The metabolism of selenomethionine, Se-methylselenocysteine, their selenonium derivatives, and trimethylselenonium in the rat.

The formation of dimethylselenide (respiratory) and trimethylselenonium (urinary) metabolites from [75Se]selenomethionine, [75Se]methylselenomethionineselenonium, [75Se]methylselenocysteine, [75Se]dimethylselenocysteineselenonium, and [75Se]trimethylselenonium was determined using single sc doses of 2 or 0.064 mg Se/kg in male and female rats. The 75Se content of liver, kidney, pancreas, testis, spleen, blood, heart, brain, and skeletal muscle was determined at 0.5 and 24 h. Respiratory 75Se after 24 h was greatest from Se-dimethylselenocysteineselenonium (38 and 17% for the high and low doses, respectively). Respiratory 75Se was about 8% for the high dose of Se-methylselenocysteine and was less for all other compounds. Total 75Se excretion in the urine was highest from rats given trimethylselenonium (about 90%, both doses) and was lowest from rats given selenomethionine (4%, low dose). Urine samples were chromatographed on SP-Sephadex cation-exchange columns and 75Se was eluted with ammonium formate; trimethylselenonium was precipitated with ammonium Reineckete solution and trimethylsulfonium carrier. Urinary trimethylselenonium excretion was greatest from rats given trimethylselenonium, but rats given Se-dimethylselenocysteineselenonium (low dose) excreted 35-45% of the dose as trimethylselenonium ion. The lowest quantity of trimethylselenonium was excreted by rats given the low dose of selenomethionine (0-3%). Pancreas, kidney, and liver showed the highest uptake (% of dose/g) of the selenium compounds. Trimethylselenonium was highly concentrated by the kidney and also showed high myocardial uptake (heart/blood ratio = 5) 0.5 h after injection; the selective uptake of trimethylselenonium in heart was not observed for the other selenonium compounds.