[Myocardial contractility and morphological changes in vital organs in 24-month-old rats with isoproterenol-induced...

Aim - an appropriate experimental model is required to investigate the development of chronic heart failure in the elderly and to evaluate pharmacological interventions. Models based on aged animals remain insufficiently characterized. To assess the degree of impairment in myocardial contractility and morphological changes in vital organs in 24-month-old rats with isoproterenol-induced chronic heart failure. Chronic heart failure was induced in 24-month-old male Wistar rats (550-600 g) by subcutaneous injections of isoproterenol hydrochloride (ISO; Sigma-Aldrich, USA). Animals in the experimental group (n=7) received ISO at a dose of 10 mg/kg four times at 3-day intervals. Control animals (n=7) received equivalent volumes of saline according to the same protocol. Sixty days after the final injection, cardiac pump function was assessed in isolated hearts using the Langendorff perfusion technique. Tissue samples from the myocardium, kidneys, lungs, and brain were fixed in formalin, stained with hematoxylin and eosin, and subjected to histopathological examination. Cardiomyocyte myofibrillar structure was evaluated using polarization microscopy. Heart rate was significantly higher in the experimental group compared with controls. At the same time, no statistically significant differences were observed in contractility parameters of isolated perfused hearts between the groups. Histological examination of myocardial, renal, pulmonary, and brain tissues revealed changes characteristic of chronic heart failure. Repeated administration of ISO (10 mg/kg, four injections) induces a compensated chronic heart failure phenotype in 24-month-old rats by day 60, characterized by morphological alterations in the myocardium and multiple organs in the absence of myocardial contractile dysfunction.