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OBJECTIVE: Prostaglandins and nitric oxide play an important role in the regulation of arteriolar tone. L-Arginine analogues inhibit nitric oxide formation, but may also inhibit arachidonic-acid induced dilation. Nitric oxide was found to stimulate cyclooxygenase activity in cultured endothelial cells. Therefore, we hypothesized that the non-specific inhibition of prostaglandin-related dilation by L-arginine analogues is a consequence of the absence of nitric oxide. METHODS: To test this hypothesis, arteriolar segments from rat cremaster muscle were studied in a pressure myograph at 75 mmHg. Segments developed spontaneous tone, the diameter reduced from 179 +/- 3 to 98 +/- 3 microns (n = 41). In this condition, responses to exogenous arachidonic acid (1 microM) were recorded and compared with responses after addition of L-NNA, and addition of either SNAP, nitroprusside or 8-Br-cGMP in the presence of L-NNA. RESULTS: Inhibition of basal nitric oxide production with L-NNA (0.1 mM) reduced arachidonic acid-induced dilation (from 52 +/- 9 to 31 +/- 6 microns). In the presence of L-NNA, responses to arachidonic acid were augmented when exogenous nitric oxide was also present (SNAP, 31 +/- 6 microns vs. 75 +/- 5 microns; nitroprusside, 31 +/- 8 microns vs. 42 +/- 7 microns). Responses were not augmented with the second messenger of nitric oxide-mediated dilation 8-Br-cGMP (37 +/- 9 microns vs. 32 +/- 9 microns). CONCLUSIONS: These results indicate that nitric oxide directly increases arachidonic acid-induced dilation. Thus, the non-specific effect of L-arginine analogues can be explained by a permissive effect of nitric oxide on endothelial arachidonic acid metabolism. 相似文献
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为了满足明渠水流入流的边界条件,扩展SPH方法在明渠恒定流模拟中的应用,本文建立SPH方法的出入流模型,通过设置相应的出入流边界条件,研究不同坡度下消力池内陡坡水跃特性。针对两种不同流量,对斜坡坡角θ分别在20°、30°、45°条件下的陡坡水跃进行数值模拟。模拟结果与文献中的实验结果进行对比分析,结果表明:出入流模型能为陡坡水跃的数值模拟提供稳定的水流。各陡坡不同流量下水面线的变化趋势基本相同,误差均在±10%内;相同坡角时,单宽流量为0.063 m~2/s的消能效果均大于单宽流量为0.105 m~2/s的消能效果。该方法处理出入流边界简单,合理准确,能够较好地模拟不同坡度下消力池内陡坡水跃,得到陡坡水跃特性,具有一定的可行性和可靠性。 相似文献
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为研究如何避免溢洪道泄洪过程中,闸墩后生成的水翅会给泄洪安全带来诸多不利的影响。本文利用量纲分析和物理模型试验方法,对溢洪道闸墩后水翅的水力特性和消减措施开展研究。试验结果表明,影响水翅长度和高度的主要因素有闸墩尾部出口处的弗劳德数Fr_0、溢洪道坡度i、闸墩宽度等;在相同泄流条件下,若泄槽坡度变小,水翅长度也随之减小,而水翅高度却相应增加;当弗劳德数Fr_0介于2.3与2.8之间时,闸墩后的水翅长度和高度均显著增大。试验还发现水翅的长度、高度与闸墩后泄流下跌角度α有关,当α增大时,水翅长度和高度也随之增大;当α较小时,水翅现象明显减弱或消失。研究结果为实际工程消除水翅现象提供了新思路,提出的复合式斜尾墩比传统四棱台型尾墩能更好地避免水翅发生,对改善溢洪道、泄洪洞闸墩后的水流流态具有参考价值。 相似文献
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介绍了红外焦平面热成像仪原理,系统采用FPGA对数据进行采集控制,采用DSP对数据进行处理并与PC机通信,在硬件上构成一个以DSP+FPGA+PC的成像电力在线检测系统。文章给出了红外成像视频信号和DSP数据处理方法,并使用VB6.0实现图像在PC机上的显示和处理。 相似文献
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Saccharomyces cerevisiae Rad51 protein is the paradigm for eukaryotic ATP-dependent DNA strand exchange proteins. To explain some of the unique characteristics of DNA strand exchange promoted by Rad51 protein, when compared with its prokaryotic homologue the Escherichia coli RecA protein, we analyzed the DNA binding properties of the Rad51 protein. Rad51 protein binds both single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) in an ATP- and Mg2+-dependent manner, over a wide range of pH, with an apparent binding stoichiometry of approximately 1 protein monomer per 4 (+/-1) nucleotides or base pairs, respectively. Only dATP and adenosine 5'-gamma-(thiotriphosphate) (ATPgammaS) can substitute for ATP, but binding in the presence of ATPgammaS requires more than a 5-fold stoichiometric excess of protein. Without nucleotide cofactor, Rad51 protein binds both ssDNA and dsDNA but only at pH values lower than 6.8; in this case, the apparent binding stoichiometry covers the range of 1 protein monomer per 6-9 nucleotides or base pairs. Therefore, Rad51 protein displays two distinct modes of DNA binding. These binding modes are not inter-convertible; however, their initial selection is governed by ATP binding. On the basis of these DNA binding properties, we conclude that the main reason for the low efficiency of the DNA strand exchange promoted by Rad51 protein in vitro is its enhanced dsDNA-binding ability, which inhibits both the presynaptic and synaptic phases of the DNA strand exchange reaction as follows: during presynapsis, Rad51 protein interacts with and stabilizes secondary structures in ssDNA thereby inhibiting formation of a contiguous nucleoprotein filament; during synapsis, Rad51 protein inactivates the homologous dsDNA partner by directly binding to it. 相似文献
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The concept of transcultural nursing is relatively new to the nursing literature. It had been less than 30 years since Madeleine Leininger first began to develop a theory of transcultural nursing as part of a doctoral study in anthropology. Much has changed in that time, and nursing staff development and inservice educators need to provide educational offerings within a multicultural context in a timely manner. Cultural diversity is the standard in the mid-1990s, and those nursing staff development programs that are sensitive to this fact produce employees with advantages over those from settings that do not prepare staff for practice in a constantly changing world. This annotated bibliography about transcultural nursing details key references for staff development and inservice programs. It is not intended as an exhaustive review but rather focuses on the most relevant, timely, and useful of the ever increasing number of publications concerning this important subject. Six major books and four of the most pertinent recent journal articles are included. Conclusions and implications for nursing staff educators are offered. 相似文献
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VG Savchenko EN Parovichnikova VG Isaev IA Demidova RG Kuliev EO Gribanova GA Kliasova RA Kucher AN Sokolov KS Momotiuk IuV Ol''shanskaia NG Tiurina LIu Tikhonova GM Galstian VM Budianski? EA Belousov VA Lapin SV Voloshin TS Konstaninova LB Filatov ON Porokhina EA Smirnova 《Canadian Metallurgical Quarterly》1998,70(7):5-11