Selenium in Nutrition, Revised Edition (1983) / Chapter Skim
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5 METABOLISM
5 METABOLISM
Pages 57-76
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From page 57... ...
Selenized yeast tablets, containing primarily organic selenium, are available as human supplements and have been shown to increase blood selenium levels (Schrauzer and White, 19781.
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From page 58... ...
The intestinal absorption of 75Se from a kidney homogenate of rabbits dosed with 75Seselenomethionine was 87 percent, as compared to 91 percent for selenomethionine mixed with unlabeled rabbit kidney homogenates (Thomson et al., 19751. 75Se-selenite or 75Se-selenomethionine was injected into the coelomic cavity of fish, and their muscle removed, homogenized, and fed in diets to rats.
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From page 59... ...
BODY RETENTION AND TISSUE DISTRIBUTION The tissue distribution of selenium in various animals using either 75Se or stable selenium has been reported by several investigators. With required dietary selenium intake, the kidney contains the highest concentration of selenium, followed by the liver and other glandular tissues such as the
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From page 60... ...
Inorganic and organic selenium contributed from brewers' grains or distillers' grains and solubles were shown to result in similar weekly serum selenium response curves within each selenium level with 4-week-old weanling swine, while selenium contributed by fish meal had lower levels (Mahan and Moxon, 1978~. At 0.4 ppm dietary selenium intake, muscular tissue selenium levels were greater, compared to the selenite source, when fish meal or brewers' grains were fed, whereas nonmuscular tissue (liver, kidney, and testes)
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From page 61... ...
(1968a) determined the selenium content of lambs fed "commercial" diets at several state agricultural experiment stations.
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62 ._ V2 so ._ o :> o .~ Ct ._ Cal A V, ._ Ct ._ ._ ._ V2 o U
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63 o CN U~o c~ c~ r~ ro~ ...
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64 .s s 1 Cal U
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From page 66... ...
The selenium content of human tissues appears to show patterns similar to tissues from animals fed diets with required levels of selenium. The mean selenium content (wet-weight basis)
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From page 67... ...
As with animals, the blood selenium levels in humans are apparently influenced by dietary intake. The blood selenium in people of New Zealand averaged about 0.07 ppm, which is low in comparison to the values reported for people (as summarized by Griffiths and Thomson, 1974)
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From page 68... ...
Among these are the chemical forms of selenium, sulfur, arsenic, metals, microorganisms, and vitamin E, and previous selenium intake. INORGANIC SELENIUM There is very little doubt concerning the ability of animal tissues to convert inorganic selenium to organic forms.
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From page 69... ...
ORGANIC SELENIUM In contrast to sulfur, selenium compounds tend to undergo reductive pathways in tissues. However, reduced selenium compounds can be metabolized by animal tissues.
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From page 70... ...
identified dimethyl selenide in the exhaled gases of rats given 75Se-labeled inorganic selenium. Dimethyl selenide can be trapped in soluble form by using nitric acid trapping solutions.
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From page 71... ...
No mortality was observed in dimethyl selenideinjected rats that had been drinking water containing 1.0 ppm selenium, whereas up to 90 percent mortality occurred in rats injected with this compound without prior treatment with selenium (Parizek et al., 19761. Thus, the reason rats used by McConnell and Portman (1952b)
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From page 72... ...
Thus, rumen microbes appear to be able to convert inorganic selenium to organic selenium compounds, as well as to incorporate organic selenium compounds into bacterial proteins. INFLUENCE OF SULFUR The sulfur analogues of selenium compounds appear to have the greatest influence on selenium metabolism.
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From page 73... ...
Hence, the alteration of selenium metabolism appears to be the greatest with sulfur-deficient animals. INFLUENCE OF ARSENIC The beneficial effect of arsenic on selenium poisoning was noted in the 1930s when 5 ppm of sodium arsenite in the drinking water was found to give full protection against liver damage in rats fed diets containing 15 ppm selenium (Moxon and Rhian, 19431.
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From page 74... ...
Moreover, cyanide protects partially against selenium toxicity in rats (Palmer and Olson, 1979~. However, attempts to induce selenium deficiency by adding cyanide to water for rats had little effect (Palmer and Olson, 19811.
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From page 75... ...
Essentially all of the selenium excreted in feces of ruminants is in insoluble forms, and very little is available for uptake by plants (Cousins and Cairney, 1961; Peterson and Spedding, 19631. The poor availability is evident by data showing that less than 0.3 percent of 75Se was taken up by three common pasture species of plants growing for 75 days on feces from sheep dosed orally with Se-selenite.
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From page 76... ...
Based on balance studies with New Zealand women, the minimum dietary requirement of selenium for maintenance of normal human health was estimated to be probably not more than 20 ,ug/day (Stewart et al.,1978~.
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