Effect of triiodothyronine (T3) excess on fatty acid metabolism in the soleus muscle from endurance-trained rats

We studied whether short-term administration of triiodothyronine (T3) for the last 3 days of endurance training would influence the rate of uptake of palmitic acid (PA) as well as metabolism in rat soleus muscle, in vitro. Training per se did not affect the rate of PA uptake by the soleus; however, an excess of T3 increased the rate of this process at 1.5 mmol/L PA, as well as the rate that at which PA was incorporated into intramuscular triacylglycerols (TG). The rate of TG synthesis in trained euthyroid rats was reduced after exercise (1.5 mmol/L PA). The rate of PA oxidation in all of the trained rats immediately after exercise was enhanced by comparison with the sedentary values. Hyperthyroidism additionally increased the rate of this process at 1.5 mmol/L PA. After a recovery period, the rate of PA oxidation returned to the control values in both the euthyroid and the hyperthyroid groups. Examination of the high-energy phosphate levels indicated that elevated PA oxidation after exercise-training in e...