Glucose uptake in rat soleus: Effect of acute unloading and subsequent reloading

The effect of acutely reduced weight bearing (unloading) on the in vitro uptake of 2-[1,2-³H]deoxy-D-glucose was studied in the soleus muscle by tail casting and suspending rats. After just 4 h, the uptake of 2-deoxy-D-glucose fell (-19%, P < 0.01) and declined further after an additional 20 h of unloading. This diminution at 24 h was associated with slower oxidation of [¹⁴C]glucose and incorporation of [¹⁴C]glucose into glycogen. Unlike after 1 day, at 3 days of unloading basal uptake of 2-deoxy-D-glucose did not differ from control. Reloading of the soleus after 1 or 3 days of unloading increased uptake of 2-deoxy-D-glucose above control and returned it to normal within 6 h and 4 days, respectively. These effects of unloading and recovery were caused by local changes in the soleus, because the extensor digitorum longus from the same hindlimbs did not display any alterations in uptake of 2-deoxy-D-glucose or metabolism of glucose. This study demonstrates that alterations in contractile activity, brought about by unloading or recovery from unloading, can influence the regulation of glucose transport in the soleus.