MORPHOFUNCTIONAL ORGANIZATION OF MUSCLES M. SOLEUS UNDER CONTINUOUS STATIC LOAD CONDITIONS

ABSTRACT

In this study, the level of expression of regeneration markers in the muscle fibers (MV) of the soleus muscle in rats under conditions of extended static load was analyzed. As a result of our study, significant destructive changes in the muscle fibers of M. Soleus are shown, manifested in hypotrophy and heterogeneity of MV against the background of extended static load. In addition, a decrease in the expression level of the activated satellite marker CD34, the proliferative activity marker Ki67 and the vascular endothelial growth factor receptor VEGFR-1 was revealed.

Keywords: Muscle fibers, static load, regeneration, immunohistochemistry.

It is known that the mode of functioning of skeletal muscles determines such important physiological characteristics as the strength and speed of contraction. Long-term static loading is unusual for some skeletal muscles and leads to significant morphological and biochemical changes that can affect both structural and functional parameters. The relevance of our study is due to insufficient knowledge of the biochemical aspects of skeletal muscle regeneration under static load.

The purpose of our study is to study the morphological aspect of the regeneration of m. Soleus in rats on the background of long-term static load.

Materials and research methods. The object of the study is the soleus muscle, which is involved in walking and maintaining a static posture.

The study was conducted on male Wistar rats 4-5 months of age (n=16), which were divided into two groups: the control group (C) n=8 - intact animals and the group of rats that were subjected to long-term static load (SN) n=8.

A long-term static load in rats was simulated for 28 days (three times for 20 minutes), by a long stay of rats in a vertical position on a wooden pole in a structure with glass walls 1 m high, from below the metal floor of the installation, to which a voltage of 60V (S Katsuta, 1974, modified by N. P. Rezvyakov et al., 1980) [3]. On the 28th day of the study, rats were anesthetized and killed by decapitation, m. Soleus, which were fixed in 10% formalin solution. All experimental animals were kept under the same conditions in accordance with the standards approved by the European Convention for the Protection of Vertebrate.

From isolated biopsies m. Soleus Histological micropreparations were prepared according to the standard method and stained with hematoxylin - eosin. Immunohistochemical study was carried out using an indirect streptavidin-biotin detection system using antibodies to CD34, Ki67, VEGF (BioNovus, USA).

Statistical data processing was performed using the STATISTICA V.10.0 software package. For all available samples, an analysis was made of the correspondence between the type of distribution of quantitative traits and the law of normal distribution using the Shapiro-Wilk test. A comparative analysis of the groups was carried outusing parametric methods (Student's t-test).

Results and its discussion. During the morphometric analysis of muscle fibers (MF), an assessment was made of their cross-sectional area, the thickness of the endomysium, as well as the number of nuclei per 100 μm of the length of the MF (Table 1).

Table 1.

Morphometric parameters of muscle fibersm. Soleusin rats against the background of prolonged static load

* Differences with the control group statistically significant p<0.05

In the group of rats to which a static load was applied, a statistically significant decrease in the area of MV m was found. Soleus by 23%, while the thickness of the endomysium increased by 47% compared to the control group. (Table 1).

According to some myologists, muscular dystrophy is observed regardless of the magnitude of the load, even when the volume load is presented in different conditions, accompanied by structural and functional changes in muscles depending on the type of load. [6, 7]

As part of an immunohistochemical studywe performed muscle fiber typing m. Soleusin rats under conditions of prolonged static load and in the control group on the level of expressionmarkers CD34, Ki67, VEGF.

In the group of rats that were presented with a static load, the proportionCD34+ satellite cells, involved in the maintenance and modulation of tissue homeostasis, in relation to the control turned out to be 75% less, which indicates a violation of the regeneration process.

Typing for the expression level of the Ki-67 proteinshowedstatistically significant decrease in the proportion of positively stained cells, in the experimental group of rats by 67% compared with the control group, which may indicate a violation of proliferative activity in the muscle fibers of the soleus muscle.

In some recent studies of the morphological features of m.Soleus against the background of dynamic loading, an increase in the blood supply of the MV associated with an increase in the number of blood vessels has been shown. [5]. Whereas inIn our study of the effect of prolonged static load on the soleus muscle, we found a decrease in the level of expression of the vascular endothelial growth factor receptor VEGFR-1. Therefore, the response of skeletal muscle to the type of exercise depends on the phenotype of muscle fibers [5].

In our study, we analyzed the morphological aspect of the regenerative potential of muscle fibers m. Soleus under static load conditions and formulated the following conclusions:

1. A hypotrophic effect was found under conditions of static load on muscle fibers m. Soleus, manifested in a decrease in the area of ​​the MV, the number of nuclei per 1 μm of muscle fiber, at the same time in the thickening of the endomysium.
2. A decrease in the expression level of the satellite cell marker CD34, the proliferation marker Ki67, and the receptor for endothelial vascular growth factor VEGF was shown against the background of a static load in MV m. Soleus, which may indicate a violation of the process of regeneration of muscle fibers.

References:

1. Boldarev, M.A. The role of static and dynamic loads in the adaptation processes of muscle tissue and the percentage of their use in the training program. Physical culture and sport at the present stage: problems, searches, solutions: Palkin, M.V. // Materials of the interregional scientific and practical conference.−2014.−S. 210.
2. Koryak Yu.A. 60-day hypokinesia and human skeletal muscle response on the example of the triceps muscle of the leg // International Journal of Applied and Fundamental Research. - 2014. - No. 4. - P. 79-88.
3. Romanova, A. R. Morphological characteristics of M. Soleus against the background of prolonged static load and anabolic steroids / A. R. Romanova, L. A. Sharafutdinova // Bulletin of the Bashkir State Medical University. - 2021. - No. 6. - P. 75-84.
4. Samsonova, A.V. Muscle biomechanics: teaching aid / A.V. Samsonova, E.N. Komissarov // Ed. A.V. Samsonova.−2008.−S. 127.
5. V.A. Pastukhova Structural restructuring of skeletal muscles under the influence of prolonged physical exertion / -2014, -Volume 12, No. 4 UDC: 591.473:796.015.6+575.113.1
6. Leonardo Carvalho, Roberto Moriggi Junior, Julia Barreira/ Muscle hypertrophy and strength gains after resistance training with different volume-matched loads: a systematic review and meta-analysis –Apr;47(4):357-368.doi:10.1139/apnm-2021-0515. Epub 2022 Jan 11.
7. MJ McDonagh, C.T. Davies/ Adaptive response of mammalian skejetaj muscle to exercise with high loads – 1984;52(2):139-55.doi:10.1007/BF00433384.