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1.
Incubation of human platelets with aspirin inhibited glycolysis and produced a fall in the concentration of adenosine triphosphate. When platelets were exposed to collagen there was an increase in glycolysis and release of adenosine diphosphate. Prior incubation of the platelets with aspirin for 5 minutes did not totally suppress the increase in glycolysis after exposure to collagen but completely inhibited the collagen-induced reaction of the release of adenosine diphosphate. It is suggested that aspirin acts on human platelets by inhibiting both release of adenosine diphosphate and the transport of glucose across the platelet membrane. 相似文献
2.
Protection from chemotherapy-induced alopecia in a rat model 总被引：7，自引：0，他引：7
Alopecia (hair loss) is among the most distressing side effects of cancer chemotherapy. Little progress has been made, however, in its prevention or treatment, partly because of the lack of suitable experimental model. In recent work on the treatment of myelogenous leukemia in the rat, the following observations were made: (i) treatment of 8-day-old rats with cytosine arabinoside consistently produced alopecia, and (ii) ImuVert, a biologic response modifier derived from the bacterium Serratia marcescens, uniformly produced complete protection against the alopecia. In subsequent experiments, both cyclophosphamide and doxorubicin also produced alopecia in this model, and the doxorubicin-induced alopecia was prevented by treatment with ImuVert. The potential relevance of these observations to chemotherapy-induced alopecia in the clinical setting should be examined. 相似文献
3.
Coat protein gp120 from the human immunodeficiency virus type-1 (HIV-1) increased intracellular free calcium and injured rodent retinal ganglion cells and hippocampal neurons in culture. Highly purified recombinant gp120 envelope protein produced these effects in a dose-dependent fashion at picomolar concentrations. Immunoprecipitation with antibody to gp120, but not with control immunoglobulin-containing serum, depleted solutions of the viral envelope protein and also prevented both the rise in intracellular calcium and neuronal toxicity. The gp120-induced increase in intracellular calcium was abrogated by transiently lowering extracellular calcium or by adding the dihydropyridine calcium channel antagonist nimodipine (100 nM). Calcium channel antagonists also prevented gp120-induced neuronal injury. In addition, intracellular stores appeared to contribute substantially to the increase in calcium elicited by gp120. Since increases in intracellular calcium have been associated with neurotoxicity, it is possible that an injurious effect of gp120 on neurons might be related to this mechanism and that treatment with calcium channel antagonists may prove useful in mitigating HIV-1-related neuronal injury. 相似文献
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5.
1,25-dihydroxyvitamin D3: a novel immunoregulatory hormone 总被引：24，自引：0，他引：24
The hormonal form of vitamin D3, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], at picomolar concentrations, inhibited the growth-promoting lymphokine interleukin-2, which is produced by human T lymphocytes activated in vitro by the mitogen phytohemagglutinin. Other metabolites of vitamin D3 were less effective than 1,25(OH)2D3 in suppressing interleukin-2; their order of potency corresponded to their respective affinity for the 1,25(OH)2D3 receptor, suggesting that the effect on interleukin-2 was mediated by this specific receptor. The proliferation of mitogen-activated lymphocytes was also inhibited by 1,25(OH)2D3. This effect of the hormone became more pronounced at later stages of the culture. These findings demonstrate that 1,25(OH)2D3 is an immunoregulatory hormone. 相似文献
6.
Cantley LC 《Science (New York, N.Y.)》2002,296(5573):1655-1657
Phosphorylated lipids are produced at cellular membranes during signaling events and contribute to the recruitment and activation of various signaling components. The role of phosphoinositide 3-kinase (PI3K), which catalyzes the production of phosphatidylinositol-3,4,5-trisphosphate, in cell survival pathways; the regulation of gene expression and cell metabolism; and cytoskeletal rearrangements are highlighted. The PI3K pathway is implicated in human diseases including diabetes and cancer, and understanding the intricacies of this pathway may provide new avenues for therapuetic intervention. 相似文献
7.
Induction of membrane ruffling and fluid-phase pinocytosis in quiescent fibroblasts by ras proteins 总被引：69，自引：0，他引：69
Expression of the ras oncogene is thought to be one of the contributing events in the initiation of certain types of human cancer. To determine the cellular activities that are directly triggered by ras proteins, the early consequences of microinjection of the human H-ras proteins into quiescent rat embryo fibroblasts were investigated. Within 30 minutes to 1 hour after injection, cells show a marked increase in surface ruffles and fluid-phase pinocytosis. The rapid enhancement of membrane ruffling and pinocytosis is induced by both the proto-oncogenic and the oncogenic forms of the H-ras protein. The effects produced by the oncogenic protein persist for more than 15 hours after injection, whereas the effects of the proto-oncogenic protein are short-lived, being restricted to a 3-hour interval after injection. The stimulatory effect of the ras oncogene protein on ruffling and pinocytosis is dependent on the amount of injected protein and is accompanied by an apparent stimulation of phospholipase A2 activity. These rapid changes in cell membrane activities induced by ras proteins may represent primary events in the mechanism of action of ras proteins. 相似文献
8.
Synaptic excitation may activate a calcium-dependent potassium conductance in hippocampal pyramidal cells 总被引：9，自引：0，他引：9
In hippocampal CAl pyramidal cells, orthodromic synaptic excitation is followed by an early hyperpolarization mediated by gamma-aminobutyric acid (GABA) and a late non-GABA-mediated hyperpolarization that has properties consistent with an increase in potassium conductance. Depolarizations produced by iontophoretically applied glutamate are followed by hyperpolarizations that have features in accordance with an increase in potassium conductance. The hyperpolarizations are independent of chloride and resistant to tetradotoxin but are blocked by a low-calcium, high-cobalt medium. Voltage clamping the glutamate depolarization does not reduce the subsequent hyperpolarization, indicating that the hyperpolarization results from a direct increase in calcium conductance produced by glutamate, rather than from activation of voltage-sensitive calcium channels. A single transmitter, possibly acting on one type of receptor and channel, may initiate both excitation and inhibition in the same postsynaptic cell. 相似文献
9.
Wittwer SH 《Science (New York, N.Y.)》1975,188(4188):578-584
Despite a growing population and increasing demands of that population for improved diets, it appears that the world is not close to universal famine (3, 53). There is enough food now produced to feed the world's hungry (54). That people are malnourished or starving is a question of distribution, delivery, and economics, not agricultural limits. The problem is putting the food where the people are and providing an income so that they can buy it. As to the future, there are clouds on the far horizon. Only increased scientific and technological innovation, coupled with a change in human behavior and in national policy with regard to increased investments in agricultural research, can avert a growing food and population crisis. Only scientists develop new technology. Only farmers produce food. Motivation and incentives are important both for scientific discovery and food production. Agricultural research is also a process. There is no finite beginning or end. It is a continuing search to unravel mysteries. We must force the pace of agricultural development, but technology must be tailored to local conditions. Thiscan be done by scientists who also know how to farm. Individual dedication and sustained government commitments are important. Rapidity of information transfer and of acceptance of technology is also crucial (55). There is a wide gap between progress in research and the point of application for human benefit (Table 5). What accounts for the vast time differences in rapidity of technology acceptance? The current avalanche of new knowledge coupled with problems of food, feed, and fiber supplies, and issues of availability, preservation, protection, renewability, and costs of resources should bring to the front the urgency of rapid information transfer and reassessment of information systems for agricultural and other renewable resources. 相似文献
10.
本文在研究监控系统的视频图像压缩基础上,提出了给予人脸对象分割的视频压缩。首先利用运动信息分割出入体轮廓,并综合运用人体的特征与形态数学的方法成功地分离出入脸大致区域;然后采用基于改进统计彩色信息模型方法,精确分割出入脸区域,去掉了不相关的冗余信息;最后提出了利用图像小波变换结合差分链码技术描述了人脸对象,并实现了高效的视频压缩。本文提出的视频压缩算法在同等压缩效率下,与MPEG-2算法相比提高了图像PSNR近3dB,而且经过本算法处理的视频序列,可以方便地用于人脸检测,为基于内容的检测打下良好的基础。 相似文献
11.
脱氧雪腐镰刀菌烯醇(DON)人工抗原及多克隆抗体的研制 总被引：1，自引：0，他引：1
脱氧雪腐镰刀菌烯醇(Deoxynivalenol, DON)是一种半抗原,没有免疫原性.为了制备抗DON的抗体,必须对其进行结构修饰,加大DON的分子量.本研究采用保护-去保护策略使DON的C3上的羟基与琥珀酸酐反应,使DON衍生后获得1个羧基.利用薄层色谱法跟踪反应进程,反应产物采用薄层色谱法纯化,高效液相色谱和电喷雾离子化质谱(ESI-MS)分析,得出[M H] 为397.2,确认为3-半琥珀酰-脱氧雪腐镰刀菌烯醇(3-HS-DON).3-HS-DON与载体蛋白采用碳化二亚胺法进行偶联,偶联物经SDS-聚丙烯酰胺凝胶电泳鉴定,推断偶联成功,并研制出多克隆抗体. 相似文献
12.
A G Fisher B Ensoli L Ivanoff M Chamberlain S Petteway L Ratner R C Gallo F Wong-Staal 《Science (New York, N.Y.)》1987,237(4817):888-893
The genome of the human immunodeficiency virus HIV-1 contains at least eight genes, of which three (sor, R, and 3' orf) have no known function. In this study, the role of the sor gene was examined by constructing a series of proviral genomes of HIV-1 that either lacked the coding sequences for sor or contained point mutations in sor. Analysis of four such mutants revealed that although each clone could generate morphologically normal virus particles upon transfection, the mutant viruses were limited in their capacity to establish stable infection. Virus derived from transfection of Cos-1 cells (OKT4-) with sor mutant proviral DNA's was resistant to transmission to OKT4+ "susceptible" cells under cell-free conditions, and was transmitted poorly by coculture. In contrast, virus derived from clones with an intact sor frame was readily propagated by either approach. Normal amounts of gag-, env-, and pol-derived proteins were produced by all four mutants and assays in both lymphoid and nonlymphoid cells indicated that their trans-activating capacity was intact and comparable with wild type. Thus the sor gene, although not absolutely required in HIV virion formation, influences virus transmission in vitro and is crucial in the efficient generation of infectious virus. The data also suggest that sor influences virus replication at a novel, post-translational stage and that its action is independent of the regulatory genes tat and trs. 相似文献
13.
Mortality rates typically increase rapidly at the onset of aging but can decelerate at later ages. Reproduction increases the death rate in many organisms. To test the idea that a delayed impact of earlier reproduction contributes to both an increase in death rates and a later deceleration in mortality, the timing of the surplus mortality produced by an increased level of egg production was measured in female Drosophila. Reproduction produced a delayed wave of mortality, coincident with the sharp increase in death rates at the onset of aging and the subsequent deceleration of mortality. These results suggest that aging has evolved primarily because of the damaging effects of reproduction earlier in life, rather than because of mutations that have detrimental effects only at late ages. 相似文献
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Chan AW Dominko T Luetjens CM Neuber E Martinovich C Hewitson L Simerly CR Schatten GP 《Science (New York, N.Y.)》2000,287(5451):317-319
Primates that are identical in both nuclear and cytoplasmic components have not been produced by current cloning strategies, yet such identicals represent the ideal model for investigations of human diseases. Here, genetically identical nonhuman embryos were produced as twin and larger sets by separation and reaggregation of blastomeres of cleavage-stage embryos. A total of 368 multiples were created by the splitting of 107 rhesus embryos with four pregnancies established after 13 embryo transfers (31% versus 53% in vitro fertilization controls). The birth of Tetra, a healthy female cloned from a quarter of an embryo, proves that this approach can result in live offspring. 相似文献
16.
Immunoglobulin production by human lymphocytoid lines and clones: absence of genic exclusion 总被引：5，自引：0，他引：5
Immunoglobulin production was studied in established lines of normal human lymphocytes. Three lines which produced both immunoglobulin G and immunoglobulin M were cloned. Among the 25 immunoglobulin-producing clones, 23 produced both classes of immunoglobulins. These findings suggest that the phenomenon of genic exclusion does not hold for immunoglobulin production in lymphocytoid cells in culture. 相似文献
17.
杨世杰 《中国农业大学学报》1987,(3):359-366
对两种凤仙花种间嫁接组合(Impatiens walleriana/Impatiensolivieri)的形成过程用光学显微镜和电子显微镜进行了系统观察。接穗与砧木间形成隔离层。隔离层两侧细胞内呈现一系列变化。愈伤组织不仅在形成层附近产生,皮层、维管束区和髓部所有活组织都参与愈伤组织的形成。隔离层首先在维管束区开始解体。接穗与砧木细胞直接接触,形成次生胞间连丝。在愈伤组织中出现形成层以前,首先由薄壁细胞分化出木质部桥连接砧木与接穗。韧皮部分子与木质部分子在愈伤组织内的分化可不依赖于形成层而独立进行。对隔离层的动态、形成层对于嫁接成功的作用、接穗与砧木细胞之间胞间连丝的次生形成和细胞内各种变化的意义进行了讨论。 相似文献
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19.
黑腹果蝇Drosophila melanogaster Meigen是杨梅、樱桃等浆果果实最主要害虫。为明确温度对黑腹果蝇种群增长的影响,掌握黑腹果蝇饲养合适温度,在室内观察了黑腹果蝇在15,20,25,30和35℃条件下的生长发育、存活与繁殖能力,并计算各温度条件下的种群增长参数。结果表明：在35℃条件下,黑腹果蝇不能完成发育,其他温度条件下黑腹果蝇从卵孵化至蛹羽化成成虫,发育速率随温度升高明显加快,在15℃下,完成发育需要长达41 d,而在30℃下,黑腹果蝇完成发育仅需7 d;黑腹果蝇成虫寿命随温度的升高而明显缩短,在15℃下,雌、雄平均寿命分别高达70,80 d,在30℃下,平均寿命都仅为30 d;黑腹果蝇在20和30℃的平均繁殖力没有显著差异,分别为138.85和137.97粒卵·雌-1,但在以上条件下的平均繁殖能力显著低于25℃条件下的平均繁殖力,25℃条件下黑腹果蝇平均产卵量高达375.4粒（P<0.01）;黑腹果蝇的种群增长参数净生殖率（R0）、内禀增长率（rm）,在25℃时达最高值分别为55.10和1.021 d-1,而在15℃条件下值最小,分别为36.67和0.189 d-1。据此得出,25℃是最适宜黑腹果蝇生长发育和繁殖的温度,温度过高或过低都不利于黑腹果蝇种群增长。黑腹果蝇的发育起点温度为12.8℃,充分完成发育所需的有效积温为123.3日·度。 相似文献
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An analysis of high-resolution microwave images of Saturn and Saturn's individual rings is presented. Radio interferometric observations of Saturn taken at the Very Large Array in New Mexico at wavelengths of 2 and 6 centimeters reveal interesting new features in both the atmosphere and rings. The resulting maps show an increase in brightness temperature of about 3 K from equator to pole at both wavelengths, while the 6-centimeter map shows a bright band at northern mid-latitudes. The data are consistent with a radiative transfer model of the atmosphere that constrains the well-mixed, fully saturated, NH(3) mixing ratio to be 1.2 x 10(-4) in a region just below the NH(3) clouds, while the observed bright band indicates a 25 percent relative decrease of NH(3) in northern mid-latitudes. Brightness temperatures for the classical rings are presented. Ring brightness shows a variation with azimuth and is linearly polarized at an average value of about 5 percent. The variations in ring polarization suggest that at least 20 percent of the ring brightness is the result of a single scattering process. 相似文献