Morphologische Untersuchungen an Hamstern des Stammes BIO 8262 mit erblicher Myopathie und Kardiomyopathie

Myopathy-dependent changes in activity of ATPase, SDH and GPDH and NOS expression in the different fibre types of hamster muscles

Proximal (vastus lateralis) and distal (gastrocnemius) muscles of 100-day-old normal and myopathic BIO TO-2 hamsters were analysed to study the effects of myopathy on the different muscle fibre types: SO (slow oxidative), FOG (fast oxidative glycolytic) and FG (fast glycolytic). Cytophotometric measurements of enzyme activities (myofibrillic adenosine triphosphatase, succinate dehydrogenase and glycerol-3-phosphate dehydrogenase), Western blot analysis of nitric oxide synthase (NOS) I, II, III isoforms and NOS II immunohistochemistry were performed. The following alterations were found in myopathic muscle fibres: all fibre types of both proximal and distal myopathic muscles showed decreased myofibrillic adenosine triphosphatase activity indicating depressed contractility. This was associated with depressed oxidative activity of the muscle fibres. A shift to more glycolytic metabolism was observed, mainly in FG fibres of proximal muscle. We found an increased NOS II expression in both myopathic muscle types investigated. It means that increased NO production inhibits force generation in myopathic muscle. NOS II immunoreactivity was found mainly in the cytoplasm of FG fibres. NOS I and NOS III expression was not significantly effected by this form of myopathy. Our findings demonstrate that muscle fibres of proximal and distal skeletal muscles of 100-day-old cardiomyopathic BIO TO-2 hamsters are altered with respect to contractility, metabolism and NOS II expression. FG fibres of the proximal muscle were effected most strongly.

Changes of enzyme activities in the myocardium and skeletal muscle fibres of cardiomyopathic hamsters. A cytophotometrical study

Cytophotometrical measurements of enzyme activities were performed in the myocardium and skeletal muscle fibres from normal and cardiomyopathic hamsters (BIO 8262) during ageing from 12-14 to 120-190 days. Myocardium as well as vastus lateralis muscles of cardiomyopathic hamsters showed changes in enzyme activities. The skeletal muscle fibres were typed into slow-oxidative, fast-oxidative glycolytic and fast-glycolytic to investigate fibre type-related changes in muscles of cardiomyopathic hamsters. The following myopathic changes were mainly found: Myofibrillic ATPase was depressed in the myocardium of both ventricles in all investigated age stages. The ATPase activity of the right ventricle was more decreased than that of the left one. Additionally, a metabolic shift was observed in myocardium and slow-oxidative muscle fibres at the onset of clinical symptoms, which appeared from day 150 to day 190. During the period from 42 up to 190 days of life an increase of oxidative (succinate dehydrogenase) activity was measured in the myocardium of both ventricles and in slow oxidative fibres of vastus lateralis muscle as a proximal muscle. At earlier ages, the fast fibres of myopathic vastus lateralis muscle showed higher glycolytic (glycerol-3-phosphate dehydrogenase) activity than those of normal muscles. However, at the age of 120-190 days the metabolic profile of fast fibres was normalized. In gastrocnemius muscle as a distal muscle no changes of enzyme activities were measured, suggesting the investigated hereditary myopathy effected proximal, but not distal muscles.

Cardiac ultrastructural abnormalities in Syrian hamsters with spontaneous cardiomyopathy or subjected to cardiac overloads

Ultrastructural and morphometric abnormalities of Syrian hamster cardiomyopathy were compared to those observed in two different models of cardiac hypertrophy produced by mechanical overload (abdominal aortic stenosis, 60-day duration) or by isoproterenol injection during 15 days in normal Syrian hamsters of the same strain. Aspects of increased protein synthesis were observed in all three groups of animals. This was the only abnormality observed in the aortic stenosis group. Cardiomyopathy was different from the two other types of overload by the existence of large calcium deposits inside of the myocytes, by the presence of thin filaments and amorphous material accumulation suggesting abnormal synthesis and by a significant reduction of myofibrils at the heart-failure phase. Nuclear abnormalities with nuclear constrictions suggesting a division process and an increased number of myocytes with two nuclei were present in both spontaneous cardiomyopathy and isoproterenol-induced cardiopathy. Therefore, Syrian hamster cardiomyopathy appears to be different from cardiopathy induced by hemodynamic overload but, in spite of specific aspects, resembles that induced by isoproterenol injections, strengthening the hypothesis of a pathogenic role of catecholamines in the Syrian hamster cardiomyopathy.

Microvascular spasm in the cardiomyopathic Syrian hamster: a preventable cause of focal myocardial necrosis

The cardiomyopathic Syrian hamster develops focal myocardial necrosis beginning at 1 month of age, which leads to eventual ventricular failure within 1 year. The pathogenesis of this myocytolytic necrosis is unknown. Based on the nature of the cell necrosis, cytochemical evidence of vascular alterations, and the sensitivity of the hamsters to catecholamines and other vasoactive substances, we believe that the cardiomyopathy may be mediated by abnormalities of the microcirculation. Nonetheless, until the present study, no significant changes have been observed in these vessels. To elucidate the pathogenesis of this disease, we perfused living cardiomyopathic hamsters with silicone rubber solutions, which revealed numerous areas of microvascular constriction, diffuse vessel narrowing and luminal irregularity. Fixed structural lesions in these vessels could not be demonstrated. Pretreatment of young hamsters with verapamil during the period when they normally develop myocardial necrosis prevented myocytolytic lesions and abolished microvascular hyperreactivity. We believe that focal, transient spasm of small blood vessels, probably secondary to vasoactive substances, may cause myocytolytic necrosis (a form of reperfusion injury) in this model. This may also be a multifactorial disease with myocellular as well as vascular abnormalities leading to myocardial degeneration. The similarity of this disease to human and experimental cardiomyopathy suggests that microvascular spasm may be a common denominator of many different cardiomyopathic syndromes.

Development of necrosis and its sequelae in the myocardium of polymyopathic hamsters (BIO 8262). An electron microscopic study

Beginning about 30 days after birth, polymyopathic Syrian hamsters of the strain BIO 8262 develop calcifying myocardial necrosis. In the final stage the resorptive granulation tissue is followed by scars with multi-nucleated giant cells containing huge amorphous calcium plaques. The ultrastructural findings reveal the importance of myocardial mitochondria as starting points for calcification. The pattern of cell damage shows marked similarity to the changes observed in the myocardiocytes of magnesium-deficient rats. However, it is different from the alterations described in degenerating myocardiocytes of dehydrotachysterol-treated animals. Spicular electron-dense inclusions are the first and only kind of intramitochondrial calcification. Granular and annular-granular inclusions, as observed in ischaemic and infarcted canine myocardium, could not be detected, indicating that different pathogenetic mechanisms operate. The increased intracellular calcium level triggering myocardial necrosis is regarded as a secondary phenomenon, based on a genetic abnormality.

The cardiomyopathy of the Syrian hamster (strain BIO 8262)--hypertrophic or dystrophic?

Chemical as well as cytophotometric studies were carried out on myocardium of cardiomyopathic hamsters of strain BIO 8262 and of healthy control hamsters of strain CLAC. Our interest was to find out whether the cardiomyopathic hamsters suffer from hypertrophic cardiomyopathy or not. The heart muscle mass was only slightly increased in the older cardiomyopathic hamsters when compared with the controls. This increase was accompanied by an elevated content of total DNS, RNS and protein. Furthermore, the number of hyperdiploid heart muscle cells was slightly increased in the older diseased animals. However, all these changes were of minor degree. Thus, a distinct hypertrophying process in the myocardium of the cardiomyopathic hamsters can be excluded. On the other hand, the connective tissue components (polysaccharides and collagen) were distinctly increased in the hearts of older cardiomyopathic hamsters. This is in accordance with morphological investigations, in which replacement of necrotic myocardium by fibrosis could be detected.

Electrocardiographic changes in cardiomyopathic Syrian hamsters (strain BIO 8262)

Under ether anesthesia electrocardiograms were derived from Syrian hamsters (strain BIO 8262) suffering from cardiomyopathy and muscular dystrophy. In addition, ventricular weights and body weight were determined. Young hamsters -- not yet showing morphological signs of the cardiomyopathy with the exception of possible left ventricular hypertrophy -- demonstrated only a longer ventricular activation time than normal hamsters. With the onset of cardiac necrotization left axis deviation in frontal plane projection and right bundle branch blocks are developing in the cardiomyopathic hamsters followed by first degree atrioventricular conduction defects. During the late stage of the cardiomyopathy left bundle branch blocks are additionally arising, while left ventricular hypertrophy is disappearing. Since no overt heart failure is occurring in this strain of cardiomyopathic hamsters, gradual development of high degree conduction defects is assumed to terminate their lives. The electrocardiographic pattern of the hamster cardiomyopathy fits partly into that of human primary as well as secondary cardiomyopathy. Nevertheless, it seems to form an entity of its own, as arrhythmias, higher degree atrioventricular conduction disturbances, typical signs of ventricular or septal hypertrophy, abnormal P and Q waves, ST segment and T wave changes are lacking.

Skeletal muscle regeneration in myopathic hamsters of strain BIO 8262

Skeletal muscle regeneration was studied in polymyopathic hamsters of the strain BIO 8262 by autoradiography. Flash labeling with 3H-thymidine revealed high labeling indices of mononuclear cells in areas with muscle cell necroses and low labeling of "interstitial cells". However, no labeled nuclei were present in myotubes. Three days after multiple injections of the radioisotope, labeled nuclei in the myotubes were present. The mean labeling intensity of these nuclei was slightly elevated on the 15th day. On the third day after multiple 3H-thymidine injections nearly all mononuclear cells were labeled; but their labeling indices slightly decreased until the 15th day. From the decrease of labeling intensity, a high turnover rate of these cells may be assumed. Labeled myotubes appeared in the neighborhood of mononuclear cells as well as in areas without pronounced round cell infiltrations. From labeled myotubes in areas with round cell infiltrations it may be concluded that they arose by fusion of rapidly proliferating satellite cells, which may be constituents of the mononuclear cell population. Labeled myotubes that appeared outside areas of mononuclear cell infiltrations may have been caused by fusion of slow proliferating satellite cells. Despite the fact of a high regeneration capacity of muscle in hamsters of the strain BIO 8262, this process is not sufficient to completely restore the muscle necroses.

[Characteristic electrolyte changes in the hereditary myopathy and cardiomyopathy of the Syrian golden hamster (strain BIO 8262) (author's transl)]

In hamsters of differing ages suffering from a hereditary myopathy and cardiomyopathy (strain BIO 8262), the electrolytes sodium, potassium, calcium, and magnesium in serum, and several tissues were compared with appropriate controls. The determinations of the electrolytes were performed by atomic absorption spectrophotometry. An enormous accumulation of calcium in the necrotizing heart and skeletal muscle was the noticeable feature besides pronounced elevation of the sodium content in the myopathic skeletal muscle. While the latter refers mainly to an interstitial edema which is a consequence of the myopathy, the calcium accumulation is assumed to be an essential part in the cycle of pathologic events occurring in the hereditary disease: it seems to induce the necrotization.