Respiratory Excretion of Selenium Studied with the Radioactive Isotope*

It is well known that the animal organism has the ability of converting both inorganic selenium and tellurium into volatile substances which are exhaled in the respiratory gases. The nature of the volatile tellurium compound has been shown to be a methylated telluride, while the contention of Hofmeister that the exhaled selenium compound is likewise a methyl derivative (1) lacks to date adequate experimental evidence (2). The metabolism of these volatile substances is not definitely known. Schultz and Lewis (2) have reported quantitative studies on the excretion of volatile respired selenium after the administration of sodium selenite. They found after subcutaneous injection of sodium selenite (2.5 to 3.5 mg. of selenium per kilo) that 17 to 52 per cent of the injected selenium was excreted within 8 hours as a volatile compound in the respiratory gases. These results do not agree with our observations following the subcutaneous injection of subtoxic amounts of sodium selenate (radioselenium), in which 3 to 10 per cent of the original dose of selenium was exhaled within 24 hours. The radioactive isotope of selenium as previously shown (3) affords an extremely sensitive analytical method for studying the metabolism of tracer amounts of this metal in the animal organism. In order to obtain information concerning the rate of formation and excretion of these volatile selenium compounds in the intact organism, time-excretion studies of exhaled selenium after the administration of sodium selenate have been made in rats with radioselenium as a tagged atom. It was found that the formation and excretion of volatile selenium compounds take place shortly after the administration of the inorganic selenium, and that the rate of excretion of these volatile substances through the lungs is more rapid during the first 3 hours than during any subsequent 3 hour period.