In this study we used 2.5% myocardial homogenates to study sarcoplasmic reticulum (SR) activity of the Ca2+ pump and Ca2+ release channel (CRC) from dogs with congestive heart failure produced by either rapid ventricular pacing or idiopathic dilated cardiomyopathy. We used the florescent indicator dye and ratiometric spectrofluorometry to monitor Ca2+ uptake while the CRC was open and closed with ryanodine. We confirmed and extended conclusions derived from previous studies of the same dogs using isolated SR. Compared to controls, activities of dogs with either form of CHF were decreased by 36% for the Ca2+ pump (33.7 ± 7.3 and 21.6 ± 4.2 nM/s), 78% for the CRC (10.0 ± 2.8 and 1.4 ± 1.2 nM/s), 53% for total Ca2+-cycling (53.1 ± 8.5 and 24.8 ± 4.4 nM/s), and 17% for net Ca2+ uptake (23.7 ± 4.0 and 19.6 ± 4.0 nM/s). In the absence of SR and mitochondrial activity, ionized Ca2+ concentration in myocardial homogenates were 70% abnormally increased in dogs with CHF, probably due to decreased concentration of Ca2+-binding proteins. Comparison of homogenate and isolated SR activities indicated lower-than-normal membrane yields for dogs with CHF. This fractionation artefact previously resulted in up to 50% overestimation of the degree of downregulation of Ca2+-cycling activities in CHF. The CRC activity was found to be decreased due to decreased activity of the Ca2+-ATPase, decreased CRC content, and inhibition. Decreased CRC activity reversed most of the effect of down-regulation of the Ca2+-ATPase pump, which is proposed to conserve energy. Maintenance of net Ca2+-pump activity is expected to maintain the amplitude of the myocardial ionized Ca2+ transient whereas downregulation of the CRC and pump are predicted to reduce the total amount of Ca2+ cycled and slow the rise and fall of the Ca2+ transient.

Characteristic alterations in the serum and urine biochemical profiles of Doberman Pinschers with congestive heart failure (CHF) resulting from idiopathic dilated cardiomyopathy were determined. We compared these alterations with those observed in 2 other models of CHF: rate overload induced by rapid ventricular pacing in dogs, and biventricular hypertrophy and dilatation induced in turkey poults by furazolidone toxicosis. Serum and urine biochemical changes in both models of CHF in dogs were mild to moderate in degree, and were moderately consistent. They could be attributed to secondary neurohumoral, hepatic, and renal effects of heart failure. The most marked and consistent changes observed were mildly decreased anion gap that developed, in part, because of decreased serum sodium concentration, moderately increased catecholamine concentrations, moderate lactaciduria, hyposthenuria, and mildly increased urea concentrations and liver enzyme activities. In birds with furazolidone cardiomyopathy, we observed mild increases in serum urate concentration, liver and muscle enzyme activities, but moderately increased sodium concentration with decreased chloride concentration. In the pacing and furazolidone models, in which CHF was rapidly induced, moderate to marked hypoproteinemia was attributable to decreases in albumin and globulin concentrations. Using the avian model we found that the hypoproteinemia could be largely attributed to blood volume expansion, and to a lesser extent, inanition. Development of hypoalbuminemia during rapid ventricular pacing and furazolidone treatment may contribute to the effects of rate overload or drug toxicity in the pathogenesis of CHF, because hypoalbuminemia may contribute to altered hemodynamics and neuroendocrine system activation. Our data indicate that clinical biochemical analysis of serum and urine may be useful for assessing progression of CHF.

1. The cardiac cycle is generally believed to be timed by a sarcoplasmic Ca-cycle and powered by a sarcoplasmic ATP-cycle that uses fatty acids as fuel and generates toxic free radicals as a side-product. 2. This study used a comparative mammal approach to test this model and the hypothesis that these cycles were closely coupled and correlated with fatty acid oxidation and peroxidative injury. 3. Fatty acid oxidation and ATP-cycling rates correlated to log heart rate whereas Ca-cycling rate was directly coupled to heart rate in a one-to-one relationship. 4. Both Ca-pump and Ca-channel activities coordinately increased as heart rate increased across species. 5. Thus, Ca-cycling activity is constant across mammals, when normalized to heart rate. 6. Comparison of Ca-ATPase and Ca-flux rates indicated that sarcoplasmic volume was inversely correlated with log heart rate. Basal lipoperoxidation of myocardium and susceptibility of SR to lipoperoxidation correlated with metabolic rate. 7. We identified that the horse is a metabolic outlier amongst mammals, with abnormally high fatty acid oxidation and ATP-synthetase activity compared to its heart rate.

To test the hypothesis that the mutation associated with porcine stress syndrome (PSS; malignant hyperthermia) was present in a large proportion of North American and English swine, a simple and rapid laboratory protocol was used for cost-effective, large-scale diagnosis of susceptibility to PSS. This PSS test was applied to 10,245 breeding swine of various breeds from 129 farms in the United States, Canada, and England. Approximately 1 of 5 swine was a heterozygous carrier of the PSS mutation, with approximately 1% being homozygotes. Prevalence of the PSS mutation was 97% for 58 Pietrain, 35% for 1,962 Landrace, 15% for 718 Duroc, 19% for 720 Large White, 14% for 496 Hampshire, 19% for 1,727 Yorkshire, and 16% for 3,446 crossbred swine. The PPS gene frequencies for these breeds were 0.72, 0.19, 0.08, 0.10, 0.07, 0.10, and 0.09, respectively. In addition to these breeds, we have identified the PSS mutation in Poland China and Berkshire breeds. These gene frequencies were 30 to 75% lower in Canadian swine than in US swine, with the exception of Yorkshires, for which the gene frequency was threefold higher in Canadian swine. English swine were similarly, or more so, affected than were US swine. Accuracy was estimated at > 99%. Cost to perform the test was < $20/animal. Depending on the perceived net balance of deleterious and beneficial effects of the mutation, the PSS test could be used to eradicate the PSS mutation from herds, or for controlled expression of the mutation.

Idiopathic dilated cardiomyopathy (IDCM) is a primary myocardial disease of unknown cause. We tested the hypothesis that IDCM was associated with a myocardial metabolic defect by determining a comprehensive biochemical profile of metabolite concentrations and enzyme activities for the major metabolic pathways of the myocardium. We used the Doberman pinscher breed as a naturally occurring canine model of IDCM and compared its myocardial profile with that of healthy adult mongrels. Compared with controls, myocardium in IDCM had markedly reduced mitochondrial electron transport activity and myoglobin concentration, in association with acidosis and energy depletion following anoxic challenge: 60% decreased NADH dehydrogenase and 50% decreased ATP synthetase activities; 90% decreased myoglobin concentration; and 30% reduced ATP and 50% increased lactate and proton concentrations. Sarcoplasmic reticulum Ca(2+)-transport ATPase was decreased by 42%. There was a 15% compensatory increase in fatty acid oxidation and Krebs cycle activity. Other biochemical changes were mild by comparison with the mitochondrial defects. We conclude that IDCM is associated with a marked impairment of mitochondrial production of ATP, arising from decreased activity of the mitochondrial electron transport system, including myoglobin. These changes may be secondary to an underlying genetic defect or may indicate a deficiency of the mitochondrial respiratory chain that predisposes this breed to heart failure.

Myoglobin is known to protect the mechanical function of the heart from hypoxia by acting as a sarcoplasmic oxygen reservoir and shuttle. We postulated a role for myoglobin in the pathogenesis of congestive heart failure. Several models of congestive heart failure were employed to test the hypothesis, including spontaneous inherited dilated cardiomyopathy in Doberman Pinschers, and heart failure produced by rapid ventricular pacing in dogs, volume overload in chickens and furazolidone toxicity in turkeys. Myocardial myoglobin was decreased by approximately 50% for all models (P less than 0.05). In Doberman Pinschers dogs which are predisposed to the development of dilated cardiomyopathy and have mild subclinical depression of cardiac performance, myocardial myoglobin (1.05 +/- 0.22 mg/g) is approximately 50% decreased compared to healthy mongrel dogs (2.15 +/- 0.52 mg/g), approximately twice as much as dobermans with heart failure (0.47 +/- 0.25 mg/g) but similar to the concentration found in dogs paced to heart failure (1.09 +/- 0.34 mg/g). Myocardium from poultry had remarkably decreased myoglobin compared to mammals (34 +/- 4 micrograms/g) with heart failure produced either by furazolidone or salt toxicity causing a further 50% reduction. In the canine models of heart failure, myocardial myoglobin concentration was demonstrated to be correlated with biochemical and physiological indicators of myocardial performance, namely, mitochondrial and sarcoplasmic reticular ATPase activities, and cardiac output, systemic vascular resistance, pulmonary capillary wedge pressure and mean arterial pressure, respectively. Our data implicates a role for myoglobin deficiency in the pathogenesis of congestive heart failure and in the predisposition of doberman pinschers to dilated cardiomyopathy.

We have previously demonstrated that in furazolidone-induced congestive heart failure in turkeys the specific Ca(2+)-ATPase activity of myocardial sarcoplasmic reticulum (SR) is 60% increased in compensation for a 50% depression in net Ca(2+)-sequestration activity. This study tested the hypothesis that SR Ca(2+)-uptake and Ca(2+)-ATPase activities were uncoupled in this cardiomyopathy because of increased Ca(2+)-release channel activity. A novel microassay was used to monitor Ca2+ transport by myocardial homogenates using the fluorescent Ca2+ dye indo 1 to indicate extravesicular ionized Ca2+. The method is applied to cyropreserved biopsy specimens of myocardium and requires only 50 mg tissue. Both SR Ca(2+)-pump and SR Ca(2+)-channel activity were estimated using the channel-inhibitor ruthenium red (RR) and the mitochondrial inhibitor sodium azide. The specificity of the RR inhibition was confirmed using ryanodine. Cardiomyopathy was induced in 2-week-old turkey poults by the addition of 0.07% furazolidone to their feed for 4 weeks. Compared with controls, myocardial maximal Ca(2+)-channel activity relative to maximal Ca(2+)-pump activity was 22% greater and duration of Ca(2+)-channel activity was 100% increased. However, the heart failure birds had 43 and 53% decreases in absolute maximal Ca(2+)-pumping and Ca(2+)-channel activities, respectively. The abnormal Ca(2+)-channel activity resulted in 200% greater time before initiation of net Ca2+ sequestration and 700% greater final myocardial Ca2+ concentrations. For all birds, the Ca(2+)-accumulating activity was highly correlated with Ca(2+)-release activity (all p less than 0.05). These data indicate that in this animal model of congestive heart failure there is defective SR Ca(2+)-channel function resulting in abnormal Ca2+ homeostasis.(ABSTRACT TRUNCATED AT 250 WORDS)

The development of muscle fatigue due to exhaustive exercise is associated with impaired sarcoplasmic reticulum (SR) Ca-transport activity. This study tested the hypothesis that SR failure is a consistent feature of cardiac and skeletal muscle fatigue owing to relative functional overload regardless of the method of induction: excessive stimulation, diminished performance capacity, or excessive excitation-contraction coupling. The Ca-transport activity was determined using three unique models of muscle fatigue: chronic and rapid ventricular pacing in dogs; metabolic inhibition caused by global cardiac ischemia in swine; and the hypermetabolic syndrome of porcine malignant hyperthermia (MH). Both pacing- and ischemia-induced fatigue resulted in reduction of SR Ca-transport ATPase activity: from 275 +/- 58 to 159 +/- 57 nmol.min-1.mg-1 (mU/mg) and from 577 +/- 82 to 177 +/- 133 mU/mg, respectively. Both pacing-induced fatigue and halothane-induced MH resulted in reduction of Ca-sequestration activity of muscle homogenates from 5.95 +/- 2.4 to 3.11 +/- 0.67 nM/s at 300 nM Ca and 38.7 +/- 10.5 to 16.3 +/- 8.0 nM/s at 1500 nM Ca, respectively (all p less than 0.01). The isolated SR Ca-ATPase activity correlated with Ca-sequestration activity of myocardial homogenates (r = 0.76; p less than 0.005). Different models were used to study the relationship of Ca-transport activity with relaxation function, degree of acidosis, and ionized Ca concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Recent studies indicate that in animals with marked cardiac hypertrophy, there is depressed function of Ca2+ sequestration by myocardial sarcoplasmic reticulum (SR) because of down regulation of the Ca(2+)-ATPase gene. However, in several animal models we have observed enhancement of myocardial Ca2+ sequestration in response to chronic cardiac stimulation. We tested the hypothesis that in animals with mild cardiac hypertrophy, there is enhanced Ca(2+)-cycling activity by the SR Ca2+ pump and Ca(2+)-release channel. Because creatine kinase activity is consistently decreased in cardiomyopathy, we also determined whether enhanced Ca2+ cycling was accompanied by down regulation or inhibition of the creatine kinase system. Mild cardiac hypertrophy was induced by volume overload; 2% salt was added to the diet of 2-week-old turkey poults for 4 weeks. Compared with age-matched controls, volume overload resulted in 14.3% increase in heart weight and 21.5% increase in heart-to-body weight ratios. The hypertrophied heart had approximately 20% increased activities of the SR Ca2+ pump and the SR Ca2+ channel. Net Ca2+ transport was increased by 16.5%. Compared with controls and in contrast to several other myocardial enzymes, creatine kinase activity was diminished in the hypertrophied hearts by 23% and creatine content was decreased by 8%. Differences between groups were not detected for lactate dehydrogenase, aspartate transaminase, and alanine transaminase. We concluded that an early adaptation of the myocardium undergoing hypertrophy in compensatory response to functional overload is an enhancement of Ca2+ cycling activity by the Ca2+ pump and Ca2+ channel of the SR.(ABSTRACT TRUNCATED AT 250 WORDS)

Hens, 59 weeks of age, were offered a corn, soya-type diet with no supplemental vitamin D3 for a 28-day period. Egg production remained relatively constant to the end of the second week and then began to fall precipitously.