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.     

Effects of various dietary levels of selenium as selenite or selenomethionine on tissue selenium levels and glutathione peroxidase activity in rats

Weanling rats were fed a basal diet or this diet plus 0.2, 1.0, 2.0 or 4.0 mg/kg selenium (Se) as either selenite or selenomethionine (SeM). Except at the 0.2 mg/kg Se level, Se accumulated in all tissues at higher levels when SeM was fed than when selenite was given, and the magnitude of difference became more pronounced with increasing levels of dietary Se. This was particularly true for muscle and brain. Se levels in whole blood, testes, kidney and lungs were not significantly different between rats fed 0.2 mg/kg Se as selenite or as SeM, but the Se levels in liver, muscle and brain were higher in rats fed SeM. Although the tissue Se concentrations differed markedly, there were no differences in the glutathione peroxidase (GPX) activity in tissues of rats fed SeM rather than selenite. The percentage of Se associated with GPX was lower in all tissues from rats fed SeM than in those from rats fed selenite. These results indicate that the chemical forms of dietary Se can have a marked influence on biological responses, including bioavailability of dietary Se.     

两种硒制剂对低硒居民红细胞谷胱甘肽过氧化物酶蛋白的影响

给克山病病区１４～１６岁居民每日口服２００μｇ亚硒酸钠硒或硒酵母硒１２周，测定红细胞硒含量、谷胱甘肽过氧化物酶（ＧＰＸ）活性和ＧＰＸ蛋白水平，以探讨硒对ＧＰＸ蛋白的影响。结果表明：（１）两补硒组在４周时红细胞硒已明显持续升高，停硒４周时仍维持在１２周时的高水平，但亚硒酸钠组在各时期均明显低于硒酵母组；（２）两补硒组红细胞ＧＰＸ活性于４周时开始明显上升，停硒４周后仍继续增高，但在各时期两组之间均无明显差异；（３）硒酵母组和亚硒酸钠组红细胞ＧＰＸ蛋白水平分别在４和８周时明显上升，前者在１２周时明显高于后者，停硒４周时与１２周时差异不显著；（４）红细胞ＧＰＸ蛋白水平与硒含量之间呈明显正相关。说明：（１）硒水平不仅可影响红细胞ＧＰＸ活性，而且对ＧＰＸ蛋白水平也有调节作用；（２）硒酵母晒对红细胞ＧＰＸ蛋白水平的调节作用比亚硒酸钠硒明显．     

Differential responses to selenomethionine supplementation by sex and genotype in healthy adults

A year-long intervention trial was conducted to characterise the responses of multiple biomarkers of Se status in healthy American adults to supplemental selenomethionine (SeMet) and to identify factors affecting those responses. A total of 261 men and women were randomised to four doses of Se (0, 50, 100 or 200 μg/d as L-SeMet) for 12 months. Responses of several biomarkers of Se status (plasma Se, serum selenoprotein P (SEPP1), plasma glutathione peroxidase activity (GPX3), buccal cell Se, urinary Se) were determined relative to genotype of four selenoproteins (GPX1, GPX3, SEPP1, selenoprotein 15), dietary Se intake and parameters of single-carbon metabolism. Results showed that supplemental SeMet did not affect GPX3 activity or SEPP1 concentration, but produced significant, dose-dependent increases in the Se contents of plasma, urine and buccal cells, each of which plateaued by 9-12 months and was linearly related to effective Se dose (μg/d per kg0·75). The increase in urinary Se excretion was greater for women than men, and for individuals of the GPX1 679 T/T genotype than for those of the GPX1 679 C/C genotype. It is concluded that the most responsive Se-biomarkers in this non-deficient cohort were those related to body Se pools: plasma, buccal cell and urinary Se concentrations. Changes in plasma Se resulted from increases in its non-specific component and were affected by both sex and GPX1 genotype. In a cohort of relatively high Se status, the Se intake (as SeMet) required to support plasma Se concentration at a target level (Se(pl-target)) is: Se(in) = [(Se(pl - target) - Se(pl))/(18.2ng d kg?.??/ml per mu g)] .     

Selenium bioavailability from buckwheat bran in rats fed a modified AIN-93G torula yeast-based diet

Selenium (Se) is an essential nutrient for humans and animals. The Se RDA for adult humans is 55 mug/d; however, dietary amounts as high as 200 mug/d in the highly available form of selenomethionine in yeast were shown to reduce the incidence of certain cancers. A number of natural foods contain relatively high amounts of Se; for the most part, however, the availability of food Se for absorption and utilization is unknown. This experiment was conducted to determine the bioavailability of Se from a high-protein, high-fiber bran-isolate of buckwheat groats that contains Se. The method used was based on the ability of Se from buckwheat bran to restore Se-dependent enzyme activities and tissue Se concentrations in Se-deficient rats. The responses produced from buckwheat bran Se were compared with a standard response curve generated by feeding graded amounts of Se as sodium selenite (Na(2)SeO(3); Na selenite) or selenomethionine (SeMet) in a newly reformulated AIN-93G-Torula yeast diet with a more balanced nutrient composition than older diets of this nature. Relative bioavailability was determined by using the slope-ratio assay method for enzyme data, or the parallel lines assay method for tissue Se concentration data. Results showed that Se availability from buckwheat bran based on the restoration of plasma Se was 70-80% as high as Na selenite or SeMet. However, when based on the restoration of muscle Se, buckwheat bran was 90% as high as Na selenite, but only 60% as high as SeMet. When using the ability of dietary Se to restore whole blood and liver glutathione peroxidase activity, buckwheat bran Se was 75-80% as high as Na selenite or SeMet. However, for the restoration of liver thioredoxin reductase, buckwheat bran Se was only 40% as high as Na selenite and 70% as high as SeMet. The relative bioavailability of Se from buckwheat bran with all variables considered was approximately 73% whether measured against Na selenite or SeMet. Although some variables indicated low bioavailability of Se from buckwheat bran, other factors such as Se speciation in the bran, digestibility of the bran, the cooking process, and combinations with other foods in the diet should be considered and analyzed before firm conclusions can be reached.     

Selenium from selenium-rich Spirulina is less bioavailable than selenium from sodium selenite and selenomethionine in selenium-deficient rats

The bioavailabilty of selenium (Se) from selenium-rich Spirulina (SeSp) was assessed in Se-deficient rats by measuring tissue Se accumulation and glutathione peroxidase (GSH-Px) activity. For 42 d, rats were subjected to dietary Se depletion by consumption of a Torula yeast (TY)-based diet with no Se; controls were fed the same diet supplemented with 75 microg Se/kg diet as sodium selenite. Se-deficient rats were then repleted with Se (75 microg/kg) by the addition of sodium selenite, selenomethionine (SeMet) or SeSp to the TY basal diet. Selenium speciation in SeSp emphasized the quasi-absence of selenite (2% of total Se); organic Se comprised SeMet (approximately 18%), with the majority present in the form of two selenoproteins (20-30 kDa and 80 kDa). Gross absorption of Se from SeSp was significantly lower than from free SeMet and sodium selenite. SeMet was less effective than sodium selenite in restoring Se concentration in the liver but not in kidney. SeSp was always much less effective. Similarly, Se from SeSp was less effective than the other forms of Se in restoring GSH-Px activity, except in plasma and red blood cells where no differences were noted among the three sources. This was confirmed by measuring the bioavailability of Se by slope-ratio analysis using selenite as the reference form of Se. Although Se from SeSp did not replenish Se concentration and GSH-Px activity in most tissues to the same degree as the other forms of Se, we conclude that it is biologically useful and differently metabolized due to its chemical form.     

亚硒酸钠和硒蛋氨酸的毒性比较

目的　比较亚硒酸钠和硒蛋氨酸毒性差异以及探讨硒中毒的指标。方法　将断乳Wistar大鼠随机分为 7组 ,每组 14只 ,雌雄各半。其中一组为对照组 ,另外六组分别给予含硒 3、6、10mg kg的亚硒酸钠或硒蛋氨酸饲料 ,于第 12周将其处死。结果　当饲料硒水平达到 3mg kg时 ,动物肝脏出现病理变化 ,在Se6mg kg时 ,体重才出现下降。饲料硒水平为 6、10mg kg时 ,同一饲料硒水平的亚硒酸钠组大鼠体重小于硒蛋氨酸组。饲料硒水平为 3、6mg kg时 ,硒蛋氨酸组大鼠的肝脏病理改变轻于亚硒酸钠组 ,雄性大鼠轻于雌性。亚硒酸钠组较硒蛋氨酸组或雌性大鼠较雄性大鼠在肝脏体重比方面变化更为明显。除雌性大鼠肝脏谷胱甘肽过氧化物酶 (GPX)活性随硒水平升高而降低外 ,其它补硒各组肝、红细胞、血浆GPX活性具有随硒水平的升高而升高的趋势。结论　大鼠硒中毒的剂量为Se 3mg kg,硒蛋氨酸的毒性小于亚硒酸钠 ,雌性大鼠对硒毒性更为敏感     

克山病病区粮食中补充蛋氨酸对大鼠膳食硒生物利用的影响

为研究在克山病病区粮食中补充蛋氨酸对大鼠组织硒和谷胱甘肽过氧化物酶 (GPX)活性的影响 ,用克山病病区生产的低硒粮食为主配成低硒基础饲料 ,其硒含量为 0 .0 0 7mg/kg。在此基础上添加不同量的硒蛋氨酸 ,使饲料硒水平分别达到 0 .0 0 7、0 .0 6和 0 .5 0 mg/kg。每一硒水平又分别补充或不补充 4g/kg DL -蛋氨酸 ,配制成含不同硒和蛋氨酸的 6种饲料 ,分别喂养雄性 Wistar断乳大鼠 8周。结果在饲料硒水平为0 .0 0 7mg/kg时 ,补充蛋氨酸组动物除肌肉硒含量低于未补充组外 ,其它组织硒含量和各组织 GPX活力与不补充蛋氨酸动物无显著差异 ;在饲料硒水平为 0 .0 6 mg/kg时 ,补充蛋氨酸组动物组织中的硒含量出现了重新分布 ,最明显的是补充蛋氨酸组动物肌肉的硒含量减少 ,而肝脏和血硒含量增加 ,且各组织中 GPX活力显著大于未补充蛋氨酸组的动物 ;在饲料硒水平为 0 .5 0 mg/kg时 ,补充蛋氨酸组动物组织中硒含量有不同程度下降 ,但 GPX活力仍保持不变。研究结果认为病区粮食中蛋氨酸不足时 ,机体首先利用膳食中的硒蛋氨酸(谷类食物中硒的主要形式 )以替代蛋氨酸参与组织蛋白质的合成。补充蛋氨酸后 ,硒蛋氨酸即可发挥其应有生理功能。进一步提示病区粮食中蛋氨酸不足可能是与克山病发病有关的另一因素。     

Chemical forms of selenium in rat tissues after administration of selenite or selenomethionine

The chemical forms of selenium (Se) were determined in erythrocyte and liver proteins after injection of 75Se as either sodium selenite or selenomethionine (Se-Met) in male weanling rats. Gel-filtration chromatography (Sephadex G-150) of erythrocyte lysate revealed labeling of four fractions corresponding to void volume proteins, glutathione peroxidase (GPx), hemoglobin (Hb) and low-molecular-weight materials. Acid hydrolysates of erythrocyte protein fractions and whole liver were analyzed by ion-exchange chromatography (Dionex DC6A). Void volume proteins contained principally selenocysteine (75Se-Cys) in [75Se]selenite-injected animals. This material contained both 75Se-Met and 75Se-Cys 1 d postinjection in 75Se-Met-injected animals, but primarily 75Se-Cys at 20 d afterwards. GPx contained 75Se as 75Se-Cys regardless of the selenium compound injected. Hb of 75Se-Met-injected animals contained principally 75Se-Met at both 1 and 20 d postinjection. In [75Se]selenite-injected animals, 75Se was present in hemoglobin as two unidentified forms. In acid hydrolysates of whole liver 75Se was recovered principally as 75Se-Cys from animals injected with [75Se]selenite. For animals injected with 75Se-Met, liver 75Se was present initially as 75Se-Met, but after 5 d the majority of liver 75Se was as Se-Cys. No differences were found in deposition of 75Se in liver, kidney, testes, erythrocytes or plasma in rats injected with labeled selenite or Se-Met, but a significantly greater retention was found in muscle of Se-Met-injected rats as compared to those given selenite.     

膳食维生素B_6对硒的生物利用率影响的研究──Ⅲ．对成年大鼠组织中硒和谷胱甘肽过氧化物酶水平的影响

１２周龄雄性大鼠饲缺维生素Ｂ６（ＶＢ６）缺硒酪蛋白蔗糖基础膳食，３周后按体重把动物分成６组。分别喂饲三种膳食，即基础膳食、基础膳食中补充硒０．２５ｍｇ／ｋｇ的亚硒酸钠或ＤＬ－硒蛋氨酸，在此基础上每种膳食又分为补充（２．５μｇ／ｇ）或不补充盐酸吡哆醇两组。实验期为１４周。补Ｖ８６各组的红细胞和骨骼肌中硒水平和谷胱甘肽过氧化物酶（ＧＳＨ－Ｐｘ）活性均显著高于相应缺ＶＢ６各组，ＶＢ６对饲亚硒酸钠大鼠肝硒和ＧＳＨ－Ｐｘ水平没有影响；但当补充硒蛋氨酸时，与补ＶＢ６大鼠相比缺ＶＢ６大鼠的肝硒水平较高而ＧＳＨ－Ｐｘ活性则显著降低。这些研究结果进一步证明，ＶＢ６与血浆硒的转运和硒的利用有关，并且可能参与了硒蛋氨酸在肝脏中的代谢过程。     

低硒大鼠对紫阳高硒小麦硒的相对生物利用率

本文用耗竭—补充—耗竭的设计,以克山病病区低硒粮饲料(含硒0.006ppm)喂养大鼠6周后,观察了补充紫阳高硒小麦(含硒1.175ppm)或亚硒酸钠,使饲料含硒分别为0.219和0.223ppm时,以及停止补硒后,大鼠组织和血液硒水平和谷胱甘肽过氧化物酶(GSH-px)活性的变化,并评估了紫阳高硒小麦的相对生物利用率。结果表明,以血浆、红细胞、肾、肝和心肌硒水平为指标时,高硒小麦硒的平均生物利用率(补硒2、4和6周时)与亚硒酸钠相似,其相对生物利用率分别为98％,104％,100％,96％和101％(亚硒酸钠为100％);而以心肌和红细胞GSH-Px活性为指标时,其生物利用率(90％和70％)低于亚硒酸钠。但在补硒的各时期,血液和各组织对高硒小麦硒的相对生物利用率不尽相同。此外,在停止补硒3周时,高硒小麦维持心、肝和红细胞硒水平以及心肌GSH-Px活性的作用优于亚硒酸钠。     

Selenium distribution in blood fractions of New Zealand women taking organic or inorganic selenium

Three groups of 11 New Zealand women each received, for 32 wk, yeast tablets with no added selenium (placebo) or 200 micrograms Se/d in tablets either as selenate or as selenium-enriched yeast (SeMet) in a double-blind selenium trial. Plasma and erythrocyte (RBC) samples were collected bimonthly. Gel filtration of plasma from women taking SeMet revealed two major selenium-containing peaks with most of the selenium in the second peak. In contrast, the first peak contained most of the selenium in plasma from women taking selenate. Chromatography of RBC lysates indicated that the majority of the selenium was with hemoglobin (Hb) in women taking SeMet but was about equally distributed between glutathione peroxidase (GSH-Px) and Hb in women taking selenate. The percentage of selenium associated with GSH-Px was found to be greater in RBCs and plasma of women taking selenate than of those taking SeMet.     

Effects of vitamin B-6 deficiency on selenium metabolism in the rat

Rats were fed for 23 d diets adequate or deficient in vitamin B-6 and containing selenium as either sodium selenite, selenocysteine (SeCys) or selenomethionine (SeMet). They were then injected with 75Se of the same chemical form and killed 2 d later. Tissue deposition of stable and radiotracer selenium and the activity of glutathione peroxidase (GSHPx) were used to assess selenium utilization. Erythrocyte levels of selenium and GSHPx were lower in vitamin B-6--deficient animals for all forms of selenium; however, 75Se deposition in erythrocytes was not affected by vitamin B-6 status. The activities of cystathionine lyase, aspartate aminotransferase and selenocysteine lyase were lower in livers of vitamin B-6--deficient rats than in vitamin B-6--supplemented rats. The proportion of liver and kidney 75Se soluble in 5% trichloroacetic acid and 0.1 M 2-mercaptoethanol was consistently lower in vitamin B-6--deficient animals, but cation-exchange chromatography of tissue extracts did not identify a specific low-molecular-weight species. Tissue retention of 75Se provided as SeMet was increased in vitamin B-6--deficient animals, but the proportion of 75Se retained in muscle and liver as SeCys was significantly reduced. These findings suggest that the conversion of SeMet to a form available for GSHPx synthesis is reduced by vitamin B-6 deficiency.     

大鼠对富硒平菇硒的生物利用率

本实验用低硒大鼠对人工栽培富硒平菇作了硒生物利用率观察。大鼠按体重随机分为9组,其中1组为低硒对照组,2～5组补充Na_2SeO_3,饲料内硒含量分别为:0.51、0.75、1.91、3.18ppm;6～9组补充富硒平菇,硒为0.45、0.72、1.59、3.41ppm。3周后处死大鼠,采血、肝、测定硒含量,并测定红细胞GSH-Px酶活性。结果表明:血、肝硒值及红细胞GSH-Px酶活性均随补硒浓度的增加而增加,以亚硒酸钠为基准,富硒平菇硒生物利用率,按血硒指标为66.66％;按肝硒指标为125％;按红细胞GSH-Px酶活性指标为123.42％,说明人工栽培富硒平菇可作为极好的食物硒来源。     

补硒对潜在型克山病患者红细胞免疫功能的影响

给潜在型克山病患者每日口服亚硒酸钠硒２００μｇ，１２周后测定红细胞硒含量和谷胱甘肽过氧化物酶（ＧＰＸ）活性、红细胞免疫粘附（ＲＣＩＡ）功能、血清ＲＣＩＡ调节功能和循环免疫复合物（ＣＩＣ）含量，以探讨补硒对潜在型克山病患者ＲＣＩＡ功能的影响。结果表明：潜在型克山病患者补硒后红细胞硒含量、ＧＰＸ活性和红细胞Ｃ３ｂ受体（Ｃ３ｂＲ）花环率明显提高，血清ＲＣＩＡ花环抑制率明显降低，但补硒对免疫复合物（ＩＣ）花环率、血清ＲＣＩＡ花环促进率和ＣＩＣ含量无明显影响。研究结果说明：补硒可使潜在型克山病患者ＲＣＩＡ功能和血清ＲＣＩＡ调节功能恢复。     

Influence of dietary methionine on the metabolism of selenomethionine in rats

To determine the influence of methionine on selenomethionine (SeMet) metabolism, weanling male rats were fed for 8 wk a basal diet marginally deficient in sulfur amino acids, containing 2.0 micrograms selenium (Se)/g as DL-SeMet and supplemented with 0, 0.3, 0.6 or 1.2% DL-methionine. Increased dietary methionine caused decreased selenium deposition in all tissues examined but increased glutathione peroxidase (GSHPx, EC 1.11.1.9) activity in testes, liver and lungs. A positive correlation was found between dietary methionine and the calculated percentage of selenium associated with GSHPx. In a second experiment, 75SeMet was injected into weanling male rats which had been fed the basal diet containing 2.0 micrograms selenium as DL-SeMet with or without the addition of 1.0% methionine. The selenoamino acid content of tissues and the distribution of 75Se in erythrocyte proteins were determined. In comparison to the rats fed the basal diet without added methionine, significantly more 75Se-selenocysteine was found in liver and muscle, more 75Se was found in erythrocyte GSHPx and less 75Se was found in erythrocyte hemoglobin of rats fed 1.0% methionine. These data suggest that methionine diverts SeMet from incorporation into general proteins and enhances its conversion to selenocysteine for specific selenium-requiring proteins, such as GSHPx.     

Bioaccumulation of selenate,selenite, and seleno-DL-methionine by the brine fly larvae Ephydra cinerea Jones

High concentrations of selenium threaten waterfowl at California San Joaquin Valley agricultural wastewater evaporation ponds. This study evaluates and compares two routes of Se exposure and uptake by third instar Ephydra cinerea (brine fly) larvae. A 48-h static bioconcentration bioassay provided information on the larval uptake of selenate, selenite, and seleno-DL-methionine (SeMet) at Se waterborne concentrations ranging from 10.0–20,000 ug/L. At equivalent concentration levels, SeMet was bioconcentrated to a greater extent than selenite, which was bioconcentrated more than selenate. Forty-eight-hour static bioconcentration vs. biomagnification bioassays allowed for comparisons of the two routes of exposure of selenate, selenite, and SeMet. Biomagnification was determined to be the primary Se uptake pathway, exemplified most notably in the selenite treatment. Measured agar-based food unit Se levels presented evidence that the uptake of selenite, and especially SeMet, by microbial populations was transferred to E. cinerea larvae as they scavenged for bacteria and yeast, etc. in the diet matrix. As a primary dietary item of waterfowl at evaporation ponds, E. cinerea in seleniferous waters presents a potentially high hazard.     

Mouse prostate proteomes are differentially altered by supranutritional intake of four selenium compounds

We have shown that, in contrast to selenomethionine (SeMet) or selenite, methylseleninic acid (MSeA) and Se-methylselenocysteine (MSeC) exert prostate cancer (PCa) inhibitory effect in preclinical models. Here we investigated the prostate proteome signatures of mice treated with each selenium (Se) form for hypothesis generation concerning their potential in vivo molecular targets and cancer risk modification. Nude mice bearing subcutaneous PC-3 xenografts were treated daily with each Se form (3 mg Se/kg) orally for 45 days. Five prostates were pooled from each group. Their proteomes were profiled by LC-MS/MS with iTRAQ labeling. Of the 1,088 proteins identified, 72 were significantly modulated by one or more Se forms. MSeA and MSeC each induced separate sets of tumor suppressor proteins and suppressed different onco-proteins. Proteins induced by selenite and shared with MSeC were related to energy metabolism (e.g., fatty-acid synthase), and those induced by SeMet included vimentin and heat-shock protein-70, favoring cancer growth. While proteome changes induced by MSeA were associated with PCa risk reduction, desirable risk-reducing signatures induced by MSeC were counterbalanced by risk-promoting patterns shared with selenite and SeMet. We propose that the balance of oncogenic vs. suppressor protein patterns in the prostate may impact the direction of PCa risk modification by a given selenium.     

Some effects of vitamin E and selenium deprivation on tissue enzyme levels and indices of tissue peroxidation in rainbow trout (Salmo gairdneri)

Duplicate groups of rainbow trout (Salmo gairdneri) (mean weight 11 g) were given for 40 weeks one of four partially purified diets that were either adequate or low in selenium or vitamin E or both. Weight gains of trout given the dually deficient diet were significantly lower than those of trout given a complete diet or a diet deficient in Se. No mortalities occurred and the only pathology seen was exudative diathesis in the dually deficient trout. There was significant interaction between the two nutrients both with respect to packed cell volume and to malondialdehyde formation in the in vitro NADPH-dependent microsomal lipid peroxidation system. Tissue levels of vitamin E and Se decreased to very low levels in trout given diets lacking these nutrients. For plasma there was a significant effect of dietary vitamin E on Se concentration. Glutathione (GSH) peroxidase (EC 1.11.1.9) activity in liver and plasma was significantly lower in trout receiving low dietary Se but was independent of vitamin E intake. The ratios of hepatic GSH peroxidase activity measured with cumene hydroperoxide and hydrogen peroxide were the same for all treatments. This confirms the absence of a Se-independent GSH peroxidase activity in trout liver. Se deficiency did not lead to any compensatory increase in hepatic GSH transferase (EC 2.5.1.18) activity; values were essentially the same in all treatments. Plasma pyruvate kinase (EC 2.7.1.40) activity increased significantly in the trout deficient in both nutrients. This was thought to be due to leakage of the enzyme from the muscle and may be indicative of incipient (subclinical) muscle damage.     

Dietary selenium requirements based on glutathione peroxidase-1 activity and mRNA levels and other Se-dependent parameters are not increased by pregnancy and lactation in rats

The hierarchy of selenium (Se) requirements for growing rats ranges from <0.01 to 0.1 microg Se/g diet, depending on the choice of Se status parameter. To further evaluate the efficacy of molecular biology markers to determine Se requirements in later periods of the life cycle, which are less amenable to traditional approaches, we studied pregnant and lactating rats. Female weanling rats were fed a Se-deficient diet (<0.01 microg Se/g) or supplemented with graded levels of dietary Se (0-0.3 microg Se/g) for >10 wk, bred, and killed on d 1, 12, and 18 of pregnancy and d 7 and 18 of lactation; Se response curves were determined for 10 parameters including liver glutathione peroxidase (GPX). Growth, and mRNA levels for selenoprotein P, 5'-deiodinase, and GPX4 were not decreased by Se deficiency. GPX4 activity required 0.05 microg Se/g diet for maximum activity, similar to growing rats. Dietary Se requirements for plasma GPX3 activity decreased 33% in pregnancy, but returned during lactation to the requirement of growing rats. The Se requirement for GPX1 activity decreased 25% in pregnancy but not in lactation. GPX1 mRNA required 0.05 microg Se/g diet for maximum levels in both pregnancy and lactation, similar to growing rats. Clearly, Se requirements do not increase during pregnancy and lactation relative to Se requirements in growing rats. Unexpectedly, Se-adequate levels of GPX1 mRNA and activity declined to <40 and 50%, respectively, of nonpregnant Se-adequate levels during pregnancy and lactation, illustrating the need to fully understand biomarkers at all stages of the life cycle.