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Kinetic Differences and Similarities Among 3 Tracers of Myocardial Glucose Uptake

Division of Cardiology, Department of Medicine, University of Texas-Houston Medical School, Houston, Texas

Correspondence: For correspondence or reprints contact: Heinrich Taegtmeyer, MD, PhD, Division of Cardiology, Department of Internal Medicine, University of Texas-Houston Medical School, 6431 Fannin, MSB 1.246, Houston, TX 77030.

ABSTRACT

Two glucose tracer analogs, uniformly labeled [¹⁴C]2-deoxyglucose ([U-¹⁴C]2DG) and FDG, are widely used to assess myocardial glucose uptake. Despite the similar electron configuration of the fluorine and hydrogen atoms, uptake of the 2 tracer analogs may not be the same because of their different electronegativity. Methods: To test this hypothesis, we determined glucose uptake in isolated rat hearts simultaneously from the accumulation of [U-¹⁴C]2DG radioactivity in the tissue, by continuous monitoring of FDG accumulation with a pair of coincidence detectors and by cumulative release of ³HOH from [2-³H]glucose. A first group of hearts was perfused at physiologic workload with Krebs-Henseleit buffer containing 10 mmol/L glucose; a second group, with the buffer containing 5 mmol/L glucose plus 0.4 mmol/L oleate and 1 mU/mL insulin. Third and fourth groups were subjected to ischemia (i.e., a 75% reduction in coronary flow) and reperfused. For the third group, the buffer contained 5 mmol/L glucose; for the fourth, 5 mmol/L glucose plus 0.4 mmol/L oleate. Results: No difference in the total amount of tracer accumulation in any group was seen between the 2 tracer analogs. The ratio [±SD] of [U-¹⁴C]2DG to FDG ranged from 0.93 ± 0.09 to 1.31 ± 0.11. However, both tracer analogs paralleled glucose uptake in the absence of insulin but underestimated glucose uptake significantly in the presence of insulin. Changes in 2DG uptake with ischemia and reperfusion could be detected only with FDG. Conclusion: Although uptake of [U-¹⁴C]2DG equals uptake of FDG quantitatively, acute changes in 2DG uptake (and, thus, in the tracer-tracee relationship) are detectable only with the fluorine-labeled tracer.

Key Words: isolated working rat heart • positron counting • autoradiography • insulin • ischemia • reperfusion • lumped constant