Promotion of radioisotope excretion.

Nuclear medicine would be greatly aided if compounds were available to promote the excretion of unwanted radioisotopes from biological systems. Such preparations would make possible greater use of long-lived radionuclides in medicine and would reduce some of the environmental hazards associated with nuclear energy. The biochemistry of radioisotope excretion is complicated because there are so many radioelements and each has its own metabolic pathway. Since study of the compounds that do promote the excretion of a few specific radio nucides has provided much information about body pools and spaces, further developments will increase the scope of nuclear medicine. Considerable progress has been made in relatively few years in developing compounds to protect against the radioisotopes present in fallout or formed dur ing nuclear accidents (1,2). Isotope dilution with stable iodine seems to be a very satisfactory protection against iodine-131. Effective chelators have been de veloped for the removal of plutonium-239 and zinc-65. Norwood (1) has shown