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Urinary Trimethylselenonium Excretion by the Rat: Effect of Level and Source of Selenium-75^1,2,

Ara T. Nahapetian^*, Morteza Janghorbani^*,, and Vernon R. Young^*

^* Laboratory of Human Nutrition, Department of Nutrition and Food Science Nuclear Reactor Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139

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.

KEY WORDS: • trimethylselenonium • selenium • selenite • selenomethionine • selenocystine

¹ A preliminary report of this work was presented at the 1982 meeting of the Federation of American Societies for Experimental Biology, New Orleans, LA. Fed. Proc. 41: 529.

² This study was supported by a grant from the National Institutes of Health (Grant No. 1-R01-CA-27917-01).

Manuscript received 19 July 1982.