Effect of hypothyroidism on the in-vivo and in-vitro uptake of sugar by rat thymocytes and on the stimulatory response to 3,5,3′-tri- l -iodothyronine

We have previously demonstrated, both in vivo and in vitro, that 3,5,3'-tri-L-iodothyronine (T3) increases the uptake of the glucose analogue 2-deoxy-D-glucose (2-DG) in rat thymocytes by acting at the level of the plasma membrane. In the present study, the effect of hypothyroidism on the basal uptake of 2-DG by rat thymocytes and their response to T3 was examined. Rats were rendered hypothyroid by thyroidectomy at 21 days of age, and experiments performed with 31- and 56-day-old animals. Uptake of 2-DG by thymocytes from hypothyroid rats, both in vivo and in vitro, was greater in 31-day-old animals and less in 56-day-old animals than that in euthyroid rats. In both age-groups, hypothyroidism increased cellular responsiveness to T3, shifting the dose-response curve to the left. Similar results were obtained in experiments in which animals were rendered hypothyroid by KCIO4. Injection of thyroid hormones into rats treated with KCIO4 reversed the effects of hypothyroidism on uptake of [3H]2-DG by thymocytes and their response to T3. From these observations it was concluded that hypothyroidism produces a time-dependent change in basal sugar uptake by rat thymocytes, and increases cellular responsiveness to the effect of T3 at the level of the plasma membrane.