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Cellular mechanisms of alterations in myocardial contractile function in experimental cardiomyopathies
V I Kapelko1, V I Veksler, M I Popovich
1Institute of Experimental Cardiology, Academy of Medical Sciences of the USSR, Moscow.
Abstract:
The high-energy-phosphate content, myocardial ultrastructure, left ventricular (LV) pressure, and pump function of isolated rat hearts were determined in four kinds of chronic myocardial damage induced by either autoimmunization, treatment of rats with adriamycin or noradrenaline in increasing doses, or infection with smallpox virus. Mild fibrosis, swollen mitochondria, and hyper-contracted and overdistended sarcomeres were typical ultrastructural alterations. The ATP and phosphocreatine content as well as cardiac output at standard load conditions were substantially lower in all four experimental groups. Mild bradycardia and increased LV diastolic pressure and stiffness occurred in all except the autoimmunized group. LV diastolic stiffness was inversely correlated with cardiac output and phosphocreatine content and directly correlated with LV systolic pressure. Both increased myofibrillar sensitivity to Ca2+ ions and energy deficiency within myofibrils may have contributed to increased myocardial stiffness. The increased stiffness limits LV filling but facilitates pressure development, and in this way partly compensates for the decreased contractility of cardiomyopathic hearts.
Insights
Chronic heart damage from various causes lowers energy phosphates and impairs pump function in rat hearts. Increased stiffness compensates for reduced contractility, impacting cardiac performance.
Area of Science:
- Cardiology
- Pathology
- Biochemistry
Background:
- Chronic myocardial damage can arise from diverse etiologies, including autoimmune responses, drug toxicity (adriamycin, noradrenaline), and viral infections.
- Understanding the impact of these conditions on cardiac energy metabolism and mechanical function is crucial for developing therapeutic strategies.
Purpose of the Study:
- To investigate the effects of four distinct models of chronic myocardial damage on high-energy phosphate content, myocardial ultrastructure, and left ventricular (LV) function in isolated rat hearts.
- To elucidate the relationship between myocardial stiffness, energy depletion, and compensatory mechanisms in cardiomyopathic hearts.
Main Methods:
- Induction of chronic myocardial damage through autoimmunization, adriamycin/noradrenaline treatment, or smallpox virus infection in rats.
- Assessment of myocardial high-energy phosphates (ATP, phosphocreatine), ultrastructural changes (fibrosis, mitochondria, sarcomeres), and LV pressure and pump function in isolated hearts.
Main Results:
- All four damage models exhibited reduced ATP and phosphocreatine levels, impaired cardiac output, and characteristic ultrastructural alterations like fibrosis and mitochondrial swelling.
- Increased LV diastolic pressure and stiffness were observed in most groups, correlating inversely with cardiac output and phosphocreatine, and directly with LV systolic pressure.
- Myocardial stiffness was attributed to increased myofibrillar Ca2+ sensitivity and energy deficiency, contributing to pressure development despite reduced contractility.
Conclusions:
- Chronic heart damage significantly compromises myocardial energy reserves and contractile function across various etiologies.
- Increased myocardial stiffness acts as a compensatory mechanism, facilitating pressure generation at the expense of diastolic filling in cardiomyopathic hearts.
- These findings highlight the complex interplay between energy metabolism, structural integrity, and mechanical performance in the failing heart.