Metabolic studies of (75Se)selenomethionine and (75Se)selenite in the rat.

I. Information was sought concerning the long-term fate of orally and intravenously administered [75Se]selenomethionine and [7SSe]selenite in rats. 2. Crinary and faecal radioactivity was assayed during the 1st week and whole-body radioactivity was determined weekly for 16 weeks. Rats were killed at intervals for analysis of 75Se tissue distribution. 3. Intestinal absorption after oral administration was estimated to be 91-93 % for selenite and 9 j-97 yo for sclenomethionine. 4. Urinary excretion of absorbed [75Se]selenite was greater than that of [7SSe]selenomethionine during the 1st week. 5 . After the 1st week, whole-body retention diminished exponentially at a similar rate in rats given either selenomethionine or selenite. Except for the erythrocytes, 75Se content of individual tissues also decreased exponentially. 6. It appears that, after an initial period, V e from either selenomethionine or selenite is metabolized similarly, suggesting that Se from both potential dietary sources is ultimately incorporated into the same metabolic pool.