To investigate whether there is a permanent translocation of Thorotras
t in the body, the liver of male Lewis rats was removed 4 weeks after
injection of Thorotrast (300 pi) and replaced by a donor liver. In hal
f of the animals the spleen was removed as well. Measuring the Th-232
content in the donor liver at different times after implantation demon
strated a permanent transport of Th-232 into the surrogate organ. Afte
r 231 days a Th-232 depot of about 1.1 mg was found, representing abou
t 3% of the total body burden. The additional removal of the spleen re
sulted in a significantly lower transport of Th-232 into the implanted
liver. Histological examinations of the donated livers revealed incre
asing local concentration of Thorotrast granules, leading to the devel
opment of conglomerates. A comparable translocation of Thorotrast was
verified in two humans who required liver transplantation more than 40
years after Thorotrast injection.