The impact of chronic radioactive stress on the immuno-physiological condition of small mammals.

The mass of internal organs and cellularity index of thymus and spleen were measured in small mammals inhabiting territories with a low level of chronic irradiation caused by the Chernobyl accident. Comparing with uncontaminated territories from the same region, bank voles (Clethrionomys glareolus) demonstrated an increase in liver and thymus mass and cellularity index of thymus, while sub-adult shrews (Sorex araneus) at contaminated territories had larger body mass, heavier spleen, kidney, and liver. These changes reflect an increase of tension in physiological and immunological processes in the small mammal populations in response to chronic irradiation, which have a non-specific, stress-causing nature. Laboratory mice, exposed to a single dose of irradiation equal to the annual dose received by wild animals at contaminated territories (0.07 Gy), in contrast, showed decreased mass of kidney, spleen and thymus, and cellularity of thymus and spleen compared to the control group. This shows a direct and specific impact of a single dose of irradiation.