Urinary Trimethylselenonium Excretion by the Rat: Effect of Level and Source of Selenium-75

Abstract

The purpose of this study was to explore in rats the urinary metabolites of selenium (Se), by using [⁷⁵Se]selenomethionine, [⁷⁵Se]selenocystine, and [⁷⁵Se]selenite, and to assess the effects of low and high levels of Se intake on trimethylselenonium ion (TMSe) excretion in urine. Male adult rats were adapted for 6 weeks to a commercial rat laboratory stock diet (0.25 ppm Se). They were then starved for 24 hours and given an oral dose of either low (16 µg Se/kg body weight) or high (1500 µg Se/kg body weight) Se as the test Se compounds. Appearance of radioactivity in TMSe and non-TMSe Se metabolites in urine was monitored for 48 hours. About 40% of the ⁷⁵Se dose was excreted in urine. TMSe was the major urinary Se metabolite (57–69% of urinary ⁷⁵Se and 16–25% of oral ⁷⁵Se dose) at high, and a minor urinary Se metabolite (10% of urinary ⁷⁵Se and 3–4% of oral ⁷⁵Se dose) at low dose levels of Se and for all three Se test compounds. At least 80% of urinary ⁷⁵Se and 26–42% of the orally administered ⁷⁵Se were excreted as non-TMSe Se metabolites in urine under the latter condition. It is hypothesized that at a requirement intake of Se either a trace or no TMSe is excreted in urine, and it becomes a major excretory metabolite of Se when the dieary trace mineral intake exceeds a requirement level, probably serving as a means of detoxification.