Ultrastructural changes in the myocardium of animals under conditions of simulated hyperhomocysteinemia, hyper- and hypothyroidism and their combination

Thyroid hormones have a significant impact on heart function through both genomic and non-genomic effects. Deficiency or excess of thyroid hormones leads to profound changes in the regulation of cardiac function and cardiovascular hemodynamics. The heart is the main target organ for the action of thyroid hormones and in patients with hypo- or hyperthyroidism there are marked changes in the work of the heart. The aim of the work was to establish ultrastructural changes in myocardial components in experimental hyperhomocysteinemia (HHCy) against the background of hyper- and hypothyroidism. Thiolactone HHCy was modelized by administering to animals an exogenous HCy in the form of thiolactone at a dose of 100 mg/kg body weight once a day for 28 days. Hyperthyroidism was modelized by daily administration of L-thyroxine at a dose of 200 μg/kg for the 21 days, hypothyroidism – daily administration of thiamazole at a dose of 10 mg/kg for the 21 days. Individual groups of animals were administered L-thyroxine and thiamazole in parallel with HCy. High levels of HCy adversely affected the walls of myocardial blood vessels. The lumens of hemocapillaries were plethoric, filled with erythrocytes. Changes in endotheliocytes were revealed, and cardiomyocytes contained deformed nuclei. In laboratory animals with hyperthyroidism, an increase in ultrastructural changes in the walls of blood vessels (edema of the walls of hemocapillaries, damaged cristae in mitochondria) were established. In animals that were modeled for hyperthyroidism and HHCy, more significant changes in endotheliocytes were revealed, most of the mitochondria were destroyed. More pronounced alterative changes were revealed in cardiomyocytes. An electron microscopic examination of the myocardium of animals with hypothyroidism showed significant degenerative changes in the ultrastructure of the walls of blood vessels, and hypertrophied mitochondria were also found. The combined influence of hypothyroidism and HHCy caused the most profound disturbances in the ultrastructure of cardiomyocytes and hemocapillaries in comparison with other groups of animals. The integrity of intercellular contacts was impaired, most of the mitochondria of myocytes had destroyed cristae and the outer membrane.