Biochemical adaptations to dive-derived hypoxia/reoxygenation in semiaquatic rodents

To meet the challenges presented by dive-derived hypoxia/reoxygenation transition, the aquatic mammals possess multi-level adaptations. However, the adjustments of the semiaquatic animals as modern analogs of evolutionary intermediates between ancestral terrestrial mammals and their fully aquatic descendants are still not fully elucidated. The aim of this study was to analyze the total lactate dehydrogenase (LDH) activity (in the lactate to pyruvate direction), the LDH patterns and the antioxidant defense in the tissues (heart, kidney, liver, lung, muscle, spleen) of semiaquatic rodents such as Eurasian beaver (Castor fiber), muskrat (Ondatra zibethicus) and nutria (Myocastor coypus). Samples from Wistar rat were used for comparison. Semiaquatic rodents had higher catalase activity compared to rats. The superoxide dismutase activity was higher and the catalase activity was lower in almost all tissues of muskrat than of both beaver and nutria. Comparing beaver and nutria, no significant differences in the antioxidant enzyme activities were found for the heart, kidney and liver. In beaver, most of the examined tissues (heart, kidney, lung and spleen) use lactate as preference to glucose as a substrate but in muskrat the heart, liver and skeletal muscle showed the increased LDH activity. Nutria had the unusual LDH properties that are needed to be further investigated. Our results suggest that beaver, nutria and muskrat have distinct mechanisms of adaptation to diving hypoxia/reoxygenation and support the hypothesis that semiaquatic mammals are the intermediate animals that help to define which potential selection factors and mechanical constraints may have directed the evolution of the aquatic forms.