Insulin-induced hypoglycemia decreases uptake of 2-[F-18]fluoro-2- deoxy-D-glucose into experimental mammary carcinoma

PURPOSE: To determine, in an animal study, whether insulin-induced hypoglycemia enhances tumor uptake of 2-[fluorine-18]fluoro-2-deoxy-D- glucose (FDG) in vivo. MATERIALS AND METHODS: Rat mammary tumors were established subcutaneously in Lewis rats. When the tumor was 1-2 cm in diameter, rats were fasted overnight and divided into two groups: control rats (n = 5) that received saline and hypoglycemic rats (n = 5) that received insulin. After 30 minutes, FDG (200 μCi [7.4 MBq]) was given intravenously. One hour after FDG injection (ie, at sacrifice), plasma glucose and insulin levels were measured and F-18 activity in tumor and normal tissues was determined. RESULTS: Mean glucose level was 32.8 mg/dL (1.8 mmol/L) and mean insulin level was 2,831.1 μU/mL (20,315 pmol/L) in the hypoglycemic animals. As compared with the control value, mean FDG uptake in tumor (percentage of injected dose [per gram of tissue] per kilogram of animal weight) significantly decreased with hypoglycemia (0.117 vs 0.331, P = .0001). Mean FDG uptake in the heart and muscle was 9.75 and 5.18 times higher, respectively, in the hypoglycemic rats (P = .0001). Thus, the tumor/muscle uptake ratio was significantly reduced with hypoglycemia (2.15 vs 31.62, P = .0002). CONCLUSION: Tumor targeting with FDG is impaired, not enhanced, by insulin-induced hypoglycemia.