Studies were conducted to ascertain the in vitro effect of 3,5,3′-triiodothyronine (T3) on the accumulation of the glucose analogue, 2-deoxyglucose (2-DG), by thymocytes freshly isolated from weanling rats. At a concentration of 1 μM, T3 stimulated the 15-min uptake of 3H-2-DG after cells had been exposed to T3 for only 30 min. Significant stimulation of 2-DG accumulation was produced by 1 nM T3, with increasing stimulation at doses ranging up to 10 μM. T3 did not alter the fraction of accumulated 2-DG that was phosphorylated, and kinetic studies indicated that its effect was associated with a significant increase in the apparent Vmax of 2-DG accumulation, but not the apparent Km. T3 also enhanced the accumulation by thymocytes of the nonmetabolized glucose analogue, 3-O-methylglucose (3-O-MG), an effect that was evidently the result of an increase in 3-O-MG transport into the cell, because it was seen in cells incubated with 3H-3-O-MG for only 30 s. The proportionate increase in 2-DG accumulation produced by T3 was not altered by preincubating cells with concentrations of puromycin or cycloheximide sufficient to reduce [3H]-leucine incorporation by 95%, and T3 over a period of >2 h had no effect on [3H]leucine incorporation itself.
Joseph Segal, Sidney H. Ingbar