Incorporation of [3-3H]Glucose and 2-[1-14C]Deoxyglucose Into Glycogen in Heart and Skeletal Muscle In Vivo: Implications for the Quantitation of Tissue Glucose Uptake

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Abstract
2-deoxyglucose has been widely used to quantitate tissue glucose uptake in vivo, assuming that 2-deoxyglucose is transported and phosphorylated but not further metabolized. We examined the validity of this assumption by infusing [3-3H]glucose and 2-[1-14C]deoxyglucose in a similar primed continuous fashion to chronically catheterized, freely moving rats during normoglycemic hyperinsulinemic conditions. The rates of 2-deoxyglucose uptake were determined from the accumulation of 2-[1-14C]deoxyglucose-6-phosphate and 2-[1-14C]deoxyglucose-6-phosphate combined with the rate of the incorporation of 2-[1-14C]deoxyglucose into glycogen in rectus abdominis muscle and the heart. When the rates of glycogen synthesis during the 2-h hyperinsulinemic period from the two tracers were compared in rectus abdominis muscle, the rate of glycogen synthesis was twofold higher when measured with [3-3H]glucose (337 ± 14 µmol · kg−1 · min−1) than when measured with 2-[1-14C]deoxyglucose (166 ± 10 µmol · kg−1 · min−1, P < 0.001). In the heart, the rate of glycogen synthesis was twofold higher when measured with 2-[1-14C]deoxyglucose (141 ± 20 µmol · kg−1 · min−1) than when measured with [3-3H]glucose (72 ± 15 µmol · kg−1 · min−1, P < 0.001). The rate of 2-deoxyglucose uptake was 29% underestimated in rectus abdominis muscle, when counts found in glycogen were not included in glucose uptake calculations (398 ± 25 vs. 564 ± 25 µmol · kg−1 · min−1, P < 0.001). In the heart, glucose uptake was underestimated by 7% if glycogen counts were not taken into account (1,786 ± 278 vs. 1,926 ± 291 µmol · kg−1 dry · min−1, P < 0.05). The fraction of [3-3H]glucose incorporated into glycogen of total glucose metabolism (calculated from 2-deoxyglucose conversion to 2-deoxyglucose-6-phosphate and glycogen) was 0.6 (337/564) in rectus abdominis muscle and 0.037 (72/1,926) in the heart. We conclude that 2-deoxyglucose is incorporated into glycogen in the heart and in skeletal muscle in vivo under normoglycemic hyperinsulinemic conditions in the rat. Failure to consider the incorporation of 2-deoxyglucose into glycogen will underestimate the rate of tissue glucose uptake. To avoid such problems, the amount of 2-deoxyglucose incorporated into glycogen should be quantitated in subsequent studies.

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