Effect of thyroidectomy on histochemical properties of the extensor digitorum longus and soleus muscles in rats / 体力科学

ABSTRACT

1. The effect of thyroidectomy on histochemical properties of the extensor digitorum longus and soleus muscles was studied in rats. Two or 13 months after thyroidectomy animals were killed and muscle sections of 10μm thickness were stained for succinate dehydrogenase and myosin adenosine triphosphatase activities.<BR>2. No significant difference of the body weight was found between the thyroidectomized and sham-operated control groups. There was also no significant difference in the muscle weight between the two groups except that 13 months after thyroidectomy the soleus muscle weight was significantly lower in the thyroidectomized group than in the sham-operated control group.<BR>3. The measurement of muscle fiber diameter revealed that fast-twitch oxidative glycolytic fibers of the soleus muscle were smaller in the thyroidectomized group than in the sham-operated control group two or 13 months after thyroidectomy.<BR>4. The percentage of fast-twitch fibers decreased significantly after thyroidectomy with a concomitant increase in the percentage of slow-twitch fibers in both the extensor digitorum longus and soleus muscles. This finding suggests the involvement of thyroid hormone in determining a phenotypic expression of muscle fiber type.<BR>5. The results show that thyroidectomy-induced changes differ not only between the extensor digitorum longus and soleus muscles but also between same types of fibers from the two muscles. The results also indicate that thyroidectomy-induced changes depend on the period after thyroidectomy.