LABORATORY INVESTIGATION CARDIOMYOPATHY Improvement in myocardial performance without a decrease in high-energy phosphate metabolites after isoproterenol in Syrian cardiomyopathic hamsters

To determine the effect of isoproterenol on cardiac energetics and function in an animal preparation of cardiomyopathy, we studied Langendorif perfused hearts from Syrian cardiomyopathic hamsters. High-energy phosphate metabolites (phosphocreatine [PCr], ATP, inorganic phosphate [Pi]) and intracellular pH (pHi) were measured by 31P nuclear magnetic resonance spectroscopy and correlated with left ventricular developed pressure, coronary flow, and 02 consumption before and during a 106M infusion of isoproterenol. Total intracellular calcium was also determined by atomic absorption spectroscopy with the use of potassium ethylenediamine tetra-acetate cobaltate as a marker for extracellular space. In cardiomyopathic hamsters, isoproterenol infusion increased mean developed pressure by 300% (p < .005 compared with control; n = 5), 02 consumption eightfold (p < .0005), and PCr by 40% (p < .05). PCr/Pi ratio, which is analogous to phosphorylation potential, improved 100% (p = .05). In normal hamsters, isoproterenol infusion resulted in an 83% increase in developed pressure (p < .001) and a 25% increase in 02 consumption (NS). However, mean PCr and PCr/Pi decreased by 30% and 50%, respectively (p < .05 for both), during isoproterenol infusion. pHi decreased in normal animals (p < .01), but tended to improve in diseased animals (NS) during isoproterenol infusion. Freeze-clamp measurements of phosphate metabolites correlated well with the nuclear magnetic resonance data. Intracellular calcium increased from 0.0102 + 0.002 to 0.144 + 0.030 gmol/ml heart water in normal hamsters during isoproterenol infusion. Cardiomyopathic hamsters had a markedly elevated baseline calcium content of 60.82 + 5.85 .mol/ml heart water due to the presence of dystrophic calcification. Isoproterenol did not significantly alter this calcium content. We conclude that in cardiomyopathic hamsters, isoproterenol markedly increases contractile function and energy demand without an associated deterioration in the high-energy phosphate profile. In contrast, normal hamsters are unable to synthesize sufficient ATP to replenish the amount used in meeting the increased workload during isoproterenol infusion. Circulation 77, No. 3, 712-719, 1988. THE ROLE of catecholamines in cardiac disease is complex and poorly understood. Adrenergic dysfunction1-5 has been implicated in the pathogenesis of the hereditary polymyopathy seen in a strain of Syrian hamsters designated UM-X7.1, a derivative of the Bio 14.6 strain.6 These animals develop a cardiomyopathy From the Departments of Medicine (Cardiology), Radiology, Pharmaceutical Chemistry, and the Cardiovascular Research Institute, University of California, San Francisco, and the Department of Pathology, Faculty of Medicine, University of Montreal. Supported in part by the Susan and Don Schleicher Fund and the George D. Smith Fund and by a grant from the Fannie E. Rippel Foundation. Dr. Camacho is supported by NHLBI Institutional NRSA grant in Heart and Vascular Diseases, HL07192. Address for correspondence: S. Albert Camacho, M.D., Division of Cardiology, University of California, San Francisco, 1186-Moffitt Hospital, San Francisco, CA 94143. Received Sept. 19, 1986; revision accepted Nov. 20, 1987. 712 with distinct phases of heart failure that has been extensively studied as a model of dilated cardiomyopathy.6' 7 Cardiac necrosis and myolysis are noted by 30 to 40 days of age. By 90 to 100 days of age the degenerative changes subside and myocardial hypertrophy, dilatation, and fibrosis develop. Congestive heart failure, manifested by tachypnea, ascites, hepatomegaly, and peripheral edema, is evident by 180 to 200 days of age.6 During the necrotic phase, increased numbers of adrenergic nerve terminals,3 increased norepinephrine uptake,4 and elevations of urinary norepinephrine levels2 have been documented, suggesting catecholamine dysfunction. Isoproterenol (a synthetic catecholamine), when given in 1 to 20 mg/kg doses, has been shown to increase total myocardial calcium content in these animals.8 This exacerbates the intracellular calCIRCULATION by gest on A ril 9, 2017 http://ciajournals.org/ D ow nladed from LABORATORY INVESTIGATION-CARDIOMYOPATHY cium overload that is a prominent feature of this myopathy.9-12 The pathologic changes observed in hearts from this myopathic strain are also reminiscent of the cardiac necrosis seen in isoproterenol overdose.5 Unexpectedly, Jasmin and Proschek13 found that long-term isoproterenol (0.05 mg/kg injection twice daily) prevented development of the myocardial necrotizing process in young cardiomyopathic hamsters. Isoproterenol-treated diseased hamsters also had a 60% reduction in serum creatine kinase and a 75% reduction in myocardial calcium when compared with untreated myopathic hamsters. This study suggests that isoproterenol, when given in appropriate doses, may have beneficial effects in this cardiomyopathic preparation. Isolated Langendorff heart preparations from cardiomyopathic hamsters in the postnecrotic stage were therefore studied to: (1) determine the hemodynamic effect of adding isoproterenol to the perfusate, (2) correlate myocardial performance with energy metabolism as measured by 31P nuclear magnetic resonance (NMR) spectroscopy, and (3) compare the effect of isoproterenol on cardiomyopathic and healthy control hamsters. Left ventricular developed pressure (developed pressure) coronary flow, and 02 consumption were monitored simultaneously with measurements of ATP, phosphocreatine (PCr), inorganic phosphate (Pi), and intracellular pH (pHi) obtained by 31P NMR spectroscopy. Traditional freeze-clamp biochemical methods were used to confirm the 31P NMR data. In addition, the effect of short-term isoproterenol administration on total intracellular calcium was evaluated by atomic absorption spectroscopy with the use of potassium ethylenediamine tetra-acetate cobaltate (KCoEDTA) as an extracellular marker.