Removal of 65Zn from mouse body by isotopic dilution and by DTPA chelation

Isotopic dilution with stable zinc and chelation with DTPA are recommended for removal of radioactive zinc from the body; however, it is unclear which method is more effective. In the present study, the efficacies of these methods were compared in order to determine which treatment should be selected in case of internal contamination with radioactive zinc. Intraperitoneal administration of stable zinc dose-dependently removed 65Zn from the mouse body. However, the dose could not be increased above 3 mg/kg due to its toxicity. Oral administration of zinc was less effective than intraperitoneal administration at the same dose. Our results suggest that the recommended dose of stable zinc (2-3 mg/kg, p.o.) has little efficacy. The efficacies of Ca-DTPA and Zn-DTPA were strongly dependent on the elapsed time after 65Zn exposure. Zn-DTPA was more effective than Ca-DTPA, and its recommended dose (30 micromol/kg) significantly removed 65Zn. Therefore, chelation therapy with Zn-DTPA should be started as soon as possible after internal contamination with radiozinc.