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Studies were conducted with mallard (Anas platyrhynchos) ducklings to determine the effects of excess dietary selenium (Se) on hepatic glutathione concentration and associated enzymes, and lipid peroxidation. Day-old ducklings were fed 0.1, 10, 20, or 40 ppm Se as seleno-DL-methionine or sodium selenite for 6 wk. Selenium from selenomethionine accumulated in a dose-dependent manner in the liver, resulting in a decrease in the concentration of hepatic-reduced glutathione (GSH) and total hepatic thiols (SH). These effects were accompanied by a dose-dependent increase in the ratio of oxidized glutathione (GSSG) to GSH, and an increase in malondialdehyde concentration as evidence of lipid peroxidation. Hepatic and plasma GSH peroxidase activity was initially elevated at 10 ppm Se as selenomethionine, whereas GSSG reductase activity was elevated at higher dietary concentrations of Se. Selenium from sodium selenite accumulated in the liver to an apparent maximum at 10 ppm in the diet, resulting in an increase in hepatic GSH and GSSG accompanied by a small decrease in total hepatic SH. Sodium selenite resulted in an increase in hepatic GSSG reductase activity at 10 ppm and in plasma GSSG reductase activity at 40 ppm. A small increase in lipid peroxidation occurred at 40 ppm. These findings indicate that excess dietary Se as selenomethionine has a more pronounced effect on hepatic glutathione metabolism and lipid peroxidation in ducklings than does selenite, which may be related to the pattern of accumulation. Effects of Se as selenite appear to be less pronounced in ducklings than reported in laboratory rodents. The effects of selenomethionine, which occurs in vegetation, are of particular interest with respect to the health of wild aquatic birds in seleniferous locations.

1. [75Se]selenite of [75Se]selenomethionine was injected in to the coelomic cavity of fish. After 2 d or 14 d the muscle portion of the fish was removed and homogenized. The long-term fate in rats of an oral dose of each labelled homogenate was compared with that of an oral dose of [75Ee]selenite or [75Se]selenomethionine mixed with unlabelled fish homogenate. 2. Urinary and faecal radioactivity were measured during the 1st week and whole-body radioactivity was determined for 10 weeks. Rats were killed at weekly intervals for 4 weeks for analysis of tissue distribution of 75Se. 3. Intestinal absorption of 75Se given as labelled fish homogenate was less complete than that of 75Se mixed with unlabelled homogenate, and the absorption of 75Se from the 14 d-labelled fish homogenate derived from [75Se]selenite was less complete than that of 75Se from the other labelled homogenates. 4. Urinary excretion of absorbed 75Se in the first 7 d was in the range 5--8% absorbed dose and was slightly greater in the rats given 75Se as selenite or derived from selenite than in those given 75Se as selenomethionine or derived from selenomethionine. Endogenous faecal excretion of absorbed Se was similar in all groups, as also were tissue distribution of retained 75Se and long-term whole-body turnover rate. 5. The results of these studies are compared with those of earlier studies of the metabolism in rats of [75Se]selenomethionine, [75Se]selenite, [75Se]selenocystine and 75Se incorporated in vivo into rabbit kidney. There were differences in the initial utilization of 75Se from these various sources but after the 1st week 75Se from all sources appeared to be metabolized similarly, suggesting that for rats dietary Se of all forms is ultimately incorporated into the same metabolic pool.

Different dosages of 125I-toluidine blue and 75Se-selenomethionine were injected intravenously into rabbits, and the concentration of radioactivity was measured in the parathyroids and surrounding tissues. The response of i.v. injected glucagon was also determined. It was found that 0.16 mg 125I-toluidine blue gave a concentration ratio of parathyroid/thyroid and parathyroid/muscle which was significantly higher than both lower and higher doses at 1 minute after i.v. injection of the labelled dye. Glucagon had little or no effect on the uptake of 125I-toluidine blue and 75Se-selenomethionine.