Dose-response relations in urinary excretion of trimethylselenonium in the rat

75Se-labeled selenite was administered to fasting rats by orogastric intubation (1.5-3000 micrograms/kg body wt). Urine was collected and characterized for total radioactivity as well as for radiolabeled trimethylselenonium (TMSe). At lower doses of selenite (up to 500 micrograms/kg body wt), 30% of the administered dose was excreted. At higher doses of selenite, fractional urine excretion decreased as a function of the dose. The observed decrease in fractional urine excretion was not caused by changes in the absorption of the administered radiolabel. There was a direct relationship between the amount of the administered dose of selenite (up to 1500 micrograms/kg body wt) and the proportion of urinary [75Se] excreted as TMSe. Pretreatment with seleno compounds (10 or 100 micrograms Se/kg body wt as selenite, or selenomethionine) for 35 d before a challenge dose of [75Se]selenite did not influence the excretion of total [75Se] or of [75Se]TMSe in urine. Ingestion of a choline-deficient diet, which should deplete the availability of methyl groups, did not have any effect on excretion of total [75Se] or of [75Se]TMSe in urine after a challenge dose of [75Se]selenite (500 micrograms/kg body wt). The data presented here permit the following conclusions: 1) Production of TMSe is dose dependent, 2) production of TMSe from a single acute dose does not depend on the history of selenium intake and 3) rats fed a methyl-deficient diet are able to eliminate Se via formation of TMSe.     

Comparison of the magnitude of the selenite-exchangeable metabolic pool and whole body endogenous selenium in adult rats

The quantitative relationship between the size of the selenite-exchangeable metabolic pool (WSe-EMP) and whole body endogenous selenium (Seend) was investigated in adult male rats. Two experiments based on multiple labeling with stable isotopes were performed. One focused on short-term (7 d, Expt. 1) and the other on long-term (60 d, Expt. 2) relationships. Rats were fed a Torula yeast diet and water supplemented with [76Se]selenite at 0.1 micrograms Se/mL; the in vivo [74Se]selenite tracer was administered orally. Groups of three or four animals were killed at timed intervals and whole carcass or selected organs were analyzed for the stable isotopes 74Se, 77Se and 82Se with hydride generation/inductively coupled plasma mass spectrometry. The value of WSe-EMP was determined from plasma or urine isotope ratios. In Experiment 1, with plasma as the sampling compartment, WSe-EMP at 24 h was 36.5 +/- 1.2% of the baseline value of whole body endogenous selenium (Seend) and 36.3 +/- 1.8% at 7 d. When urine was the sampling compartment, the corresponding values were 3.9 +/- 0.3% and 43.1 +/- 2.8%, respectively. In Experiment 2, WSe-EMP (plasma) was 38.9 +/- 1.3% of Seend at 7 d, increasing to 45.5 +/- 1.6% at 60 d. The corresponding values for urine as the sampling compartment were 45.5 +/- 2.0% (7 d) and 61.5 +/- 1.7% (60 d), respectively.     

Absorption and retention of 75SeO3 in relation to soybean protein intake in the rat

The absorption and retention of ⁷⁵Se, given as an oral dose of ⁷⁵SeO₃, was studied in young male rats receiving different levels and sources of soy protein, with and without selenite and methionine supplementation. Rats fed a protein-free diet had a higher cumulative urine ⁷⁵Se excretion and a sligtly lower ⁷⁵Se absorption and ⁷⁵Se retention than rats fed diets containing 10% protein supplied as soya flour. Results indicated that supplementation with selenite decreased the fractional absorption and retention of selenium, but the overall effect was a marked increase in the total amount of selenium ingested, absorbed and retained. Methionine supplementation of a diet based on soya increased growth and PER: it also decreased slightly cumulative feces ⁷⁵Se excretion and increased ⁷⁵Se absorption, but only in rats fed diets supplemented with selenium. The present findings are consistent with the view that selenium homeostasis in the rat is maintained largely through changes in the urinary excretion of selenium and they show that an inadequate protein diet reduces the efficiency of retention of absorbed selenite.     

蛋氨酸和维生素E对大鼠硒中毒的解毒机制

在大鼠饲料中加入硒酸钠(Na_2SeO_4),使其硒含量分别为0.2,2.0和5.0ppm,每一剂量水平又分为补充与不补充维生素E(VE)和蛋氨酸(Met)组。7周后,观察VE和Met对不同硒水平大鼠代谢的影响,并探讨可能存在的解毒机制。结果显示:未补充VE-Met的5.0ppm高硒组大鼠出现了硒中毒,补充组有明显的解毒效果,血、肝、肾和骨骼肌等组织硒含量显著下降,生化指标好转,尿三甲基硒离子硒(TMSe~+——Se)排出率由不补充组的22％上升为33％(P<0.05),但对其它补充组无此作用。表明:VE-Met联合使用对硒中毒有解毒作用,其机制是加强了机体硒的甲基化去毒能力,推测,除尿TMSe~+外,呼气中的二甲基硒(DMSe)也可能有所增加。     

Quantitative significance of measuring trimethylselenonium in urine for assessing chronically high intakes of selenium in human subjects

The purpose of the present study was to investigate the effects of Se restriction on the excretion of Se in men who had consumed high levels of this element during their entire lives. With the use of stable isotopes of Se as selenite, the excretion of methylated Se in urine was investigated in Chinese men (n 10) who had habitual chronic high intakes of this element. The relationship between either urine Se or trimethylselenonium (TMSe) to the estimated long-term Se intake was not linear over the entire range of intake, which was also true for the infusion of labelled selenite. A non-linear relationship was also found between urine TMSe and urine Se both for TMSe arising from catabolism of endogenous body Se and that from infused selenite. The data suggest a close precursor-product relationship of urine Se and its TMSe component based on the nearly identical specific activities for these two selenocompounds. Although dimethylselenide in breath was not measured in the present study, combining urinary TMSe with this breath test may be more useful in the assessment of long-term Se status.     

Experimental selenium restriction in healthy adult humans: changes in selenium metabolism studied with stable-isotope methodology

Mechanisms responsible for selenium homeostasis were investigated in healthy adult men receiving diets adequate or low in Se (eight subjects per group). The appearance of a stable isotope of Se, 74Se, in plasma, urine, and feces was measured after oral administration of 74Se-selenite. One group received a restricted level of Se (18 +/- 1 micrograms/d) for 30 d, which resulted in a decrease in urinary, fecal, and plasma Se content compared with the group that consumed 119 +/- 1 micrograms/d. Low Se intake also resulted in decreased urinary 74Se excretion (27.2 +/- 1.4% vs 32.5 +/- 2.3% of the absorbed dose for the adequate intake), increased body retention of 74Se (74.8 +/- 3.1% vs 67.6 +/- 3.8% of the absorbed dose for the adequate group), and a contracted selenite-exchangeable metabolic pool (Se-EMP) (9782 micrograms for adequate Se and 6314 micrograms for the low-Se group; p less than or equal to 0.05). Measurement of Se-EMP may provide an additional and sensitive approach for assessing Se nutriture in human subjects.     

Increase of urinary ketone body excretion in selenium-deficient rats is a ketone-specific change.

The effects of selenium (Se) deficiency on urinary ketone body excretion in starved rats were examined. Rats were fed a basal diet which was Se-deficient (Se content: 0.011 micrograms/g) or a Se-adequate diet (the basal diet supplemented with 0.1 micrograms Se/g as sodium selenite). On the 11th and 22nd week of the feeding period, Se-deficient status in rats fed the basal diet was verified by the observation that the Se content and glutathione peroxidase activity in their plasma, erythrocytes, and livers were markedly lowered. On the 4th, 6th, 11th, 15th, and 22nd week, the rats were starved for 48 h and the urinary excretion of ketone bodies (acetoacetate (AcAc) and 3-hydroxybutyrate (3-OHBA)), urea, and creatinine were examined. The urinary excretion of AcAc and 3-OHBA during the second 24 h of the 48-h starvation period were markedly higher in the Se-deficient rats than in the Se-adequate rats for all weeks examined, while the urine volume and the excretion of urea and creatinine were similar in the Se-deficient and Se-adequate rats, irrespective of the feeding period and the number of hours of starvation. On the 22nd week, the plasma ketone body levels were also determined and significantly higher plasma 3-OHBA levels were observed in the Se-deficient rats than in the Se-adequate rats 72 h after starvation began. These results indicate that Se deficiency causes an increase of urinary ketone body excretion in starved rats and that the increase is ketone-specific with no changes in major urinary profiles.     

Urinary and fecal excretions and absorption of a large supplement of selenium: superiority of selenate over selenite

A correction needs to be made to the form of selenium used in earlier studies; what was believed to be selenite-Se in solution is now known to have been selenate-Se. In the present study, excretion of Se was followed in 13 women after ingestion of 1 mg Se as selenite or selenate in solution. Fecal excretion of selenate-Se was less than for selenite-Se reflecting a higher apparent absorption [94 +/- 4% (SD), 62 +/- 14%, respectively]. Peak excretion of Se occurred 3 h earlier for selenate-Se than for selenite-Se and was 6 times higher. Total urinary excretion of selenate-Se was 3 times that of selenite-Se and still 2 times as high when expressed as % absorbed dose. Total recovery of Se in urine and feces was similar for both forms. There was remarkable agreement between these results and those reported earlier for selenate-Se (Selovet-1) and selenite-Se.     

Selenium status of exclusively breast-fed infants as influenced by maternal organic or inorganic selenium supplementation

A longitudinal dietary Se supplementation study on lactating mothers was performed to determine the possibilities of improving the Se status of exclusively breast-fed infants. A total of 200 mothers randomized into three groups received either no Se supplements, 100 micrograms of selenite, or 100 micrograms of yeast-Se daily. Maternal and infant serum Se concentrations showed a linear correlation during exclusive breast-feeding. Yeast-Se in the dose administered was safe and more effective than selenite in increasing the Se concentrations of maternal serum and milk, and infant serum. The mean estimated daily Se intakes of the infants were 7.7 +/- 2.2, 8.9 +/- 2.2, and 11.5 +/- 4 micrograms, in the control, selenite, and yeast-Se groups respectively. Though the infant Se intakes of the unsupplemented and selenite-supplemented mothers were below the lower limit of the safe and adequate range as set by the US National Research Council, their serum Se concentrations increased steadily over the 6-mo study period. As maternal serum Se also increased by over 50% during the same period the results suggest that a maternal daily intake of 50-75 micrograms is adequate during lactation.     

Urinary excretion of iodide and fluoride from supplemented food grade salt.

Iodide and fluoride supplemented food grade salt (NaCl) is a common source of these two micronutrients. In a pilot study, we investigated whether increased intake of NaCl supplemented with iodide (I-) and fluoride (F-) results in their higher bioavailability. Twelve healthy adult human volunteers ingested increasing quantities (1, 3, 6 and 9 g) of NaCl with usual diet over 8 days. Sodium (Na+), I- and F- were measured in 24 hour urine specimen. During the 4 day basal period when no additional NaCl was ingested, ingestion of NaCl calculated from urinary Na+ concentration and diuresis was 8.25 +/- 0.67 g/24 h. During the same period 0.11 +/- 0.01 and 0.61 +/- 0.04 mg of I- and F- respectively were excreted in the urine per 24 h. Increased ingestion of supplemented NaCl resulted in higher urinary excretion of sodium while urinary creatinine remained stable. 92% of I- and 40% of F- contained in the additional amount of NaCl ingested were excreted in the urine. These results indicate that with increased ingestion of supplemented (I- and F-) NaCl, almost the totality of I- is excreted in the urine while fluoride is either incompletely absorbed or retained by the body to a higher extent. I- and F- supplemented NaCl is, therefore, an effective vehicle to provide these micronutrients when ingested with diet.     

Selenium intake and metabolic balance of 10 men from a low selenium area of China

Selenium intake and urinary and fecal Se excretion of 10 healthy men from a low Se area in China were determined for three consecutive days, in summer, fall, and winter of 1983, and the spring of 1984 while self-selected diets were being consumed. Mean daily Se intake was 8.8 micrograms/day with a range of 2.3-35.5 micrograms/day, and was far below the recommended range of safe and adequate Se intake of 50-200 micrograms Se/day (National Academy of Sciences/National Research Council). Mean urinary and fecal Se outputs were 3.7 and 3.4 micrograms Se/day, respectively. Mean Se balance during this time was +1.8 micrograms Se/day. Apparent absorption of Se approximated 57%. The low Se intake in this area is a cause for concern since the residents of Molimo may be at risk for Se deficiency diseases.     

慢性氟中毒大鼠体氟积累排泄动态变化及硒的影响

Ｗｉｓｔａｒ大鼠饮３０和５０ｍｇ／Ｌ高氟（Ｆ）水造成慢性氟中毒，同时另外两组大鼠饮高Ｆ水、饲２ｍｇ／ｋｇ加硒（Ｓｅ）饲料。１年内每月测饮水、摄食和排尿量，而后计算其日平均摄Ｆ、排Ｆ量，并每月测尿液Ｆ含量。喂养至４、８、１４个月时将大鼠分３批处死，测尿液、肝脏、血清Ｓｅ和骨骼、肝脏、肾脏、血清Ｆ含量。结果两组氟中毒大鼠与对照组比较摄Ｆ量升高，排Ｆ／摄Ｆ比值降低。尿Ｆ的升高与水Ｆ浓度及饮Ｆ时间呈正相关。骨、肝Ｆ大量蓄积出现于氟中毒中期，血Ｆ在氟中毒晚期明显上升。同未加Ｓｅ氟中毒大鼠比较，两组加Ｓｅ组大鼠尿、肝、血Ｓｅ升高。与此同时大鼠摄食、饮水状况改善，体重增加；排尿量升高；尿Ｆ排泄量和排Ｆ／摄Ｆ比显著提高；同时骨、肝、肾和血清Ｆ含量降低。     

Tissue distribution and prediction of total body folate of rats

To clarify relationships between dietary folic acid intake, blood levels and body stores of folate, rats were fed an amino acid-based diet supplemented with 0, 0.125, 0.5, 1, 2 or 4 mg folic acid/kg diet for 25 d. Folate concentrations of carcass, liver, gastrointestinal (GI) tract, kidney, spleen, testes, heart and lung from rats fed the folate-free diet were 0.06 +/- 0.01, 0.73 +/- 0.08, 0.05 +/- 0.01, 0.39 +/- 0.01, 0.05 +/- 0.01, 0.17 +/- 0.01, 0.02 +/- 0.01 and 0.02 +/- 0.01 micrograms/g, respectively. Serum and erythrocyte concentrations and total body stores were 0.88 +/- 0.16 ng/mL, 0.30 +/- 0.01 micrograms/mL and 13.9 +/- 0.7 micrograms, respectively. Body folate distribution was carcass, 55.6 +/- 1.4%; liver, 26.0 +/- 1.9%; erythrocytes, 7.7 +/- 0.4%; kidney, 4.8 +/- 0.2%; GI tract, 3.0 +/- 0.2%; and testes, 2.5 +/- 0.2%. Carcass content dropped to 38% whereas liver content increased to 44% in rats fed the highest dietary level. Tissue concentrations were correlated with one another and with dietary folate levels. Under these experimental conditions total body folate could be predicted from serum folate, but the general applicability of this relationship requires further study.     

An evaluation of the bioavailability of selenium in high-selenium yeast.

The bioavailability of selenium (Se) in high-Se yeast (SeY) was evaluated by measuring tissue Se accumulation and glutathione peroxidase (GSHPx) activity. For 4 weeks, 4-week-old male Wistar rats were fed a Torula yeast-based Se-deficient diet (basal diet) or a diet supplemented with a graded level (0.04, 0.08, 0.16, and 0.32 microgram/g) of Se as either sodium selenite or SeY, which was obtained from two different sources. Se supplementation did not influence growth, hematological values, or serum biochemical tests. Se contents and GSHPx activities in the liver, serum, and erythrocytes increased gradually with increases of the supplemented Se. At lower Se levels (0.04 and 0.08 microgram/g), selenite produced higher Se deposition and higher GSHPx activities than SeY did, but at a higher Se level (0.32 microgram/g), SeY showed higher measures. Strong correlations were detected between the supplementary Se levels and the tissue Se contents or GSHPX activities when the regression was fitted to this equation: R-Rb = m log X + k, where R represented tissue Se content or GSHPx activity in rats fed the diet supplemented with Se at X level, Rb corresponding mean value in rats fed the basal diet, m slope, and k constant. The bioavailability of Se in SeY, as assessed by slope ratio analysis using selenite as a reference Se, was 135% to 165% in the tissue Se content and 105% to 197% in the GSHPx activities. These results indicate that Se in SeY is more bioavailable than selenite Se, and therefore it is the preferred form for supplementation.     

Zinc status before and after zinc supplementation of eating disorder patients.

Reduced food consumption is a major manifestation of zinc (Zn) deficiency. Many manifestations of Zn deficiency are complications of anorexia nervosa and bulimia nervosa. We evaluated serum and 24-hour urinary Zn values in 12 healthy volunteers and 33 eating disorder patients before and after hospitalization which included either Zn supplementation (75 mg Zn/day) or placebo. Bulimics had depressed serum Zn concentrations (p < 0.025). Admission urinary Zn was lower in bulimics (258 +/- 44 micrograms/day), and significantly depressed in anorexics (196 +/- 36 micrograms/day, p < 0.005) vs controls (376 +/- 45 micrograms/day). During hospitalization, serum Zn concentrations increased in all supplemented patients vs no change with placebo. Urinary Zn excretion increased in supplemented bulimics (p < 0.001) and placebo (p < 0.05). Urinary Zn excretion markedly increased in supplemented anorexics (179 +/- 65 to 1052 +/- 242 micrograms/day); however, placebo values fell or remained unacceptably low (admission 208 +/- 48 micrograms/day; discharge 160 +/- 17 micrograms/day). By dietary history, controls consumed the Recommended Dietary Allowance (RDA) for Zn (11.95 +/- 1.25 mg/day); anorexics 6.46 +/- 1.14 mg/day; and bulimics 8.93 +/- 1.29 mg/day. We suggest that Zn deficiency may act as a "sustaining" factor for abnormal eating behavior in certain eating disorder patients.     

Urinary excretion of arginine-vasopressin and prostaglandin E2 in essential fatty acid-deficient rats after oral supplementation with unsaturated fatty acid esters

Essential fatty acid-deficient rats were supplemented with 300 mg/d of pure fatty acid esters: oleate (O), linoleate (L), arachidonate (A), and columbinate (C) for 10 d. The 24-h urine collections from each animal, collected 3 d before supplementations and again the last 3 d of the 10-d supplementation period, were analyzed for volume, and by radioimmunoassay for arginine-vasopressin (AVP) and prostaglandin E2 (PGE2). Linoleate and arachidonate supplements both decreased the initial high urinary AVP excretion, whereas it was further increased by the oleate supplement. There was no effect of columbinate supplementation on urinary AVP excretion. Urinary PGE2 excretion was increased ca. twofold by both linoleate and oleate supplements, increased ca. fivefold by arachidonate supplementation but was unaffected by columbinate supplementation. There was no effect of any of the supplemented fatty acids on urine output. Fatty acid analysis of total kidney lipids revealed a low percentage of 20:3(n-9) in the rats supplemented with (n-6) fatty acid (L, A and C). The triene-tetraene ratio was 1.8 +/- 0.6 (n = 6) in the kidneys of the oleate-supplemented rats. No relationship was found between urinary PGE2 excretion and the percentage of arachidonate or the ratio of 20:3 (n-9)/20:4(n-6) in total kidney lipids. It is suggested that increased urinary AVP excretion in EFA-deficient rats is mainly caused by a change in the renal excretatory mechanism of AVP rather than reflecting an increased plasma AVP concentration. Furthermore it is suggested that renal PGE2 synthesis in vivo is unaffected by high levels of 20:3(n-9) in kidney lipids.     

Kinetics of a single administration of 74Se-selenite by oral and intravenous routes in adult humans

The purpose of this study was to explore the fate of a single dose of labeled selenium as determined by its route of administration. Thus, the appearance of a stable isotope of selenium, administered as 74-Se-selenite, was measured in plasma, urine, and feces, with neutron activation analysis, following a 81.7 micrograms dose of 74Se-selenite given either intravenously or orally in two groups (n = 4) of healthy, young adult men, who were otherwise maintained on a diet providing a constant and adequate selenium intake. From these isotopic data, measurable parameters of urine excretion, total body retention and selenite-exchangeable metabolic pool (Se-EMP) were defined to provide a quantitative assessment of selenium metabolism in these subjects. The initial 24-hr urine excretion of the label was higher for the intravenously administered label (18.2 +/- 2.1% of dose) compared to the oral dose (11.7 +/- 2.6% absorbed dose). Thereafter, the excretion of isotope was the same for both groups. For equivalent entry of Se into the body, measured total body retention and Se-EMP were the same for both groups. These initial kinetic data suggest that the overall utilization of selenium from a single administration of selenite is comparable for the two routes of intake and that the host's selenium requirement can probably be met adequately via the intravenous administration of selenite.     

The form of selenium determines the response to supplementation in a selenium replete population

In an ongoing study of selenium bioavailability, effects of supplementation with organic and inorganic forms of selenium were investigated in healthy, Norwegian women, aged 23-50 years. In phase I of the study, 58 women received 200 micrograms selenium per day either as selenite or selenium-rich pea flour for 3 months. The selenium tablets were taken together with placebo or ascorbic acid in a double blind design. Initial blood and serum selenium concentrations were 153 +/- 15 micrograms/l and 117 +/- 12 micrograms/l, respectively. These are average values for Norwegians. Indications of increased blood levels were seen in all groups, but the rise reached significance only for the subgroup receiving selenite and ascorbic acid, 14 micrograms/l, P less than 0.05. On the other hand, selenium analysis of 72-h urine samples confirmed that at an average 50 per cent of the selenium supplements had been absorbed. In phase II of the study, 28 of the participants continued for another 5 weeks, still on 200 micrograms Se per day, but this time consuming commercially available preparations. Of four preparations that were tested, two consisted of yeast Se. Only one of these produced a significant rise in blood and serum selenium levels, 60 and 55 micrograms/l respectively. Blood glutathione peroxidase values were not affected by any supplementation. The study demonstrates that different forms of organic selenium elicit widely different responses when administered to a relatively selenium-replete population, and that the explanation for this must be sought at the metabolic level.     

Some factors affecting the nitrogen sparing action of methionine and threonine in rats fed a protein free diet.

It was previously reported that methionine and threonine supplementation of a protein free diet had a greater nitrogen sparing action than methionine supplementation alone. Investigated in this study were (1) effects of depletion of labile body protein on the nitrogen sparing action of methionine and threonine supplementation of a protein free diet, (2) the effects of graded levels of methionine and threonine on urinary nitrogen excretion, (3) the effect of supplementation of other amino acids to the protein free diet plus methionine and threonine on the urinary excretion of nitrogen and (4) sex differences in the nitrogen sparing action of methionine and threonine supplementation of a protein free diet. After 10 days of feeding a protein free diet to deplete the body labile proteins, nitrogen excretion in urine of female rats was significantly reduced within the first 2 days of feeding a protein free diet supplemented with methionine and threonine. After 7 days of feeding a protein free diet supplemented with methionine and threonine, nitrogen excretion was reduced when even as little as 0.0188% of each amino acid was added. The supplementation of all essential amino acids to the protein free diet did not reduce the urinary excretion of nitrogen further than the supplementation of methionine and threonine, but improved the nitrogen balance slightly. The excretion of urinary nitrogen by female rats fed the protein free diet supplemented with small amounts (0.0188%) of methionine and threonine was significantly reduced after 7 to 14 days of feeding. In males, small amounts of methionine and threonine had no significant effect at either 7 or 14 days.     

Effect of dietary methionine and arginine on uric acid excretion of cocks fed a protein-free diet.

Cocks were fed a protein-free diet supplemented with methionine plus arginine or glutamic acid for 25 days to investigate the effect of these amino acids on fecal and urinary nitrogen excretion. Addition of either methionine plus arginine or glutamic acid did not change the fecal nitrogen excretion. Methionine plus arginine supplementation reduced the urniary nitrogen excretion compared to the protein-free diet, whereas glutamic acid supplementation increased it. The reduced urinary nitrogen excretion resulting from supplementation with methionine plus arginine was mostly accounted for by a reduction in uric acid excretion. In the methionine plus arginine group, free amino acid analysis showed that free glutamine and glutamic acid content significantly decreased in liver while no differences were found in plasma. Since glutamine may play an important role in the formation of uric acid for chickens, the reduced amount of free glutamine and glutamic acid in the liver of cocks fed the diet suplemented with methionine plus arginine might account for the reduced excretion of uric acid, and therefore for the nitrogen sparing action of methionine plus arginine in chickens fed a protein-free diet.