Age-Dependent Myocardial Remodeling and Fibrotic Vulnerability in Rats Subjected to Resistance-Loaded Swimming
DOI:
https://doi.org/10.52340/GBMN.2026.01.01.172Keywords:
Aging, Cardiac Fibrosis, Cardiac Remodeling, Echocardiography, Left Ventricle, Rat Model, Resistance Exercise, SwimmingAbstract
BACKGROUND. Aging is characterized by cardiomyocyte loss, extracellular matrix expansion, increased ventricular stiffness, and reduced stress reserve. Exercise can induce adaptive cardiac hypertrophy, but sustained high-intensity overload may also promote maladaptive remodeling and fibrosis. Rodent swimming models with external loading are widely used to intensify exercise demand, yet age-stratified structural responses of the myocardium remain insufficiently characterized. OBJECTIVES. To evaluate age-related differences in functional and histopathological myocardial remodeling in rats subjected to resistance-loaded swimming. METHODS. Twenty-one (n=21) male Wistar rats were stratified into juvenile (3–4 months), adult (12–13 months), and geriatric (18–19 months) cohorts, with 7 (n=7) animals per cohort. All animals underwent a 6-week swimming protocol with a tail load equal to 4% of body weight. Hearts were harvested 24 hours after the final session and examined histologically using hematoxylin-eosin and Masson trichrome staining. Two blinded observers performed systematic assessment of four left ventricular regions. Fibrosis was quantified as percentage collagen area using digital image analysis. RESULTS. Resistance-loaded swimming induced distinct age-dependent patterns of myocardial remodeling. Juvenile rats exhibited mild vascular congestion with minimal fibrosis (mean collagen area: 1.9±0.8%). Adult rats displayed the most extensive injury, characterized by marked perivascular and interstitial fibrosis (mean collagen area: 7.8±2.1%) and multifocal cardiomyocyte necrosis. Geriatric rats showed dystrophic changes with moderate focal fibrosis (mean collagen area: 4.6±1.5%). Differences in fibrosis among age cohorts were statistically significant (p<0.001, one-way ANOVA). CONCLUSIONS. In this rat model, resistance-loaded swimming induced age-dependent myocardial remodeling. Adult animals’ physiological adaptation from maladaptive remodeling when interpreting cardiac responses to high-intensity exercise across the lifespan.References
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