The effects of hypo- and hyperthyroidism on nuclear, cytosolic, endoplasmic and mitochondrial fractions of sialoglycoproteins in rabbit hepatocytes.

Enhanced sialylation of glycoproteins occurs during hypo- and hyperthyroidism. The role of sialic acid (SA) in cell membranes is well-standing, but its role in intracellular structures is still under analysis. We wanted to evaluate the influence of thyroid hormones on the sialylation ratio of intracellular proteins presented in cytosolic, mitochondrial, endoplasmic and nuclear fractions of rabbit hepatocytes. Twenty-one New Zealand male rabbits were divided into three groups. Hypothyroidism (N = 7) or hyperthyroidism (N = 7) was induced by adding propylthiouracyl (2 mg/l) or L-thyroxine (12 mg/l), respectively, to the drinking water for four weeks. Results were compared with healthy (euthyroid) control animals (N = 7). After isolation of intracellular fractions, standard SDS-PAGE electrophoresis and transfer onto nitrocellulose membrane were performed. Identification of SA residue was carried out with digoxigenin- labelled lectins: Sambucus nigra agglutinin (SNA) and Maackia amurensis agglutinin (MAA). We noticed significantly higher level of SNA than MAA linkage sialoglycoproteins in all evaluated fractions. The sialylation ratio was significantly lower (P < 0.05) in the nuclear fraction in case of hyperthyroidism (detected with both agglutinins). In contrast to the nuclear fraction the content of SNA-detected sialoglycoproteins was significantly reduced in mitochondrial fraction of hyperthyroid hepatocytes (P < 0.05). Non-significant augmentation of MAA-detected sialoglycoproteins was observed in the mitochondrial fractions in both hypo- and hyperthyroidism. The fluctuations of sialoglycoproteins in endoplasmic fraction were not significant. Our work showed that the subcellular structures are rich in SA residues. Differing effects of thyroid hormones on sialylation ratio suggest an important role for hypo- and hyperthyroidism in sialoglycoprotein metabolism.

The changes in the antioxidant status of heart during experimental hypomagnesemia in balb/c mice.

The present experiment was performed to assess if hypomagnesemia can influence antioxidant status in mice heart. The results could explain possibly a free radical theory of heart damage in magnesium deficiency. We used a rodent model of hypomagnesemia. The magnesium sufficient group received a standard diet whereas a magnesium deficient group received the diet containing a trace amount of magnesium. The activities of the most important antioxidant enzymes--catalase, glutathione peroxidase and superoxide dismutase were assessed in mice heart and liver in a time dependent manner, on the 10th and the 20th day of experiment. The level of magnesium in plasma of animals receiving the magnesium deficient diet dropped twice after the 8th day and four times after the 13th day and then reached a plateau value. The activity of catalase in heart in the magnesium deficient group increased gradually and was significantly (P < 0.05) elevated by 27% on the 20th day of experiment whereas the superoxide dismutase activity was significantly decreased by 17% on the 20th day. Glutathione peroxidase activity was insignificantly elevated. The alterations of antioxidant enzyme activities in the heart indicate cardiomyocytes's exposure to oxidative stress, which can be responsible for the cardiac lesions observed during hypomagnesemia.

Mitochondrial tRNA in hyperthyroidism.

The mitochondrial tRNA were prepared from liver and brain tissues of thyroxinized and control rabbits. The presence of tRNA for twenty amino acids both in liver and brain mitochondria was revealed. The quantity of radioactive amino acids bound to the mitochondrial tRNA was higher in hyperthyreosis than in control animals but considerable differences between the brain and liver tissues were observed.

Activity of aminoacyl-tRNA synthetases in experimental hyperthyroidism in muscle tissues of the rabbit.

In cardial and femoral muscles of rabbits specific activities of aminoacyl-tRNA synthetases for twenty amino acids were generally similar, namely the activities towards amino acids and their amides, leucine, isoleucine, histidine, tyrosine, proline and serine were considerably lower than towards the remaining amino acids. Specific activities of most aminoacyl-tRNA synthetases were higher in hyperthyroidism than in euthyreosis, and were higher in femoral muscle than in heart. The response to thyroxine treatment of individual aminoacyl-tRNA synthetases in both kinds of muscles varied with respect to most of the amino acids.

[Tissue levels of some elements in hyperthyreosis in rabbits]. / Tkankowe stezenia niektórych pierwiastków w hypertyreozie u królików.

The aim of the present study was to estimate the concentration of Cu, Zn, Mg, Ca in the following tissues: brain, heart, lung, liver, kidney and femoral muscles in conditions of experimentally induced hyperthyreosis. In general, in state of hyperthyreosis the concentration of all elements was considerably higher compared to euthyreosis. However, there are a few exceptions. Liver and heart tissue possessed higher concentration of Zn and Cu and kidney of Cu in euthyreosis.

Membrane ATPase, erythrocyte sodium and potassium in haemodialysis patients.

This study was undertaken to evaluate the effect of chronic renal failure as well as dialysate sodium concentration during haemodialysis on membrane ATPase activity and erythrocyte sodium and potassium concentration. Intracellular Na and K were not changed in patients when compared to normal subjects. There was, however, a significant decrease of Na-K-ATPase activity in patients versus controls. Erythrocyte sodium increased during haemodialysis with low and normal sodium dialysate. The present results suggest that sodium dialysate concentration has an influence on the intracellular cationic homeostasis.