[Effect of thyroxine on distribution of lactate dehydrogenase isoenzymes and content of pyruvic and lactic acids in tissues of rats of various ages].

Distribution of lactate dehydrogenase (LDH) isoenzymes and content of lactic and pyruvic acids were studied in the heart, kidneys and skeletal muscle of rats at the age of 1, 3, 12 and 24 months at normal state and after thyroxine administration. With age the activity of aerobic isoenzymes of LDH increases and that of hybrid anaerobic isoenzymes of LDH decreases in the heart and kidneys; in the skeletal muscle the activity of LDH5 increases and that of LDH3 and LDH4 decreases, the content of the studied acids in the heart, kidneys and skeletal muscle changes irregularly. Under the effect of thyroxine the activity of aerobic isoenzymes of LDH increases in the heart of one-month animals and in the kidneys of one- and three-month animals, as well as in the skeletal muscle of 24-month rats; the activity of LDH5 rises in the skeletal muscle of one- and three-month animals. Thyroxine causes an increase in the content of pyruvic acid in the tissues of all the studied rats.