The rabbit’s cardiomyocytes ultrastructure at the experimental hypothyroidism manifestation

Hypothyroidism is one of the most frequently endocrine diseases caused by dysfunction of the thyroid gland. Hypothyroidism is accompanied by reactive changes in all organs and tissues, which is due to the presence of many targets for the thyroid hormones thyroxine and triiodothyronine and the role of these hormones in the animals and human's body. Striated cardiac muscle tissue is one of the most often involved in the reactive process during hypofunction of the thyroid gland in human, and the developing changes in the myocardium are of important clinical significance. The purpose of the study is ultrastructural changes in rabbit's cardiomyocytes with experimental hypothyroidism at the manifest stage of obvious signs. Male Soviet Chinchilla kind rabbits aged 12-14 months and weighing 3.1-3.5 kg (n=10) were used as the object of the study. The animals were divided into 2 equal groups: 1) experimental (n=5), in which experimental modeling of hypothyroidism was carried out through oral administration of the antithyroid drug thiamazole (10 mg/kg for 4 weeks), which inhibits the formation of thyroid glands hormones; 2) control (n=5), who received placebo and were in a physiological state. Electron microscopy was used to study ultrastructural changes in cardiomyocytes. According to the results of the study, numerous ultrastructural changes were revealed in all compartments of cardiomyocytes: in the nucleus (wrinkling, uneven contours of the nucleus and the appearance of invaginations of the nuclear membrane, chromatin condensation), in the contractile apparatus (thinning of myofibrils, the appearance of areas of excess contraction of myofibrils with contractures), in the energy apparatus ( change in the shape of mitochondria from oval to round, swelling of mitochondria, signs of destruction of the outer and inner membranes of mitochondria), in the sarcoplasmic system (expansion of the cisterns of the sarcoplasmic reticulum), in supporting apparatus (deformation of the intercalary discs between cardiomyocytes). These changes in the ultrastructure of cardiomyocytes probably underlie the impairment of myocardial contractile functions, apoptosis of cardiomyocytes and the gradual development of heart failure against the background of hypothyroidism.