The Effects of Exercise Modality on Myosin Heavy Chain Isoform Remodeling in the Post-Infarct Myocardium

Date
2017
Authors
Cruger, Justin R.
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Abstract

Following myocardial infarction (MI), myosin heavy chain (MyHC) isoform expression shifts from α-MyHC to β-MyHC, which associates with contractile dysfunction. The purpose of this study was to evaluate the effects of resistance training (RT) and endurance training (ET) on the MyHC isoform shift in rats with MI. It was hypothesized that both RT and ET would beneficially attenuate post-MI cardiac remodeling and systolic dysfunction. MI was induced via surgical ligation of the left descending anterior coronary artery (LAD) in six-week-old male Sprague-Dawley rats. Sham-operated rats underwent identical surgical procedures, only without LAD ligation to serve as non-MI controls. Rats were assigned to 4 groups: Sham (no MI, no exercise; n=7), MI-Sed (MI, no exercise; n=7), MI-RT (MI+ resistance training; n=7), and MI-ET (MI+ endurance training; n=7). Exercise training began 1-week after surgery for the MI-RT and MI-ET groups and continued for 10 weeks. MI-RT training consisted of progressively weighted ladder climbs on a 1m ladder with 2cm grip steps inclined at 85º, 3 days per week. MI-ET exercise entailed 10-16m/min running on a rodent treadmill inclined to 5° for 50 minutes per day, 5 days per week. Results showed significant increases in highly contractile α-MyHC cardiac isoforms in both the MI-RT and MI-ET groups compared to MI-Sed (P<0.05). Furthermore, echocardiographic assessments revealed improvements in percent fractional shortening for both exercise groups which positively correlated with increases in α- to β-MyHC isoform ratios (P<0.05, R2=0.535). These results indicate beneficial effects of both RT and ET exercise modalities on post-infarct myocardial remodeling.

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Keywords
endurance training, exercise, heart, myocardial infarction, myosin heavy chain, resistance training
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Department
Health and Kinesiology