75Se Activity Research Articles

RE-TRANSLOCATION OF SELENIUM DURING GENERATIVE GROWTH IN WHEAT

The effect of nitrogen (N) and sulfur (S) availability on the re-translocation of selenium (Se) in spring wheat (Triticum aestivum) in a greenhouse experiment using 75Se labeled selenate was performed. Spring wheat was grown hydroponically and pulsed with 75selenate at growth stage Z1.4, Z 4.0, and grown in nutrient solutions having N/S ratios of 4, 7, 15, 25 and 35. Plants were separated into leaves, stem, ear and grains prior to 75Se Becquerel activity (Bq) measurements. The wheat plant 75Se activity varied from 72 to 702 Bq. Selenium and N application at heading maximized the plant Se re-translocation from leaf and stem to grains. High levels of N enhanced the re-translocation of 75Se while S inhibited this process. The S supply to the wheat plant should not be deficient due to decreased yield and thereby reduced total Se re-translocation, but the Se concentration of the single grains may be high.

Translocation and re-translocation of selenium taken up from nutrient solution during vegetative growth in spring wheat

Selenium (Se) is an essential micronutrient for humans, but the Se level in food plants in northern Europe is generally inadequate to meet human nutritional requirements. Commonly, food plant Se fortification is achieved by selenate fertilisation, but the effect of nitrogen (N) and sulphur (S) supply on the translocation and re-translocation of Se is unknown. Therefore the effect of N and S supply on ⁷⁵selenate/⁷⁵Se translocation and re-translocation during vegetative growth in spring wheat (Triticum aestivum) was studied. The ⁷⁵Se activity in wheat varied from 148 to 549, from 277 to 1815 and from 171 to 1343 Bq ⁷⁵Se in plants exposed at Zadoks growth stages Z1.4, Z1.5 and Z1.6 respectively. Approximately 85% of the plant ⁷⁵Se was translocated into young leaves. High N supply enhanced the re-translocation of ⁷⁵Se from the stem to maturing leaves, while S inhibited this process. The relative proportion of ⁷⁵Se in L4, L5 and L6 increased with increasing N supply at low sulfate concentrations. Selenium in the stem is more re-transportable than Se in the leaves, and the re-translocation is dependent on sulfate supply. When the sulfate supply is sufficient for plant development, less ⁷⁵Se is re-translocated from older to growing leaves.

BIPM comparison BIPM.RI(II)-K1.Se-75 of activity measurements of the radionuclide 75Se and links for the international comparison CCRI(II)-K2.Se-75

Since 1976, seven national metrology institutes (NMIs) and an international organization have submitted 20 samples of known activity of 75Se to the International Reference System (SIR) for activity comparison at the Bureau International des Poids et Mesures (BIPM), with comparison identifier BIPM.RI(II)-K1.Se-75. The activities ranged from about 1.4 MBq to 15 MBq. The results of a CCRI(II) comparison held in 1992 for this radionuclide, with comparison identifier CCRI(II)-K2.Se-75, are linked to the BIPM comparison for 18 participants through individual measurements of the comparison ampoules in the SIR. This has enabled six NMIs to update their earlier SIR results and another 11 NMIs and the BIPM to have degrees of equivalence in the key comparison database (KCDB). The degrees of equivalence between each equivalent activity measured in the SIR and the key comparison reference value (KCRV) have been calculated and the results are given in the form of a matrix for 18 NMIs and the BIPM. A graphical presentation is also given.Main text.To reach the main text of this paper, click on Final Report.Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by Section II of the Consultative Committee for Ionizing Radiation (CCRI(II)), according to the provisions of the Mutual Recognition Arrangement (MRA).

75Se as a new neutrino source for calibrating low-threshold detectors of solar neutrinos

A new artificial neutrino source on the basis of the 75Se isotope for calibrating low-threshold solar-neutrino detectors like GNO, SAGE, and LENS is considered. It is shown that 75Se possesses some advantages over sources based on 51Cr: the energies of its basic neutrino lines are close to the endpoint of the neutrino spectrum associated with proton-proton interactions in the solar cycle, and the production cross section for the former and its half-life are much larger. A Russian L-2 heavy-water reactor can be used to generate the required activity of 75Se in an optimal mode.

Information on the Selenium Status of Several Body Compartments of Rats from the Selenium Concentrations in Blood Fractions, Hair and Nails

The suitability of the selenium concentrations in blood plasma, red blood cells, hair and nails to serve as indicators for the selenium status in the main body pools and for the chemical forms of the element ingested was investigated in an animal model. Selenium-deficient male rats, fed a methionine-supplemented low selenium diet, were replenished over a period of 3 months by repeated oral administration of 75Se-labeled sodium selenite or L-selenomethionine in amounts equivalent to the intake from diets with selenium concentrations of 0.3 mg/kg and 2 mg/kg. As the tracer was found to reflect the selenium distribution in the main compartments, quantitative selenium analysis in whole body, liver, skeletal muscle, heart and the monitor materials in the four groups was carried out by measuring the 75Se activity. The blood selenium level was the most suitable parameter for assessing the selenium status in the liver, while the nail selenium concentration was most suited for whole body, skeletal muscle and heart. The differences in the amount and chemical form of dietary selenium were best reflected by the ratios of the selenium levels in hair and plasma or in nails and plasma. The results suggest that with adequate or high selenium intake it might be possible to obtain information on the selenium status of the main body compartments by evaluating the selenium concentrations in several appropriate monitor materials.

Metabolic relevance of selenium in the insect Corcyra cephalonica. Uptake of 75Se and subcellular distribution.

Requirement, uptake, and subcellular distribution of Na2(75)SeO3 in the larvae of the insect C. cephalonica was investigated. That Se is well tolerated by C. cephalonica upto an added level of 2 ppm in the diet is suggested by the observed increase in body weight, total protein, and succinate dehydrogenase levels. Significant increases in the State 3 respiration ensued with Se supplementation up to 2 ppm in the mitochondrial oxidation of D-glycerol 1-phosphate, succinate and NADH, along with concomitant unaltered State 4 respiration, leading to enhanced RCR values. Maximal uptake of 75Se was registered in the larvae maintained on basal diet when subjected to short-term exposure to 0.5 ppm 75Se level. When exposure level was further increased up to 20 ppm, the observed decrease in the uptake of 75Se suggested that Se status of larvae itself controlled the tissue uptake. Subcellular distribution pattern revealed maximal incorporation of 75Se (cpm/g tissue) in the supernatant fraction, whereas, maximal specific 75Se activity (cpm/mg protein) was associated with the mitochondrial fraction. Autoradiography of the soluble fractions indicated the presence of single selenoprotein in the larval group with short term 2 ppm 75Se exposure. Inherent Se controls both the extent and the nature of distribution of mitochondrial 75Se incorporation. Uptake of 45Ca by the insect mitochondria was enhanced by dietary Se up to 2 ppm but was unaffected by addition of in vitro 75Se in the medium. A more fundamental role for Se in the mitochondrial energy metabolism emerges from these studies.

Measurement of 75Se activity by correlation and coincidence counting

A 75Se solution has been standardized by simultaneous coincidence and correlation counting, as part of the 1992 BIPM international comparison of activity measurements of this nuclide. The correlation measurements provided an explicit correction to allow for the effect of the isomeric state in the daughter 75As, and enabled a direct measurement of its half-life at 16.23±0.33 ms.

75SeHCAT fractional turnover rate in primary biliary cirrhosis

Objective: To assess whether short-term ursodeoxycholic acid treatment in patients with primary biliary cirrhosis modifies the bile acid fractional turnover rate. Design: The fractional turnover rate of bile acids was measured according to the half-life of the orally administered γ-emitting bile acid analogue 75Selena homocholic acid taurine (75SeHCAT) in eight women with primary biliary cirrhosis before and after 4 weeks of treatment with 600 mg/day ursodeoxycholic acid. Methods: The half-life of 75SeHCAT was measured according to the daily exponential decrease of 75Se activity over the gall bladder area; in the five patients who had been cholecystectomized previously, the 75SeHCAT half-life was measured from the exponential decrease of total abdominal activity using the non-collimated γ-camera. Results: Short-term ursodeoxycholic acid treatment caused a significant reduction in the 75SeHCAT half-life from 5.9±5.4 to 2.7±1.7 days (mean±SD, P<0.02), resulting in values below the normal range (2.0 days) being found in four out of the eight patients. Conclusion: Our results suggest that ursodeoxycholic acid administration in primary biliary cirrhosis increases the bile acid fractional turnover rate. Considering that ursodeoxycholic acid has been reported not to modify the mass of all other bile acids in the enterohepatic circulation of such patients, we hypothesize that this effect is due to a combination of down-regulation of the ilea) absorption efficiency of bile acids and increased bile acid hepatic excretion.

Time-dependent distribution of selenate and selenite selenium in male C57L/J mice

The distribution and retention of selenate and selenite in C57L/J mice was investigated using 75Se radioisotope. The comparison is made with the normal distribution of the element determined by using radioisotope-induced x-ray fluorescence, RIXRF methods. The distribution of the two oxidation states measured as activity of 75Se was almost identical but differed from the normal trace elemental profile, TEP. The excretion rates of the two selenium species in the initial phase are different with more selenate being excreted than selenite in the first 2 days. It was found that the wholebody excretion rates followed a pure first-order pattern this was not true for the individual organs of the animals.

Standardization of 75Se by 4π(e, x)-γ coincidence counting method

The activity of 75Se has been evaluated by means of the 4π(e, x)-γ coincidence counting method. The efficiency in the β-channel was changed by the method of electronic threshold level variation. The detection efficiency which varied from 25 to 68% was extrapolated into the second order least squares fitting. The delayed transitions originating from the isomeric state of 304 keV were taken into the account of activity evaluation, and the calculated value from decay data in literatures was 5.9%. The activity of 75Se was also measured by means of γ-ray spectrometry. The final results from two methods show a good agreement within the range of uncertainty.

Trial comparison of the measurement of the activity of 75Se

The activity concentration of a solution of 75Se was measured by five laboratories in a trial comparison organized by the BIPM. A long-lived metastable level presents a serious obstacle to an absolute measurement of this radionuclide and, therefore, two different approaches were adopted. The first technique uses the traditional beta-gamma coincidence method, while the second method relies on a calibrated high-efficiency gamma-ray detector and circumvents the problems which arise from the isomeric state. For the coincidence measurements, the percentage of delayed events must be known accurately, so that the corresponding correction can be either derived from external data or measured by correlation techniques. The experimental results show a larger spread than anticipated, and subsequent investigations have sought to explain the observed discrepancy.

Activity measurement of 75Se using integral gamma-ray counting with a 4π-NaI(Tl) detector

In the high efficiency integral counting method the activity A is obtained from A = N/ϵN, where N is the integral countrate and ϵN the average detection efficiency per disintegration. This efficiency is calculated for 75Se using the energy-dependent calibration of the 4π-NaI(Tl) detector and 75Se decay scheme data. The calculation includes the decay via the isomeric state. An assumption in this calculation is the nonexistence of a direct EC decay to the ground state. The overall uncertainty of the 75Se activity obtained is 0.35% (standard deviation). Gamma-ray emission probabilities are determined by gamma spectrometry with germanium and Si(Li) detectors using the activity value measured.

Metabolism of selenite, selenomethionine and feed-incorporated selenium in lactating goats and dairy cows

The objective of this study was to investigate the metabolism of inorganic and organic Se sources at different dietary Se levels in lactating goats and dairy cows. The study consists of two experiments on goats dosed singly, either orally with grass sprayed with Na275SeO3 one week before cutting, intraruminally (I.R.) with Na275SeO3, or intravenously (I.V.) with Na275SeO3 or 75Se-selenomethionine. Follow-up periods were from 15 to 28 d long. Dietary Se levels were 0.05, 0.22 and 0.34 mg/kg DM. Values for 75Se absorption, excretion in milk, urine and faeces, 75Se activity in plasma, erythrocytes and hair are presented. In another experiment lasting 539 d, 48 dairy cows were fed either Na275SeO3 or grass silage sprayed with Na275SeO3 one week before cutting. Dietary Se levels were from 0.03 to 1.8 mg/kg DM. Se content in milk, plasma and erythrocytes, and GSH-Px activity in erythrocytes and plasma are given. True absorption of 75Se was 63 % and 65 %, and excretion of 75Se in milk 4 % and 7 % in the goats dosed I.R. with Na275SeO3 and orally with 75Se-labeled grass. The effect of dietary Se content was non-significant. After I.V. dose, 3.6 % and 33 % of 75Se was excreted in milk in goats dosed with Na275SeO3 and 75Se-selenomethionine, respectively, Na275SeO3 being eliminated mainly via urine. In cows receiving selenium as Na275SeO3, milk contained 0.011, 0.011, 0.016 and 0.020 mg Se/l at dietary Se levels 0.11, 0.17, 0.42 and 0.68 mg/kg DM, respectively. In cows receiving Se-sprayed silage, milk Se content was 0.023, 0.020, 0.029 and 0.040 mg/l when the diet contained 0.09, 0.20, 0.45 and 1.20 mg Se/kg DM. Se incorporated into silage was more efficient (p

Subcellular distribution of selenoproteins in the liver of the rat

After in vivo labeling [ 75Se]seletine, the intracellular distribution of selenoproteins in the liver was investigated in selenium-adequate and selenium-deficiet rats. In the subcellular fractions, which were obtained by differential centrifugation, the proteins were separated by mean of SDS-PAGE and the selenium compounds were identified via their 75Se activity. In this way twelve selenium-containing proteins or protein subunits with molecular weights between 12100 and 75400 were found. Glutathione peroxidase was concentrated in the cytosol and in the mitochondria. With the newly detected selenoproteins, some were enriched in the cytosol, one was mainly found in the nuclear fraction and some, which were present mainly in the mitochondrial and microsomal fractions, are most probably membrane-bound. In the liver of selenium-depleted rats the selenium administered was used predominantly to restore the levels of some of the newly found selenoproteins, while in the liver of selenium-adequate animals most of the selenium retained was incorporated into the glutathione peroxidase. The differences in the distribution among the subcellular fractions and the specific incorporation of the element in selenium deficiency into certain compounds suggest that there are several metabolic pathways for selenium and that the selenoproteins are involved in several different processes of intracellular metabolism.

A conjugate counting method to determine [ 75Se]SeHCAT retention in the human body

To evaluate the functional integrity of the distal part of the ileum the retention of a γ-labelled bile acid (SeHCAT) in the human body can be measured with a detector. Due to the lack of a whole body counter at our institution a two detector system was designed to measure SeHCAT retention and an evaluation of such a system has been made. The detectors are positioned on either side of a patient lying supine on a hospital trolley. The trolley is stepped forward in 100 mm steps, to determine the SeHCAT activity in the patient. With these counts the location of the SeHCAT activity and total activity present in the body can be determined. A water rilled phantom and a phantom consisting of nine 1-L saline bags with 75Se activity placed in them was used to determine system performance. Four patients with no history of bowel disease were compared with published data for normals. Results showed that the system performed satisfactorily, and accurate quantitative measurements could be made, showing that this inexpensive system could be used where a whole body counter is not available.

The metabolism of 75Se-selenomethionine in sheep given supplementary copper and molybdenum.

Four groups of three ram lambs were fed, in group pens, the following diets from 4 to 19 wk of age: 1) control (6 mg Cu/kg and 1 mg Mo/kg); 2) control plus 10 mg Cu/kg; 3) control plus 10 mg Mo/kg and 4) control plus 10 mg/kg of both Cu and Mo. Copper and Mo were added to the diet as copper sulfate and sodium molybdate. The main ingredients of the diets were alfalfa hay (20%), oats (20%) and corn (59%). At 19 wk, the animals were allocated randomly to individual metabolism cages and received a single oral dose of 75Se-selenomethionine. Liver Cu concentrations at slaughter (22 wk) were 77, 259, 68 and 316 mg/kg fresh weight for treatments 1 through 4. There was clinical evidence of Cu poisoning in lambs on treatment 2. Sheep given Cu supplements without additional Mo had reduced (P less than .05) levels of 75Se activity in muscle compared with control animals. This decrease in muscle 75Se in Cu-supplemented lambs was associated with a nonsignificant increase in 75Se content of other tissues and a nonsignificant increase in fecal excretion of 75Se. Apparent absorption and net retention of 75Se was 80% and 74%, respectively. Long-term ingestion of moderate levels of Cu influenced the metabolism of Se fed as selenomethionine, possibly through effects of chronic Cu toxicity on liver function.

Abundance and tissue distribution of selenocysteine-containing proteins in the rat

The form and distribution of selenium (Se) in proteins from selected tissues of the rat were studied by measuring 75Se radioactivity in animals provided for 5 months with [ 75Se]selenite as the main dietary source of Se. Equilibration of the animals to a constant specific activity of 75Se allowed the measurement of 75Se to be used as a specific elemental assay for Se. Skeletal muscle, liver and blood accounted for 73% of the whole-body Se and 95% of the total Se-dependent glutathione peroxidase activity. Over 80% of the whole-body Se was in protein in the form of the selenoamino acid, selenocysteine. All other forms of Se that were measured accounted for less than 3% of the whole-body Se. The Se in protein was distributed in seven subunit sizes and nine chromatographic forms. The Se in glutathione peroxidase accounted for one-third of the whole-body Se. These results show that the main use of dietary Se, as selenite, in rats is for the synthesis of selenocysteine-containing proteins. Furthermore, the presence of two-thirds of the whole-body Se in nonglutathione peroxidase, selenocysteine-containing proteins suggests that there may be other important mammalian selenoenzymes besides glutathione peroxidase.

Application of two-stage 4 π LS - coincidence method in the measurement of 75Se activity

The method of activity measurements of 75Se with the use of a two-stage coincidence and liquid scintillation counter /LS/ has been presented. The main difficulty in 75Se counting is due to delay in gamma-ray emission of about 17 ms. The anticoincidence method can not be used, as the delay is too significant. The coincidence extrapolation method has been applied with efficiency function of X-ray and electron counting in LS. The extrapolated counting rate contains the decay rate of 75Se but also conversion electrons from the delayed gamma emission and some additional effect due to efficiency of LS for the delayed gamma rays. This effect is determined by the first correction factor. The second correction factor is concerned with the Compton effect in a gamma-ray-counting channel of the scintillation counter with NaI(Tl) crystal, i.e. scattered gamma rays from the delayed gamma rays. This effect can not be avoided even if the channel window is set in such a way that the delayed radiation was not counted directly. The second correction factor was obtained from 51Cr measurements, where the detector efficiency was calculated for the scattered gamma rays from the 320-keV gamma ray. The results of activity measurements are given in the paper with random + systematic counting uncertainty of 0,6 % at a 0,99 confidence level (6 df). The presented method was applied in activity measurements of 75Se sources used for the determination of the gamma-emission probability of this radionuclide and also for the standardization of a 75Se solution.

Selenium metabolism in the dairy cow: the influence of the liver and the effect of the form of Se salt.

1. Six adult Friesian cows were given 75Se as either 75SeO32- or 75SeO42- intravenously. Five of the cows had cannulas in an hepatic vein, the portal vein and one carotid artery to enable the uptake of 75Se by the liver to be measured. Radioactive balance studies were carried out on two of the cows given 75SeO32- and two given 75SeO42-. A seventh cow was given an oral dose of 75Se-labelled barley and the excretion of 75Se in faeces, urine and milk was measured for 14 d. 2. After the injection of 75SeO32- plasma 75Se concentration decreased during the first 30 min with a mean half-life (t 1/2) of 15.6 min. From 30 to 60 min after dosing the concentration of radioactivity increased to reach approximately 50% of the level present 2 min after dosing. Following the injection of 75SeO42- the 75Se was cleared with a mean t 1/2 of 28.5 min during the first 30 min and plasma radioactivity increased only slightly during the next 30 min. 3. during the phase of rapid clearance of 75Se after the injection of 75SeO32- the hepatic venous 75Se concentration was approximately 5% lower than portal venous 75Se concentration. During the period when plasma 75Se activity was increasing the activity in hepatic venous plasma was 3% greater than portal activity. Of the 75Se cleared from plasma after injecting 75SeO32- 40% was calculated to be removed by the liver. 4. After intravenous dosing with 75SeO32- or 75SeO42- approximately 9.5 and 17.0% respectively of the dose injected was excreted in faeces and 10% in urine within 14 d. Almost three times as much 75Se was excreted in urine and 3.5 times as much in faeces during the first 24 h after dosing with 75SeO42- as after 75SeO32-.

Interactions between cadmium, selenium and glutathione peroxidase in rat testis

In rats given a minimal damaging dose of 109CdCl 2 (0.011 mmole/kg, s.c.), a visible hemorrhagic response was evident after 48 h when testicular Cd uptake exceeded a level of approx. 150 ng/g. Glutathione peroxidase (GSH-Px) activity was elevated in homogenates of these damaged testes. In rats whose testes were not damaged, the Cd levels were below 150 ng/g and the GSH-Px activity was similar to that of control animals injected with sodium acetate. Rat testis cytosol was found to contain two different GSH-Px activities when assayed with cumene hydroperoxide. These could be separated by gel filtration chromatography. The larger species (GSH-Px A) was eluted in the void volume on Sephadex G-150 and incorporated 75Se from Na 2 75SeO 3 given 4 weeks earlier. The smaller species, of approx. 42 000 molecular weight (MW) (GSH-Px B), did not incorporate 75Se and could be distinguished from GSH-Px A by its insensitivity to cyanide (10 mM). CdCl 2 (1 mM) did not inhibit GSH-Px activity when added in vitro to GSH-Px A or B from testicular cytosol, or to purified GSH-Px isolated from ovine erythrocytes. When 109CdCl 2 was given in vivo to rats injected 4 weeks previously with a tracer dose of Na 2 75SeO 3 or added in vitro to cytosol prepared from similarly labeled rats, Sephadex G-150 chromatography of cytosol showed that most of the 109Cd was eluted in a major peak of 34 000 MW. Little or no 109Cd was found in association with 75Se (major peak 140 000 MW) or GSH-Px activity. When 109CdCl 2 was injected into rats given an equimolar dose of Na 2 75SeO 3 30 min previously, 109Cd uptake in cytosol was increased and both 109Cd and 75Se was shifted into a peak of 110 000 MW. The 109Cd-binding peak of approx. 30 000–34 000 MW was the major Cd-binding fraction in cytosol of 7-week-old rats but was not detectable in 4-week-old rats. Susceptibility of the testes to Cd did not correlate with the presence of this peak, however, since 4-week-old rats were occassionally damaged by CdCl 2.