[Histochemical study on disuse atrophy of skeletal muscle in rabbit (author's transl)].

Histological and histochemical study was carried out to investigate disuse atrophy on skeletal muscle in adult albino rabbits. Untreated anterior tibial muscle and gastrocnemius muscle were studied. Three fiber types were recognized with myosin ATPase reaction, viz. type I, IIA and IIB fibers under a positive correlation with succinate dehydrogenase, phosphorylase, lactate dehydrogenase and NADH. TR stain. Statistical analysis in histogram of fiber diameter was also done. Soleus muscle mainly consisted of type I and type IIA fibers. As to developing skeletal muscle after birth in rabbits, especially in neonatal periods, type IIC fiber and also myotubes were demonstrated, with a gradual decrease in the process of growth. Fiber type ratio were examined in the anterior tibial and soleus muscle. In soleus muscle, type I fiber increased in numbers along with growth. Fibers, reacting with both ATPase pH 9.4 and SDH stain decreased in number. In the anterior tibial muscle, on the other hand, numbers of type I fiber were unremarkable, but all of the fibers were stained moderately with succinate dehydrogenase in neonatal periods, and fibers, with evident ATPase (pH 9.4) and SDH stain, decreased in numbers with growth. Instead, type IIB fibers appeared. Cast immobilization were applied on the legs of rabbits under three different positions, namely in so-called neutral, relaxed and stretched, in order to examine anterior tibial and gastrocnemius muscle respectively. In the neutral posture, three to four weeks after immobilization, decrease in size of type IIA fibers in the anterior tibial muscle was remarkable, whereas, in gastrocnemius muscle less than three weeks after immobilization type IIA and also type I fibers were involved predominantly. In gastrocnemius muscle under relaxed posture, type IIA and also type I fiber were decreased in fiber diameter only two weeks after immobilization, whereas, under stretched posture only type IIA fibers were involved three to four weeks after immobilization. In the anterior tibial muscle under stretched posture, same results were not obtained as in the gastrocnemius muscle. Less significant change of fiber type ratio was recognized in the anterior tibial muscle after four weeks immobilization.