Glutathione depletion in a liver microsomal assay as an in vitro biomarker for reactive metabolite formation

Glutathione (GSH) plays a major role in cytoprotection, acting as a nucleophile trap for reactive species derived from xenobiotics. This has led to the development of an assay for the detection of reactive species generated by liver microsomal metabolism of xenobiotics. This assay has been used extensively to study reactive metabolites which initiate toxicity through a direct (non-immunological) mechanism, but there are few data on its ability to detect reactive metabolites that initiate toxicity through neo-antigen formation, or to detect xenobiotics that cause GSH loss by oxidation mediated by a redox cycling process. Accordingly, the ability of rat and human liver microsomes to metabolize xenobiotics to GSH-depleting metabolites has been investigated further. Of the five neo-antigen-forming xenobiotics tested, four (amodiaquine, phenobarbitone, procainamide, and sulphanilamide) displayed GSH reactivity that was either dependent or independent (amodiaquine) on metabolism. The other neo-antigen-forming xenobiotic (carbamazepine) was inactive in all microsomal samples tested. Four quinones believed to exert toxcity through arylation (1,4-benzoquinone) and/or redox cycling (duroquinone, menadione, mitomycin c) displayed GSH reactivity, as did nitrofurantoin and diquat, two other redox cycling xenobiotics. Induction of the mixed function oxidase system with Aroclor afforded little advantage when using rat liver microsomes, whilst there was considerable inter-individual variation in the ability of human liver microsomes to mediate metabolism-dependent GSH depletion. It is concluded that the liver microsome GSH depletion assay may be of general utility as a screen for a number of xenobiotic-derived reactive species.     

农林生态系统中营养元素N,P,K流动的网络分析

对农林业系统沙兰杨－小麦－玉米群落类型中Ｎ、Ｐ、Ｋ流动网络分析表明,系统中Ｎ、Ｐ、Ｋ的循环指数分别为０．０７１、０．０３９、０．１３９,均小于传统的循环系数（ＣＣ等于回归量／吸收量）,而在群落中的总滞留时间分别为２２．４１、７９．７２、２６．５７ａ．     

白骨壤模拟湿地系统中Pb的分布、迁移及其净化效应

在温室中建立红树林植物白骨壤模拟湿地系统,分别用正常(NW)、5倍(FW)和10倍(TW)浓度人工配置的城市污水每周定时定量对模拟系统污灌2次,用海水作对照(CL),持续1年。研究重金属Pb在湿地系统中的分布、迁移及其被净化的效果。结果表明：加入系统中的Pb主要存留于土壤子系统中,很少迁移到植物体和凋落物中：植物各器官中的Pb含量在根中最高;模拟系统对重金属。Pb的净化效果显著,各污水处理组分别为：NW组97．97％、FW组97．86％、TW组98．06％。根据物质平衡模型计算得土壤子系统。Pb的环境容量较大,因此整个模拟系统对Pb污染的承受力较大。     

Effects of pollution on the nutrient return via litterfall for Pinus radiata plantations in the Basque Country

The effects of atmospheric pollution on two 10 year old Pinus radiata D. Don forests (Manzanal and Posadero) was studied in the Basque country, analysing the concentration of different nutrients and nutrient input via litterfall. Litterfall production peaked in autumn, and 97.5% of the litterfall consisted of pine needles at Posadero (the less-polluted area), whereas this figure was found to be 88.6% at Manzanal (the polluted area). Posadero had a higher production of litterfall than Manzanal due to the higher tree density. Nutrient concentration showed a similar seasonal variation over the year at both sites. Pine litterfall in the polluted area, Manzanal, had significantly higher concentrations of iron, copper, zinc, sulphur, calcium, sodium and magnesium than in Posadero, while the concentrations of nitrogen, phosphorous and potassium did not differ between sites. Calcium, sodium, magnesium, sulphur, iron and copper input to the forest via litterfall was significantly higher for the polluted area, but the inputs of nitrogen, phosphorous, potassium and zinc did not significantly differ between sites. Both sites showed high nutrient use efficiencies for phosphorous and calcium compared with other coniferous forests. The highest efficiency was for phosphorous, possibly due to the low availability of this ion in the soil. Trees at Posadero were consistently more efficient for calcium than at Manzanal due to the effect of pollution on the latter site. Molar ratios between aluminium and the basic cation nutrients calcium and magnesium in soil were higher at the polluted area, as a result of the increased inputs of anions to the forest soil (Al:Ca = 1.9:1 and Al:Mg = 6.9:1 at Posadero and Al:Ca = 5.7:1 and Al:Mg = 14:1 at Manzanal). The current pollution level of Manzanal is leading to a loss of cations that may cause future changes in the functioning of this forest.     

有机-无机态肥氮在微型农业生态系统的转移和循环研究

本文应用~(15)N示踪法研究了有机态和无机态肥料氮在微型农业生态系统中循环的机理,以及配施下各自的功能和相互影响。初步结果表明,在土壤-黑麦草-兔亚系统中,草对硫铵~(15)N利用率达59.36％;以草饲兔,所收集兔粪~(15)N回收率为11.78％,尿为17.98％。兔粪尿N与硫铵N以1:0,0.5:0.5,0.3:0.7和0.1配施种稻,结果表明,在土壤-水稻亚系统中:(1)0.5:0.5配施促进穗头和根系发育;(2)稻株吸收有机态和无机态肥料N的比例,受配施比例的影响;(3)与单施无机肥料氮比较,配施下无机肥料氮利用率未提高或甚至下降;(4)0.3:0.7配比使有机态肥料N利用率提高;(5)0.5:0.5配比,有机肥能明显地促进无机态肥料N从秆向谷运输;(6)有机肥使无机态肥N在土壤中的固化作用增加,从而使无机肥料氮向环境转移量下降。农业生态系统具有多组分和牧食-碎屑复合食物链,氮素再循环指数达0.5,生态稳定性和发育程度优于单一种植系统。     

Distribution,Accumulation, and Cycling of Several Mineral Elements of the Lower Subtropical Evergreen Broad-Leaved Forest in Heishiding Nature Reserve

The distribution, accumulation, and cycling of N, P, K, Na, Ca, and Mg in terms of their concentration in the biomass was quite different from those in soil in Heishiding Nature Reserve (111°53′ E, 23°27′ N). The concentrations of N, Ca and P were higher in plant, and much lower in soil. The average content of the elements in different organs was in the order as: leaf>branch>bark>root>wood, although this was not true for all the elements. Trunk and leaf had the most and the least accumulation of the elements, respectively, and branch and root were comparable. In the forest, most of the elements (97 %) were concen- trated in the tree layer. The total amount of elements in the ecosystem was 3324.2 kg· ha-1 among which N amounted 1470.5, P 51.0, K 1097.7, Na 22.6, Ca 566.2, and Mg 116.2. Yearly absorption of the elements was 432.2 kg · ha-1 among which N amounted 207.1, P 6.5, K 144.9, Na 6.9, Ca 52.6, and Mg 14. 1; and element absorption among different organs accounted as 35.0 kg · ha-1 · a-1 in wood, 14.8, in bark, 66.1 in branch, 143.2 in leaf, 25.3 in root, and 147.7 in fine root (D<3 mm). Total return of the elements from litterfall, death and fallen trees was 311.8 kg · ha-1 · a-1, among which N accounted for 154.3, P 4.7, K 102.1, Na 6.2, Ca 34.5, and Mg 10.0. Return from different organs was: wood 10.2, bark 4.3, branch 17.0, leaf 123.0, root (not in- cluding fine root) 9.4, and fine root 147.7. Total retention was 120.4 kg · ha-1 · a-1 among which N accounted for 52.8, P 1.8, K 42.8, Na 0. 7, Ca 18. 1, and Mg 4.1; retention in different organs was: wood 24.8, bark 10.5, branch 49.1, leaf 20. 2, and root 15.9. Ca, Mg and P have higher cycling and utilization efficiencies.     

Effect of Pedal Rate on Diurnal Variations in Cardiorespiratory Variables

Recently, it was observed that the freely chosen pedal rate of elite cyclists was significantly lower at 06:00 than at 18:00 h, and that ankle kinematics during cycling exhibits diurnal variation. The modification of the pedaling technique and pedal rate observed throughout the day could be brought about to limit the effect of diurnal variation on physiological variables. Imposing a pedal rate should limit the subject's possibility of adaptation and clarify the influence of time of day on physiological variables. The purpose of this study was to determine whether diurnal variation in cardiorespiratory variables depends on pedal rate. Ten male cyclists performed a submaximal 15 min exercise on a cycle ergometer (50% W_max). Five test sessions were performed at 06:00, 10:00, 14:00, 18:00, and 22:00 h. The exercise bout was divided into three equivalent 5 min periods during which different pedal rates were imposed (70 rev · min^?1, 90 rev · min^?1 and 120 rev · min^?1). No significant diurnal variation was observed in heart rate and oxygen consumption, whatever the pedal rate. A significant diurnal variation was observed in minute ventilation (p=0.01). In addition, the amplitude of the diurnal variation in minute ventilation depended on pedal rate: the higher the pedal rate, the greater the amplitude of its diurnal variation (p=0.03). The increase of minute ventilation throughout the day is mainly due to variation in breath frequency (p=0.01)—the diurnal variation of tidal volume (all pedal rate conditions taken together) being non‐significant—but the effect of pedal rate×time of day interaction on minute ventilation specific to the higher pedal rate conditions (p=0.03) can only be explained by the increase of tidal volume throughout the day. Even though an influence of pedal rate on diurnal rhythms in overall physiological variables was not also evidenced, high pedal rate should have been imposed when diurnal variations of physiological variables in cycling were studied.     

Effects of aerobic exercise on the torque-velocity relationship in cycling

The kinetics of the torque-velocity (T-ω) relationship after aerobic exercise was studied to assess the effect of fatigue on the contractile properties of muscle. A group of 13 subjects exercised until fatigued on a cycle ergometer, at an intensity which corresponded to 60% of their maximal aerobic power for 50 min (MAP60%); ten subjects exercised until fatigued at 80% of their maximal aerobic power for 15 min (MAP80%). Of the subjects 7 exercised at both intensities with at least a 1-week interval between sessions. Pedalling rate was set at 60 rpm. The T-ω relationship was determined from the velocity data collected during all-out sprints against a 19 N · m braking torque on the same ergometer, according to a method proposed previously. Maximal theoretical velocity (ω₀) and maximal theoretical torque (T ₀) were estimated by extrapolation of the linear T-ω relationship. Maximal power (P _max) was calculated from the values of T ₀ and ω₀ (P _max = 0.25 ω₀ T ₀). The T-ω relationships were determined before, immediately after and 5 and 10 min after the aerobic exercise. The kinetics of ω₀, T ₀ and P _max was assumed to express the effects of fatigue on the muscle contractile properties (maximal shortening velocity, maximal muscle strength and maximal power). Immediately after exercise at MAP60% a 7.8% decrease in T ₀ and 8.8% decrease in P _max was seen while the decrease in ω₀ was nonsignificant, which suggested that P _max decreased in the main because of a loss in maximal muscle strength. In contrast, MAP80% induced a 8.1% decrease in ω₀ and 12.8% decrease in P _max while the decrease in T ₀ was nonsignificant, which suggested that the main cause of the decrease in P _max was probably a slowing of maximal shortening velocity. The short recovery time of the T-ω relationship suggests that the causes of the decrease of torque and velocity are processes which recover rapidly. Accepted: 25 November 1996     

Use of Ferric and Ferrous Iron Containing Minerals for Respiration by Desulfitobacterium frappieri

The potential of Desulfitobacterium frappieri strain G2, which was isolated from subsurface smectite bedding, to participate in iron redox reactions was investigated. Strain G2 can use poorly crystalline Fe(III) oxide, soluble forms of Fe(III) and Fe(III) in the structure of phyllosilicate minerals as electron acceptors. It can also oxidize Fe(II)-NTA or Fe(II) in the structure of phyllosilicate minerals with nitrate as the electron acceptor. These results suggest for the first time that strains of Desulfitobacterium frappieri may play an important role in iron cycling in sedimentary environments.     

Morning‐to‐Evening Differences in Oxygen Uptake Kinetics in Short‐Duration Cycling Exercise

This study analyzed diurnal variations in oxygen (O₂) uptake kinetics and efficiency during a moderate cycle ergometer exercise. Fourteen physically active diurnally active male subjects (age 23±5 yrs) not specifically trained at cycling first completed a test to determine their ventilatory threshold (T_vent) and maximal oxygen consumption (VO_2max); one week later, they completed four bouts of testing in the morning and evening in a random order, each separated by at least 24 h. For each period of the day (07:00–08:30 h and 19:00–20:30 h), subjects performed two bouts. Each bout was composed of a 5 min cycling exercise at 45 W, followed after 5 min rest by a 10 min cycling exercise at 80% of the power output associated with T_vent. Gas exchanges were analyzed breath‐by‐breath and fitted using a mono‐exponential function. During moderate exercise, the time constant and amplitude of VO₂ kinetics were significantly higher in the morning compared to the evening. The net efficiency increased from the morning to evening (17.3±4 vs. 20.5±2%; p<0.05), and the variability of cycling cadence was greater during the morning than evening (+34%; p<0.05). These findings suggest that VO₂ responses are affected by the time of day and could be related to variability in muscle activity pattern.