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Personne :
Lachance, Dominic.

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Lachance

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Dominic.

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Département de Médecine expérimentale, Faculté de Médecine, Université Laval

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Voici les éléments 1 - 4 sur 4
  • PublicationAccès libre
    Moderate exercise training improves survival and ventricular remodeling in an animal model of left ventricular volume overload.
    (Lippincott Williams & Wilkins, 2009-09-15) Lachance, Dominic.; Roussel, Élise; Couët, Jacques; Champetier, Serge.; Drolet, Marie-Claude.; Plante, Éric; Arsenault, Marie
    BACKGROUND: Exercise training has beneficial effects in patients with heart failure, although there is still no clear evidence that it may impact on their survival. There are no data regarding the effects of exercise in subjects with chronic left ventricular (LV) volume overload. Using a rat model of severe aortic valve regurgitation (AR), we studied the effects of long-term exercise training on survival, development of heart failure, and LV myocardial remodeling. METHODS AND RESULTS: One hundred sixty male adult rats were divided in 3 groups: sham sedentary (n=40), AR sedentary (n=80), and AR trained (n=40). Training consisted in treadmill running for up to 30 minutes, 5 times per week for 9 months, at a maximal speed of 20 m/minute. All sham-operated animals survived the entire course of the protocol. After 9 months, 65% of trained animals were alive compared with 46% of sedentary ones (P=0.05). Ejection fractions remained in the normal range (all above 60%) and LV masses between AR groups were similar. There was significantly less LV fibrosis in the trained group and lower LV filling pressures and improved echocardiographic diastolic parameters. Heart rate variability was also improved by exercise. CONCLUSIONS: Our data show that moderate endurance training is safe, does not increase the rate of developing heart failure, and most importantly, improves survival in this animal model of chronic LV volume overload. Exercise improved LV diastolic function, heart rate variability, and reduced myocardial fibrosis.
  • PublicationAccès libre
    Effects of exercise in volume overload : insights from a model of aortic regurgitation
    (Lippincott Williams & Wilkins, 2009-06-01) Lachance, Dominic.; Roussel, Élise; Couët, Jacques; Bouchard Thomassin, Andrée-Anne; Champetier, Serge.; Plante, Éric; Arsenault, Marie
    Background : Aortic valve regurgitation (AR) imposes a pathologic volume overload to the left ventricle (LV), whereas aerobic exercise causes physiologic volume overloading. The impact of combining both LV volume overloads (pathologic and physiologic) is unknown. Considering the known beneficial effects of aerobic training on the cardiovascular system, we hypothesized that the positive effects would outweigh the negative ones and that exercise would improve the tolerance of the LV to AR. Methods : Forty female adult Wistar rats were randomly divided in the following groups: 1) sham sedentary (SS), 2) sham trained (ST), 3) AR sedentary (ARS), and 4) AR trained (ART). Training consisted in treadmill running for 30 min five times per week at 20 m·s−1 for 24wk. In vivo follow-up was made by echocardiography and invasive intracardiac pressure measurements. Hearts were harvested for tissue analysis. Results : Echocardiography revealed less LV dilation and hypertrophy in ART versus ARS as well as improved myocardial performance index. LV ejection fractions remained similar and within normal range in ART versus ARS. Invasive cardiac pressures yielded improved dP/dt− in ART versus ARS but similar dP/dt+. β1-Adrenergic receptor mRNA expression was improved in the ART group versus ARS. Conclusion : Our data suggest that a moderate aerobic exercise program helps minimize LV dilation and hypertrophy and improves diastolic cardiac performance in heart submitted to chronic volume overload due to severe aortic valve regurgitation in this animal model.
  • PublicationAccès libre
    Early left ventricular remodeling in acute severe aortic regurgitation : insights from an animal model.
    (Hertfordshire : ICR, 2008-05-03) Lachance, Dominic.; Roussel, Élise; Couët, Jacques; Drolet, Marie-Claude.; Plante, Éric; Arsenault, Marie
    BACKGROUND AND AIM OF THE STUDY: Chronic aortic regurgitation (AR) induces left ventricular (LV) hypertrophy and eventually LV dysfunction. While the effects of chronic AR on the left ventricle are well known, the effects of acute AR have not been adequately evaluated. It was hypothesized that the LV tissues would be rapidly remodeled by acute AR, and that the renin-angiotensin system would be involved in that acute remodeling. METHOD: The early LV adaptations to acute AR were evaluated serially over a period of 14 days, using a rat model. Adaptations were evaluated in vivo by echocardiography, and in vitro on explanted heart tissue after one, two, or 14 days. RESULTS: After 14 days, the left ventricle of AR rats was already significantly hypertrophied and dilated (end-diastolic diameter +16% (p <0.05) versus sham; LV mass +16% (p <0.01) versus sham). A short and transient increase in fractional shortening was observed during the first 48 h after AR induction. The cardiomyocyte cross-sectional area and perivascular fibrosis were significantly increased after 14 days of AR. The number of fibronectin-positive cells in LV sections rapidly increased, as did the fibronectin protein and mRNA content of LV crude homogenates. The expression of pro-matrix metalloproteinase 2 was clearly abnormal after two days. Significant shifts in the expression of angiotensin II receptors were also detected as early as one 1 day. CONCLUSION: Significant macroscopic and microscopic abnormalities were present in the left ventricle of rats with acute AR, soon after its induction. Considerable hypertrophy, perivascular fibrosis and extracellular matrix (ECM) remodeling were present after only 14 days. These results suggest that, in AR, the myocytes and ECM are affected significantly at a very early stage of the disease.
  • PublicationAccès libre
    Gene profiling of left ventricle eccentric hypertrophy in aortic regurgitation in rats : rationale for targeting the β-adrenergic and renin-angiotensin systems
    (American Physiological Society, 2009-03-01) Lachance, Dominic.; Roussel, Élise; Couët, Jacques; Bojmehrani, Azadeh; Beaudoin, Jonathan; Champetier, Serge.; Plante, Éric; Arsenault, Marie
    Aortic valve regurgitation (AR) imposes a severe volume overload to the left ventricle (LV), which results in dilation, eccentric hypertrophy, and eventually loss of function. Little is known about the impact of AR on LV gene expression. We, therefore, conducted a gene expression profiling study in the LV of rats with acute and severe AR. We identified 64 genes that were specifically upregulated and 29 that were downregulated out of 21,910 genes after 2 wk. Of the upregulated genes, a good proportion was related to the extracellular matrix. We subsequently studied a subset of 19 genes by quantitative RT-PCR (qRT-PCR) to see if the modulation seen in the LV after 2 wk persisted in the chronic phase (after 6 and 12 mo) and found that it did persist. Knowing that the adrenergic and renin-angiotensin systems are overactivated in our animal model, we were interested to see if blocking those systems using metoprolol (25 mg·kg−1·day−1) and captopril (100 mg·kg−1·day−1) would alter the expression of some upregulated LV genes in AR rats after 6 mo. By qRT-PCR, we observed that upregulations of LV mRNA levels encoding for procollagens type I and III, fibronectin, atrial natriuretic peptide, transforming growth factor-β2, and connective tissue growth factor were totally or partially reversed by this treatment. These observations provide a molecular rationale for a medical strategy aiming these systems in the medical treatment of AR and expand the paradigm in the study of this form of LV volume overload.