspected to be used as a doping practice. Such a treatment is suspected to improve endurance performance by increasing oxygen transport. However the effects of a PHI treatment on heart morphology and function has never been investigated. Therefore the aim of this study was to evaluate whether potential effects of PHI on cardiac function could contribute to explain its beneficial effect on aerobic performance. We tested the effects of a 1 week treatment with a PHI (DMOG, 150 mg.kg –1 , I.P.) or a placebo (NaCl) on both sedentary (Sed) and trained rats (Ex; trained during 5 weeks before treatment started; 40min at 25 m.min –1 per day; 5days/week). Our first result was that PHI increased running performance (+12%, p<0,05) in both Sed and Ex groups. This increased performance was associated with a major increase in total hemoglobin in PHI-treated animals (+13% p<0,05). However, regarding cardiac function and cardiac remodeling no beneficial effect of PHI was observed. Indeed, in hearts of sedentary as well as exercised rats no significal change in any morphological parameters (LVEDs, LVEDd, AWTd, PWTd and RWT) was found. Moreover, no change in systolic function likely to explain enhanced exercise performance was observed in PHI-treated hearts, when evaluated by intraventricular pressure probe (Millar®). Finally it is interesting to note that in sedentary rat hearts an impairment of diastolic function characterized by an altered E/A and dp/dt min ratios was found when they were challenged with isoproterenol (0,5 mg.kg -1 ). These last results obtained in sedentary hearts could suggest that a more prolonged treatment with such PHI could have deleterious consequences on heart health and point out the danger of such a doping strategy; however, this point remains to be more precisely investigated.

Exercise-induced cardioprotection: a role for eNOS uncoupling and NO metabolites

Exercise is an efficient strategy for myocardial protection against ischemia-reperfusion (IR) injury. Although endothelial nitric oxide synthase (eNOS) is phosphorylated and activated during exercise, its role in exercise-induced cardioprotection remains unknown. This study investigated whether modulation of eNOS activation during IR could participate in the exercise-induced cardioprotection against IR injury. Hearts isolated from sedentary or exercised rats (5 weeks training) were perfused with a Langendorff apparatus and IR performed in the presence or absence of NOS inhibitors [N-nitro-L-arginine methyl ester, L-NAME or N5-(1-iminoethyl)-L-ornithine, L-NIO] or tetrahydrobiopterin (BH₄). Exercise training protected hearts against IR injury and this effect was abolished by L-NAME or by L-NIO treatment, indicating that exercise-induced cardioprotection is eNOS dependent. However, a strong reduction of eNOS phosphorylation at Ser1177 (eNOS-PSer1177) and of eNOS coupling during early reperfusion was observed in hearts from exercised rats (which showed higher eNOS-PSer1177 and eNOS dimerization at baseline) in comparison to sedentary rats. Despite eNOS uncoupling, exercised hearts had more S-nitrosylated proteins after early reperfusion and also less nitro-oxidative stress, indexed by lower malondialdehyde content and protein nitrotyrosination compared to sedentary hearts. Moreover, in exercised hearts, stabilization of eNOS dimers by BH4 treatment increased nitro-oxidative stress and then abolished the exercise-induced cardioprotection, indicating that eNOS uncoupling during IR is required for exercise-induced myocardial cardioprotection. Based on these results, we hypothesize that in the hearts of exercised animals, eNOS uncoupling associated with the improved myocardial antioxidant capacity prevents excessive NO synthesis and limits the reaction between NO and O₂·- to form peroxynitrite (ONOO⁻), which is cytotoxic.

Abstract 278: Exercise Training Ameliorates LV Dysfunction in Mice with a Calcium Influx Mediated Cardiomyopathy

Background— Ca 2+ influx through L-type Ca 2+ channels (LTCCs) induces Ca 2+ release from the SR to induce and regulate cardiac contraction. We have characterized a mouse model with cardiac-specific expression of the β2a subunit of the LTCC (β2a), leading to pathological hypertrophy due to excessive LTCC Ca 2+ entry. Chronic exercise causes physiological hypertrophy in normal hearts. We determined if swim training improved or further deranged the performance of β2a mice. Methods and Results— β2a (n=12) and WT (n=20) mice were swim trained for 21 consecutive days. ECHO was performed at beginning and end of swim training. Ejection fraction (EF) and fractional shortening (FS) increased significantly with swim training in WT animals. (EF pre-swim: 57±2.02% vs. post-swim: 70±2.88%; FS pre-swim: 30±1.34% vs. post-swim: 39±2.42%). β2a mice were hypercontractile before swimming and had no significant change after training (EF pre-swim: 70±1.75% vs. post-swim: 74.06±2.72%; FS pre-training: 38±2.38% vs. post-training: 42±2.22%). Contractile performance was significantly greater in β2a mice versus WT before but not after training. There was a significant increase in HW/BW [mg/gm] ratio in trained WT (n=8) versus sedentary WT (n=8) (swim: 5.75±0.19 vs. sed: 4.63±0.2) but training did not cause additional hypertrophy in β2a (n=8) versus sedentary (n=7) (swim: 5.98±0.31 vs. sed: 5.96±0.25). Isolated WT and β2a hearts were placed on a Langendorff apparatus and a balloon was inserted into the LV to record isovolumic pressure. Each heart underwent 15 min of ischemia followed by 30 min of reperfusion. End diastolic pressure (EDP) increased in all hearts during ischemia. There were no protective effects of training on ischemia-induced increases in EDP in WT hearts. EDP increased more in sedentary β2a during ischemia but this effect was eliminated in trained β2a hearts. LV developed pressure (LVDP) fell with ischemia and partially recovered with reperfusion. LVDP recovery was significantly greater in trained versus sedentary WT hearts. Swim training also significantly improved LVDP recovery in β2a hearts. Conclusions— Chronic exercise training reduces pathological hypertrophy and damaging effects of ischemia in a murine model of LTCC overexpression.

Abstract 19552: Exercise-Induced Changes in Mechanotransduction Improve Myocardial Function in a Porcine Model of Chronic Occlusion

Introduction: Exercise training has been shown to improve cardiac dysfunction both in patients and animal models of coronary artery disease; however, the underlying cellular and molecular mechanisms have not been completely understood. Transmembrane integrins that connect the extracellular matrix (ECM) and intracellular cytoskeleton are important for mechanotransduction in cardiomyocytes. Hypothesis: The binding probability and adhesion force between integrins-ECM, and their subsequent signaling that is cell stiffness will be increased in the myocytes from exercise-trained animals when compared to the sedentary group. Methods: Ameroid occluders were surgically placed around the proximal left circumflex coronary artery of adult female Yucatan pigs. Twenty-two weeks postoperatively, myocardium was isolated from non-occluded and collateral-dependent regions of sedentary and exercise trained (treadmill run; 5 days/wk for 14 wks) pigs. We used atomic force microscopy for measuring cell stiffness and adhesion force between integrin and fibronectin (FN) in pig cardiomyocytes. In addition, integrins and FN expression were determined. Results: While exercise-trained pigs showed an increase in β1 integrin expression, β3 integrin expression was detected at an increased level in the sedentary myocardium. An increase in the amount of total FN and its fragments were found in the myocardium from collateral-dependent regions of exercise-trained and sedentary pigs when compared to the non-occluded myocardium regions. The peak bond rupture force of FN-integrin (46.4±0.3 pN vs 34.8±0.2 pN), the probability of adhesion (72% vs 54%) and cell stiffness (67.9±4.7 kPa vs 29.0±1.8 kPa) were significantly increased (p&lt;0.05; n=10) in myocytes from exercise-trained pigs when compared to sedentary hearts, which were prevented by function blocking α5 and αv integrin antibodies, respectively. Conclusion: Our data demonstrate that the differences seen in adhesion force, probability and stiffness between the sedentary and exercise-trained myocytes are due to interactions of FN to different integrins, e.g., αvβ3 in sedentary and α5β1 in exercise-trained cells, suggesting potential importance of mechanotransduction pathway for therapeutic development.

Ischemia reperfusion injury, KATPchannels, and exercise-induced cardioprotection against apoptosis

Exercise is a potent stimulus against cardiac ischemia reperfusion (IR) injury, although the protective mechanisms are not completely understood. The study purpose was to examine whether the mitochondrial or sarcolemmal ATP-sensitive potassium channel (mito K(ATP) or sarc K(ATP), respectively) mediates exercise-induced cardioprotection against post-IR cell death and apoptosis. Eighty-six, 4-mo-old male Sprague Dawley rats were randomly assigned to treadmill exercise (Ex; 30 m/min, 3 days, 60 min, ∼70 maximal oxygen uptake) and sedentary (Sed) treatments. Rats were exposed to regional cardiac ischemia (50 min) and reperfusion (120 min) or Sham (170 min; no ligation) surgeries. Exercise subgroups received placebo (saline), 5-hydroxydecanoate (5HD; 10 mg/kg ip), or HMR1098 (10 mg/kg ip) to inhibit mito K(ATP) or sarc K(ATP) channel. Comprehensive outcome assessments included post-IR ECG arrhythmias, cardiac tissue necrosis, redox perturbations, and autophagy biomarkers. No arrhythmia differences existed between exercised and sedentary hearts following extended-duration IR (P < 0.05). The sarc K(ATP) channel was confirmed essential (P = 0.002) for prevention of antinecrotic tissue death with exercise (percent infarct, Sed = 42%; Ex = 20%; Ex5HD = 16%; ExHMR = 42%), although neither the mito K(ATP) (P = 0.177) nor sarc K(ATP) (P = 0.274) channel provided post-IR protection against apoptosis (terminal deoxynucleotidyl transferase deoxy UTP-mediated nick-end labeling-positive nuclei/mm(2), Sham = 1.8 ± 0.5; Sed = 19.4 ± 6.7; Ex = 7.5 ± 4.6; Ex5HD = 14.0 ± 3.9; ExHMR = 11.1 ± 1.8). Exercise preconditioning also appears to preserve basal autophagy levels, as assessed by Beclin 1 (P ≤ 0.001), microtubule-associated protein-1 light-chain 3B ratios (P = 0.020), and P62 (P ≤ 0.001), in the hours immediately following IR. Further research is needed to better understand these findings and corresponding redox changes in exercised hearts.

Swim-exercised mice show a decreased level of proteinO-GlcNAcylation and expression ofO-GlcNAc transferase in heart

Swim-training exercise in mice leads to cardiac remodeling associated with an improvement in contractile function. Protein O-linked N-acetylglucosamine (O-GlcNAcylation) is a posttranslational modification of serine and threonine residues capable of altering protein-protein interactions affecting gene transcription, cell signaling pathways, and general cell physiology. Increased levels of protein O-GlcNAcylation in the heart have been associated with pathological conditions such as diabetes, ischemia, and hypertrophic heart failure. In contrast, the impact of physiological exercise on protein O-GlcNAcylation in the heart is currently unknown. Swim-training exercise in mice was associated with the development of a physiological hypertrophy characterized by an improvement in contractile function relative to sedentary mice. General protein O-GlcNAcylation was significantly decreased in swim-exercised mice. This effect was mirrored in the level of O-GlcNAcylation of individual proteins such as SP1. The decrease in protein O-GlcNAcylation was associated with a decrease in the expression of O-GlcNAc transferase (OGT) and glutamine-fructose amidotransferase (GFAT) 2 mRNA. O-GlcNAcase (OGA) activity was actually lower in swim-trained than sedentary hearts, suggesting that it did not contribute to the decreased protein O-GlcNAcylation. Thus it appears that exercise-induced physiological hypertrophy is associated with a decrease in protein O-GlcNAcylation, which could potentially contribute to changes in gene expression and other physiological changes associated with exercise.

Effects of Forskolin on Inotropic Performance and Phospholamban Phosphorylation in Exercise-Trained Hypertensive Myocardium

Beta-adrenergic receptor (beta-AR) responsiveness is downregulated in left ventricular (LV) hypertrophy induced by chronic hypertension. While exercise training in hypertension enhances beta-AR responsiveness, the role of adenylyl cyclase remains unclear. The purpose of the present study was to test whether treadmill running in the spontaneously hypertensive rat (SHR) model improves LV responsiveness to forskolin (FOR) or the combination of FOR + isoproterenol (FOR+ISO). Female SHR (16-wk) were randomly placed into sedentary (SHR-SED; n = 7) or treadmill-trained (SHR-TRD; n = 8) groups. Wistar-Kyoto (WKY; n = 7) animals acted as normotensive controls. Langendorff, isovolumic LV performance was established at baseline and during incremental FOR infusion (1 and 5 micromol/l) and FOR+ISO (5 micromol/l + 1x10(-8) mol/l). Heart rate, systolic blood pressure, and heart-to-body weight ratio were lower in WKY relative to both SHR groups (P < 0.05). LV performance and heart rate significantly increased in all groups to a similar extent with incremental FOR infusion. However, in the presence of 5 micromol/l FOR, ISO increased LV developed pressure, positive change in LV pressure, and negative change in LV pressure to a greater extent in SHR-TRD relative to SHR-SED (P < 0.05). Phospholamban phosphorylation at the Thr17 was greater in SHR-TRD relative to SHR-SED and WKY (P < 0.05). Absolute LV developed pressure was moderately correlated with phospholamban phosphorylation at both the Ser16 (r = 0.64; P < 0.05) and Thr17 (r = 0.52; P < 0.05). Our data suggest that the adenylyl cyclase step in the beta-AR cascade is not downregulated in the early course of hypertension and that the enhanced beta-AR responsiveness with training is likely mediated at levels other than adenylyl cyclase. Our data also suggest that beta-AR inotropic responsiveness in the presence of direct adenylyl cyclase agonism is improved in trained compared with sedentary SHR hearts.

Exercise does not Attenuate Increased Fatty Acid Metabolism in Ex Vivo Diabetic Hearts

Diabetes mellitus produces an altered metabolic phenotype in the heart, with increased fatty acid oxidation and decreased glucose metabolism. This study determined whether regular exercise training could attenuate the consequences of enhanced cardiac fatty acid (FA) oxidation in streptozotocin-injected type 1 diabetic mice (T1D). Control (CD-1) and diabetic mice were exercised (EX) by running for 60 min/d, 5 d/wk for 6 wk at low-moderate intensity. Non-exercised sedentary (SED) groups were also studied. Hearts from T1D and control mice at 12 weeks of age were subjected to a 60-min working heart perfusion with glucose and palmitate. Oxidation of radiolabeled palmitate (complexed to albumin) was measured (μmol/min/g dry weight) along with parameters of contractile function. Diabetic mice exhibited hyperglycemia compared to CD-1 controls (P<0.01). Importantly, EX T1D group showed a significant 12% reduction in plasma glucose levels compared to T1D SED mice (41.4 vs 50.3 mM). Hearts from CD-1 and T1D groups showed no changes with exercise for any of the measured parameters of contractile function. Palmitate oxidation was increased by nearly 2-fold in T1D SED hearts compared to CD-1 SED hearts (0.72±0.12 vs 0.40±0.05 μmol/min/g dry weight). However, steady-state rates of palmitate oxidation were not significantly different between T1D SED and T1D EX hearts (0.72±0.12 vs 0.63±0.08). These results suggest fatty acid oxidation rates during perfusion, although significantly elevated in the diabetic heart, are not altered by exercise. As well 6 weeks of low-moderate exercise is not enough to improve diabetic cardiac function. However, lower blood glucose levels in T1D EX mice suggest a beneficial effect of exercise on whole-body glucose utilization. Supported by CIHR (DS).

Exercise‐Induced Increase in Pro‐ and Macroglycogen Content in Hearts from Type 1 Diabetic Mice

Diabetes adversely affects glucose metabolism, resulting in elevated levels of heart glycogen. Exercise training increases glycogen synthesis activity in diabetes; therefore the aim of this study was to examine the effects of exercise on glycogen content in hearts from streptozotocin-induced (insulin-deficient for duration of study) type 1 diabetic mice (T1D) mice compared to CD-1 controls. Mice were exercised by running for 60 min/d, 5 d/wk for 6 wk at low-moderate intensity. Hearts from T1D and control mice at 12 wk of age were subjected to a 60 min working heart perfusion with glucose and palmitate, prior to glycogen measurements (μmol/g dw) as total glycogen (Gt), proglycogen (PG) and macroglycogen (MG). Gt for T1D sedentary (SED) hearts was not significantly different from SED or exercised (EX) non-diabetic, CD1 controls. In T1D SED hearts, PG contributed 60% of total glycogen, which was significantly elevated compared to EX controls but not to SED controls. EX T1D hearts showed a nearly 2-fold increase in Gt compared to SED diabetic hearts (935±86 vs 584±20) with PG and MG contributing 558±21 and 436±80 glucosyl units respectively. There are intriguing aspects of this data: i) there was no difference in Gt between SED T1D and controls implying glycogen synthesis is not impaired in T1D hearts. (ii) Elevated PG levels in T1D hearts reflects a distinct selective process in glycogen formation compared to controls, suggesting T1D hearts form new granules at the expense of MG to maintain Gt. (iii) An exercise-induced improvement in glucose disposal may account for elevated PG and MG levels in EX T1D perfused hearts. Supported by CIHR (DS) and Genome Alberta (JS).

Antioxidants and ecto‐5′‐nucleotidase are not involved in the training‐induced cardioprotection against ischaemia–reperfusion injury

Isolated Langendorff-perfused hearts from sedentary and prolonged (24 weeks) treadmill-trained rats were subjected to 30 min of normoxic perfusion either alone or followed by 20 min of global ischaemia, or by 20 min of global ischaemia and 15 min of normoxic reperfusion. Pre-ischaemic values of antioxidant enzyme activities and ecto-5'-nucleotidase activity were not different in sedentary and trained hearts but a 5-fold increase of 72-kDa heat shock protein (HSP72) levels was detected in trained myocardium. After ischaemia and reperfusion (I/R), metabolic recovery was better in trained than in sedentary hearts as indicated by higher ATP and creatine phosphate levels. However, antioxidant enzymatic activities, glutathione reductase, and total and mitochondrial superoxide dismutase decreased in trained rats after I/R, whereas they remained unchanged in the sedentary ones. Ecto-5'-nucleotidase activity was modified by I/R in sedentary as well as in trained hearts while HSP72 content did not change. Ecto-5'-nucleotidase activity and HSP72 content increased in parallel by the 30-min perfusion period. In conclusion, the cardioprotection induced by long-term training could be mediated by the exercise-induced increase in HSP72 levels and is not related to enhanced antioxidant systems or ecto-5'-NT activity.

Prior exercise training improves the outcome of acute myocardial infarction in the rat: Heart structure, function, and gene expression

The aim of this research was to investigate the structural, functional, and molecular features of the remodeling heart in prior swim-trained infarcted rats. Physical exercise training is a known protective factor against cardiovascular morbidity and mortality. The structural and molecular aspects underlying this protection in the remodeling heart have not been investigated. After seven weeks of swimming exercise training, rats underwent surgical ligation of the left coronary artery followed by a four-week sedentary period. Untrained control rats underwent the same surgical protocol. Left ventricular function was assessed by echocardiography four weeks after infarction, and hearts were sampled for histological and molecular analysis. Ribonucleic acid from the surviving left ventricle was analyzed by complementary deoxyribonucleic acid arrays followed by Northern blotting or quantitative reverse transcription polymerase chain reaction of selected messenger ribonucleic acids (mRNAs). Scar area was 1.6-fold smaller (p = 0.0002), arteriolar density was 1.7-fold higher (p = 0.0002), and left ventricular shortening fraction was 1.9-fold higher (p = 0.003) in the exercise-trained compared with sedentary hearts. Eleven genes whose expression level varied by at least +/-1.5-fold distinguished the prior exercised rats from their sedentary counterparts. Compared with sedentary, the exercised hearts displayed 9- and 2.4-times lower levels of atrial natriuretic peptide and aldolase mRNA (p = 0.03 and 0.04, respectively), and a 2.7- and 1.9-fold higher abundance of cytochrome c-oxidase and fatty acid binding protein, respectively (p < 0.03, each). Swimming exercise training before acute myocardial infarction reduces scar size, increases arteriole density, and manifests adaptation of stress- and energy-metabolism-related genes that may contribute to the improved heart function observed during remodeling.

Altered basal and adenosine‐mediated protein flux from coronary arterioles isolated from exercise‐trained pigs

The aim of the study was to determine if and by what mechanism(s) nitric oxide inhibition modulates the susceptibility of the duodenum to hydrochloric acid-induced disturbances of mucosal integrity. A second aim was to investigate whether basal permeability is a determinant of epithelial acid barrier function. Using an in situ duodenal perfusion model, mucosal permeability, alkaline secretion and morphology were investigated in anaesthetized rats. Luminal perfusion with 50 mM hydrochloric acid increased duodenal mucosal permeability in the control animals. In animals receiving the nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME 3 mg kg(-1) and 1 mg kg(-1) h(-1)) and in those receiving vasopressin (1 IU kg(-1) h(-1)), however, the mean increase in permeability in response to acid was markedly higher. In rats treated with either hexamethonium (20 mg kg(-1)) or atropine (0.5 mg kg(-1)) L-NAME failed to augment the acid-induced increase in permeability. Perfusion with hypotonic saline (25 mM) increased basal permeability but did not influence the response to acid. Exposure of the duodenum to hydrochloric acid caused very subtle changes of duodenal morphology. It is concluded that both inhibition of endogenous nitric oxide synthesis and vasopressin treatment augment the acid-induced increase in mucosal permeability. The mechanisms involved may be related to changes of Starling forces in the microcirculatory bed. Endogenous nitric oxide may protect the duodenal mucosa by regulating vascular permeability and interstitial fluid pressure.

Altered basal and adenosine-mediated protein flux from coronary arterioles isolated from exercise-trained pigs.

Solute flux per unit surface area and concentration gradient, (J(S)/SdeltaC), was quantified in arterioles isolated from hearts of sedentary (SED) and exercise-trained (EX) female Yucatan Miniature Swine. Apparent permeability (P(S)) was assessed from measures of J(S)/SdeltaC for two proteins, alpha-lactalbumin (alpha-lact) and porcine serum albumin (PSA), under basal conditions and following 5 min suffusion with 10(-5) M adenosine (ADO). Both proteins were labelled with the fluorescent dye tetramethyl rhodamine isothiocyanate. Basal P(S) to alpha-lact differed with exercise training ((P(S)alpha-lact)SED = 5.2+/-1.8 (median+/-median absolute deviation (MAD), n = 9 pigs) versus (P(S)alpha-lact)EX = 7.4+/-1.1 x 10(-7) cm s(-1), n = 9, P < 0.05). For the larger protein PSA, basal P(S) did not change with training (P(S)PSA)SED = 50+/-1.6, N = 11 vs. (P(S)PSA)EX = 4.1+/-1.2 x 10(-7) cm s(-1), N = 11). Suffusion of the arterioles (33+/-4 microm diameter, n = 18 vessels) from SED hearts (n = 14) with 10(-5) M ADO decreased P(S)alpha-lact 15+/-8% relative to control and was without effect on P(S)PSA. By contrast, in arterioles (39+/-4 microm diameter, n = 22 vessels) from EX hearts (n = 14), ADO increased P(S)alpha-lact and P(S)PSA by 32 and 65% respectively, indicating that receptor-mediated changes in permeability were also sensitive to exercise training. These data demonstrate that, for coronary arterioles, permeability to macromolecules adapts to exercise training. The adaptive mechanisms may involve more than one structural component of the vessel wall as the changes in permeability were size-dependent.

Physical conditioning and membrane receptors for cardioregulatory hormones.

To seek possible mechanisms for the relative bradycardia induced by physical conditioning we studied the effects of an eight-week swimming programme upon cardiac beta-adrenergic and muscarinic-cholinergic receptors in rats. A training effect was documented by an increase in the ratio of heart wet weight to body weight in the conditioned animals compared with sedentary controls. Cardiac beta-adrenergic receptors as assessed in crude membrane fractions by the binding of (-) (3H) dihydroalprenolol did not differ significantly in either number or affinity in conditioned hearts (30 +/- 2 fmol.mg-1 protein; KD = 1.4 +/- 0.1 nmol.litre-1) compared with sedentary hearts (33 +/- 2 fmol.mg-1; KD = 1.5 +/- 2 nmol.litre-1). Likewise cardiac muscarinic-cholinergic receptors as assessed by the binding of (3H) quinuclidinyl benzilate to crude cardiac membranes did not differ significantly in either number or affinity in conditioned hearts (116 +/- 6 fmol.mg-1 protein; KD = 0.17 +/- 0.03 nmol.litre-1) compared with sedentary hearts (125 +/- 11 fmol.mg-1; KD = 0.19 +/- 0.03 nmol.litre-1). We conclude that the bradycardia of physical training is probably mediated by mechanisms other than alterations in cardiac beta-adrenergic or muscarinic-cholinergic receptors.