Myocardial Glucose Uptake Measured with Fluorodeoxyglucose: A Proposed Method to Account for Variable Lumped Constants

Quantitative assessment of myocardial glucose uptake by the glucose tracer analog 2-deoxy-2-[18F]fluoro-D-glucose (FDG) depends on a correction factor (lumped constant [LC]), which may vary. We propose that this variability is caused by different affinities of FDG and glucose for membrane transport and phosphorylation and can be predicted from the time course of FDG retention. We therefore measured the LC under steady-state metabolic conditions and compared the results with values predicted from the tracer retention alone. Methods: We mea sured rates of myocardial glucose uptake by tracer ([2-3H]glu-cose) and tracer analog methods (FDG) in isolated working Sprague-Dawley rat hearts perfused with Krebs buffer and glucose, or glucose plus insulin or ß-hydroxybutyrate. In sepa rate experiments, we established the theoretical upper and lower limits for the LC (R, and Rp),which are determined by the relativ