INFLUENCE OF CHRONIC HYPERHOMOCYSTEINEMIA ON METABOLISM OF SULFUR CONTAINING AMINO ACIDS IN THE RATS' HEART AND BRAIN ON THE BACKGROUND OF HYPERTHYREOSIS AND HYPOTHYREOSIS.

The effect of experimental HHCy on the processes of transsulfuration of sulfur amino acids in the tissues of heart and brain, the levels of HCy, cysteine, H2S in blood serum of experimental animals with hyperthyroidism and hypothyroidism has been studied in the research. The experiment was performed on white male rats with simulated HHCy, hyper- and hypothyroidism, HHCy with different thyroid function. In the heart, the activity of cysteine aminotransferase (CAT), γ-glutamate cysteine ligase (γ-GCL), sulfite oxidase (SO) was determined. In the brain, the activity of cystathionine-β-synthase (CBS), cysteine ​​dioxygenase (CDO), GCL and SO was determined. In serum the total level of HCy, cysteine ​​and H2S was evaluated. HHCy caused inhibition of transsulfuration pathway of cysteine in the brain that was evidenced by decreased activity of CBS and CAT in heart that caused increase in the level of HCy and cysteine ​​as well as decrease in the level of H2S in blood serum. Hyperthyroidism causes increased activity of CBS in brain and of CAT in heart. Hyperthyroidism leads to decrease in the level of HCy in blood serum compare to the control, as well as increase in the level of H2S compare to the group of animals with HHCy. Hypothyroidism causes inhibition of cysteine ​​metabolism, decrease in of HCy and cysteine levels. In cases of HHCy simulated by administration of thiolactone-HCy the activity of CBS and SO in the brain of rats, and CAT in the heart is increased. Hyperthyroidism causes increase of the activity of the CBS, CDO, and SO in the brain, as well as CAT in the heart. At the same time, the simultaneous administration of L-tyroxysin into the animals with HHCy leads to increase in the enzyme activity of CBS, CDO, γ-GCL and SO in the brain of the animals and increase of CAT and γ-GCL in the myocardium. Hypothyroidism in the brain of animals causes a decrease in the activity of the CBS, CAT and SO, and at the same time, the activity of SO only decreases in the myocardium of animals. An increase in the level of HCy and cysteine, a decrease in the level of H2S in the blood of experimental animals during hypothyroidism, as well as inhibition of the transsulfuration enzyme activity in the brain and heart are significant markers of the development of cardiovascular pathologies and mortality associated with hypothyroidism.