Accumulation and depuration of polychlorinated biphenyls from field-collected sediment in three freshwater organisms

As laboratory-based bioaccumulation methods are standardized and expanded to include other test species, kinetic studies assessing the major classes of contaminants with these species are needed to adequately select the standard duration for bioaccumulation tests. In the present study we measured the uptake (28-d exposure) of polychlorinated biphenyls (PCBs; total and selected congeners) from field-contaminated sediment in the oligochaete Lumbriculus variegatus, mayfly nymph Hexagenia spp., and fathead minnow Pimephales promelas. Depuration (25 d) of PCBs was measured in organisms that had been transferred to clean sediment after the 28-d exposure. Uptake and elimination of PCBs was rapid in L. variegatus and Hexagenia spp. Tissue residues reached steady-state concentrations within 28 d; elimination rates and biota-sediment accumulation factors (BSAFs) of the PCB congeners were not correlated with K(OW). Uptake and elimination rates of PCBs were slower in P. promelas, and it is not clear whether steady-state was reached in fish tissues. Elimination rates of the PCB congeners significantly decreased with increasing K(OW) in fish. The appropriateness of a 28-d exposure for measuring steady-state concentrations in tissue of the invertebrates was confirmed, but further study is required for fish.     

Effect of hypothyroidism on hormone profiles in virgin,pregnant and lactating rats,and on lactation

Thyroid dysfunctions can produce reproductive problems. Untreated maternal hypothyroidism has serious consequences on development of offspring, resulting in stunted growth and mental retardation. The effects of propylthiouracyl-induced hypothyroidism (0.1 g l(-1) in drinking water starting 8 days before mating, or given to virgin rats for 30 or 50 days) on the serum profiles of hormones related to reproduction and mammary function (prolactin, growth hormone (GH), progesterone, corticosterone, oestradiol, insulin-like growth factor I (IGF-I), thyroid-stimulating hormone (TSH), triiodothyronine and tetraiodothyronine), and on mammary function in virgin, pregnant and lactating rats, were investigated. Propylthiouracyl treatment severely decreased circulating triiodothyronine and tetraiodothyronine concentrations, and increased serum TSH concentrations. Virgin rats showed prolonged periods of vaginal dioestrus, increased circulating progesterone concentrations and afternoon peaks of prolactin concentration, which are indicative of prolactin-induced pseudopregnancy. Propylthiouracyl-treated virgin rats had mammary development comparable to that of midpregnancy, and half of these rats had increased mammary casein and lactose concentrations. Serum prolactin concentrations were decreased on the afternoon of day 5 of pregnancy, increased during late pregnancy (days 15-21) and were normal during lactation. Circulating GH concentrations decreased on days 15-21 of pregnancy, whereas progesterone concentrations increased during late pregnancy and early lactation. Circulating oestradiol (measured in late pregnancy and in virgin rats), IGF-I and corticosterone concentrations were decreased. Although assessment of mammary histology showed no differences in extent of development, casein content was increased in propylthiouracyl-treated rats on day 21 of pregnancy; litter growth was severely reduced and at day 20 of age the pups were hypothyroid, with decreased GH serum concentrations. An acute suckling experiment was performed on days 10-12 of lactation to determine whether some impairment in mammary function or the suckling reflex might account for these differences. After an 8 h separation of mothers from their litters and 30 min of suckling, circulating prolactin values were not affected by propylthiouracyl treatment, but serum oxytocin concentration and milk excretion were reduced. In conclusion, hypothyroidism induces various alterations in the hormone profiles of virgin and pregnant rats, and induces pseudopregnancies and mammary development in virgin rats. These alterations do not appear to have an overt impact on the outcome of pregnancy and on mammary function during lactation, with the exception of the milk ejection reflex, which may account at least partially for the reduced litter growth.     

Formation and Degradation of Beta-casomorphins in Dairy Processing

Milk proteins including casein are sources of peptides with bioactivity. One of these peptides is beta-casomorphin (BCM) which belongs to a group of opioid peptides formed from β-casein variants. Beta-casomorphin 7 (BCM7) has been demonstrated to be enzymatically released from the A1 or B β-casein variant. Epidemiological evidence suggests the peptide BCM 7 is a risk factor for development of human diseases, including increased risk of type 1 diabetes and cardiovascular diseases but this has not been thoroughly substantiated by research studies. High performance liquid chromatography coupled to UV-Vis and mass spectrometry detection as well as enzyme–linked immunosorbent assay (ELISA) has been used to analyze BCMs in dairy products. BCMs have been detected in raw cow's milk and human milk and a variety of commercial cheeses, but their presence has yet to be confirmed in commercial yoghurts. The finding that BCMs are present in cheese suggests they could also form in yoghurt, but be degraded during yoghurt processing. Whether BCMs do form in yoghurt and the amount of BCM forming or degrading at different processing steps needs further investigation and possibly will depend on the heat treatment and fermentation process used, but it remains an intriguing unknown.     

Internalization of Escherichia coli O157:H7 following biological and mechanical disruption of growing spinach plants

The internalization and persistence of a bioluminescent Escherichia coli O157:H7 Ph1 was investigated in growing spinach plants that had been either biologically or mechanically damaged. In control (undamaged) plants cultivated in soil microcosms inoculated with E. coli O157:H7 Phl, the bacterium was recovered from surface-sterilized root tissue but not from leaves. Mechanical disruption of the seminal root and root hairs of the plants did not result in the internalization of the pathogen into the aerial leaf tissue. When imprints of the root tissue were made on plates of tryptic soy agar plus ampicillin, no colonies of E. coli O157:H7 were observed around damaged tissue. The roots of growing plants were exposed to the northern root-knot nematode, Meloidogyne hapla, in the presence of E. coli O157:H7. Although this treatment caused knot formation on the roots, it did not enhance the internalization of the bacterium into the plant vascular system. Coinoculation of intact leaves with E. coli O157:H7 and the phytopathogen Pseudomonas syringae DC3000 resulted in localized necrosis, but the persistence of the human pathogen was not affected. The mechanical disruption of roots does not result in the internalization of E. coli O157:H7 into the aerial tissue of spinach, and there does not appear to be any effect of P. syringae in terms of enhancing the persistence of E. coli O157:H7 in spinach leaves.     

Nuclear-cytoplasmic incompatibility and inefficient development of pig-mouse cytoplasmic hybrid embryos

Inter-species somatic cell nuclear transfer (iSCNT) embryos usually fail to develop to the blastocyst stage and beyond due to incomplete reprogramming of donor cell. We evaluated whether using a karyoplast that would require less extensive reprogramming such as an embryonic blastomere or the meiotic spindle from metaphase II oocytes would provide additional insight into the development of iSCNT embryos. Our results showed that karyoplasts of embryonic or oocyte origin are no different from somatic cells; all iSCNT embryos, irrespective of karyoplast origin, were arrested during early development. We hypothesized that nuclear-cytoplasmic incompatibility could be another reason for failure of embryonic development from iSCNT. We used pig-mouse cytoplasmic hybrids as a model to address nuclear-cytoplasmic incompatibility in iSCNT embryos. Fertilized murine zygotes were reconstructed by fusing with porcine cytoplasts of varying cytoplasmic volumes (1/10 (small) and 1/5 (large) total volume of mouse zygote). The presence of pig cytoplasm significantly reduced the development of mouse zygotes to the blastocyst stage compared with control embryos at 120?h post-human chorionic gondotropin (41 vs 6 vs 94%, P<0.05; 1/10, 1/5, control respectively). While mitochondrial DNA copy numbers remained relatively unchanged, expression of several important genes namely Tfam, Polg, Polg2, Mfn2, Slc2a3 (Glut3), Slc2a1 (Glut1), Bcl2, Hspb1, Pou5f1 (Oct4), Nanog, Cdx2, Gata3, Tcfap2c, mt-Cox1 and mt-Cox2 was significantly reduced in cytoplasmic hybrids compared with control embryos. These results demonstrate that the presence of even a small amount of porcine cytoplasm is detrimental to murine embryo development and suggest that a range of factors are likely to contribute to the failure of inter-species nuclear transfer embryos.     

Effect of the Sugar Replacement by Citrus Fibre on the Physical and Structural Properties of Wheat-Corn Based Extrudates

Citrus fibre was used as a substitute for sucrose in the formulation of wheat-corn-based extrudates produced using twin screw extruder. Replacing 5 % sugar with an equal quantity of fibre resulted in an increase in die pressure, torque and specific mechanical energy (SME), and consequently the expansion ratio increased. A further increase in fibre content to 10 % (e.g. reducing sugar to 0 %) had little effect on the extrusion processing parameters. The microstructure of extrudates examined by X-ray computed tomography shows that the porosity of the extrudates increased with increasing fibre content, which was attributed to an increased number of large pores. As the citrus fibre content increased, the maximum force required to fracture the extrudate increased; however, the cell wall thickness decreased. This suggests that the fibre component may have contributed to the strength of the cell wall. This study demonstrated a potential utilisation of fibre from by-product of juice extraction as a source of dietary fibre in low sugar-extruded products.     

21世纪机床纵横谈

在CIMT’99展览会上,我们有幸与国内外一些著名的机床厂商探讨21世纪机床发展的趋势,并获得共识。现刊登部分厂家对21世纪机床发展的战略规划与思路。展望21世纪的全球化制造世界正以我们前所未料的速度发生着变化。发展中国家正日益开放市场,并从全球范围内广泛吸引投资,为制造业带来了更多的就业机会。这种新发展有利于提高许多国家的人民生活水平,而生活水平的提高又为新产品开拓了更广阔的前景。另外,电子商务也正对新客户、新竞争者的产生带来极其重要影响。然而,这些新兴市场具有高风险的待征,因此进入新兴市场的企业必须尽…     

The chemistry of ethyl silicate binders in refractory technology

The chemistry of the processes involved when an alkyl silicate such as ethyl silicate acts as a binder in refractory technology is described. The gel forming process involving catalysed hydrolysis and condensation of ethyl silicate and tetra-alkyl silicates has been studied using amine catalysts. Thermal studies of gels obtained from technical ethyl silicate and of gels obtained from technical ethyl silicate incorporated in refractory materials, together with infrared spectroscopy studies of gels obtained from technical ethyl silicate, suggest the nature of the degradation products, and the weight-loss patterns observed support the proposed mechanisms.     

Studies on modeling and control of spouted bed reactors—II: Control

Control and operability characteristics of an adiabatic spouted bed reactor with a first order reaction are investigated. The reactor transient response to changing operating conditions is analyzed and the generic control problems are formulated. Reduced-order state space models suitable for process control studies are constructed by utilizing the methods of orthogonal collocation and singular perturbation.Based on modern control and estimation techniques a hierarchy of different control systems is systematically generated. The assessment of alternative d