Age-Related and Seasonal Changes in Muscle Antioxidant Defense and Erythrocyte Morphometric Parameters of a Muskrat Ondatra zibethicus

During adaptation to a semi-aquatic lifestyle, the muskrat ( Ondatra zibethicus ) developed numerous biochemical adaptations to maintain oxygen homeostasis. The aim of the study was to explore age-related and seasonal changes in muscle tissue antioxidant defenses and erythrocyte morphometric parameters in the muskrat. Animals were captured in autumn (juveniles and adults) and spring (adults) in the North-West of Russia (Republic of Karelia). Some physiological and biochemical parameters of “autumn” animals showed an age-related variability: in adult muskrats (most adapted to diving), as compared to juveniles, catalase activity in skeletal muscles was lower, while the respiratory function of blood was higher (due to a lower total surface area of erythrocytes). Adult muskrats demonstrated seasonal changes in some parameters: in “spring” animals, activities of catalase in the heart and superoxide dismutase in skeletal muscles were higher, while levels of low-molecular-weight antioxidants (α-tocopherol and glutathione) both in cardiac and skeletal muscles were lower compared to “autumn” animals. After a long winter (ice-fishing) season, the blood of “spring” animals contained mainly mature erythrocyte forms (normocytes), with their average diameter and surface area being larger than in adult “autumn” muskrats. Our findings, as well as data obtained on other species, support the involvement of the antioxidant system and erythrocytes in the mechanisms that maintain oxygen homeostasis in diving mammals.