Comparative effect of selenate and selenite on serum selenium concentration and glutathione peroxidase activity in selenium-depleted rats

The biological effect of selenate and selenite was compared in selenium-depleted rats by using both serum selenium concentration and glutathione peroxidase activity as an indicator of body selenium status. A single oral dose of selenium (125 micrograms/kg body weight) as sodium selenate or sodium selenite increased serum selenium concentration and glutathione peroxidase activity significantly (p less than 0.001). The effect of selenate and selenite on serum selenium and glutathione peroxidase activity was similar. Serum selenium concentration correlated positively with serum glutathione peroxidase activity both before (r = 0.815; p less than 0.001) and after (r = 0.800; p less than 0.001) treatment. These results indicate that the biological availability of selenate and selenite is similar.     

Effects of K(ATP) channel openers, P-1075, pinacidil, and diazoxide, on energetics and contractile function in isolated rat hearts

We investigated the metabolic effects of a potent opener of ATP-sensitive K(+) (K(ATP)) channels, P-1075, in perfused rat hearts with the help of(31)P NMR spectroscopy. A 20 min infusion of 5 microm P-1075 depleted phosphocreatine and ATP by approximately 40%, concomitantly with a two-fold increase in inorganic phosphate, while oxygen consumption by the hearts increased by 50%. P-1075 induced a cardiac contracture (left ventricular end diastolic pressure increased from 6 to 60 mmHg) and a cardiac arrest after an infusion of approximately 9 min. The effects were fully reversed by glibenclamide (5 microm), but not by sodium 5-hydroxydecanoate (0.4 m m). A P-1075-related K(ATP) opener, pinacidil (0.3 m m), partially reversed the effects of P-1075, but a structurally unrelated opener, diazoxide (0.5 m m), had no effect. Pinacidil and diazoxide alone did not significantly affect PCr and ATP levels. Bioenergetic and functional effects similar to those of P-1075 were induced by infusion of a classic mitochondrial uncoupler, 2,4-dinitrophenol (50 microm); however, they were not abolished by glibenclamide. In addition, it was shown, using(87)Rb NMR, that both agents, P-1075 and 2,4-dinitrophenol, resulted in a stimulation of Rb(+) efflux from the Rb(+) loaded rat hearts by approximately 130 and 65%, respectively, in a glibenclamide-sensitive manner. An inhibitory effect of P-1075 on ATP synthesis cannot be explained by its well-known action on sarcolemmal K(ATP) channels. We concluded that, unlike an uncoupling effect of 2,4-dinitrophenol, an inhibitory effect of P-1075 is produced by uncoupling of oxidative phosphorylation through the activation of mitochondrial K(ATP) channels.     

Effects of ouabain and isoproterenol on left ventricular diastolic function during low-flow ischemia in isolated, blood-perfused rabbit hearts

Myocardial ischemia causes both systolic and diastolic dysfunction. A variety of positive inotropic agents with different subcellular mechanisms may be used clinically in an attempt to reverse ischemic contractile failure. We tested the hypothesis that two inotropic agents, isoproterenol (a beta-adrenergic agonist) and ouabain (a sodium pump inhibitor), might have different effects on left ventricular (LV) diastolic function during ischemic failure despite an equivalent inotropic effect. Isolated isovolumic (balloon-in-LV) blood perfused rabbit hearts were paced at constant physiological heart rate (4 Hz), given either no drug (controls, n = 7), isoproterenol (n = 7), or ouabain (n = 7), and then subjected to 6 minutes of low flow ischemia (75% reduction of baseline coronary flow). The doses of isoproterenol and ouabain were selected to produce equivalent modest inotropic effects (15% increase in LV + dP/dt) in each heart during baseline perfusion conditions. During the ischemic period, there was a marked decrease in contractility, and neither isoproterenol nor ouabain demonstrated a positive inotropic effect relative to the control group. However, these agents had markedly different effects on diastolic chamber distensibility (assessed by end-diastolic pressure at constant LV volume) during ischemia. In the control and isoproterenol groups, diastolic chamber distensibility did not change during the ischemic period. In contrast, ouabain treatment resulted in a marked decrease in diastolic chamber distensibility during ischemia; this change was not completely reversible during the 10-minute reperfusion period. The mechanism by which ouabain decreased diastolic chamber distensibility relative to isoproterenol was assessed indirectly. The ouabain and isoproterenol groups were subjected to equivalent degrees of ischemia as assessed by oxygen supply/demand imbalance; during ischemia, each drug group did not differ with regard to myocardial perfusion rates, determinants of myocardial oxygen demand (heart rate, LV developed pressure, LV + dP/dt), myocardial oxygen consumption, lactate production, and ATP and creatine phosphate content. We therefore inferred that the greater decrease in diastolic distensibility in the ouabain group was not due to a greater metabolic severity of ischemia. These observations are consistent with a mechanism of cytosolic calcium overload induced by ouabain, resulting in persistent active myofilament tension development throughout diastole, to cause the observed decrease in diastolic chamber distensibility during ischemia in the ouabain group.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of sodium selenite on the course of acute experimental myocardial infarct

The effect of sodium selenite on experimental myocardial infarction was investigated in 47 domestic pigs, with a major emphasis on the hemodynamic antiarrhythmic effects of selenium. Intravenous sodium selenite administered in a dose of 1-2 mg/kg body weight produced a favorable pharmacologic effect. The hemodynamic action consisted in an increase of heart rate, and the maximum aortic flow rate, cardiac output, minute volume of the heart and coronary flow, as well as a decrease in total peripheral resistance. Selenium's antiarrhythmic effect was manifested in reduced occurrence of ventricular extrasystoles and flutter, and the disappearance of "late potentials" in the peri-infarction area.     

Sodium selenite induces apoptosis in acute promyelocytic leukemia-derived NB4 cells by a caspase-3-dependent mechanism and a redox pathway different from that of arsenic trioxide

Two relatively recent discoveries stand behind our current effort to investigate the effects of the chemopreventive agent, selenium, on the proliferation and survival of NB4 cells. The first is that certain selenium compounds such as sodium selenite have pro-oxidant ability to catalyze the oxidation of thiols and simultaneously generate superoxide. The second lies in the exquisite susceptibility of NB4 cells to arsenic trioxide-induced, reactive oxygen species (ROS)-mediated apoptosis due to less efficiency of the cellular defense system. In this study, we demonstrated that sodium selenite could induce apoptosis in NB4 cells via the classic mitochondrial pathway involving caspase-3 activation and Bcl-2 cleavage. An increase in the basal cellular glutathione (GSH) content rendered NB4 cells resistant to arsenic trioxide, but could sensitize NB4 cells to sodium selenite. Moreover, combined treatment of NB4 cells with all-trans retinoic acid (ATRA) at low concentration and sodium selenite exhibited a synergistic effect on apoptosis induction. Together, our results suggest that selenite is a promising candidate for treatment of acute promyelocytic leukemia (APL) and the mechanism underlying its anticancer effects warrants further investigation.The first two authors have contributed equally to this work     

Experimental selenium toxicity in guinea pigs: haematological studies

Haematological studies were conducted in recently weaned guinea pigs fed selenium-enriched barley (organic selenium) and barley mixed with sodium selenite (inorganic selenium). An attempt was made to study the effect of sodium arsenite supplementation in sodium selenite toxicity. A significant (p less than 0.01) decrease was noticed in the mean values of haemoglobin, haematocrit, mean corpuscular haemoglobin and mean corpuscular volume thereby indicating a microcytic hypochromic anaemia. The anaemia was comparatively more marked in guinea pigs fed selenium-enriched barley than in those kept on barley mixed with sodium selenite. There was a significant decrease in total leucocyte count which was the result of lymphocytopenia in organic toxicity and a decrease in both neutrophils and lymphocytes in inorganic toxicity. Dietary supplementation with sodium arsenite resulted in less reduction in the mean values of different erythrocytic indices thereby indicating that addition of sodium arsenite has some protective effect against toxicity with sodium selenite.     

Corrosion Protective Film Formation on Mg Alloy AZ31 by Exposure to Dilute Selenite Solutions

The study of protective film formation on Mg alloys by exposure to sodium selenite solutions was conducted. Anodic polarization studies, electrochemical impedance spectroscopy studies, morphological analysis, and Energy-dispersive X-ray spectroscopy were performed on AZ31 Mg alloy after coating treatment in different concentrations of sodium selenite. The corrosion resistance was improved by around 5 times compared with control. Improved resistance to localized corrosion was observed in the coatings treated by 5 mM or 10 mM sodium selenite. The protection mechanism was ascribed to the transformation of selenite to insoluble selenium, the formation of insoluble MgSeO₃ hydrate, and polymerization of amorphous selenium.     

Protective effects of selenium on ultrastructural changes in heart muscles with experimental free-glucose and anoxia in organ culture]

Fetal hearts taken from the 16th to 18th day of pregnant mice were cultured in MEM + 0.5 microgram/ml of sodium selenite [Na2SeO3] (MEMS), and in MEM alone with oxygen for 24 hours, and then the two groups of hearts were exposed to 10, 15, 20, 30, 40, 60 min and a long term of anoxia in glucose-free MEMS and glucose-free MEM respectively. Results showed that the survival and beating of the cultured fetal mouse hearts with experimental free-glucose and anoxia were prolonged by selenium. The application of lanthanum as a marker demonstrated that the permeability function of myocardial cell membrane and mitochondrial membrane of early experimental anoxia were protected by selenium. By using electron microscopy when structural damages occurred, it was shown that the time of occurrence of irreversible injuries could be postponed by selenium. From the fact that ribosomes increased in the cell of selenium-treated hearts, we concluded selenium may play a promotive role in the synthesis of protein in experimental free-glucose and anoxic conditions.     

Effect of cardiotropic agents on the myocardial dysfunction of hyperdynamic sepsis

We have previously shown that in vitro myocardial performance is impaired in rats during the hyperdynamic, hypermetabolic phase of sepsis. Although the heart in the resting animal generated an elevated cardiac output, the isolated, perfused heart showed a depressed ventricular function curve. In the present studies, interventions to improve contractile function (increased perfusate calcium concentration or perfusion with ouabain) or to decrease calcium availability to the myofibrils (verapamil and tetracaine) were investigated using the isolated perfused working heart. These studies showed that increasing or decreasing calcium concentration in the perfusion medium had little effect on ventricular performance in the septic group, whereas ouabain enhanced performance by approximately 25%. Addition of verapamil at a dose that caused a minimal decrease in myocardial work (cardiac output X peak systolic pressure) in control hearts showed a 20-25% increase in work in the experimental hearts. Increased levels of verapamil caused a greater depression in myocardial performance in the control hearts than in the hearts from septic rats. Thus, it appears that a multifaceted defect may be present in these hearts with a derangement that can be slightly improved with either ouabain or verapamil. Since neither intervention could completely reverse the myocardial dysfunction in hyperdynamic sepsis, it appears that the defect may be due to other factors in addition to calcium availability for contraction.     

硒对铊致培养大鼠软骨细胞损伤的保护作用观察

实验表明硫酸铊致培养大鼠软骨细胞有损伤作用,证实硒对软骨细胞的损伤有保护作用。     

Experimental selenium toxicity in guinea pigs: biochemical studies

Biochemical studies were conducted in experimentally induced selenium toxicity in recently weaned guinea pigs. A significant drop in blood glucose level, in comparison to controls, was observed in animals fed selenium-enriched barley (organic form) as well as those fed ordinary barley mixed with sodium selenite (inorganic form). Estimation of total serum proteins also revealed a significant drop in both these groups. SGOT (EC 2.6.1.1) activity was comparatively lower but no significant alteration was noticed in SGPT (EC 2.6.1.2). The erythrocytic glutathione peroxidase activity was significantly increased in inorganic selenosis followed by that in organic one, in comparison to controls. All these alterations were of mild degree in guinea pigs which were given sodium arsenite (10 ppm) along with sodium selenite (30 ppm) in the feed.     

碘硒双补防治地方性甲状腺肿的研究

采用１／５万碘盐加亚硒酸钠，对云南省武定县碘硒缺乏地区的六个自然村进行地方性甲腺肿的防治研究。结果提示：１．缺硒是该地区地方性甲状腺肿流行因素之一；２．碘硒缺乏地区，碘硒双补法防治地方性甲状腺肿的效果优于单纯补碘法。     

Effects of growth in low potassium medium or ouabain on membrane Na,K-ATPase, cation transport, and contractility in cultured chick heart cells

Growth of cultured cells in low potassium medium has been shown to result in an increase in the number of Na,K-ATPase sites. This phenomenon and its physiological and pharmacological consequences were examined in spontaneously beating monolayers of cultured chick heart cells. Growth of cells in 1 mM extracellular potassium, 2 microM ouabain, or 1 microM veratridine for 48 hours caused 60%, 40%, or 20% increases, respectively, in the total number of specific ouabain binding sites measurable in intact cells. Acute exposure of control cells grown in 4 mM to 1 mM extracellular potassium caused elevation of steady state [Na+]i by 37%, while 1 microM veratridine exposure increased [Na+]i by 12%. After 48 hours of growth in 1 mM extracellular potassium, intracellular sodium concentrations declined to near-control levels. In cells grown in low extracellular potassium and then equilibrated with 4 mM potassium for 30 minutes, the positive inotropic effects of 1 mM extracellular potassium and 0.3 microM isoproterenol, expressed as a percent of contractile response to 3.6 mM calcium, were 40 +/- 6% and 37 +/- 5% (means +/- SEM), respectively, in low potassium-grown cells, compared with 63 +/- 8% and 35 +/- 4% in control cells. Growth of cells in low potassium shifted the concentration-effect curve for ouabain to the right. The rapid component of calcium uptake in zero extracellular sodium was significantly lower in low potassium-grown cells than in control cells after equilibration in 1 mM extracellular potassium for 30 minutes. These findings demonstrate that prolonged exposure of cultured heart cells to 1 mM extracellular potassium or ouabain causes induction of additional functional sarcolemmal sodium pump sites. The increased levels of intracellular sodium caused by these interventions appear to be an important determinant of sodium pump site density. The reduced contractile response of cells grown in 1 mM extracellular potassium and ouabain (but not isoproterenol) supports the view that elevated intracellular sodium due to Na,K-ATPase inhibition mediates the positive inotropic response to low extracellular potassium and ouabain, probably via augmented transsarcolemmal sodium-calcium exchange. In addition, our results support a mechanism of inotropic action of digitalis glycosides based on inhibition of the sodium pump rather than altered calcium binding properties of sarcolemmal sites due to cardiac glycoside binding to Na,K-ATPase.     

The origin of calcium overload in rat cardiac myocytes following metabolic inhibition with 2,4-dinitrophenol

We have investigated the characteristics of the rise in cytoplasmic calcium that occurs when rat isolated cardiac ventricular myocytes are exposed to 2,4-dinitrophenol using conventional and confocal fluorescence microscopy and patch clamp. 2,4-dinitrophenol (200 microM) caused cytoplasmic calcium to increase in two phases: (1) an initial rise in fluo-3 fluorescence of 36+/-2% that was maintained until rigor contraction; (2) a further progressive rise so that fluo-3 fluorescence had increased by 177+/-12% 535 s after 2,4-dinitrophenol addition. Both phases were unaffected by removal of external Ca(2+). 2,4-dinitrophenol caused mitochondrial depolarization, measured using tetramethyl rhodamine ethyl ester fluorescence. Mitochondrial depolarization was associated with a decrease in intra-mitochondrial calcium measured with rhod-2, and experiments on myocytes loaded with both fluo-3 and rhod-2 showed that fluo-3 fluorescence increased as rhod-2 fluorescence fell. The correlation of the onset of the second phase of the increase in cytoplasmic calcium with rigor suggested that this phase was consequent on ATP depletion. DNP also caused activation of an ATP-sensitive potassium current. Depletion of sarcoplasmic reticulum calcium stores by pretreatment with ryanodine, thapsigargin and caffeine prior to the addition of 2,4-dinitrophenol did not affect the initial increase in cytoplasmic calcium, but abolished phase 2. Our results suggest that the initial rise in cytoplasmic calcium seen on application of 2,4-dinitrophenol results from release of mitochondrial calcium because of mitochondrial depolarization, while the second phase is caused by progressive release of calcium from the sarcoplasmic reticulum following depletion of intracellular ATP.     

Establishment of a parathyroid hormone-responsive phosphate transport system in vitro using cultured renal cells

A new system was established using primary cultured mouse kidney epithelial cells to study the effect of PTH on renal tubular phosphate transport. The cells used in our study had alkaline phosphatase activity. They showed increased cAMP content in response to PTH, calcitonin, and vasopressin. Thus, these cells were thought to be a mixture of cells originating from the proximal and distal renal tubules. To explore the mechanism of phosphate handling in these cells, the accumulation of radioactive phosphate from the medium into the cells and the spaces between the cell layer and culture plate (submonolayer spaces) was measured. The accumulation of phosphate by the cells was a sodium-dependent, energy-dependent process, which was demonstrated by inhibition both in the absence of sodium and in the presence of ouabain or 2,4-dinitrophenol. Furthermore, phosphate accumulation was decreased significantly by PTH presumably acting through cAMP. PTH inhibited phosphate accumulation not by affecting the efflux process, but by affecting the uptake process through the apical membrane of the cultured cells without altering the compartmental mental distribution of the accumulated phosphate. These characteristics of phosphate accumulation resemble those of renal tubular phosphate transport.     

Studies on the specificity of the effects of oxygen metabolites on cardiac sodium pump

Isolated myocytes of rat heart, and sealed sarcolemmal vesicles of bovine heart, were used to examine the selectivity of the effects of partially reduced oxygen species (generated by a mixture of xanthine and xanthine oxidase) on cardiac sodium pump and several other ion transporters of the plasma membrane. When myocytes were exposed to xanthine plus xanthine oxidase, there were time-dependent inhibitions of ouabain-sensitive 86Rb+ uptake and (Na+ + K+)-ATPase activity that could be prevented by allopurinol, or by catalase and superoxide dismutase; suggesting the involvements of H2O2 or oxygen free radicals in the inhibition of the pump. This inhibition preceded any significant decrease in cellular ATP or in the number of viable cells. While ouabain increased 45Ca2+ uptake by myocytes as expected, exposure to xanthine plus xanthine oxidase decreased 45Ca2+ uptake; suggesting that the Na+, Ca2(+)-exchanger of the intact myocytes is also inhibited by oxygen metabolites. Simultaneous inhibitions of the pump, the Na+, Ca2(+)-exchange, the Na+, H(+)-exchange, and the Na+, Pi-cotransport activities also occurred in sarcolemmal vesicles that were treated with xanthine plus xanthine oxidase. These findings indicate that inactivations of the sodium pump and other sarcolemmal ion carriers are early events in the oxidant-induced damage to the cardiomyocyte. In the rat heart myocytes, a fraction of (Na+ + K+)-ATPase that seems to be more sensitive to ouabain, was inactivated more rapidly upon exposure of myocytes to xanthine plus xanthine oxidase; raising the possibility of the existence of different pump populations with different sensitivities to extracellularly generated oxygen metabolites.     

Selenium compounds inhibit the biological activity of blood platelets

The action of inorganic forms of selenium (Se) on blood platelet aggregation, secretion and the arachidonate pathway in vitro was studied. It was shown that sodium selenite, after 30 min preincubation, inhibited platelet aggregation induced by 0.1 U/ml of thrombin and by 10 microM ADP (about 30% inhibition of aggregation after pretreatment of platelets with 10(-4) M of Se). Contrary to sodium selenite, sodium selenate did not affect the platelet aggregation induced by either agonist. Pretreatment of blood platelets with sodium selenite resulted in a statistically significant decrease in adenine nucleotide secretion ( P < 0.01) and release of malonyldialdehyde (MDA), produced in equal amounts to TXA(2) , in thrombin-stimulated platelets ( P <0.001). However, selenite did not change the level of MDA/TXA(2) in sodium arachidonate-stimulated platelets. We conclude that the inhibitory effects of sodium selenite on platelet activation could be the result of decreased synthesis and release of secondary agonists (TXA(2), ADP) in stimulated platelets. It is also possible that sodium selenite blocks the release of arachidonic acid from platelet membranes via phospholipases.     

富含硒玉米对低硒大鼠血硒和GSH-Px活性的影响

为了研究富含硒玉米对低硒粮饲料喂养大鼠血硒状态的影响 ,观察了补充富含硒玉米或亚硒酸钠时和停止补硒后大鼠血硒水平和谷胱甘肽过氧化物酶 ( GSH- Px)活性的变化。结果显示 :1两种补硒形式均可有效地增高血浆、红细胞的硒水平和红细胞的 GSH- Px活性 ;2富含硒玉米增高和维持血浆和红细胞硒水平作用与亚硒酸钠相同 ;3富含硒玉米升高红细胞 GSH- Px活性的作用低于亚硒酸钠 ,但停止补硒后两者维持 GSH- Px活性作用相似。表明富含硒玉米能有效地改善低硒大鼠的血硒状态     

Diltiazem attenuates the inotropic and peripheral vascular effects of cardiac glycosides

The influence of diltiazem on the hemodynamic effects of ouabain in 10 preinstrumented awake dogs was studied. Mean aortic pressure increased from 102 to 119 mm Hg with ouabain (p less than 0.05), an effect that was attenuated by pretreatment with diltiazem. The increase in systemic vascular resistance of 30% with ouabain was ablated by prior diltiazem. Heart rate did not significantly change with ouabain or with diltiazem plus ouabain, but intravenous diltiazem alone produced a reflex increase in heart rate of 26%. Left ventricular (LV) end-diastolic dimension was significantly greater with ouabain alone, but not with ouabain after pretreatment with diltiazem. LV dP/dt max increased by 40% with ouabain alone, but by only 23% (p less than 0.001) after pretreatment with diltiazem plus ouabain. When observed at matched preload and heart rate, diltiazem markedly attenuates the positive inotropic and peripheral arterial constrictive effects of acute ouabain administration in the conscious animal with normal LV function.     

Selenium absorption by canine jejunum

Deficiency of the trace element selenium causes disease in domestic animals and may also be implicated in the pathogenesis of some human itlness. In this study, the triplelumen perfusion method was used to measure the rate of absorption of trace quantities of selenium (50 g/liter in a physiological electrolyte solution) from the jejunum when given asd,l-selenomethione,d,l-selenocystine, or sodium selenite to healthy dogsin vivo. Selenium absorption from the test segment (expressed as percent administered dose per centimeter±sem) was 1.97±0.04 fromd,l-selenomethionine, 1.15±0.06 fromd,l-selenocystine, and 0.51±0.07 from sodium selenite (P<0.01,N=5). In separate studies in four anesthetized dogs, the jejunum was perfused withl-[⁷⁵Se]selenomethionine while concentrations of⁷⁵Se were measured in the portal venous blood; these studies established that [⁷⁵Se]selenomethionine disappearing from the gut lumen corresponded quantitatively to⁷⁵Se appearing in the portal venous effluent (74±6%) and incorporated into intestinal tissue (24±5%). These results are consistent with the hypothesis that the absorption of amino acid-bound selenium is accelerated by the specific amino acid active transport mechanisms in the gut mucosa. Sodium selenite is absorbed more slowly, possibly by simple diffusion through the intestinal mucosa, than the amino acid-bound selenium compounds.Financial assistance was received from the Medical Research Council of New Zealand, the Medical Research Distribution Committee, the Telford Trust and the Medical Research Service of the Veterans Administration.