Identification and quantitative determination of 3-chloro-2-hydroxypropylmercapturic acid and α-chlorohydrin in urine of rats treated with epichlorohydrin

Epichlorohydrin (ECH) is used in many industrial processes. Different toxic effects of ECH were found in rodents. The metabolism of ECH was investigated before in rats using [¹⁴C]ECH. The aim of this investigation was the development of non-radioactive quantitative analytical methods for measuring two urinary metabolites of ECH, namely 3-chloro-2-hydroxypropylmercapturic acid (CHPMA) and α-chlorohydrin (α-CH). The identity of CHPMA and α-CH excreted in urine of rats treated with 5 to 35 mg/kg ECH was confirmed by GC-MS. The quantitative analysis of CHPMA, involving ethyl acetate extraction from acidified urine and subsequent methylation and analysis by gas chromatography-flame photometric detection (GC-FPD), showed a method limit of detection of 2 μg/ml. The analysis of α-CH, based on ethyl acetate extraction and subsequent analysis by GC-ECD, showed a method limit of detection of 2 μg/ml. CHPMA and α-CH derivatives could be determined quantitatively down to concentrations of 0.5 and 0.4 μg/ml urine, respectively, by selected-ion monitoring GC-MS under EI conditions. Cumulative urinary excretion of CHPMA and α-CH by rats treated with ECH were found to be 31 ± 10 and 1.4 ± 0.6% (n = 13) of the ECH dose, respectively. For CHPMA, the dose-excretion relationship suggested partially saturated ECH metabolism. For α-CH, the dose-excretion relationship was linear. With fractionated urine collection it was found that approximately 74 and 84% of the total cumulative excretion of CHPMA and α-CH, respectively, took place within the first 6 h after administration of ECH. From these investigations it is concluded that the GC-FPD and GC-ECD based methods developed are sufficiently sensitive to measure urinary excretion of CHPMA and α-CH in urine from rats administered 5 to 35 mg/kg ECH. It is anticipated that the analysis of CHPMA and α-CH based on GC-MS may be sufficiently sensitive to investigate urinary excretion from humans occupationally exposed to ECH.     

矮嵩草草甸植物群落的光合特性研究

 矮嵩草草甸植物群落的光合、暗呼吸和土壤呼吸的研究表明：光合作用的日变化在6月份接近平坦型,7、8月份呈午间降低型。矮嵩草草甸植物群落的光合作用受较低的光合面积指数及冠层叶片的受光势态的影响,存在着明显的光饱和现象,光补偿点及光饱和点相对于全日照光合有效辐射均较低,接近于单叶的光响应特性。裸露地面的土壤呼吸和植物与土壤体系的暗呼吸不仅与温度有关,而且与土壤水分状况和降雨量也有密切联系。影响草甸群落光合特性的主要因素有：高原地区强烈的太阳辐射,较低的光合面积指数和植物根系与土壤紧密结合所形成的草结皮层结构。     

Effect of water-miscible aprotic solvents on kyotorphin synthesis catalyzed by immobilized α-chymotrypsin

Summary Immobilized -chymotrypsin was used as catalyst to synthesize a kyotorphin derivative (Bz-Tyr-Arg-OEt) in the presence of five water-miscible aprotic solvents (dimethylsulphoxide, dimethylformamide, acetonitrile, acetone and tetrahydrofurane) at 30 °C. By using a kinetically-controlled approach, the maximum synthetic activity was obtained when Arg-OEt was used as nucleophile donor at a concentration 1.5-times higher than the acyl-acceptor substrate (Bz-Tyr-OEt). The water-miscible aprotic solvents enhanced greatly the synthetic activity proportionally to their hidrophilicity properties adequately measured by the log P parameter. At the optimum solvent concentration for the enzymatic peptide synthesis, both the water activity (Aw) of the media and the water content of the immobilized derivative showed a saturation profile against the log P parameter. As a function of the solvent hydrophilicity, these water parameters were shown as key parameters for the increase in the synthetic activity of the enzyme by the presence of these solvents.     

Role of endogenous gibberellins in germination of melon (Cucumis melo) seeds

The effect of the plant growth retardants ancymidol. mefluidide and uniconazole on germination of two melon accessions differing in their ability to germinate at 14°C was examined. The accessions were the cold sensitive Noy Yizre'el and the cold tolerant Persia 202. The three growth retardants were able to delay the germination of intact Noy Yizre'el seeds, but did not affect that of intact Persia 202 seeds. On the other hand germination of decoated seeds of both accessions was unaffected by these inhibitors at normal oxygen concentration, but was inhibited at 5% oxygen. When gibberellin-like activity was measured by a dwarf rice biological assay following HPLC fractionation, it was found that seeds of Persia 202 contained much more gibberellin-like activity than Noy Yizre'el seeds. Among the extracted compounds several endogenous gibberellins were identified by combined gas chromatography-mass spectrometry (GC-MS). They included GA₄, GA₂₀, GA₁ and GA₃ in Noy Yizre'el and GA₃₄, GA₂₀, GA₁ and GA₈ in Persia 202. It is suggested that the better germination of intact Persia 202 seeds, compared to Noy Yizre'el seeds at low temperature and low oxygen concentration, is due to a higher endogenous level of GA and a better seed coat permeability to oxygen.     

Casein kinase 2 inactivation by Mg2+, Mn2+ and Co2+ ions

In order to elucidate the relationship between hypertension and hypertrophy in the production of heat shock proteins, we studied the induction of the HSP72 synthesis by the heart and gracilis muscles of normo (WKY) and hypertensive (SHR) rats subjected to hyperthermia (42°C±0.5 for 15 min). Two age groups were investigated in each strain: young (2 months, with developing cardiac hypertrophy) and old (18 months, with fully developed chronic cardiac hypertrophy). The gracilis muscle never developed hypertrophy, independently of hypertension or aging. 72 kDa inducible protein was determined by Western blot analysis using a specific monoclonal antibody. We also used a commercial standard, loaded on each blot, to quantitate densitometrically the signal.The heart of young SHR responds to heat shock more than their normotensive age-matched control (298.8±24.7% vs 88.3 ±8.5%, p<0.001). This response is not maintained during aging as we did not find any significant difference between normo-and hypertensive old rats after exposure to hyperthermia (43.6±5.3% vs 65.3±10.4%).Unlike the heart, the gracilis muscle shows a basal spontaneous HSP72 synthesis in both the SHR (71.4±10.8%) and WKY (40.6±11.7%) animals. There was a significant increase in HSP72 synthesis in the gracilis muscle of young SHR with respect to their control (186.2±18.7% vs 115.8±9.9%, p<0.02) which was maintained also during aging (171.9±17.3% vs 95.2±10.5%, p<0.01).In conclusion, these data show that hypertension results in an increased synthesis of HSP72 both in cardiac and gracilis muscle in response to heat shock. This abnormal response is attenuated by aging in the heart but not in the gracilis muscle. Thus, the abnormality seems to be independent from hypertrophy and linked to genetic determination of the disease.     

Biosorption of uranium by Myxococcus xanthus

This paper deals with uranium biosorption by Myxococcus xanthus biomass in which dry biomass, accumulating up to 2.4 mM of uranium g⁻¹, is demonstrated to be a more efficient biosorbent than wet biomass. For uranium concentrations of 0.1–0.3 mM, between 95.79% and 95.99% of the uranium was taken up from the solution. Dry biomass biosorption was found to be relatively rapid, reaching equilibrium after 5–10 min. In addition, the pH influenced biosorption, pH 4.5 promoting maximum uptake. It was also established that the biosorbed uranium is located on the cellular wall and within the extracellular mucopolysaccharide of this microorganism. Furthermore, using sodium carbonate as a desorbent agent, 80.82% of the biosorbed uranium could be recovered. The results obtained indicate the possible utilization of M. xanthus biomass to solve some problems of the water contaminated by uranium.     

Eating-Induced Dopamine Release from Mesolimbic Neurons Is Mediated by NMDA Receptors in the Ventral Tegmental Area: A Dual-Probe Microdialysis Study

Abstract: This study was aimed at identifying the neuronal pathways that mediate the eating-induced increase in the release of dopamine in the nucleus accumbens of the rat brain. For that purpose, a microdialysis probe was implanted in the ventral tegmental area and a second probe was placed in the ipsilateral nucleus accumbens. Receptor-specific compounds acting on GABA_A (40 µ M muscimol; 50 µ M bicuculline), GABA_B (50 µ M baclofen), acetylcholine (50 µ M carbachol), NMDA [30 µ M (±)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP)], and non-NMDA [300 µ M 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)] receptors were infused into the ventral tegmental area by retrograde dialysis, whereas extracellular dopamine was recorded in the ipsilateral nucleus accumbens. Intrategmental infusion of muscimol or baclofen decreased extracellular dopamine in the ipsilateral nucleus accumbens; CPP and CNQX were without effect, and bicuculline and carbachol increased dopamine release. During infusion of the various compounds, food-deprived rats were allowed to eat for 10 min. The infusions of muscimol, bicuculline, baclofen, carbachol, and CNQX did not prevent the eating-induced increase in extracellular dopamine in the nucleus accumbens. However, during intrategmental infusion of CPP, the eating-induced increase in extracellular dopamine in the nucleus accumbens was suppressed. These results indicate that a glutamatergic projection to the ventral tegmental area mediates, via an NMDA receptor, the eating-induced increase in dopamine release from mesolimbic dopamine neurons.