Nulceoprotein changes in the hearts of cardiomyopathic turkeys.

The possible involvement of nuclear proteins in the pathogenesis of a spontaneously occurring model of congestive cardiomyopathy in turkeys was examined. This model is characterised by cardiac hypertrophy and dilatation, reduced cardiac output and depressed contractility. The protein composition of myocardial nuclei was compared in normal (n = 9) and cardiomyopathic (n = 18) turkeys, 70 to 140 days old. Myopathic hearts as a group have a higher histone content (1.75 +/- 0.09 (SD) mg . mg DNA-1 vs 1.65 +/- 0.07 in controls, P less than 0.01) and histone/nonhistone protein (NHP) ratio (1.07 +/- 0.07 vs 0.95 +/- 0.02 in controls, P less than 0.01). The latter was independent of age and correlated well with the degree of cardiac dilatation. The electrophoretic patterns of chromatin proteins was decreased in myopathic hearts. This decrease was primarily accounted for by lower NHP phosphorylation (5.78 +/- 1.38 pmol 32P . mg prot-1 . 15 min-1 vs 8.33 +/- 0.81 in controls, P less than 0.01). DEAE-Sephacel chromatography separated cyclic AMP-dependent and -independent nuclear protein kinases with similar substrate specificities but lower specific activities in myopathic hearts. SDS-polyacrylamide similar substrate specificities but lower specific activities in myopathic hearts. SDS-polyacrylamide gel electrophoresis of phosphorylated nucleoproteins revealed differences in the lower molecular species of NHPs between control and myopathic hearts. There was a significant correlation between NHP phosphorylation and degree of cardiac dilatation (r = -0.78) or contractility as reflected by left ventricular systolic time intervals (r = -0.57). These results suggest that development of this model of spontaneous cardiomyopathy is associated with, and may, in part, be secondary to changes in the composition and function of myocardial nucleoproteins.

Early alterations in the function of sarcoplasmic reticulum in a naturally occurring model of congestive cardiomyopathy.

In a naturally occurring model of congestive cardiomyopathy-round heart disease of turkeys, Ca2+ transport of isolated cardiac sarcoplasmic reticulum was evaluated at 1, 10, 28, and 56 days of age. Ca2+ binding in round heart disease birds was reduced to between 55% and 75% of values measured in age-matched commercial control turkeys (P less than 0.05 to less than 0.01). Similarly, Ca2+ uptake in round heart disease birds was reduced to between 52% and 87% of values measured in age-matched commercial control turkeys (P less than 0.05 and less than 0.01). Ca2+-stimulated ATPase values were similar in 1-, 10-, and 28-day-old round heart disease and commercial control turkeys. However at 56 days of age, when all round heart disease birds showed moderate to marked left ventricular dilatation. Ca2+-stimulated ATPase was reduced to 75% of control values (P less than 0.05). Depression of Ca2+ binding and Ca2+ uptake preceded the appearance of cardiac dilatation and may contribute to the pathogenesis of round heart disease. Depression of Ca2+-stimulated ATPase, present only after cardiac dilatation developed, appears to be secondary to cardiac failure. Sarcoplasmic reticulum function in round heart disease birds immunosuppressed by cyclophosphamide treatment (40 mg . kg-1 . d-1 for the first 4 days of age) was evaluated at 10 days of age. This treatment increased Ca2+ binding by 73% (P less than 0.05), and Ca2+-uptake by 58% (P less than 0.01) over values measured in untreated round heart disease birds. Reversal of the altered Ca2+ transport in sarcoplasmic reticulum by early immunosuppression supports the hypothesis that the immune system plays an integral part in the development of the congestive cardiomyopathy of round heart disease.

Effect of early propranolol treatment in an animal model of congestive cardiomyopathy. II. beta-adrenergic receptors and left ventricular function.

Young turkeys inbred for congestive cardiomyopathy (CCM) were treated with propranolol prior to the development of cardiac enlargement. One-day-old inbred CCM and commercial turkeys received 2 mg X kg-1 X day-1 of propranolol for 1 month and were compared with untreated age matched inbred CCM and commercial turkeys. Heart weight, body weight, and binding characteristics of cardiac beta-adrenergic receptors, using (-)3H-dihydroalprenolol as a ligand, were determined at 10 and 28 days. Left ventricular shortening fraction was determined at 28 days and at 32 days, 4 days after propranolol was discontinued, in treated and untreated inbred CCM and commercial turkeys. Propranolol did not prevent the development of cardiac hypertrophy in inbred CCM turkeys at 28 days of age and did not effect body weight or heart weight in either inbred CCM or commercial turkeys at 10 or 28 days of age. In the inbred CCM turkeys, the maximum number of binding sites (Bmax) and the binding affinity (Kd) of beta-adrenergic receptors were not changed by propranolol treatment. In the propranolol-treated commercial turkeys, Bmax the of beta-receptors was increased at 28 days of age compared with untreated age matched controls, 382 vs 194 fmol X mg-1 (p less than 0.05). Untreated inbred CCM turkeys when compared with untreated age matched commercial turkeys show a significant reduction of binding affinity of beta-receptors at both 10 and 28 days of age, Kd = 10.4 vs 6.2 nmol X litre-1 at 10 days and 11.3 vs 5.2 nmol X litre-1 at 28 days (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of early propranolol treatment in an animal model of congestive cardiomyopathy: I Mortality and Ca2+ transport in sarcoplasmic reticulum.

Young turkeys inbred for congestive cardiomyopathy were treated with propranolol prior to the development of cardiac enlargement. One-day-old inbred and commercial turkeys received propranolol, 2 mg X kg-1 X day-1 for 1 month. Propranolol treated inbred birds showed a significantly reduced mortality from 5 to 15 days of age when compared with untreated inbred birds. However, by 28 days of age, cumulative mortality in the treated inbred birds was equal to that in the untreated inbred birds, 29 and 32%, respectively. Propranolol-treated and untreated commercial birds have a 28-day cumulative mortality of 5%. Ca2+ transport in isolated cardiac sarcoplasmic reticulum was studied at 10 and 28 days of age. At 10 days of age Ca2+ uptake and Ca2+ binding in propranolol-treated birds was reduced to 56% and 83%, respectively, of values in untreated inbred birds. By 28 days of age Ca2+ uptake and Ca2+ binding in treated and untreated inbred birds were similar. Ca2+-stimulated ATPase activity was significantly elevated in treated inbred birds compared with age-matched untreated inbred birds at 10 and 28 days of age. Ca2+ transport in isolated cardiac SR from propranolol-treated commercial control birds was not significantly different from the values in untreated commercial birds at 10 or 28 days of age. Improvement in early mortality may be due to the prevention of arrhythmias. Propranolol alters Ca2+ transport in isolated cardiac SR from inbred birds by uncoupling Ca2+-stimulated ATPase. Whether this is due to a direct effect of propranolol on the SR membrane or occurs from its beta-adrenergic blocking action is unclear.

Regional myocardial blood flow and cardiac function in a naturally occurring congestive cardiomyopathy of turkeys.

Round heart disease, a presumed viral myocarditis of turkeys, provides a unique opportunity for the study of congestive cardiomyopathy. Regional myocardial blood flow and cardiac output measurements were made in nine, 19 to 34 day old anaesthetised birds using 141Ce labelled microspheres (15 micron diameter). Atrial, right ventricular and weighted-average left ventricular myocardial blood flow values were similar in control (n = 5) and round heart disease (n = 4) turkeys. The left ventricular subendocardial/subepicardial blood flow ratio of 0.89 +/- 0.02 (mean +/- SE) in round heart disease birds was, however, reduced compared with the value of 1.19 +/- 0.09 in the control birds (P < 0.05). Round heart disease turkeys also had lower systemic pressures and lower cardiac outputs when compared with control birds. M-mode echocardiograms were obtained in 42 unanaesthetised 17 to 37 day old turkeys, 34 control and eight with round heart disease. Echocardiographic evidence of left ventricular dysfunction characterised by left atrial and left ventricular dilation and a markedly reduced left ventricular shortening fraction was found in round heart disease turkeys. Paradoxical motion of the interventricular septum was present in two of eight round heart disease turkeys but in none of the control turkeys. The interventricular septum/left ventricular posterior wall ratio in control and round heart turkeys were similar. Although the body weight of control and round heart disease turkeys were similar, and the diastolic thickness of the left ventricular wall were not substantially different, the ventricular weight/body weight ratio in round heart disease turkeys was increased approximately 52%. The increased ventricular weight was not due to myocardial oedema, as myocardial water content was similar in control and round heart disease turkeys. The features which characterise round heart disease in turkeys: left atrial and left ventricular dilatation, reduced left ventricular shortening fraction, systemic hypotension, low cardiac output, relative subendocardial underperfusion, and an increase in ventricular mass, make it a useful model for congestive cardiomyopathy.

Inducible ventricular arrhythmias in a naturally occurring model of cardiomyopathy.

This study examined inducibility of ventricular tachyarrhythmias in turkeys with and without naturally occurring dilated cardiomyopathy. Using a transvenously positioned electrode catheter, 32 cardiomyopathy and 12 control unsedated turkeys aged 2 to 4 months were studied by right ventricular endocardial extrastimulus testing at basic pacing cycle lengths of 200 and 170 ms with both 1 and 2 extrastimuli and burst pacing at progressively shorter cycle lengths (200 to 100 ms). Following study, a dilatation index (determined as the ratio of left ventricular endocardial and epicardial diameter at level of the apex-base midpoint) was utilized to assess the functional severity of cardiomyopathy. All control turkeys had a dilatation index less than 0.3. In cardiomyopathic turkeys, dilatation index was normal (less than 0.3) in 3/32, showed mild to moderate dilatation in 25/32 (0.3 to 0.6), and severe dilatation in 4/32 (greater than 0.6). Results showed no difference in right ventricular effective or functional refractory periods between control and cardiomyopathic turkeys. Control turkeys had no inducible ventricular tachyarrhythmias, but 16/32 cardiomyopathic turkeys (p less than 0.005) had inducible ventricular tachyarrhythmias, consisting most frequently of two beats of rapid ventricular tachycardia supervened by ventricular fibrillation. In the cardiomyopathic turkeys, inducible tachyarrhythmias occurred in 1/3 with normal dilatation index, in 11/25 with mild to moderate dilatation, and in 4/4 with severe dilatation. Thus, inducibility of ventricular tachyarrhythmias in cardiomyopathic turkeys is closely associated with increasing ventricular dilatation, but does not correlate with altered right ventricular refractoriness. This model may be suitable for studying the relationship between ventricular tachyarrhythmias and cardiomyopathy.

Reduced lipid peroxidation in dilated hearts of cardiomyopathic turkeys.

Adverse pulmonary reactions to some nitrofuran antibiotics are thought, in part, to involve production of reactive oxygen radicals. Furazolidone, a nitrofuran antibiotic, causes a dilated cardiomyopathy in domestic turkeys. The mechanism of this drug induced cardiomyopathy is unknown. We investigated the possible role of free radical injury in this heart failure model. Left ventricular lipid peroxidation capacity, assessed by two methods (the thiobarbituric acid reactive substances and lipid hydroperoxides assays respectively), was investigated in five 5-8 week old cardiomyopathic turkeys with severe cardiac dilatation, left ventricular dysfunction and systemic hypotension, and in five control birds. Superoxide dismutase activity, total and manganese, was also measured in the crude left ventricular homogenates. Both lipid peroxidation products were reduced in the myopathic hearts: thiobarbituric acid reactive substances (malondialdehyde) 70(SEM 4) v 86(3) nmol.100 mg protein-1 in controls, p less than 0.02; and lipid hydroperoxides 29(7) v 74(14) nmol.100 mg protein-1, p less than 0.02. Total superoxide dismutase activity was similar in cardiomyopathic and control hearts: 670(26) v 657(105) nitrite units.100 mg protein-1. Although total superoxide dismutase activity was unchanged, we found decreased manganese superoxide dismutase in the dilated hearts compared with controls (54% v 84% of total activity, p less than 0.02). In separate in vitro experiments furazolidone (2-10 mg.g wet weight-1) did not increase malondialdehyde production in turkey (or rat) left ventricular homogenates. These results indicate that cardiomyopathy induced by furazolidone is associated with decreased myocardial lipid peroxidation. Although as yet unexplained, the decrease may be due to a diminished amount of heart lipid susceptible to peroxidation accompanying the process of cardiac hypertrophy and dilatation.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular electrophysiological changes in "round heart disease" of turkeys: a potential basis for dysrhythmias in myopathic ventricles.

Arrhythmias are commonly recorded in "round heart disease", a presumed viral, congestive cardiomyopathy of turkeys. To assess whether cellular electrophysiological changes may be associated with arrhythmia susceptibility, we compared transmembrane action potential characteristics in left and right ventricular endocardial muscle fibres from 19 inbred myopathic turkeys with findings in 13 normal control turkeys (age 1 to 74 days). In left ventricular tissue, as a group, action potential duration at 50% repolarisation (APD50) was reduced in myopathic hearts (201+/-6(SEM) vs 228+/-9 ms in controls. P less than 0.01), while the maximum rate of phase 0 (dV/dtmax) action potential amplitude, diastolic resting membrane potential and action potential duration at 90% repolarisation (APD90) did not differ from control turkeys. By contrast, in myopathic right ventricular tissue, as a group, both APD50 (186+/-5 vs 206+/-4 ms in controls) and APD90 (208+/-4 vs 228+/-3 ms in controls) were shorter (P less than 0.01). The plateau potential in both right and left ventricular tissue was significantly higher in inbred turkeys. Since a spectrum of cardiac dilatation and hypertrophy is present in myopathic turkeys, we examined the effect of hypertrophy on action potential characteristics. In "round heart disease" turkeys, left ventricular hypertrophy was characterised by reduced dV/dtmax (98+/- vs 274+/-26 V.s-1, P less than 0.01) and right ventricular hypertrophy by further shortening of both APD50 (174+/-7 vs 202+/-6 ms, P less than 0.01) and APD90 (193+/- vs 224+/-5 ms, P less than 0.01), but no change in dV/dtmax (105+/-13 vs 120+/-9 V.s-1, P = NS). These results indicate that certain electrophysiological differences (eg reduced action potential duration), may, in part, contribute to dysrhythmia susceptibility in this presumed viral cardiomyopathy model.

Reduced heart lipid peroxidation precedes cardiac dilatation in turkeys with naturally occurring cardiomyopathy.

STUDY OBJECTIVE: The aim of the study was to determine if reduced heart lipid peroxidation in 1-2 month old turkeys with furazolidone induced dilated cardiomyopathy is drug related and model dependent, a non-specific characteristic of the dilated turkey heart, or if alterations of heart lipid peroxidation can occur prior to onset of cardiac dilatation, and therefore may be involved in its pathogenesis. DESIGN: Ventricular lipid peroxidation capacity and superoxide dismutase activity were measured in controls and in turkeys with spontaneous cardiomyopathy at various ages (newly hatched, 7-10 d, and 1-2 months) and stages of the disease. SUBJECTS: 46 turkeys with naturally occurring dilated cardiomyopathy and 29 age matched controls were used at hatch, 7-10 d, and 1-2 months of age. MEASUREMENTS AND MAIN RESULTS: Heart lipid peroxidation, measured by thiobarbituric acid reactive substances (malondialdehyde), was found to be reduced not only in the dilated hearts of 1-2 months old cardiomyopathic turkeys [114(SEM 10) v 176(21) nmol.100 mg-1 protein, p = 0.023] but also in the non-dilated hearts of 9-10 day old cardiomyopathic turkeys [135(17) v 274(35) nmol.100 mg-1 protein, p = 0.004]. Ventricular superoxide dismutase activity was similar in control and cardiomyopathic turkeys at all stages and there was the expected increase with age. In control turkeys ventricular superoxide dismutase activity in 1-2 month old birds, at 718(52) nitrite units.100 mg-1 protein, was significantly higher than values in 7-10 day old turkeys [398(31) nitrite units.100 mg-1 protein, p = 0.001]. CONCLUSIONS: Decreased lipid peroxidation capacity is present in the dilated hearts of spontaneously cardiomyopathic turkeys. However, it is also decreased in cardiomyopathic turkeys at 9-10 d (the time of highest mortality) prior to the onset of cardiac dilatation. Therefore, alterations in heart lipid composition may be involved in the pathogenesis of this cardiomyopathy and not simply a result of the cardiac dilatation/hypertrophy process.

Myocardial lipid composition in turkeys with dilated cardiomyopathy.

OBJECTIVE: The aim was to determine if reduced heart lipid peroxidation in turkeys with two forms of dilated cardiomyopathy, previously reported, was related to an alteration in the lipid composition of the ventricle. METHODS: Myocardial lipid composition was measured in turkeys with two types of dilated cardiomyopathy. Twenty six turkeys with naturally occurring dilated cardiomyopathy, six with furazolidone induced dilated cardiomyopathy, and 18 age matched control birds were used at 1 day, 9-10 days, and 38-78 days of age. Left ventricular fatty acid composition of the phospholipid, triglyceride, free fatty acid, and cholesterol ester fractions was analysed using gas chromatography. RESULTS: Significant age related changes were identified in the fatty acid composition of the heart. In the phospholipid fraction, linoleic acid (18:2 omega 6) values increased with age, while arachidonic acid values decreased. The saturated to unsaturated fatty acid ratio in control hearts was unchanged as a function of age in the phospholipid fraction. In the triglyceride fraction, however, this ratio decreased substantially between newly hatched and nine day old birds and then markedly increased in two month old controls. There was a striking alteration in the saturated to unsaturated fatty acid ratio in the triglyceride fraction of 2 month old cardiomyopathic birds; this ratio was markedly increased in the furazolidone induced cardiomyopathic turkey hearts (5.14 v 2.79 in controls) and markedly diminished (ie, 0.97 to 1.21) in the spontaneously cardiomyopathic turkeys. A significant increase in myristic (14:0) and decrease in linoleic (18:2 omega 6) acid concentration in the furazolidone group v control and a marked decrease in myristic and increase in linoleic acid concentrations in the spontaneously cardiomyopathic group v controls was present. CONCLUSIONS: (1) There is an age related alteration in the fatty acid composition of control turkey hearts. (2) Previously identified reduced lipid peroxidation in furazolidone induced and spontaneous cardiomyopathy in turkeys does not appear to be related to reduced concentration of polyunsaturated fatty acids. (3) The two forms of dilated cardiomyopathy are associated with markedly disparate alterations in the concentration of polyunsaturated fatty acids in the triglyceride fraction of 1-2 month old turkey hearts. The changes may be related, in part, to the pathogenesis in these two different forms of dilated cardiomyopathy.

Catecholamines in turkeys with alcohol-induced cardiomyopathy.

Although alcoholic cardiomyopathy has been difficult to reproduce in animals, turkeys fed 5% ethanol develop a dilated congestive cardiomyopathy. We therefore used this model to examine the adrenergic response to left ventricular dysfunction induced by alcohol. In normal turkeys, norepinephrine in kidneys decreased markedly with age from 1 day to 2 mo, with a similar but less dramatic decrease in cardiac norepinephrine. By 2 mo, chronic alcohol ingestion depleted cardiac norepinephrine compared with controls (217 +/- 22 vs. 316 +/- 41 ng/g, P < 0.05), even though cardiac norepinephrine is relatively low in turkeys compared with many other animals and humans. Norepinephrine in aorta was also decreased with alcohol administration, but kidney norepinephrine was unaffected. Dopamine was unaltered in any of the organs studied. Plasma norepinephrine is normally high in turkeys with arterial levels greater than venous (2,898 +/- 746 vs. 1,987 +/- 531 pg/ml at 2 mo). Venous plasma norepinephrine did not differ from control (2,595 +/- 547 pg/ml) after 2 mo of alcohol. Thus, as in humans, cardiomyopathy in alcohol-fed turkeys is associated with reduced cardiac norepinephrine, but unlike humans with cardiomyopathy, circulating norepinephrine remains normal.

Occurrence of myocarditis in sudden death in children.

This study suggests that the prevalence of "silent" myocarditis may be higher in the pediatric population than is generally suspected and may contribute to a significant number of sudden and unexpected deaths in children, particularly those older than one year of age. The incidence of histologic myocarditis in children dying a violent death is similar to that reported as an incidental finding in adults.

Alteration by immunosuppression of early mortality in a naturally occurring cardiomyopathy.

Turkeys from a highly inbred flock, which shows a 100 per cent incidence of naturally occurring cardiomyopathy, were treated daily for 3 weeks following hatching with cortisone acetate, or for 4 days following hatching with parenteral cyclophosphamide, or underwent surgical removal of the bursa of Fabricius at hatching. Mortality was significantly reduced during the first 10 days of age when each of the treated groups was compared with its own control group. By 5 weeks of age, the mortality rates in the bursectomized and cyclophosphamide-treated birds were not significantly different than their control groups. Five-week mortality in the cortisone acetate-treated group, however, was significantly lower than in its control group. Long-term morbidity, as reflected by the incidence of cardiac dilatation and hypertrophy in all birds during or killed through one year of age, was lower in the cortisone acetate-treated birds and significantly reduced in the bursectomized birds. These data suggest that the humoral immune system may function in the pathogenesis of this naturally occurring cardiomyopathy in the turkey.

Beta-adrenergic function in a congestive cardiomyopathy model.

We investigated the cardiac beta-adrenergic-adenylate cyclase (AC) system in turkeys inbred for congestive cardiomyopathy (CCM) and the relation of this system to echocardiographically determined left ventricular shortening fraction (LVSF) in individual 56-day-old birds. The isoproterenol (Iso)-stimulated, NaF-stimulated, and basal AC activities in CCM birds were decreased to 69, 72, and 86%, respectively, of control values, P less than 0.05. By linear regression analysis there was significant direct correlation of initial LVSF in CCM birds with each of the following: change in heart rate (HR) after Iso function; Iso-stimulated, NaF-stimulated, and basal AC activities, and density of beta-adrenergic receptors. In addition, we investigated the effect of Iso infusion (0.4 microgram X kg-1 X min-1) on systemic hemodynamics. In CCM birds the initial LVSF was 72% of the control value, P less than 0.01; the initial HR was 112% of the control value, P less than 0.01. During Iso infusion both the LVSF and HR in control birds were increased, whereas in CCM turkeys with marked cardiac dilatation neither of these parameters changed. In 10-day-old CCM turkeys, which show no cardiac dilatation, NaF-stimulated AC activity was reduced to 70% of the control values, whereas basal and Iso-stimulated AC activities were unchanged. Thus an abnormality in the beta-adrenergic-adenylate cyclase system is present in CCM birds before development of cardiac dilatation; when cardiac dilatation is severe, a global defect in this system can be directly related to depressed inotropic and chronotropic responsiveness to Iso infusion in individual turkeys.