Re-evaluation of myocardial FDG uptake in hyperglycemia

Myocardial [¹⁸F] fluorodeoxyglucose (FDG) uptake depends on several metabolic variables in vivo. The effect of different levels of experimentally induced hyperglycemia on myocardial FDG uptake was examined. Methods: FDG uptake was studied in young Donryu rats 1 hr after intravenous injection under various pretreatments that increased serum glucose levels. Serum samples were analyzed for glucose, insulin and free fatty acids. Myocardial distribution of FDG was examined with autoradiography. Results: Administration of glucose (n = 42), triiodothyronine (n = 7), epinephrine (n = 7), dehydroascorbic acid (n = 5) and 4 mg streptozotocin (Szt, n = 10) increased glucose levels to 120-200 mg/dl. Dexamethasone (Dex, n = 34) and 6 mg Szt (n = 6) increased glucose levels to 200-450 mg/dl. Myocardial FDG uptake increased proportionately with increases in serum glucose level up to 200 mg/dl. In severe hyperglycemia (serum glucose: 200-450 mg/dl), however, the FDG uptake decreased and did not correlate with blood glucose level. A study of fractional FDG uptake calibrated by the arterial FDG curve confirmed the same results. Heterogeneous distribution of FDG was observed in the myocardium, both in fasting and in severe hyperglycemic conditions. The pattern of FDG uptake by skeletal muscles was similar to that of the myocardium, although the uptake was lower than that in the myocardium. Changes in insulin and free fatty acids levels could not explain the FDG uptake pattern in severe hyperglycemia. Blood FDG uptake level remained constant regardless of glucose level. Conclusion: Hyperglycemia induced a biphasic pattern of myocardial FDG uptake, common with skeletal muscles. The understanding of myocardial FDG uptake characteristics and their dependence on blood glucose is helpful in interpreting myocardial FDG-PET images.