Caesium retention during pregnancy in mice

The effect of pregnancy on caesium retention in mice was assessed. Fifteen female mice were injected with caesium-137 solution intraperitoneally and measurements of body radioactivity were performed. For the control group of mice (n=8), caesium retention could be adequately described, for the time period from day T=7 to 26 post-injection, by a two exponential model, where 90% of caesium was eliminated by a component with a biological half-time of (2.83±0.78) d and 10% by a component with a biological half-time of (16.3±7.3) d. However, an alteration of caesium elimination rate, which affects the component with the longer half-time was observed in the group of pregnant mice (n=7). The observed effect was a decrease in excretion rate, in contrast to recent human observations where an increase was found. This difference in mice is associated with changes in metabolic rate, and, to a first approximation, is related to the gain in mass during pregnancy.