INTERACTION OF THYROID STATE AND DENERVATION ON SKELETAL MYOSIN HEAVY-CHAIN EXPRESSION

The goal of this study was to examine the effects of altered thyroid s tate and denervation (Den) on skeletal myosin heavy chain (MHC) expres sion in the plantaris and soleus muscles, Rats were subjected to unila teral denervation (Den) and randomly assigned to one of three groups: (1) euthyroid; (2) hyperthyroid; (3) and hypothyroid, Denervation caus ed severe muscle atrophy and muscle-type specific MHC transformation, Denervation transformed the soleus to a faster muscle, and its effects required the presence of circulating thyroid hormone, In contrast, de nervation transformed the plantaris to a slower muscle independently o f thyroid state, Furthermore, thyroid hormone effects did not depend u pon innervation status in the soleus, while they required the presence of the nerve in the plantaris, Collectively, these findings suggest t hat both thyroid hormone and intact nerve (a) differentially affect MH C transformations in fast and slow muscle; and (b) are important facto rs in regulating the optimal expression of both type I and IIB MHC gen es. This research suggests that for patients with nerve damage and/or paralysis, both muscle mass and biochemical properties can also be aff ected by the thyroid state. (C) 1997 John Wiley & Sons, Inc.