Improvement in myocardial performance without a decrease in high-energy phosphate metabolites after isoproterenol in...

To determine the effect of isoproterenol on cardiac energetics and function in an animal preparation of cardiomyopathy, we studied Langendorff 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 O2 consumption before and during a 10(-6)M 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 less than .005 compared with control; n = 5), O2 consumption eightfold (p less than .0005), and PCr by 40% (p less than .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 less than .001) and a 25% increase in O2 consumption (NS). However, mean PCr and PCr/Pi decreased by 30% and 50%, respectively (p less than .05 for both), during isoproterenol infusion. pHi decreased in normal animals (p less than .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 mumol/ml heart water in normal hamsters during isoproterenol infusion. Cardiomyopathic hamsters had a markedly elevated baseline calcium content of 60.82 +/- 5.85 mumol/ml heart water due to the presence of dystrophic calcification.(ABSTRACT TRUNCATED AT 250 WORDS)