Effect of dietary zinc content on 65Zn metabolism in mice

65Zn is one of the induced radioactive nuclides which are generated in power reactors. In the present experiment, several parameters of 65Zn metabolism were studied in mice maintained on diets with various zinc contents from 45 to 4,500 mg/kg to evaluate the efficacy of the dilution method for radiation protection against internal contamination with 65Zn. Gastrointestinal absorption of 65Zn was suppressed and its excretion accelerated as the dietary zinc content increased over a wide range. Clearance of 65Zn from tissues was generally accelerated by feeding mice a high-zinc diet, but that from the femurs was not affected by dietary zinc content. Zinc concentrations in tissues were regulated homeostatically up to a dietary zinc content of 1,350 mg/kg. Although a significant accumulation of zinc occurred in the liver, pancreas, kidneys, and femurs when mice were given 4,500 mg/kg diet, the concentrations except in the femurs recovered within a few days after switching to a normal-zinc diet. These results suggest that oral administration of zinc is effective for preventing the absorption and for enhancing the excretion of 65Zn to protect the body from internal radiation exposure with this isotope.