Active sulfate reabsorption in the proximal convolution of the rat kidney: Specificity,Na+ and HCO 3 − dependence

Using the standing droplet technique in the proximal convolution and simultaneous microperfusion of the peritubular capillaries, the decrease in luminal sulfate concentration with time and the zero net flux transtubular concentration difference of sulfate ( ) at 45 s was determined — the latter being taken as a measure of the rate of active sulfate reabsorption. Starting with 0.5 mmol/l sulfate in both perfusates the value of 0.35 mmol/l was approached exponentially with a half value time of 4.3 s. The values in the early proximal and late proximal convolution did not deviate from each other. If the Na⁺ concentration in the perfusates was reduced, the approached zero and extrapolated to a slightly negative value (c _i>c _o). When 1 mmol/l ouabain was added to the perfusates decreased by 66% (the latter experiments were performed in the golden hamster which is more sensitive to ouabain than the rat). 1 mmol/l thiosulfate diminished by 68% and 1 mmol/l molybdate by 24%. Omitting or replacing bicarbonate by HEPES or glycodiazine reduced the sulfate reabsorption significantly, while acetazolamide (0.1 mmol/l) and increasing the CO₂-pressure from 4.66 to 14.0 kPa (i.e. 5–15% CO₂) had no effect. SITS 1 mmol/l had no effect on sulfate reabsorption.The data indicate that the sulfate reabsorption is driven by a Na⁺ gradient and inhibited by thiosulfate and molybdate, i.e. molecules which have a similar tetrahedral molecule structure. The sulfate reabsorption depends in an undefined manner on the presence of bicarbonate ions.     

Unusual activation of glassy carbon electrodes for enhanced adsorption of monomeric molybdate(VI)

We have found that an exclusively cathodically pretreated glassy carbon electrode, which has been hitherto considered ineffective in many redox systems, is highly activated towards monomeric Mo(VI) adsorption and its reduction. The most commonly used anodic pretreatment produces an inactive GCE surface with poor response. X-ray photoelectron spectroscopy has been used to probe the surface concentration change of O- and C-containing species with the pretreatment, and identify the nature of the molybdate species adsorbed on the pretreated GCE surfaces. The results obtained clearly show that the precathodisation produces > CO-surface groups, and that there is a correlation between the saturation surface coverage of Mo(VI) determined by cyclic voltammetry experiments and the alcohol O/total O ratio of the pretreated electrodes calculated from XPS measurements. The unusual activation by precathodisation is explained by a mixed potential mechanism.     

Reduction of molybdate to molybdenum blue by Klebsiella sp. strain hkeem

A novel molybdate-reducing bacterium, tentatively identified as Klebsiella sp. strain hkeem and based on partial 16s rDNA gene sequencing and phylogenetic analysis, has been isolated. Strain hkeem produced 3 times more molybdenum blue than Serratia sp. strain Dr.Y8; the most potent Mo-reducing bacterium isolated to date. Molybdate was optimally reduced to molybdenum blue using 4.5 mM phosphate, 80 mM molybdate and using 1% (w/v) fructose as a carbon source. Molybdate reduction was optimum at 30 °C and at pH 7.3. The molybdenum blue produced from cellular reduction exhibited absorption spectrum with a maximum peak at 865 nm and a shoulder at 700 nm. Inhibitors of electron transport system such as antimycin A, rotenone, sodium azide, and potassium cyanide did not inhibit the molybdenum-reducing enzyme. Mercury, silver, and copper at 1 ppm inhibited molybdenum blue formation in whole cells of strain hkeem.     

90-Day subchronic toxicity study of sodium molybdate dihydrate in rats

This study investigated the subchronic toxicity of molybdenum (Mo) in Sprague–Dawley rats given sodium molybdate dihydrate in the diet for 90 days at dose levels of 0, 5, 17 or 60 mg Mo/kg_bw/day. The study complied with OECD Test Guideline (TG) 408, with additional examination of estrus cycles and sperm count, motility, and morphology from OECD TG 416. The overall no-observed-adverse-effect level was 17 mg Mo/kg_bw/day, based on effects on body weight, body weight gain, food conversion efficiency and renal histopathology (females only) at 60 mg Mo/kg_bw/day. No treatment-related adverse effects on reproductive organ weights or histopathology, estrus cycles or sperm parameters were observed at any dose level. No adverse effects were observed in the high dose animals after the 60-day recovery period, with the exception that male rats did not fully recover from reduced body weight. Serum blood, liver and kidney samples were analyzed for molybdenum, copper, zinc, manganese, iron, cobalt and selenium; high levels of molybdenum and copper were found in the serum, blood, liver and kidneys of rats treated with 60 mg Mo/kg_bw/day. In conclusion, the LOAEL and NOAEL for molybdenum were determined to be 60 and 17 mg Mo/kg_bw/day, respectively.     

海马和海龙中磷脂成分与脂肪酸的分析研究

海马、海龙均为脊索动物门鱼纲海龙科动物,性味甘、温,入肝、肾经,具有补肾壮阳、消肿散结的功效,临床上用于治疗阳痿、遗尿、虚喘、症积、疗疮肿毒等症,为名贵强壮补益中药。据报道它们的化学成含有总氮、氨基酸及微量元素等,而对磷脂和脂肪酸成分     

Developmental toxicity study of sodium molybdate dihydrate administered in the diet to Sprague Dawley rats

Molybdenum is an essential nutrient for humans and animals and is a constituent of several important oxidase enzymes. It is normally absorbed from the diet and to a lesser extent from drinking water and the typical human intake is around 2 μg/kg bodyweight per day. No developmental toxicity studies to contemporary standards have been published and regulatory decisions have been based primarily on older studies where the nature of the test material, or the actual dose levels consumed is uncertain.In the current study the developmental toxicity of sodium molybdate dihydrate as a representative of a broad class of soluble molybdenum(VI) compounds, was given in the diet to Sprague Dawley rats in accordance with OECD Test Guideline 414. Dose levels of 0, 3, 10, 20 and 40 mg Mo/kg bw/day were administered from GD6 to GD20. No adverse effects were observed at any dose level on the dams, or on embryofetal survival, fetal bodyweight, or development, with no increase in malformations or variations. Significant increases in serum and tissue copper levels were observed but no toxicity related to these was observed. The NOAEL observed in this study was 40 mg Mo/kg bw/day, the highest dose tested.     

New studies on the in vitro genotoxicity of sodium molybdate and their impact on the overall assessment of the genotoxicity of molybdenum substances

The potential of molybdenum substances to cause genotoxic effects has been studied previously. However, a review of existing in vitro data, including an assessment of relevance and reliability, has shown that inconsistent results have been observed in the past. To resolve the inconsistencies, new studies were performed with the highly soluble sodium molybdate dihydrate according to OECD test guidelines. In a bacterial reverse mutation assay sodium molybdate dihydrate did not induce reverse mutations in five strains of Salmonella typhimurium. No mutagenic or clastogenic effect was observed at the tk locus of L5178Y mouse lymphoma cells. In a micronucleus test in cultured human peripheral blood lymphocytes no clastogenic or aneugenic effects were seen. These results can be read across to other inorganic molybdenum substances, that all release the molybdate ion [MoO₄]²⁻ under physiological conditions as the only toxicologically relevant species. In summary, a weight of evidence assessment of all available in vitro data shows no evidence of genotoxicity of molybdenum substances.     

Kinetics of isotopic exchange between strontium polymolybdate and strontium ions in aqueous solution

A heterogeneous isotopic exchange reaction of strontium polymolybdate in strontium chloride solution was studied using ⁹⁰Sr as a tracer. The effects of low and high strontium chloride concentration on the rate and mechanism of the isotopic exchange reaction were investigated. It was found that, at high concentrations, the rate is independent of strontium concentration, but, at low concentrations, the rate is proportional to the strontium concentration. These results support a hypothesis that, at low concentrations, the rate is controlled by film diffusion, whereas at high concentrations it is controlled by particle diffusion. Experiments were performed at 293, 303 and 313 K. Activation energy of isotopic exchange reaction and thermodynamic parameters ΔH^*, ΔS^*, and ΔG^* were calculated using the Arrhenius and Eyring equations. The results also indicated that recrystallization is a predominant factor in the present exchange reaction.     

Molybdate stabilizes soluble [H]dexamethasone binding sites in rat brain tissue in incubations at room temperature (22 °C)

We have described an in vitro procedure for the measurement of glucocorticoid receptor concentrations in soluble fractions prepared from rat brain tissue using a relatively short incubation period of 1 h at room temperature (22 °C). Using [³H]dexamethasone as ligand we found that, with the addition of sodium molybdate (Na₂MoO₄) to the buffer, estimates of receptor-binding parameters derived from Scatchard analysis (K_dandB_max) did not differ significantly between assays using 4–5 h incubations at 0–4 °C and those using a 1 h incubation performed at room temperature (22 °C). The use of molybdate was critical; 1 h incubations at 22 °C in the absence of molybdate resulted in a substantial ( 65%) loss of [³H]dexamethasone binding.     

钼和汞联合染毒对小鼠骨髓多染红细胞微核率影响

［目的］探讨对钼对汞遗传毒性的影响。［方法］观察采用腹腔注射钼酸钠和氯化汞联合染毒对小鼠骨髓多染红细胞微核率的影响。［结果］连续４天给小鼠注射ＨｇＣｌ２［１．０ｍｇ／ｋｇ（ｂｗ）］的同时注射１０、１００ｍｇ／ｋｇ（ｂｗ）］的Ｎａ２ＭｏＯ４可显著降低ＨｇＣｌ２的致小鼠微核率（Ｐ〈０．００１）;在ＨｇＣｌ２［１．０ｍｇ／ｋｇ（ｂｗ）给小鼠染毒前３天连续注射１００ｍｇ／ｋｇ（ｂｗ）Ｎａ２ＭｏＯ４可显著地