Production of urinary selenium metabolites in the rat following 75SeO32- administration

Urinary metabolites of 75Se were studied in male Holtzmann rats fed a Torula yeast diet with either no selenium (basal) or 0.5 ppM selenium (selenium) added as sodium selenite. The animals were anesthetized, a ureter was cannulated, and 20 μCi of 75SeO32- were injected intraportally. Only a small fraction (1.3 percent) of the injected 75Se was excreted in 6 h by animals fed the basal diet but 13.3 percent was excreted by animals fed the selenium diet. Paper chromatography showed that both groups excreted mostly inorganic 75Se in the first 10 min. A decrease in 75Se excretion followed, and then, 70 min after the collection was started, the selenium diet group had an increase in 75Se excretion which persisted for the rest of the 6 h and consisted mainly of the organic metabolites trimethylselenonium ion and U-2. 75Se excretion remained low in the basal diet group. Liver uptake and release of 75Se in the 1 h following intraperitoneal 75SeO32- injection was much greater in the selenium diet rats than in the basal diet rats. These results suggest that the greater excretion of 75Se by rats fed the selenium diet than that by rats fed the basal diet was due to increased production of organic urinary selenium metabolites by the liver. (U.S.)