[Histochemical studies of muscle fibers of the triceps surae in the rat under different types of tonus].

To investigate the relationship between muscle atrophy and its tonus, triceps surae in four groups of rats were studied changing the muscle tonus by cutting of Achilles tendon, by shortening or lengthening of the tibia and compared with those of control groups. During the eight weeks after the operation, rats were sacrificed every week except for the seventh. The muscles were evaluated by histochemical methods (NADH-TR and myosin ATPase reaction), in which the diameter of the muscle fiber was measured according to the Brooke method. The following results were obtained; (1) Targetoid fibers were observed more frequently among type 1 fibers as the muscle tonus was decreased. (2) Diameter of both fiber types was reduced as the muscle tonus changed. (3) These changes were reversible as the muscle tonus was restored to normal.