Study on the techniques to stimulate in vivo excretion of radioactive substances through complex formation

This study was made aiming to develop a reagent which can form specific stable complexes with extremely toxic radioactive metals such as 63Ni, 109Cd, 210Pb and 125Sb, and rapidly excrete them from the body. Further, to solve the problems of the exposure to those metals, an establishment of radiopreventive technology was attempted using such reagents. Thus, it was needed to obtain fundamental data of various radioactive metals in respects of their uptake pathways to each organ, the accumulation level and the existing forms. Here, the effects of Ni, Cd and Pb administrations on the rat were investigated with regard to 1) changes in the body weight, 2) changes in organ weights, 3) accumulation levels in major organs and 4) values of blood chemical examination. Although most of essential elements are in the homeostatic conditions, there are no homeostatic mechanisms for Cd and Pb, resulting that the accumulation levels of the two were dependent on each uptake amount. However, any significant poisoning symptoms were not observed in the rats which daily received a total amount of heavy metals, 100 mg/body for 23 days. This is likely mediated by the function of metallothioneine. Therefore, it seems necessary to develop a complexing agent which can form more stable complexes with both hydrophilic and hydrophobic properties. (M.N.)