Energy metabolism and oxidative status of rat liver mitochondria in conditions of experimentally induced hyperthyroidism.

The aim of the present work was to investigate the energy metabolism and antioxidant status of rat liver mitochondria using a model of hyperthyroidism. In experimental animals, the level of triiodothyronine and thyroxine was increased 3- and 4-fold, respectively, in comparison with that in the control group, indicating the development of hyperthyroidism in these animals. Oxygen consumption was found to be higher in rats with experimentally induced hyperthyroidism (from 20 to 60% depending on the experimental scheme used), with a slight decrease in the efficiency of oxidative phosphorylation and respiratory state ratio. It was shown for the first time that the level the respiratory complexes of the electron transport chain in hyperthyroid rats increased; however, the quantity of complexes III and V changed unreliably. The assay of respiratory chain enzymes revealed that the activities of complexes I, II, and citrate synthase increased, whereas the activities complexes II + III, III, IV decreased in liver mitochondria of the experimental animals. Alterations in the oxidative state in liver mitochondria were found: a 60% increase in the hydrogen peroxide production rate and a 45% increase in lipid peroxidation. The activities of superoxide dismutase and catalase in the liver of experimental rats were higher than in the control. At the same time, the activity of glutathione peroxidase did not change. The data obtained indicate that the known activation of metabolism and changes in the oxidative status in thyrotoxicosis are associated with variations in the respiratory chain functioning and the antioxidant enzymes of mitochondria.

Formation of lamellar bodies in rat liver mitochondria in hyperthyroidism.

In the present work, ultrastructural changes of rat liver mitochondria in hyperthyroidism were studied. Hyperthyroidism was induced in male Wistar rats by daily administration of 100 µg thyroxin per 100 g body weight for 5 days. The level of triiodothyronine and thyroxine increased 3- and 4-fold, respectively, in comparison with the same parameters in the control group, indicating the development of hyperthyroidism in experimental animals. It was found that under this experimental pathology 58% of the mitochondria are swollen, with their matrix enlightened, as compared to the control. In 40% of the profiles, the swollen mitochondria in the liver under hyperthyroidism exhibited rounded mono- or multilayer membrane structures, called lamellar bodies (LBs), presumably at different stages of their development: from the formation to the release from the organelles. Most LBs were located in the mitochondria near the nuclear zone (27%), while their number was reduced in the part of the cell adjacent to the plasma membrane. In a number of swollen mitochondria the cristae were shown to change their orientation, being directed radially toward the center of the mitochondria. We suggested that it is the first stage of formation of LBs. The second stage can be attributed to the formation of monomembrane structures in the center of the organelles. The third stage is characterized by the fact that the membrane of the lamellar bodies consists of several layers, and in this case the bodies were located closer to the outer mitochondrial membrane. The evagination of the outer mitochondrial membrane and its connection with lamellar structure can be recognized as the fourth stage of formation of LBs. At the fifth stage the developed lamellar formations exited the mitochondria. At the same time, following the exit of LBs from the mitochondria, no damage to the mitochondrial membrane was registered, and the structure of the remaining part of the mitochondria was similar to the control. The nucleus of the hepatocyte also underwent structural changes in hyperthyroidism, exhibiting changes in the membrane configuration, and chromatin condensation. The nature and structure of the LBs, as well as their functional role in the liver mitochondria in hyperthyroidism, require further investigation.

Energetic, oxidative and ionic exchange in rat brain and liver mitochondria at experimental audiogenic epilepsy (Krushinsky-Molodkina model).

The role of brain and liver mitochondria at epileptic seizure was studied on Krushinsky-Molodkina (KM) rats which respond to sound with an intensive epileptic seizure (audiogenic epilepsy). We didn't find significant changes in respiration rats of brain and liver mitochondria of KM and control rats; however the efficiency of АТР synthesis in the KM rat mitochondria was 10% lower. In rats with audiogenic epilepsy the concentration of oxidative stress marker malondialdehyde in mitochondria of the brain (but not liver) was 2-fold higher than that in the control rats. The rate of H2O2 generation in brain mitochondria of КМ rats was twofold higher than in the control animals when using NAD-dependent substrates. This difference was less pronounced in liver mitochondria. In KM rats, the activity of mitochondrial ATP-dependent potassium channel was lower than in liver mitochondria of control rats. The comparative study of the mitochondria ability to retain calcium ions revealed that in the case of using the complex I and complex II substrates, permeability transition pore is easier to trigger in brain and liver mitochondria of KM and КМs rats than in the control ones. The role of the changes in the energetic, oxidative, and ionic exchange in the mechanism of audiogenic epilepsy generation in rats and the possible correction of the epilepsy seizures are discussed.