The aim of this study was to analyze the species-specific features and age-related changes in the total lactate dehydrogenase activity (LDh, EC 1.1.1.27) and LDh patterns in some tissues in three species of rodents (Rodentia) with different ecological characteristics – the northern birch mouse Sicista betulina (Pallas, 1779), the European water vole Arvicola amphibius (L., 1758) and the tundra vole Microtus oeconomus (Pallas, 1776). Compared to the European water vole and the northern birch mouse, the tundra vole had a higher content of M-subunits and the amount of LDh-5 isoenzyme in the liver and skeletal muscles, higher contents of aerobic LDh-1 isoenzymes and, respectively, of h-subunits in kidneys and heart. In the heart and kidneys, the hybrid fractions
(LDh-2, LDh-3, LDh-4) dominated over LDh-1 and LDh-5 in the northern birch mouse. The total LDh activity in the liver and kidneys of the northern birch mouse was higher than in the tundra vole. The extent of anaerobic ATP production in the liver of small rodents varied – the liver of the diving European water vole contained more LDh-2, LDh-3, LDh-4 and h-subunits than the corresponding tissue in the non-diving tundra vole. In kidneys of the northern birch mouse and European water vole, the content of the LDh-5 isoenzyme increased through the ontogeny. The LDh activity was higher in the heart
of European water vole adults compared to young animals. Species-specific differences in LDh isoenzyme spectra and total LDh activity in the studied mammals reflect their adaptation to the semi-aquatic and hibernating lifestyles.