Aging- and training-induced alterations in collagen characteristics of rat left ventricle and papillary muscle

We evaluated the single and interactive effects of aging and exercise training on selected parameters of myocardial interstitium in both the left ventricle (LV) and LV papillary muscle of female Fischer 344 specific pathogen-free rats. Ten weeks of treadmill running resulted in significant LV hypertrophy as well as elevated plantaris muscle citrate synthase activity in both young adult (5-mo-old) and senescent (23-mo-old) trained animals (YT, young trained; OT, old trained) compared with age-matched sedentary controls (YC, young control; OC, old control). Proline and hydroxyproline pools were significantly higher (both P < 0.05) in 23-mo-old vs. 5-mo-old papillary muscles. Degree of maturation (nonreducible cross-linking) of LV collagen was evaluated by measurement of hydroxylysylpyridinoline concentration ([HP]). In a comparison of YC with OC rats, ventricular [HP] increased approximately fivefold from 0.059 ± 0.007 to 0.285 ± 0.018 (SE) mol HP/mol collagen (P < 0.001). Whereas training had no effect on ventricular [HP] in young adult rats, it significantly reduced LV collagen cross-linking in OT rats (0.131 ± 0.027) so that HP values in this group were less than one-half of those observed in OC rats. Because both collagen concentration and degree of cross- linking are thought to affect muscle stiffness characteristics, we conclude that the observed changes should be considered in any explanation for aging- and training-induced alterations in LV and papillary muscle contractile indexes.