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The aim of the study. The aim of this study was to establish the features of the structural organization of the chewing and lateral pterygoid muscles of immature rats during the developmental stages of experimental hypothyroidism. Materials and methods. The material for the study was the chewing and lateral pterygoid muscles of 48 white mongrel immature rats-males. The following research methods were used: mercazole-induced hypothyroidism modelling, injection method for studying the bloodstream, histological examination of blood vessels and tissue elements, electron microscopy, morphometric analysis, biochemical methods, statistical evaluation of the results. Results. A violation of thyroid homeostasis (a decrease in the concentration of thyroid hormones in the blood) has been established. In the bloodstream, edematous changes are observed histologically and submicroscopically. A decrease in the number of hemocapillaries per unit area and the number of hemocapillaries per muscle fiber have been established morphometrically. In muscle fibers, cross striation with vacuolization of endomysia and perimisia is lost. Edematous changes are observed, which are aggravated depending on the duration of experimental hypothyroidism. The glycolytic muscle fibers are more affected, and the changes are aggravated depending on the duration of the experiment. It has also been found out that there is a redistribution in the amount of muscle fibers. There is a tendency to a decrease in oxidative-glycolytic and a significant increase in glycolytic muscle fibers. The morphological changes that have been found out are accompanied by violations of the macroelement balance, in particular, the content of Ca, P, Mg, which determine the functioning of skeletal muscle tissue. Conclusion. Thus, at different periods of hypothyroidism, edematous changes occur both in the vascular wall and in muscle fibers, which are aggravated depending on the duration of hypothyroidism and are caused by a decrease in the basic metabolic rate, slowing of redox processes and tissue hypoxia. At the same time, chromotropic substances are released from bonds with proteins and accumulate in the intermediate substance with the subsequent replacement of collagen fibers by mucus-like masses.

TRANSFORMATION OF STRUCTURAL COMPONENTS OF MASTICATORY MUSCLES OF IMMATURE ANIMALS IN DIFFERENT STAGES OF MERCAZOLILUM-INDUCED HYPOTHYROIDISM