Selenium in the central nervous system of rats exposed to 75-Sel-selenomethionine and sodium selenite

The aim of the present study is to investigate the accumulation and retention of organic and inorganic selenium in the central nervous system (CNS) of the rat. Selenium accumulation was investigated after oral treatment (3.0 mg Se/L drinking water) or ip injection (1.7 mg Se/kg body wt) of rats exposed to 75-Se L-selenomethionine (SeMeth) or sodium selenite (NaSe). Significant higher concentrations were observed after exposure to organic compared to inorganic selenium after oral as well as ip administration. Highest concentrations in both experiments were observed in cerebellum followed by the nearly identical levels in the cerebral hemisphere and spinal cord independent of the chemical form of selenium or the route of administration. The difference in concentrations observed between the different parts of the CNS investigated in each group were, however, not significant. Retention of selenium in the CNS was investigated after a single ip injection (1.7 mg Se/kg body wt) of 75-Se SeMeth or NaSe. In both groups, we observed an initial fast excretion phase followed by a slower excretion phase resembling a first-order reaction. Organic selenium disappeared much slower from all parts of the central nervous system compared to NaSe after a single injection.     

Selenium in the anterior pituitary of the rat after a single injection of75Se sodium selenite

In order to investigate the selenite metabolism in the anterior pituitary and compare it with other endocrine organs, rats were injected intraperitoneally with⁷⁵Se sodium selenite (5 mg/kg). The rats were whole body counted shortly after injection and recounted just before sacrifice, which was performed 2, 24, 48 h, and 4, 10, 20, 30, 40, 60, and 80 d after injection. Besides the anterior pituitary, the selenium content was also estimated in the thyroid gland, testis, adrenals, liver, kidney, and blood. The maximum selenium content was observed in all organs 2 h after injection, at which time the anterior pituitary contained 2.9 μg/g wet wt, compared to 13.5 μ/g wet wt in liver and .6 μg/mg wet wt in testis. The excretion of selenite from the anterior pituitary resembled that seen in most other organs investigated, i.e., an initial rapid excretion and a slower secondary phase resembling a first order reaction. Practically all selenium was excreted by 60 d after injection.     

Application on Timm sulphide silver method for electron microscope localization of lead ions in blood cells.

The application of the Timm sulphide silver method for the demonstration of lead ions in peripheral blood cells is investigated, using male white adult Wistar rats treated with a single dose of lead acetate, range 150 mg/kg b.w. To improve the Timm reaction for electron microscopy, fixation of whole cells with glutaraldehyde fixative solution saturated with H2S, an agarose embedding and physical development of thick sections without prior cryostat sectioning are presented. At 6.0 hours after injection both erythrocytes as well as white cells reveal the positive Timm reaction. All types of blood cells contain numerous cytoplasmic precipitates illustrating the intracellular lead accumulation. It is shown that the invaginations of white cell nuclear membrane possess a storing function as areas of lead depots. As a rule, the neutrophils display a highest amount of cytoplasmic precipitates and exclusively a low amount of reaction products in basophils is observed. At 14 days after injection, precipitates are present only in erythrocytes and monocytes. A suggestion of a possible functional significance of changes in the Timm staining pattern in blood cell types is discussed in this paper.     

Combined effects of selenium and drought on photosynthesis and mitochondrial respiration in potato.

The possible effects of selenium (Se) foliar spraying and drought were studied for 3 months in potato (Solanum tuberosum L.) cultivar Desiree in Ljubljana, Slovenia. Four combinations of treatments were conducted: well-watered plants with and without Se foliar spraying, and drought exposed plants with and without Se foliar spraying. The following parameters were monitored 2 and 4 weeks after treatments: net photosynthesis, transpiration rate, quantum yield of photosystem II (PSII), and respiratory potential measured by electron transport system activity. After 3 months of treatments, leaf water potential and tuber yield were determined. The content of Se in tubers was measured after harvesting time. Several effects of drought and Se foliar spraying and their combinations were found. Net photosynthesis and respiratory potential were lower in drought exposed plants 4 weeks after treatments. Se induced higher respiratory potential in the leaves 4 weeks after treatments. Higher efficiency of energy conversion in PSII, expressed by a higher effective quantum yield, was observed in Se treated plants 2 weeks after treatments. Foliarly applied Se was efficiently absorbed by plant leaves and transported to the tubers.     

Effect of long-term administration of arsenic (III) and bromine with and without selenium and iodine supplementation on the element level in the thyroid of rat

The aim of this study was to evaluate the influence of arsenic and bromine exposure with or without iodine and selenium supplementation on the element level in the thyroid of rats. Four major groups of Wistar female rats were fed with respective diets: group A - standard diet, group B - iodine rich diet (10 mg I/kg food), group C - selenium rich diet (1 mg Se/kg) and group D - iodine and selenium rich diet (as in group B and C). Each group was divided into four subgroups per 7 animals each receiving either NaAsO(2) ip (6.5 mg.kg(-1) twice a week for two weeks and 3.25 mg.kg(-1) for six weeks) or KBr in drinking water (58.8 mg.l(-1)) for 8 weeks or combined administration of both substances. Remaining subgroup served as controls. After 8 weeks thyroid glands were analyzed by ICP-MS for As, Br, Se, and I content. The exposition of rat to arsenic or bromine causes the accumulation of these elements in the thyroid gland ( approximately 18 ppm of As, approximately 90 ppm of Br) and significantly affects iodine and selenium concentration in the thyroid. In iodine and/or selenium supplemented rats the bromine intake into the thyroid was lowered to approximately 50% of the level in unsupplemented animals. Also selenium thyroid level elevated due to KBr administration was lowered by iodine supplementation in the diet. The accumulation of arsenic in the thyroid was not influenced by selenium or iodine supplementation; however, As(III) administration increased iodine thyroid level and suppressed selenium thyroid level in selenium or iodine supplemented group of animals.     

Effects of Selenium Administration on Erythrocyte and Blood Plasma Glutathione Peroxidase Activity in Goats

The activity of glutathione peroxidase (GSH-Px, E.G. 1.11.1.9.) was determined in heparinized whole blood, blood plasma and washed erythrocytes from goats before and up to 4 weeks after the administration of selenium (0.4 mg/10 kg BW) and vitamin E (20 mg/10 kg BW) or only vit. E (20 mg/10 kg BW). It was found that Se administration caused a significant increase in enzyme activity in whole blood and washed erythrocytes first detected 2 weeks after the intramuscular injection of Se. No changes were observed in plasma from the treated animals. Minor and insignificant changes were seen in the vit. E treated control animals. It is concluded that GSH-Px activity in blood plasma or serum is of no value as a short-term indicator of the selenium status of goats but whole blood is a good indicator of the long-term status.     

Uptake and distribution of sodium selenite in rat brain tumor

Eighteen weanling male Wistar rats with brain gliomas were divided into three groups, which received 0., 2.0, 5.0 ppm selenium (Se) in their drinking water. The accumulation and retention of selenium in the brain bearing tumor was investigated. Significantly higher concentrations of Se were observed in tumor tissue than normal brain tissue after exposure to sodium selenite. Tumors were observed in the 2.0 Μg/g selenium group. The difference in selenium concentration between the tumor tissue and contralateral normal brain tissue was not influenced by the weight of brain or body, and water consumption. We observed that selenium accumulated in tumor tissue more than in normal brain tissue.     

The effect of selenium on the localization of autometallographic mercury in dorsal root ganglia of rats

The autometallographic technique was used to demonstrate the localization of mercury in dorsal root ganglia of adult Wistar rats. The animals were either exposed to mercury vapour, 100 μg Hg m⁻³, 6 h day⁻¹, 5 days per week, or treated with organic mercury in the drinking water, 20 mg CH₃HgCl per litre, for 4 weeks. The effect of orally administered sodium selenite on the pattern of intracellular distribution of mercury in these two situations was investigated. In rats exposed to mercury vapour alone, faint staining was present in ganglion cells. The selenite induced a conspicuous increase in the number of stained cells and in the intracellular staining intensity. In rats treated with organic mercury, mercury deposits were detected within ganglion cells and macrophages. The number of mercury-containing cells was increased by co- administration of selenite. In addition, satellite cells, the capsule and vessel walls were faintly stained. Twenty weeks after cessation of the organic mercury treatment, mercury staining was reduced. Again, selenite treatment enhanced staining intensity. When studied using the electron microscope, mercury was restricted to lysosomes, irrespective of treatments. The present study shows that the deposition of autometallographic mercury in the dorsal root ganglia depends on the chemical type of mercury, the co-administration of selenite and the length of the survival period. This revised version was published online in November 2006 with corrections to the Cover Date.     

Glycoproteins in membranes of secretory granules of the anterior pituitary gland.

Rat anterior pituitary glands were examined by electron microscopy after staining with five different histochemical stains. Histochemical reactions were observed in the cell coat, cell membrane and the membrane surrounding the secretory granules in all anterior pituitary cells following staining with phosphotungstic acid (PTA), chromic acid and PTA, the periodic acid-thiosemicarbazide-silver protein method (PA-TSC-SP) of Thiéry, ruthenium red and concanavalin A. The staining was abolished when the sections were preincubated with pronase, neuraminidase or trypsin and subsequently exposed to PTA, chromic acid and PTA or PA-TSC-SP. The possible functional role of the glycoproteins present in the membrane surrounding the secretory granules is considered.     

Distribution of epidermal growth factor binding sites in the adult rat anterior pituitary gland

The distribution of epidermal growth (EGF) binding sites was studied in the pituitary gland using light and electron microscope autoradiography which was performed at different time intervals (2 to 60 min) after intravenous (IV) injection of [125I]EGF into adult rats. At the light microscopic level, the labeling was found over cells of the anterior pituitary gland. The time-course study performed by light microscope autoradiography showed that the maximal values were reached at the 2 min time interval. At this time interval, most silver grains were found at the periphery of the target cells. After, the number of silver grains decreased progressively and the localization of silver grains in the cytoplasm indicated the internalization of [125I]EGF. Electron microscope autoradiography showed that labeling was mostly restricted to mammotrophs and somatotrophs. Control experiments indicated that the autoradiographic labeling was due specific interaction of [125I]EGF with its binding site. These results indicate that EGF binding sites are present in at least two anterior pituitary cell types and suggest that EGF can exert a physiological role in the pituitary gland.     

Glycoproteins in membranes of secretory granules of the anterior pituitary gland

Summary Rat anterior pituitary glands were examined by electron microscopy after staining with five different histochemical stains. Histochemical reactions were observed in the cell coat, cell membrane and the membrane surrounding the secretory granules in all anterior pituitary cells following staining with phosphotungstic acid (PTA), chromic acid and PTA, the periodic acid-thiosemicarbazide-silver protein method (PA-TSC-SP) of Thiéry, ruthenium red and concanavalin A. The staining was abolished when the sections were preincubated with pronase, neuraminidase or trypsin and subsequently exposed to PTA, chromic acid and PTA or PA-TSC-SP. The possible functional role of the glycoproteins present in the membrane surrounding the secretory granules is considered.     

Ameliorating effect of selenium on chromium (VI)-induced oxidative damage in the brain of adult rats

Chromium is known for its wide toxic manifestations. This experiment aims to evaluate the effect of selenium against oxidative stress induced by chromium in the cerebrum and cerebellum. Female Wistar rats were randomly divided into four groups of six each: group I served as controls which received the standard diet; group II received drinking water K(2)Cr(2)O(7) alone (700 ppm); group III received both K(2)Cr(2)O(7) and Se (0.5 mg Na(2)SeO(3)/kg of diet); and group IV received Se (0.5 mg/kg of diet) for 3 weeks. The exposure of rats to K(2)Cr(2)O(7) promoted oxidative stress in the cerebrum and cerebellum with an increase in malondialdehyde and a decrease of nonenzymatic antioxidant levels such as glutathione, nonprotein thiol, and vitamin C. An increase of enzyme activities like catalase, glutathione peroxidase, and superoxide dismutase activities was also observed. Acetylcholinesterase activity was inhibited after treatment with K(2)Cr(2)O(7). Co-administration of Se restored the parameters cited above. The histopathological findings confirmed the biochemical results.     

Exogenous selenium in the brain

Summary 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.     

Autometallographic demonstration of gold in the adrenal gland of rats exposed to sodium aurothiomalate

The presence of gold was investigated in sections of the adrenal glands from rats which had been exposed to intraperitoneal sodium aurothiomalate (32 to 120 mg). Gold was histochemically detected in cortical endocrine cells, chromaffin cells and in fibroblasts and macrophages of both the cortex and medulla. Invisible traces of gold were silver enhanced by autometallography making them readily visible at both the light and electron microscopic levels. The intracellular staining intensity was dose-dependent. In general, the number as well as the staining intensity of individual cells, were highest in the zona glomerulosa and zona reticularis. In gold-containing cells the silver-amplified deposits were present in lysosomes.     

AgNOR numbers in rat pituitary corticotrophs following adrenalectomy or corticotrophin releasing factor administration

Using a combined silver staining/immunoalkaline phosphatase technique, nucleolar organiser regions (AgNORs) were visualised and quantified in rat anterior and intermediate lobe pituitary corticotrophs following bilateral adrenalectomy or sham surgery. Compared to sham operated animals, the mean number of AgNORs was increased in anterior lobe corticotrophs in adrenalectomized rats and there was a shift to the right in the distribution. At 2 weeks after adrenalectomy, AgNOR numbers were greater than at 6 weeks. AgNOR numbers were also quantified in anterior lobe corticotrophs of intact rats receiving daily intraperitoneal injections of ovine CRF-41 at 50 micrograms/kg, which has been shown to stimulate ACTH release and to produce morphological evidence of increased corticotroph stimulation. CRF-41 did not produce an increase in AgNOR numbers, compared to saline injected controls.     

Cadmium-induced alterations in the antioxidant defense system of the rat eye in relation to dietary selenium intake

Cytosolic activity of glutathione peroxidase (GSH-Px), selenium-independent GSH-Px, and catalase, thiobarbituric acid reactive substances (TBARS), and glutathione and selenium (Se) concentration were measured in ocular tissues of rats maintained on a low (0.05 ppm) or adequate (0.10 ppm) Se diet and treated with 0 or 25 ppm cadmium (Cd) in their drinking water for fourteen weeks. Feeding rats a low Se diet resulted in a significant decrease in GSH-Px activity when compared to rats maintained on adequate dietary Se, irrespective of Cd treatment. Se-independent GSH-Px activity of rats maintained at 0.05 ppm Se decreased 27% when compared to Se-adequate controls, whereas activity increased 38% in the Cd-treated low-Se group. When comparisons were made between ocular TBARS in rats maintained at either level of dietary Se and treated with 0 or 25 ppm Cd, a trend toward decreased amounts of TBARS in Cd-treated groups was observed. A significant decrease in ocular Se concentration occurred in rats fed 0.05 ppm Se when compared to the Se-adequate group. Administering Cd to the low-Se group increased ocular Se levels 100%. A negative correlation between ocular Se concentration and TBARS was observed, suggesting a possible alternate role for Se as an antioxidant in the eye.     

Accumulation and volatilization of different chemical species of selenium by plants

Selenium (Se) removal from polluted waters and soils is especially complicated and highly expensive. Phytoremediation has been suggested as a low-cost, efficient technology for Se removal. Plants remove Se by uptake and accumulation in their tissues, and by volatilization into the atmosphere as a harmless gas. Unraveling the mechanisms of Se uptake and volatilization in plants may lead to ways of increasing the efficiency of the phytoremediation process. The objectives of this study were: (i) to determine the effect of different Se forms in the root substrate on the capacity of some plant species to take up and volatilize Se; (ii) to determine the chemical species of Se in different plant parts after the plants were supplied with various forms of Se; and (iii) to determine the influence of increasing sulfate levels on plant uptake, translocation, and volatilization of different Se species. Plants of broccoli (Brassica oleracea var. botrytis L.), Indian mustard (Brassica juncea L.), sugarbeet (Beta vulgaris L.) and rice (Oryza sativa L.) were grown hydroponically in growth chambers and treated for 1 week with 20 μM Se as Na₂SeO₄, Na₂SeO₃ or L-selenomethionine (SeMeth) and increasing sulfate levels. The data show that shoots of SeO₄-supplied plants accumulated the greatest amount of Se, followed by those supplied with SeMeth then SeO₃. In roots, the highest Se concentrations were attained when SeMeth was supplied, followed by SeO₃, then SeO₄. The rate of Se volatilization by plants followed the same pattern as that of Se accumulation in roots, but the differences were greater. Speciation analysis (X-ray absorption spectroscopy) showed that most of the Se taken up by SeO₄-supplied plants remained unchanged, whereas plants supplied with SeO₃ or SeMeth contained only SeMeth-like species. Increasing the sulfate level from 0.25 mM to 10 mM inhibited SeO₃ and SeMeth uptake by 33% and 15–25%, respectively, as compared to an inhibition of 90% of SeO₄ uptake. Similar results were observed with regard to sulfate effects on volatilization. We conclude that reduction from SeO₄ to SeO₃ appears to be a rate-limiting step in the production of volatile Se compounds by plants. Inhibitory effects of sulfate on the uptake and volatilization of Se may be reduced substantially if Se is supplied as, or converted to, SeO₃ and/or SeMeth rather than SeO₄. Received: 27 February 1998 / Accepted: 30 March 1998     

Accumulation of mercury in the anterior pituitary of rats following oral or intraperitoneal administration of methyl mercury

A sensitive histochemical technique has been used to visualize the ultrastructural localization of mercury in the anterior pituitary of rats which have been exposed to methyl mercury. After administration of methyl mercury in the drinking water (20 mg X l-1 methyl mercury in distilled water) or intraperitoneally (daily dose 100 ug or 200 ug methyl mercury) intracellular accumulations of mercury were found in the lysosomes and granules of secretory cells (somatotrophs, thyrotrophs and corticotrophs). In non-secretory cells (follicular cell and marginal layer cells) mercury deposits were found in lysosomes. In orally treated rats, the number of mercury deposits increased significantly with time up to day 21. In rats exposed intraperitoneally, a continuous increase was seen in intracellular mercury accumulation. Apart from vacuolation of lysosomes, no structural damage was observed in the cells containing mercury.     

Distribution of angiotensinogen immunoreactivity in rat anterior pituitary glands

Angiotensin II (AII) has been previously shown to be localized in the gonadotropes of the rat anterior pituitary gland. Renin and angiotensin-converting enzyme, two enzymes that participate in the generation of AII, also have been shown to be present in gonadotropes. To determine whether angiotensinogen, the precursor to AII, is present in the same cells, we have stained rat anterior pituitary sections with an antirat angiotensinogen antiserum. Angiotensinogen staining was observed in cells that had a distinctive distribution at the periphery of the gland; the number of these cells and the intensity of the staining were increased in the pituitaries of rats that had been nephrectomized 24 hr before sacrifice. When double staining was performed, we never observed colocalization of angiotensinogen with any of the known pituitary hormones or with S100 protein. The results show that in the rat anterior pituitary gland, angiotensinogen is present, at least for the most part, in cells that are different from those containing renin, angiotensin-converting enzyme, and AII.     

The effects of dietary selenium on the biotransformation of 7,21-dimethylbenz[a]anthracene

The influence of dietary selenium on the mutagenic activation of 7,12-dimethylbenz[a]anthracene (DMBA) by rat liver S9 was studied using the Ames test. Rats received supplemental selenium, as sodium selenite, in the drinking water or in the diet. All rats additionally received 0, 20, 50, 100, or 500 mg Aroclor 1254 per kg body weight. Revertant counts decreased 72 and 31% at the 20- and 100-mg/kg induction levels, respectively, with S9 preparations from rats given selenium supplementation, compared to controls. No significant effects of selenium on S9 preparations was observed in rats treated with 500 mg/kg Aroclor. Preparations of S9 from rats receiving 2.5 ppm Se in their diet produced 46, 84 and 70% less revertants than controls at the 20-, 50- and 100-mg/kg induction levels. Increasing the selenium concentration in the diet to 5 ppm reduced the revertant counts by 71, 68 and 65%, at the 20-, 50- and 100-mg/kg induction level of Aroclor, respectively. Dietary selenium supplementation was shown to decrease the mutagenic activation of DMBA by liver microsomes. These studies indicate that in vivo selenium supplementation may reduce susceptibility to the action of various carcinogens.