Abstract
Purpose: In this study, we investigated the effect of treadmill exercise training on cardiac hypertrophy, collagen deposition, echo parameters and serum levels of cardiac troponin I (cTnI) in rats, and how they differ with various exercise intensities, hence exploring potential signal transduction.Methods: Male Sprague-Dawley rats were randomly divided into sedentary (SED), low-intensity running (LIR), medium-intensity running (MIR), and high-intensity running (HIR) groups. Each exercise group had 3 subgroups that were sacrificed for cardiac tissue analyses at 1, 4, and 8 weeks, respectively, and all rats participated in a daily 1 h treadmill routine 5 days per week. Echocardiographic measurements were performed 24 h after the last exercise session. Additionally, myocardium samples and blood were collected for histological and biochemical examinations. Changes in the extracellular signal-regulated kinases 1/2 (ERK1/2) signal pathway were detected by Western blotting.Results: After a week of running, ventricular myocyte size and the phosphorylation of ERK1/2 increased in the HIR group, while left ventricular (LV) diastolic diameter values and LV relative wall thickness increased in the LIR and MIR groups. In addition, we observed heart enlargement, cTnI decrease, and ERK1/2 signal activation in each of the exercise groups after 4 weeks of running. However, the HIR group displayed substantial rupture and increased fibrosis in myocardial tissue. In addition, compared with the LIR and MIR groups, 8 weeks of HIR resulted in structural damage, fiber deposition, and increased cTnI. However, there was no difference in the activation of ERK1/2 signaling between the exercise and SED groups.Conclusion: The effect of running on cardiac hypertrophy was intensity dependent. In contrast to LIR and MIR, the cardiac hypertrophy induced by 8 weeks of HIR was characterized by potential cardiomyocyte injury, which increased the risk of pathological development. Furthermore, the ERK signaling pathway was mainly involved in the compensatory hypertrophy process of the myocardium in the early stage of exercise and was positively correlated with exercise load. However, long-term exercise may attenuate ERK signaling activation.
Highlights
Exercise and physical activity are effective ways to reduce the risk of cardiovascular diseases, such as heart attack and stroke, and can provide valuable benefits beyond those of medications
Pathological hypertrophy is initially induced as a compensatory response to the growth of the ventricle, this kind of hypertrophy progresses to ventricular chamber dilatation, with wall thinning through the loss of myocytes and contractile dysfunction, resulting in adverse cardiovascular events (Nakamura and Sadoshima, 2018)
When comparing the heart mass (HM)/body mass (BM) ratios, 4 and 8 weeks of different treadmill running intensities resulted in a significant increase (p < 0.05), no significant differences were found between the SED group and other exercise groups after 1 week, which was consistent with the gross morphologic examination
Summary
Exercise and physical activity are effective ways to reduce the risk of cardiovascular diseases, such as heart attack and stroke, and can provide valuable benefits beyond those of medications. Studies in animal models of exercise-induced cardiac hypertrophy (here in response to treadmill exercise, voluntary wheel running, and swim training) have shown preserved or enhanced contractile function and relative cardiac hypertrophy (Konhilas et al, 2004; Radovits et al, 2013; Mi et al, 2019). Most studies have shown that low- and moderate-intensity exercise attenuates abnormal cardiac remodeling and myocardial dysfunction and improves functional capacity (Mi et al, 2019; Pagan et al, 2019). Given that intensity dependence for cardiac function remains controversial, it is imperative to better understand how different treadmill running intensities alter the phenotype of the murine heart
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