Effect of thyroxine on the lactate dehydrogenase isoenzyme composition of chicken tissues in ontogeny

Using disc electrophoresis in polyacrylamide gel, studies have been made on the content of isoenzymes of lactate dehydrogenase in the mitochondria and cytoplasm from the brain, heart and liver after thyroxine administration to embryonal, early postnatal and adult hens. After this administration, the isoenzymic composition becomes more complex, redistribution of separate isozymes being observed in ontogenesis. The level of aerobic form of LDH increases at early stages of ontogenesis, that of anaerobic ones--in adult birds. Basing on their different functional role due to the presence of H- and M-subunits, it may be suggested that thyroxine administration results in a compensatory increase of the oxidative or glycolytic processes at the corresponding stages of ontogenesis, these changes reflecting phylogenetic peculiarities of the formation of the hormonal control of lactate dehydrogenase in tissues of birds.