A new disease model of chronic congestive heart failure: studies on its pathogenesis

N-Methyl-D-aspartate receptor blockade by dizocilpine prevents stress-induced sudden death in cardiomyopathic hamsters

We previously demonstrated that repeated cold-immobilization stress exposure had lethal effects in cardiomyopathic Syrian hamsters. To clarify the mechanisms of the sudden death, we investigated the effects of N-methyl-D-aspartate (NMDA) receptor blockade by dizocilpine on the sudden death of cardiomyopathic hamsters. Repeated exposure (5 days) to cold-immobilization stress induced a lethal effect in the cardiomyopathic hamsters in agreement with our previous results. Dizocilpine (0.1-10 mg/kg, i.p.), administered just prior to the stress, for 5 consecutive days markedly prevented the lethal effects of the stress. It was further demonstrated that treatment drug significantly reduced the observed increase in organ weights. These results suggest that NMDA receptors have an important role in stress-induced sudden death in cardiomyopathic hamsters and provide the first evidence for the potential therapeutic value of NMDA antagonists against cardiac sudden death.

A dopamine D(1/5) receptor antagonist, SCH23390, prevents stress-induced sudden death in cardiomyopathic hamsters

Stress is known to have an impact on the development of life-threatening cardiovascular dysfunction. We have previously demonstrated that repeated exposure to cold-immobilization stress had lethal effects on cardiomyopathic Syrian hamsters (BIO 14.6), and that stress-induced sudden death was prevented by daily treatment with propranolol, suggesting an important role of sympathetic nerves in the etiology of stress-induced cardiac sudden death. In an attempt to clarify further the mechanisms of the sudden death, in the present study we investigated the effects of D(1/5) receptor blockade by SCH23390 on the sudden death of cardiomyopathic hamsters. In accordance with our previous results, repeated exposure for 5 days to cold-immobilization stress induced a lethal effect in the cardiomyopathic hamsters but not in control healthy hamsters. SCH23390 (0.1-10 mg/kg, IP), administered just before the exposure for 5 consecutive days, dose-dependently and significantly prevented the lethal effects of the stress. Furthermore, it was demonstrated that the drug significantly reduced the increase in the weights of the adrenal and kidneys observed in the stressed-cardiomyopathic hamsters. On the other hand, specific D(2) antagonist haloperidol (0. 1-10 mg/kg) failed to prevent the stress-induced sudden death and minimally affected the increase in organ weights. Collectively, these results suggest that D(1/5) receptors had an important role in the etiology of stress-induced cardiac sudden death of the cardiomyopathic hamsters, and provide the first experimental evidence of the potential therapeutic values of D(1/5) antagonists against cardiac sudden death associated with stress.

Effect of prolonged treatment with amlodipine on enhanced vascular contractility in cardiomyopathic hamsters

This study examined the effects of prolonged treatment with amlodipine on the enhanced vascular contractions in dilated cardiomyopathic (CM) hamsters. From the ages of 5 to 20 weeks, CM hamsters (BIO 53.58) orally received amlodipine. Then we compared the contractile responses to vasoconstrictors in aortas and mesenteric arteries from CM hamsters with or without treatment with those in the arteries from controls (F1b). We also investigated the effect of amlodipine treatment on the Ca2+ sensitivity of tension in beta-escin-skinned smooth muscle of mesenteric artery. The contractile responses to phenylephrine, angiotensin II, and high K+ in both aorta and mesenteric artery were greatly enhanced in CM hamsters compared with controls. Amlodipine treatment slightly but significantly inhibited the enhanced responses in aorta but did not alter the responses in mesenteric arteries. The Ca2+ sensitivity of tension was significantly increased in CM hamster preparations, which was unaffected by amlodipine treatment. These data indicate that amlodipine treatment differentially affects the enhanced responses to vasoconstrictors between large and small blood vessels from CM hamsters. The lack of effect of amlodipine treatment on the responsiveness of CM mesenteric artery leads to the suggestion that the preventive effect of amlodipine on focal myocytolytic necrosis of cardiomyocytes, which was previously reported to be the main cause of cardiomyopathy, results from an action on cardiomyocytes.

Enhanced Na(+)-Ca2+ exchange activity in cardiomyopathic Syrian hamster

The signaling of contraction by Ca2+ in the Syrian hamster (BIO 14.6) heart in the late stage of the cardiomyopathy (220 to 300 days old) was compared with that in age-matched healthy hamster hearts. Membrane current and cell shortening or intracellular Ca2+ transients were measured simultaneously in isolated whole-cell-clamped myocytes. The density of the L-type Ca2+ current was smaller in myopathic than in normal myocytes (2.13 +/- 0.3 versus 3.21 +/- 0.4 pA/pF at 0 mV, P < .05). In both control and myopathic myocytes, the L-type Ca2+ current gated the release of Ca2+ and activation of contraction. In myopathic myocytes, activation of contraction also activated a slowly inactivating inward current of 1.73 +/- 0.2 pA/pF. The Na(+)-Ca2+ exchanger generated this current (INa-Ca), because it was suppressed by rapid replacement of Na+ with Li+ and depletion of the intracellular Ca2+ pool by caffeine. INa-Ca, activated by rapid application of caffeine, was not significantly different in both groups (3.7 +/- 0.5 pA/pF in control hearts versus 3.9 +/- 0.5 pA/pF in cardiomyopathic hearts). The activation of the inward exchanger current in myopathic myocytes coincided with a significant prolongation of contraction and the intracellular Ca2+ transient and a delay in the onset of relaxation. These results suggest that the enhanced activity of the Na(+)-Ca2+ exchanger may be related to compromised sequestration of Ca2+ in these animals.

Hypothesis: increased calcium and decreased magnesium in heart muscle and liver of pigs dying suddenly of microangiopathy (mulberry heart disease): an animal model for the study of oxidative damage

The role of calcium (Ca) and magnesium (Mg) was evaluated in pigs that died suddenly of microangiopathy (mulberry heart disease) characterized by myocardial and endothelial cell damage and capillary microthrombosis. Myocardial and hepatic Ca concentration in pigs with microangiopathy was significantly (p less than 0.001) higher than in pigs with other diseases and in healthy slaughter pigs. On the other hand, myocardial and hepatic Mg concentrations in pigs with microangiopathy was significantly (p less than 0.001) lower than in pigs with other diseases and in healthy slaughter pigs. The results indicate that increased Ca concentration was associated with decreased Mg concentration in pigs with microangiopathy. Altered Ca and Mg concentrations might reflect disturbed electrolyte homeostasis related to oxidative cardiovascular damage. The results encourage the study of the efficacy of antioxidants for prevention of myocardial Ca overload. The combined use of Mg and of Ca-antagonists with antioxidants should be evaluated for protection against experimental microangiopathy.

Enhanced alpha 1-adrenergic responsiveness in cardiomyopathic hamster cardiac myocytes. Relation to the expression of pertussis toxin-sensitive G protein and alpha 1-adrenergic receptors

The pathogenesis of the myopathy occurring in the heart of the cardiomyopathic strain of the Syrian hamster is not well understood but is believed to be associated with abnormal calcium handling by myopathic cells. The purpose of this study was to determine whether the cardiomyopathy occurring in strain BIO 14.6 animals is associated with an enhanced alpha 1-adrenergic receptor-mediated rise in cytosolic calcium, whether a pertussis toxin-sensitive G protein is involved in coupling the alpha 1-adrenergic receptor to changes in intracellular calcium and whether enhanced alpha 1 responsiveness is associated with an increase in the level of expression of the alpha 1-adrenergic receptor or in the pertussis toxin-sensitive G protein or proteins. To test the hypothesis that the cardiomyopathic state is associated with a greater alpha 1-receptor-mediated rise in cytosolic calcium, we studied the effect of phenylephrine (in the presence of propranolol) on time-averaged cytosolic calcium concentration ([Ca2+]i) in isolated cardiac myocytes from cardiomyopathic and age-matched control hamsters. Phenylephrine caused a greater increase both in time-averaged [Ca2+]i (an increase of 48 +/- 8% versus 12 +/- 3%, p less than 0.01) and in contractility (+181 +/- 22% versus +35 +/- 9%, p less than 0.01) in cardiomyopathic than in normal cardiac myocytes. Exposure to pertussis toxin (200 ng/ml for 3 hours) attenuated the alpha 1-adrenergic receptor-mediated increase in contractility and time-averaged [Ca2+]i in both cardiomyopathic and normal cells. The level of pertussis toxin-sensitive G protein, as determined by pertussis toxin-mediated [32P]ADP-ribosylation, was 1.6-fold higher in cardiomyopathic versus normal hamster hearts. The density of alpha 1-adrenergic receptors, as measured by the antagonist radioligand [3H]prazosin and the affinity of the receptor for agonist and antagonist were similar in myopathic and normal heart membranes. Thus, in cardiac myocytes from hamsters, the alpha 1-adrenergic receptor-mediated effects on [Ca2+]i and contractility appear to be mediated by a pertussis toxin-sensitive G protein or proteins. In myocytes from cardiomyopathic hamsters, these alpha 1-adrenergic effects were increased in magnitude, as was the level of pertussis toxin-sensitive G protein, but there was no measurable alteration in the density or ligand binding properties of alpha 1-adrenergic receptors.

Inotropic and calcium kinetic effects of calcium channel agonist and antagonist in isolated cardiac myocytes from cardiomyopathic hamsters

The mechanism by which heart cells of cardiomyopathic (CM) hamsters become calcium overloaded is not known. We examined the number of slow calcium channels, calcium uptake via slow calcium channels, calcium pool sizes, and the contractile response to Bay K 8644, verapamil, and nifedipine using isolated cardiac myocytes from 8-9-month-old CM hamsters (BIO 14.6) and age-matched normal controls. The number of dihydropyridine binding sites as assessed by specific binding of [3H]PN200-110 was similar in the two groups (control hearts: Bmax = 333 +/- 89 [mean +/- SD] fmol/mg; CM hearts: Bmax = 357 +/- 75 fmol/mg; n = 5 experiments, p = 0.6). Current density through L-type calcium channels was determined using the whole-cell clamp technique (at -50 mV holding potential and -10 mV test potential) and was the same in CM myocytes (17.8 +/- 1.5 [mean +/- SD] pA/pF) and control myocytes (18.6 +/- 2.1 pA/pF) (n = 5 experiments, p = 0.5). The current-voltage relation (test potentials varied from -40 to +50 mV) was also the same in CM and control cells, as was apparent threshold, peak current, and reversal potential. However, the initial rate of 45Ca influx as well as the size of the rapidly exchangeable calcium pool was significantly greater in myocytes obtained from CM than from normal hamsters. In both myocyte preparations, Bay K 8644 increased the rate of 45Ca uptake by 25% at 60 seconds; verapamil decreased 45Ca uptake at 60 seconds by 16% and 17% in normal and CM hamsters, respectively. A similar inhibitory effect was observed with nifedipine. The amplitude of cell motion in cells driven at 1.5 Hz as assessed by an optical-video system increased progressively with increasing concentrations of extracellular calcium or Bay K 8644 in cardiac myocytes from normal or CM hamsters. However, the concentration-effect curves for the two effectors were shifted to the left in CM cells compared with cells from normal hamsters. Both preparations demonstrated similar contractile responses to verapamil and nifedipine. These findings demonstrate that single enzymatically dissociated cardiac myocytes from CM hamsters have impaired contractile properties analogous to those seen in the intact heart and thus provide a useful experimental system in which to study underlying cellular mechanisms operative in this model of heart failure. Our results further indicate that calcium overload in CM hamster cardiac myocytes may not be due to increased calcium influx via dihydropyridine-sensitive calcium channels, as suggested previously, but rather to abnormalities of intracellular calcium homeostasis.

Heart protein kinase C activity increases during progression of disease in the cardiomyopathic hamster

Protein kinase C activity in the particulate fraction of the heart increases two-fold during mid-stage of disease in the cardiomyopathic hamster. No change in the corresponding enzyme activity occurs with aging in healthy control hamsters. In the solubilized particulate fraction of hearts from both myopathic and control animals, Ca++/phospholipid-dependent endogenous phosphorylation of proteins of Mr 26, 31, 45, 53, 69, 98, 105 and 126 kDa are observed. All of these proteins are more highly phosphorylated in the protein kinase C-enriched preparation from the myopathic heart compared to the control. No significant differences between myopathic and control hamsters are observed in the activities of protein kinase C or phosphoinositide-specific phospholipase C from heart cytosol.

Photoaffinity labeling of the calcium channel antagonist receptor in the heart of the cardiomyopathic hamster

The high affinity 1,4-dihydropyridine receptors of the cardiac membrane calcium channel from Syrian Cardiomyopathic hamsters were studied using [3H] PN200-110 and [3H]azidopine as ligands. [3H]Azidopine was photoincorporated covalently into bands of 180, 100, 79, 45 and 31 kDa, as determined by SDS/polyacrylamide gel electrophoresis. Photolabeling of the 180 kDa band is protected by 2 microM [1H]PN200-110 whereas the lower Mr bands are not. Thus, only the 180 kDa band is the calcium channel linked 1,4 dihydropyridine receptor. The photoincorporation into this 180 kDa band is doubled with samples of myopathic hamsters vs. control hamsters. It is suggested that the increase in calcium channel receptors may be involved in the pathogenesis of this cardiomyopathy.

Defective Ca2+-pumping ATPase of heart sarcolemma from cardiomyopathic hamster

The Syrian cardiomyopathic hamster has a hereditary disease characterized by a progressive myocyte necrosis and intracellular calcium overload. Several systems in the heart sarcolemma that regulate the rate of Ca2+ entry or efflux were examined. There is a selective decrease of Ca2+-pumping ATPase activity in the heart sarcolemma of 40-day-old myopathic hamsters, while the Na+-Ca2+ exchange system and the ouabain-sensitive (Na+ + K+)-ATPase activity remain intact. This age-dependent decrease in Ca2+-ATPase activity closely parallels the time course of lesion development. Both the affinity for Ca2+ (Km) and the maximal velocity (Vmax) of the Ca2+-dependent ATP hydrolysis are altered. In addition, there is also an increased number of calcium channel receptor binding sites. Thus the data suggest that the imbalance in Ca2+ fluxes across the cardiac plasma membrane may be involved in the pathogenesis of this cardiomyopathy.

Calcium antagonist receptors in cardiomyopathic hamster: selective increases in heart, muscle, brain

The Syrian cardiomyopathic hamster has a hereditary disease in which a progressive myocardial necrosis mimics human forms of cardiac hypertrophy. Lesions are associated with calcium overload and can be prevented with the calcium antagonist verapamil. Numbers of receptor binding sites for calcium antagonists in heart, brain, skeletal muscle, and smooth muscle were markedly increased in cardiomyopathic hamsters. The uptake of calcium-45 into brain synaptosomes was also increased in cardiomyopathic hamsters. The increase in calcium antagonist receptors and related voltage-sensitive calcium channels may be involved in the pathogenesis of this cardiomyopathy.

Low blood mononuclear cell magnesium in intensive cardiac care unit patients

Magnesium deficiency may play a role in the pathogenesis of atherosclerosis, cardiac arrhythmias, and coronary spasm. Because less than 1% of magnesium (Mg) is extracellular, the serum magnesium (sMg) does not always accurately reflect intracellular Mg stores. To determine the frequency of Mg deficiency in patients with cardiovascular disease, we measured blood mononuclear cell Mg content (mMg) and sMg concentrations in 104 unselected patients admitted to our intensive cardiac care unit (CCU). Twenty-seven normal healthy controls and 33 hypomagnesemic patients with chronic alcoholism and/or malabsorption syndrome served as reference groups. The sMg concentration in the CCU patients was 2.05 +/- 0.03 mg/dl (mean +/- SEM), and did not differ from normal controls (mean 2.01 +/- 0.03 mg/dl). Only 8 of 104 CCU patients were hypomagnesemic (7.7%). mMg in the CCU patients, however, was significantly lower than in the normal controls (1.15 +/- 0.02 micrograms/mg protein and 1.34 +/- 0.02 micrograms/mg protein respectively, p less than 0.001). Fifty-three percent (55 of 104) of CCU patients had mMg contents less than 1.119 micrograms/mg protein, i.e., below that of the lowest normal control. mMg was significantly lower in those patients with congestive heart failure (mMg = 1.08 +/- 0.03 micrograms/mg protein) when compared to those patients without congestive heart failure (1.23 +/- 0.02 micrograms/mg protein, p less than 0.001). We conclude that the incidence of intracellular Mg deficiency in patients with cardiovascular disease is much higher than the sMg would lead one to suspect, and may contribute to clinical cardiovascular morbidity.

The role of alkaline protease in the development of cardiac lesions in myopathic hamsters: effect of verapamil treatment

The role of alkaline protease in the development of myocardial lesions in myopathic hamsters was studied. There was abnormal elevation of alkaline protease in the myopathic heart at 1 month of age, preceding the development of cardiac lesions. In vivo treatments of verapamil were carried out in 1-month-old myopathic animals for 30 days. Results indicated that the drug treatment was effective in preventing the occurrence of the severe myocardial lesions found in the untreated animals at 2 months of age. Reduced lesion development was associated concomitantly with lowered levels of alkaline protease activity. Withdrawal of drug treatment caused the return of severe lesions and high levels of alkaline protease. The study of the alkaline protease activity in the skeletal muscle of the myopathic hamster also showed a parallel relationship between the enzyme levels and severity of lesions. The results are discussed in light of possible involvement of a serine protease and a Ca2+-activated protease in producing the cardiac lesions.

Intracellular elemental content of cardiac and skeletal muscle of normal and dystrophic hamsters

To test the hypothesis that the genetic lesion causing muscular dystrophy might be reflected in an abnormal intracellular elemental content, the elemental content of individual cardiac and skeletal muscle fibers in 50-day-old male control and cardiomyopathic BIO 53.58 hamsters was determined. The technique of electron probe x-ray microanalysis of freeze-dried tissue was employed. No electrolyte content differences were found between control and diseased animals for nuclei, myofibrillar cytoplasm, or mitochondrially-enriched cytoplasm of cardiac myocytes. Sulfur was elevated in dystrophic cardiac myocytes and was the only element significantly different in heart tissue of control and cardiomyopathic animals. Sulfur was also elevated in dystrophic soleus muscle fibers. The pattern of electrolyte content of these cells reflected a mixture of normal cells and damaged cells with altered electrolyte content. In this hamster model, alteration of electrolyte content of myocytes appears to be a result of the disease process and not an inherent characteristic of muscular dystrophy. The elevated sulfur in dystrophic hamster myocytes reflects a biochemical lesion which deserves further study.

A simple ashing method for determination of Mg and Ca in laboratory animal feed and tissues

A simple procedure has been developed for preparation of animal tissues and diet mixtures for Mg and Ca analysis by atomic absorption spectroscopy. This procedure involves wet ashing in warm 30% hydrogen peroxide and extraction of metals, from the dried ash, into cold, dilute nitric acid. Less than 200 mg of tissue or feed are required. Measurements obtained by this method for hamster and rat myocardium give values similar to those found previously by more cumbersome methods. Concentrations of Mg and Ca in hamster serum, bone, kidney, and liver are also reported. Recovery of magnesium from bone and heart tissue was 101% and 102%, respectively. For calcium the respective values were 99% and 98%. This procedure is simple to carry out, does not generate corrosive fumes or require expensive equipment. It can be conveniently used to prepare large numbers of samples for atomic absorption spectrophotometry.

Therapeutic trials in hamster dystrophy

Verapamil and prenylamine, which antagonize calcium influx into heart muscle cells, Dibenamine and propanolol, alpha and beta adrenergic bockers, respectively, and prostaglandin E1, which acts on permeability of cell membranes and on adrenergic neurotransmission, were all shown to markedly reduce the severity of heart lesions in UM-X7.1 cardiomyopathic hamsters. The beneficial effects of these compounds seen essentially preventive, in that they do not afford protection for fully developed skeletal muscle lesions. The occurrence of the pathologic changes in the myocardium coincides with an increased adrenergic nerve activity, and it is believed that these drugs function mainly by decreasing calcium conductivity across the sarcolemmal membranes of cardiocytes.

Glyceride metabolism in the myopathic hamster

Analysis of plasma lipids of 30- and 185-day-old BIO 82.62 myopathic hamsters and age-matched normal controls revealed a decrease in only the concentration of cholesteryl esters of 185-day-old diseased animals. Measurement of lipoprotein lipase (LPL) activity in heart, muscle, and adipose tissue showed no difference between the activity of the enzyme in the heart and muscle of the cardiomyopathic hamsters and that of the age-matched controls. In adipose tissue, however, LPL activity was depressed in the diseased animals in both age groups. No difference was found in the activity of hormone sensitive lipase. Incorporation of sn[U-14C] glycerol-3-phosphate into total lipids was found to be depressed in homogenates of heart, muscle, and adipose tissue but unchanged in liver homogenates of diseased animals. It was concluded that the decrease in the capacity to synthesize glycerides, rather than limiting substrate concentrations, could be the cause of the decrease in the lipid content in some tissues of the cardiomyopathic hamster.

Excitation-contraction coupling in heart. VII. Calcium accumulation in subcellular particles in congestive heart failure

The ability of heavy microsomes and mitochondria, isolated from the control and failing hearts of genetically dystrophic hamsters (BIO 14.6 strain), to accumulate calcium was examined. The rate and extent of energy-linked calcium binding (in the absence of oxalate) by the heavy microsomes of the failing heart were markedly depressed. The calcium uptake (in the presence of 5 mM oxalate) by the heavy microsomes of the failing heart was similar to that of the control heart. On the other hand, both the rate and extent of energy-linked calcium binding (in the absence of Pi and succinate) and calcium uptake (in the presence of 4 mM Pi and 5 mM succinate) by mitochondria were greatly reduced in the failing heart in comparison to the control. No difference in the total adenosine triphosphatase activities (Ca(++)-Mg(++) stimulated) of heavy microsomes or mitochondria was observed between the control and failing hearts. These results indicate an abnormality of subcellular membranes of the failing heart to bind calcium and support the growing conviction concerning the defective "calcium pump" as a molecular abnormality associated with a moderate degree of congestive heart failure.