Exercise Training Post-MI Favorably Modifies Heart Extracellular Matrix in the Rat

YENGO, C. M., S. D. ZIMMERMAN, R. J. McCORMICK, and D. P. THOMAS. Exercise Training Post-MI Favorably Modifies Heart Extracellular Matrix in the Rat. Med. Sci. Sports Exerc., Vol. 44, No. 6, pp. 1005-1012, 2012. Purpose: In order to assess the effect of daily exercise on extracellular matrix remodeling in the heart after myocardial infarction (MI), we measured collagen concentration (%COL) and nonreducible collagen cross-linking (hydroxylysylpyridinoline, HP) in the right ventricle (RV), and regionally within the infarcted (INF) and viable left ventricular free wall (LVF) and septum (LVS), using a rodent MI training model. Methods: Infarcts (19%-24% of LV) were surgically induced in adult rats that were assigned to either trained (MI-TR) or sedentary (MI-SED) groups and compared to sham-surgery sedentary controls (SHAM). Results: In LVF, 10 wk of treadmill running had no effect on the increase (P < 0.001) in %COL seen with MI (MI-SED = 7.14%+/- 0.15%, MI-TR = 7.61%+/- 0.19%, SHAM = 3.55%+/- 0.19%). However, it normalized the increase (P < 0.05) in HP cross-linking (MI-SED = 0.43 +/- 0.02, MI-TR = 0.27 +/- 0.03, SHAM = 0.30 +/- 0.04 mol HP.mol(-1) collagen). The INF scar in MI-SED rats showed a sevenfold increase in %COL (P < 0.001) compared to SHAM LVF myocardium, an increase that was attenuated by training (MI-SED = 26%+/- 1% vs MI-TR = 21%+/- 2%; P < 0.05). However, training had no effect on MI-induced increases in cross-linking in the INF scar (1.01 +/- 0.22 vs 0.84 +/- 0.14 mol HP.mol(-1) collagen). In LVS, although a small but significant increase in %COL was seen in both MI groups, HP cross-linking was unaltered compared to SHAM rats. Training also normalized the increase observed in cross-linking in RV after MI. Conclusions: Because increased HP cross-linking in the heart is associated with decreased chamber compliance, these findings may help to explain the improved heart function seen after daily exercise in cardiac rehabilitation patients.