Effects of thyroid hormones on muscle and bone in mice.

ABSTRACT: BACKGROUND: : The significance of muscle-bone interactions in bone metabolism and the pathophysiology of osteoporosis has been recognized. However, the effects of thyroid hormones on muscle-bone interactions remain unclear. ABSTRACT: METHODS:: We herein investigated the effects of hyperthyroidism on muscle and bone by administering L-thyroxin to male mice for 4 weeks. ABSTRACT: RESULTS:: A micro-computed tomography analysis showed that the administration of L-thyroxin significantly decreased trabecular bone mineral density, bone volume/tissue volume, trabecular number, trabecular thickness, and connectivity density at the femurs of mice and slightly reduced cortical thickness. However, the administration of L-thyroxin did not affect muscle mass in the lower limbs, tissue weights of the soleus and gastrocnemius muscles, or grip strength. Among the myokines examined, the administration of L-thyroxin significantly decreased the messenger RNA level of follistatin in the soleus muscle and simple regression analyses showed a positive correlation between follistatin levels and bone volume/tissue volume; however, it did not affect serum follistatin levels. ABSTRACT: CONCLUSIONS:: The present results suggest that hyperthyroidism induced by the administration of L-thyroxin caused trabecular-dominant osteopenia without reducing muscle mass or grip strength in mice. The direct effects of thyroid hormones on bone, but not muscle-bone interactions, may be crucial for hyperthyroidism-induced osteoporosis.