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Hereditary and acquired cardiomyopathies in experimental animals: mechanical, biochemical, and structural features
Insights
Hereditary hamster cardiomyopathy impairs muscle contractility and biochemistry, while diabetic cardiomyopathy affects relaxation. Both conditions show distinct molecular and structural changes impacting cardiac function.
Area of Science:
- Cardiovascular Research
- Muscle Physiology
- Biochemistry
Background:
- Cardiomyopathies, including hereditary and diabetic forms, significantly alter cardiac muscle function.
- Understanding the molecular and mechanical underpinnings of these diseases is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the biochemical, ultrastructural, and contractile alterations in hereditary hamster cardiomyopathy.
- To examine the structural and mechanical changes in experimental diabetic cardiomyopathy.
Main Methods:
- Isometric tension and rate of tension development measurements.
- Analysis of contractile proteins, including myosin and sarcoplasmic reticulum function.
- Biochemical assays for neurotransmitters and protein composition.
- Microscopic examination for ultrastructural changes.
Main Results:
- Hereditary cardiomyopathy depressed contractile performance and altered force-frequency relationships, linked to sarcoplasmic reticulum dysfunction and myosin degradation.
- Diabetic cardiomyopathy primarily impaired muscle relaxation, with altered length dependence and reduced contractility reserve.
- Combined diabetes and hypertension exacerbated both contraction and relaxation deficits.
Conclusions:
- Hereditary and diabetic cardiomyopathies exhibit distinct pathophysiological mechanisms affecting cardiac muscle.
- Alterations in contractile proteins, sarcoplasmic reticulum, and neurotransmitter systems contribute to disease progression.
- Diabetic cardiomyopathy, especially with coexisting hypertension, presents a significant challenge to cardiac function.
Abstract:
Evidence has been presented regarding alterations of contractile behavior muscle biochemistry, and ulstrastructure during the course of the hereditary hamster cardiomyopathy. Also, preliminary structural and mechanical data were presented on the acquired cardiomyopathy of diabetes mellitus in experimental animals. In the hamster model, contractile performance, measured as isometric tension and rate of tension development, was shown to be depressed throughout the course of the disease, whereas normalized force-velocity relationships returned to normal only during the compensated stages of hypertrophy. Force-frequency relationships were depressed in myopathic muscles, indicating the presence of alterations in the muscle activation system, namely, the biochemical and functional integrity of the sarcoplasmic reticulum. Analysis of the contractile proteins in myopathic muscle has revealed depressions of Ca2+ activity in purified myosin in addition to an independently increased neutral protease activity that results in the specific degradation of LC2 of myosin. Sympathetic time and norepinephrine turnover increase progressively during the course of the disease. These changes are accompanied by decreasing tissue levels of neorepinephrine and increasing levels of dopamine, indicating a shift in the rate-limiting step for norepinephrine synthesis. Alterations were also noted in nuclear protein composition and serotonin levels. Microscopically, the myolytic and calcification changes that characterize the hamster cardiomyopathy have been confirmed. In addition, contraction bands and lysosomal changes have been observed that may relate to cateholamine hypersensitivity. In the experimental model of diabetic cardiomyopathy, a significant alteration in relaxation process was demonstrated despite the fact that peak tension development and its rate of development were unaltered. Also, the length dependence of contractile behavior was altered when compared to that of age-matched controls, indicating a potential loss of contractility reserve. When animals with combined hypertension and diabetes were studied, bothe contraction and relaxation processes were affected to a greater degree.