[Changes in muscle fibers of the somatic type in experimental thyrotoxic myopathy]

In mice used as a thyrotoxic myopathy model, activity of some oxidation-reduction enzymes, phosphorilase and glycogen content have been studied. Three series of experiments with separate controls have been carried out. Powdered thyroidin is given to the mice per os through a special cannula. The experiment is performed for 5 months. Musculus rectus femoris is studied. With development of thyrotoxicosis and myopathy, the diameter decreases and the form of the muscle fiber undergoes certain changes. alpha-glycerophosphate dehydrogenase (GPhDG) and succinate dehydrogenase activity increases. A definite division of fibers into two types, I and II remains unchanged, while differences between the fibers of I and Ia types disappear. The core-targetoid fibers are found among muscle fibers of I and Ia types, while those of "moth-eaten" belong to the II type. Glycogen content and phosphorilase activity decrease. Subdivision of the muscle fibers into the types according to the reactions revealing glycogen and phosphorilase activity is poorly expressed or absent. Adenosintriphosphatase and lactate dehydrogenase activities do not differ essentially from that in the control. Evidently, at hyperthyroidism the oxidation-reduction processes in the muscle fibers are disturbed and first of all in the link which is connected with the main enzyme (GPhDG) activity. This results in decay and disturbance of the myofibrillar proteins synthesis, serving as one of the reasons for appearance of the muscle atrophy.