Altered myosin isoform expression in rat skeletal muscles induced by a changed thyroid state

The aim of our study was to find out, which are the thyroid linked mechanisms responsible for the changes in myosin isoform composition which accompany endurance training (ET) in rodents. We studied the interaction between ET and altered sedentary group with no thyroid treatment or Se group. Six groups of rats were compared: (1) a trained group with no thyroid treatment or T group; (2) a thyroid state in rats; (3) a sedentary group rendered hypothyroid with 6-n-propyl thio uracil (H); (4) a sedentary group rendered hyperthyroid with T3 (150 microg kg(-1) every other day for 4 weeks) (St); (5) trained rats rendered hyperthyroid with T3 (150 microg kg(-1) every other day for 4 weeks) (Tt) and (6) a trained group kept euthyroid with T3 (150 ng kg(-1) every other day for 4 weeks) (Te). In each group myosin isoform composition was determined in five muscles, three locomotor muscles: (1) extensor digitorum longus, (2) superficial lateral gastrocnemius, (3) deep medial gastrocnemius, (4) an antigravity muscle, the soleus and (5) a rhytmic respiratory muscle, the crural diaphragm. Different muscles responded in a specific way to variations of the thyroid state and training.