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Ultrastructural changes in spontaneous cardiomyopathy
ULTRASTRUCTURAL CHANGES IN SPONTANEOUS CARDIOMYOPATHY
A.W. GOUGH, R.G. THOMSON AND F.A. DE LA IGLESIA. Warner-Lambert Research Institute) Mississauga, Ontario, Canada; University of Prince Edward Island) Charlottetown, P.E.I., Canada and Warner-Lambert Pharmaceutical Research Division, Ann Arbor, Michigan, U.S.A.
Cardiomyopathy is usually defined as an acute, subacute or chronic disorder of heart muscle where the etiology is unknown or obscure. The needs for development of experimental models to study this condition are obvious. One animal model possessing macroscopic and hemodynamic parameters comparable to congestive cardiomyopathy of man is the spontaneous cardiomyopathy (SC) or "round heart disease" in turkey poults characterized by marked cardiomegaly) biventricular dilatation and an augmented myocardial mass. We have addressed ourselves to the anatomic pathology of SC. To investigate this disease, 4 week old male SC and non-affected birds were collected from a flock of poults inflicted by this natural occurring disease. The first group was sacrificed and small pieces from both ventricles and septum were fixed by immersion using a 0.1M phosphate-buffered 2% glutaraldehyde solution at pH 7.4. Aqueous calcium chloride solution was added to a final 196 (v/v) concentration in the fixative. Post fixation was with a 196 osmium tetroxide solution. The second group was anesthetized with ether and retrograde perfusion of the heart was achieved by utilizing an i n t r a - a r t e r i a l gravity feeding system in which the initial Tyrode's balance salt solution was perfused through the aorta for one minute immediately followed by 196 glutaraldehyde solution for l i v e minutes. The remaining procedure was similar to that described for the first group. The perfusion method minimized the artefacts following myocardium excision and those arising from unopposed muscle cell contraction of stretched cardiomyopathic tissue Fig. I. Discrete organelles of the cardiomyocytes were morphologically unaltered and salient subcellular changes were confined to the sarcomere and related structures. Sarcomere abnormalities were focally distributed and consisted of thickened, irregular Z-bands, some of which appeared to be undergoing transectional division Fig. 2 and an associated loss of Z-band register in surrounding myofibrils Fig. 3. Ceils with these abnormal Z-bands were presumed to be cardiomyocytes, but differentiation from conduction fibres in avian species is d i f f i c u l t since both cells lack a T-tubule system (I). Subsarcolemmal and i n t e r f i b r i l l a r dense mats were observed occasionally. Tortuous intercalated discs incorporating excessive electron-dense material were attendant with mild myofibrillar disarray of adjacent sarcomeres. Minor ultrastructural changes distinguished SC birds from non-affected poults, and consequenlty the alterations described herein are not easily related to the remarkable gross cardiac lesions. The increased myocardial mass may be the result of enhanced water content due to increased intercellular tissue fluids, cytosol accumulation or elevated plasma volume with expanded coronary microcirculation. The application of morphometric techniques in experimental myocardial hypertrophy in rats has demonstrated a significant increment in cardiomyocyte volume and the addition of I)440 sarcomeres to the average cardiomyocyte (2). In SC birds) the alterations in Z-band morphology and the evidence of transectional separation of Z-band constituents suggest an accelerated sarcomerogenic activity.
(I) (2)
3.R. Sommer and E.A. 3ohnson) Comparative ultrastructure of cardiac cell membrane specializations. A review) Am. 3. Cardiol. 25) 154 (1970). P. Anversa) G. Olive-~'~ ~ . ' ~ r i and A.V. Loud) Morphometric study of myocardial hypertrophy induced by abdominal aortic stenosis, Lab. Invest. 40, 341 (1979).
219
220
A. W, Gough, R. G. Thomson and F. A. de la Iglesia
Fig. I
Right ventricular myocardium with preservation of Z-band register from SC bird.
Fig. 2 and 3 Left ven~ricular myocardium of SC bird, Z-bands (arrows),
Pattern of irregular
A.W. GOUGH, R.G. THOMSON AND F.A. DE LA IGLESIA. Warner-Lambert Research Institute) Mississauga, Ontario, Canada; University of Prince Edward Island) Charlottetown, P.E.I., Canada and Warner-Lambert Pharmaceutical Research Division, Ann Arbor, Michigan, U.S.A.
Cardiomyopathy is usually defined as an acute, subacute or chronic disorder of heart muscle where the etiology is unknown or obscure. The needs for development of experimental models to study this condition are obvious. One animal model possessing macroscopic and hemodynamic parameters comparable to congestive cardiomyopathy of man is the spontaneous cardiomyopathy (SC) or "round heart disease" in turkey poults characterized by marked cardiomegaly) biventricular dilatation and an augmented myocardial mass. We have addressed ourselves to the anatomic pathology of SC. To investigate this disease, 4 week old male SC and non-affected birds were collected from a flock of poults inflicted by this natural occurring disease. The first group was sacrificed and small pieces from both ventricles and septum were fixed by immersion using a 0.1M phosphate-buffered 2% glutaraldehyde solution at pH 7.4. Aqueous calcium chloride solution was added to a final 196 (v/v) concentration in the fixative. Post fixation was with a 196 osmium tetroxide solution. The second group was anesthetized with ether and retrograde perfusion of the heart was achieved by utilizing an i n t r a - a r t e r i a l gravity feeding system in which the initial Tyrode's balance salt solution was perfused through the aorta for one minute immediately followed by 196 glutaraldehyde solution for l i v e minutes. The remaining procedure was similar to that described for the first group. The perfusion method minimized the artefacts following myocardium excision and those arising from unopposed muscle cell contraction of stretched cardiomyopathic tissue Fig. I. Discrete organelles of the cardiomyocytes were morphologically unaltered and salient subcellular changes were confined to the sarcomere and related structures. Sarcomere abnormalities were focally distributed and consisted of thickened, irregular Z-bands, some of which appeared to be undergoing transectional division Fig. 2 and an associated loss of Z-band register in surrounding myofibrils Fig. 3. Ceils with these abnormal Z-bands were presumed to be cardiomyocytes, but differentiation from conduction fibres in avian species is d i f f i c u l t since both cells lack a T-tubule system (I). Subsarcolemmal and i n t e r f i b r i l l a r dense mats were observed occasionally. Tortuous intercalated discs incorporating excessive electron-dense material were attendant with mild myofibrillar disarray of adjacent sarcomeres. Minor ultrastructural changes distinguished SC birds from non-affected poults, and consequenlty the alterations described herein are not easily related to the remarkable gross cardiac lesions. The increased myocardial mass may be the result of enhanced water content due to increased intercellular tissue fluids, cytosol accumulation or elevated plasma volume with expanded coronary microcirculation. The application of morphometric techniques in experimental myocardial hypertrophy in rats has demonstrated a significant increment in cardiomyocyte volume and the addition of I)440 sarcomeres to the average cardiomyocyte (2). In SC birds) the alterations in Z-band morphology and the evidence of transectional separation of Z-band constituents suggest an accelerated sarcomerogenic activity.
(I) (2)
3.R. Sommer and E.A. 3ohnson) Comparative ultrastructure of cardiac cell membrane specializations. A review) Am. 3. Cardiol. 25) 154 (1970). P. Anversa) G. Olive-~'~ ~ . ' ~ r i and A.V. Loud) Morphometric study of myocardial hypertrophy induced by abdominal aortic stenosis, Lab. Invest. 40, 341 (1979).
219
220
A. W, Gough, R. G. Thomson and F. A. de la Iglesia
Fig. I
Right ventricular myocardium with preservation of Z-band register from SC bird.
Fig. 2 and 3 Left ven~ricular myocardium of SC bird, Z-bands (arrows),
Pattern of irregular