Showing papers on "Selenium published in 1982"

Selenium: toxicity and tolerance in higher plants

Abstract: Summary 1. Different plant species show considerable variation in their selenium content. Primary indicators, also termed selenium accumulators, many of which are members of the genus Astragalus, are highly tolerant of selenium; they are known to contain tissue levels of several thousand µg selenium/g. Secondary indicators, tolerant to low concentrations of the element, may absorb up to 1000 µg selenium/g. Non-accumulators are poisoned by selenium. 2. The toxicity of selenate (SeO4-) and selenite (SeO3-) to most plants can be attributed to a combination of three factors. Firstly, selenate and selenite are readily absorbed from the soil by roots and translocated to other parts of the plant. Secondly, metabolic reactions convert these anions into organic forms of selenium. Thirdly, the organic selenium metabolites, which act as analogues of essential sulphur compounds, interfere with cellular biochemical reactions. 3. Incorporation into proteins of the amino acid analogues selenocysteine and selenomethionine, in place of the equivalent sulphur amino acids, is considered to be the underlying cause of selenium toxicity. The physical and chemical differences between selenium and sulphur will result in small, but significant, changes in the biological properties of a selenium-substituted protein. 4. Selenium-tolerant accumulator plants differ in at least two respects from sensitive species. Large quantities of Se-methylselenocysteine and selenocystathionine, two non-protein selenoamino acids rarely detected in non-accumulators, have been isolated from the tissues of selenium accumulators. In addition, selenium is kept from entering proteins so that the selenium levels in proteins of accumulator plants is significantly lower than the levels in selenium-sensitive plants. 5. Exclusion of selenium from the proteins of accumulators is thought to be the basis of selenium tolerance. Discrimination against selenocysteine during protein synthesis seems to prevent incorporation of this selenoamino acid into proteins of accumulators. Furthermore, synthesis of Se-methylselenocysteine and selenocystathionine, which results in diversion of selenium away from the synthesis of selenomethionine, will restrict the amount of this compound available for protein synthesis. 6. Selenium accumulation among unrelated plant genera is a striking example of convergent evolution. The possibility that accumulation of this element is associated with a nutritional requirement for selenium, although explored in the past, is still in need of further clarification.

Exogenous selenium in the brain. A histochemical technique for light and electron microscopical localization of catalytic selenium bonds.

Abstract: Transcardial perfusion or intraperitoneal injections with sodium selenite result in the creation of selenium bonds that can be visualized by physical development. The present paper describes how these catalytic bonds are made visible in the tissues by surrounding them with shells of metallic silver. Based on experiments with chelating agents, the possibility that selenium-metal bonds are the catalysts is discussed. In the brain, the selenium pattern is delicate and highly laminated, the grains of silver being orderly arranged corresponding with the neuropil morphology. The precipitate is most densely packed in cortical regions. The difference in staining intensity seen in different regions of the CNS reflects the density of selenium reactive terminals. The visualized selenium bonds are predominantly located within boutons, and examination in the electron microscope reveals accumulation in the presynaptic regions. In a few places precipitates can also be found in axons, but have not been observed in perikarya or dendrites. The only non-neuronal locations of selenium were sparsely scattered, astrocyte-like neuroglia, predominantly found in the cerebellum and the hypothalamus; infrequently a few blood vessels were also stained. Sections from kidney and liver are presented as examples of localizations outside the CNS of exogenous selenium.

Selenium in reducing waters.

Abstract: The analysis of selenium species in reducing waters provides important insight into the element's biogeochemical cycle. The absence of selenate and selenite in reducing waters suggests that some removal mechanism could be operative, but the presence in these waters of about 1 nanomole per liter of dissolved organic selenide indicates that the regeneration of selenium in the form of organic species may be the dominant process. The data demonstrate that the regenerative and biogeochemical cycles of selenium are quite complex.

Determination of selenium concentration and glutathione peroxidase activity in plasma and erythrocytes.

Abstract: We determined selenium concentrations and activities of the selenoenzyme, glutathione peroxidase (EC 1.11.1.9), in the plasma and erythrocytes of 38 apparently healthy women. We determined selenium concentrations directly by polarized Zeeman-effect flameless atomic absorption spectroscopy. Within-run precision studies for the assays gave CVs of 5.6% for a mean erythrocyte selenium concentration of 149.9 (SD 8.3) microgram/L (n = 10) and 6.4% for a mean plasma selenium concentration of 97.3 (SD 6.2) microgram/L (n = 12). For the women, mean selenium concentrations were 141.4 (SD 14.3) microgram/L of erythrocytes [0.49 (SD 0.07) microgram/g of hemoglobin and 96.3 (SD 14.2) microgram/L of plasma. Glutathione peroxidase activities were measured by a modification of the method of Paglia and Valentine (J. Lab. Clin. Med. 70: 158--169, 1967). Within-run precision studies for the glutathione peroxidase assays gave CVs of 12.8% for mean erythrocyte glutathione peroxidase activity of 77.2 (SD 9.9) U/g of hemoglobin (n = 13), and 8.1% for mean plasma activity of 312.5 (SD 25.2) U/L (n = 11). Mean enzyme activity was 78.7 (SD 12.9) U/g of hemoglobin for erythrocytes and 424 (SD 40) U/L for plasma. Erythrocyte selenium concentrations and glutathione peroxidase activities were positively, but poorly, correlated (r = 0.41, p less than 0.01).

Determination of Selenium Concentration andGlutathione Peroxidase ActivityinPlasmaandErythrocytes

Abstract: We determined selenium concentrations and activities of the selenoenzyme, glutathione peroxidase (EC 1.11.1.9), in the plasma and erythrocytes of 38 apparently healthy women. We determined selenium concentrations directly by polarized Zeeman-effect flameless atomic absorption spectroscopy. Within-run precision studies for the assays gave CVs of 5.6% for a mean erythrocyte selenium concentration of 149.9 (SD 8.3) microgram/L (n = 10) and 6.4% for a mean plasma selenium concentration of 97.3 (SD 6.2) microgram/L (n = 12). For the women, mean selenium concentrations were 141.4 (SD 14.3) microgram/L of erythrocytes [0.49 (SD 0.07) microgram/g of hemoglobin and 96.3 (SD 14.2) microgram/L of plasma. Glutathione peroxidase activities were measured by a modification of the method of Paglia and Valentine (J. Lab. Clin. Med. 70: 158--169, 1967). Within-run precision studies for the glutathione peroxidase assays gave CVs of 12.8% for mean erythrocyte glutathione peroxidase activity of 77.2 (SD 9.9) U/g of hemoglobin (n = 13), and 8.1% for mean plasma activity of 312.5 (SD 25.2) U/L (n = 11). Mean enzyme activity was 78.7 (SD 12.9) U/g of hemoglobin for erythrocytes and 424 (SD 40) U/L for plasma. Erythrocyte selenium concentrations and glutathione peroxidase activities were positively, but poorly, correlated (r = 0.41, p less than 0.01).

Selenium in the Testis of the Rat: Studies on Its Regulation and Its Importance for the Organism

Abstract: In male rats, fed for 10 weeks on a Torula yeast-based, low selenium and low vitamin E diet, the selenium level and the glutathione peroxidase activity in the blood and in several tissues decreased by 50 to 98% compared with animals that received the same basal diet supplemented with 0.25 mg Se/kg sodium selenite. In the testes, however, the selenium content did not differ from that of the control animals. Despite the low selenium levels in the extragonadal tissues and their increased requirement of this element due to the low vitamin E status, the selenium from an intravenously injected dose of sodium selenite was retained above all in the testes. After the removal of the pituitary gland, because of the decrease in the testicular mass and in the selenium content in the remaining testicular tissue, the amount of selenium in the testes was greatly reduced. After administration of pregnant mare's serum gonadotropin (PMS), due to the regeneration of the tissue and the simultaneous restoration of the selenium content, a relatively large amount of this element was shifted to the testes even though the selenium status in the other tissues was low. The results of these studies show that the selenium level in the male gonads is maintained by regulation mechanisms and that the supply of sufficient amounts of selenium to the testes has priority over the supply to other tissues.

Chemical Form and Distribution of Mercury and Selenium in Edible Seafood

Abstract: The content, chemical form, and distribution of mercury and selenium in edible tissue were determined for several samples of fish and other marine animal organisms (mollusks, crustaceans and pods). For most fish samples, except Pacific blue marlin, 53 to 94% of the total mercury content was present as methylmercury, being notably higher in freshwater species. Other marine organisms, except shrimp, contained only 29 to 47% methylmercury. For all samples, a significant part of the total selenium content (4 to 47%) was present as selenate (Se VI). Tissue selenium levels did not correlate with corresponding mercury levels. In freshwater and older processed (canned) marine fish, except marlin, 55 to 80% of the total mercury content was water-extractable. For non-processed (fresh) and newly-processed marine samples, only 22 to 47% was extractable. On a percentage basis, inorganic mercury was generally more extractable than methylmercury. For all fish samples, except marlin, 55 to 60% of the total selenium content was water-extractable, while only 35 to 45% was extractable for other marine species. On a percentage basis, Se VI was more extractable than selenite (Se IV) and selenide (Se II).

Fluorometry of selenium in serum or urine.

Abstract: This fluorometric procedure for determining selenium in human serum or urine is sensitive (requiring only 0.4 mL of sample), accurate, simple, and can be performed on several samples concurrently. Using this technique, we found a mean selenium concentration in the serum of normal Canadian men of 142.9 (SD 16.1) micrograms/L. The mean urinary excretion rate was 124.5 (SD 76.0) micrograms/day.

Inhibition by Dietary Selenium of Colon Cancer Induced in the Rat by Bis(2-oxopropyl)nitrosamine

Abstract: Wistar-derived MRC rats were fed casein diets supplemented with 0.1 or 2.0 ppm selenium as sodium selenite from 7 weeks of age. At 8 weeks, weekly injections (5 mg/kg body weight s.c.) of bis(2-oxopropyl)nitrosamine (BOP) were started. Rats were killed after 50 injections; blood samples were collected after 1, 10, 25, and 50 weeks; and tissue samples were retained at killing for measuring hematology and selenium status. Carcinogen treatment did not influence body weight or survival. The high selenium level reduced female growth and improved male survival. Hemoglobin was reduced and mean corpuscular volume was increased in both sexes by feeding high-selenium diets. In addition, white blood cell counts were increased in BOP-treated males. Blood, liver, pancreas, and kidney selenium rose in rats fed the high-selenium diets. BOP treatment reduced liver selenium at the low dietary level and increased pancreas selenium at the high level. Glutathione peroxidase values in erythrocytes and plasma increased with the high-selenium diets, whereas its activity in the liver was not influenced by dietary selenium but was reduced in male rats by BOP treatment. Colon adenocarcinoma yield was reduced in male rats fed the high selenium level (16 carcinomas in 30 rats) by comparison with the low selenium level (28 carcinomas in 29 rats). Lung adenocarcinoma incidence decreased to none in 30 male rats fed the high-selenium diet from 4 in 29 male rats (14%) given the low selenium level. Female rats did not develop colon or lung adenocarcinomas at either selenium level. The influence of dietary selenium in the colon was related to an increased repair rate of BOP-induced DNA damage in this tissue.

Temporal variations in dissolved selenium in a coastal ecosystem

Abstract: In oceanic environments biological processes are now known to have a central role in establishing the redox state and spatial distribution of certain dissolved trace elements. Biological effects on the natural cycles of Cr, As, Se, Cd, Ni and Al are inferred from the existence of thermodynamically unfavourable species, from non-conservative vertical profiles or because trace element levels in planktonic debris are such that the subsequent regeneration of material could produce the observed profiles1–7. In cases where biological activity has been implicated as a determinant of either redox state or spatial distribution in the oceans no field investigations have yet been made into the relationships between rapid fluctuations of biological parameters and trace element levels and speciation. We now present a temporal study of the response of selenium levels and redox state to pulses of primary productivity in a coastal ecosystem. The sampling time series demonstrated selective assimilation of the lower oxidation state, selenite [Se(IV)]. Ratios of particulate selenium to particulate organic carbon (Se:C) allowed an estimation of the selenium levels in a natural phytoplankton population and the flux of selenium from surface ocean water to deep water.

Clinical consequences of low selenium intake and its relationship to vitamin E

Abstract: Great differences in dietary selenium intake have resulted in naturally occurring human selenium deficiencies and toxicities in certain parts of the world. Most North American diets, however, provide levels of selenium that fall within the estimated safe and adequate range of intake (50 to 200 microgram/day for adults) as established by the U.S. National Research Council. Low selenium status may develop in individuals fed certain therapeutic diets or given total parenteral nutrition. Attempts have been made to link low selenium intake with cancer and heart disease, but additional research is needed in this area. Selenium, as a constituent of glutathione peroxidase, plays a role in the antioxidant defense systems of the body, but other metabolic roles for selenium may yet be discovered.