Effects of dietary selenite, selenocystine and selenomethionine on selenocysteine lyase and glutathione peroxidase activities and on selenium levels in rat tissues.

Weanling male rats were fed a basal selenium (Se)-deficient diet or this diet plus 2 ppm Se as either selenite, selenocystine (SeCys) or selenomethionine (SeMet) for 9 wk. The rats were killed by decapitation while anesthetized with ether, and tissues were assayed for glutathione peroxidase (GPx) and selenocysteine lyase activities, and for Se content. Dietary Se had no effect upon the activity of tissue selenocysteine lyase. This activity was highest in the liver, followed by kidney, muscle and testis in decreasing order. Although the GPx activity was lower in tissues of the Se-deficient rats, there were no significant differences in its activity between animals given the different chemical forms of dietary Se. Except for the kidney, the tissue Se concentrations were similar in rats fed selenite or SeCys, but the Se content in testis, muscle, pancreas, heart, spleen, whole blood, erythrocytes and plasma was significantly higher in rats fed SeMet than in those fed either selenite or SeCys. The greatest increase due to SeMet compared with the selenite and SeCys treatments was about 10-fold in the muscle compared with 1.3- to 3.6-fold for the other tissues.