尿素动力学模型及尿素反弹的实验研究

综述了尿素动力学模型的研究进展,并分析了几种模型的优缺点。建立了串联双室模型实验系统,研究了在透析间期尿素反弹的情况。该系统通过控制泵流量（F）来模拟两室室间溶质清除率（KIE）;用KCl代替尿素,通过实验曲线拟合得到KIE、R^2;通过与临床数据比较,获得了适合于尿素反弹系统的KIE,并研究了非灌注室浓度（A）对KIE的影响。结果显示,F=580ml／min较好地匹配了患者透析的尿素动力学特征;基于F=580ml／min进行的A对KIE影响的实验中,A与KIE没有必然联系,KIE平均值为512ml／min,标准差为10．25。且室间溶质浓度达到平衡所需的时间均为35-5min。尿素反弹的串联双室模型实验系统能够对患者透析后的尿素动力学进行较好的模拟,并具有较强的稳定性。     

Denaturing Urea Polyacrylamide Gel Electrophoresis (Urea PAGE)

Urea PAGE or denaturing urea polyacrylamide gel electrophoresis employs 6-8 M urea, which denatures secondary DNA or RNA structures and is used for their separation in a polyacrylamide gel matrix based on the molecular weight. Fragments between 2 to 500 bases, with length differences as small as a single nucleotide, can be separated using this method¹. The migration of the sample is dependent on the chosen acrylamide concentration. A higher percentage of polyacrylamide resolves lower molecular weight fragments. The combination of urea and temperatures of 45-55 °C during the gel run allows for the separation of unstructured DNA or RNA molecules.In general this method is required to analyze or purify single stranded DNA or RNA fragments, such as synthesized or labeled oligonucleotides or products from enzymatic cleavage reactions.In this video article we show how to prepare and run the denaturing urea polyacrylamide gels. Technical tips are included, in addition to the original protocol ^1,2.     

Liposome clearance

The clearance rate of liposomal drugs from the circulation is determined by the rate and extent of both drug release and uptake of liposomes by cells of the mononuclear phagocyte system (MPS). Intravenously injected liposomes initially come into contact with serum proteins. The interaction of liposomes with serum proteins is thought to play a critical role in the liposome clearance. Therefore, in this review, we focus on the role of serum proteins, so-called opsonins, that enhance the clearance of liposomes, when bound to liposomes. In addition to opsonin-dependent liposome clearance, opsonin-independent liposome clearance is also reviewed. As opposed to the conventional (non-surface modification) liposomes, we briefly address the issue of the accelerated clearance of PEGylated-liposomes (sterically stabilized liposomes, long-circulating liposomes) on repeated injection, a process that has recently been observed.     

Mucociliary clearance in chronic sinusitis: related human nasal clearance and in vitro bullfrog palate clearance

Nasal mucociliary clearance was measured in both healthy subjects and patients with chronic sinusitis using saccharin granule technique. Nasal mucociliary transit time (ST) was significantly slower in the patients with chronic sinusitis compared with that in controls (p less than 0.005). Nasal mucus collected from each nasal cavity was used for in vitro bullfrog palate clearance studies and compared to the in vivo nasal ST. Mucociliary clearance rate (MTR) on frog palate was 12.5 +/- 2.5 mm/min in the mucus from control subjects, 6.1 +/- 1.5 mm/min in the mucus from the patients. The difference was statistically significant (p less than 0.005). The MTR on frog palate in the patients whose nasal ST was within normal range was significantly slower than that in controls (p less than 0.005), but not significantly different from that in the patients whose nasal ST was over the normal range. These results suggest that the nasal mucous properties which decreased the mucociliary clearance on frog palate did not contribute to the mucociliary clearance of the patients who had a normal one. No significant correlation existed between MTR on frog palate and nasal ST in both control and chronic sinusitis. In chronic sinusitis patients, decelerated nasal ST was recovered significantly by normal saline nebulization compared with the value before the nebulization (p less than 0.01). None of the significant change of ST was observed in control before and after the nebulization.     

Urea as a probiotic signature

Summary Experiments have demonstrated the possibility of analyzing for urea in geologic-type specimens by reflectance from paper-phase enzymatic color reactions. This serves as a plausible system that can be employed in the extraterrestrial search for evidence of biological or prebiological phenomena.     

Urea Recycling in Muroid Rodents

The results of urease activity studies in the digestive tract of muroid rodents Microtus socialis and Meriones meridianus are considered. It was noted that the absolute values of urease activity turned out to be comparable with those of lagomorphs, but were less than the results obtained for ungulates. The pronounced postgastric character of urealytic fermentation was shown. The possibility of significant urea recycling in muroid rodents aimed at compensating for dietary nitrogen deficiency and water conservation is considered.     

Urea formation by postoperative liver

The effect of liver left lobe resection (LR, 15–20% of the organ weight) on hepatic urea formation was investigated in 84 albino rats. The objects used for analysis of urea content included: operated left lobe (LLL), non-operated middle (MLL) lobe of the liver, blood (aorta, v. hepatica, v. porta), and choledochal bile. Arginase activity was examined in liver homogenate. On the day 3 and day 7 after resection reduced arginase activity was detected. LR caused a decrease in urea content in v. hepatica, but increased urea content in the arterial blood and v. porta. The increase in bile urea on day 7 was then changed for its decrease observed on day 14 of the postoperative period. The urea content in the liver on day 3 after LR was below the norm, while on days 7 and 14 it became normal. Results of this study suggest impaired urea formation by hepatocytes of the operated liver and activation of extrahepatic mechanisms of urea formation from arginine.     

关于"尿素循环"的商榷

尿素循环是蛋白质及氨基酸分解代谢一章的重点内容 ,其物质代谢和能量代谢应在教学过程中能很明确地阐述出来。本人在教学实践的过程中 ,认为教材 [沈同先生等编《生物化学》(第二版 )下册 ,以下同 ]中关于尿素循环的内容不尽完美 ,于是作了一些补充 ,应用于教学后产生了很好的效果。因此在这里提出来 ,供大家讨论和参考。尿素循环的内容在教材第 2 30页图 16 6 ,现将原图的内容 (实线部分 )和补充的内容 (虚线部分 )绘在一起 (如图 1)。　　教材中关于尿素循环的总反应式 (第 2 32页 )为 :NH+ 4 +CO2 +3ATP +天冬氨酸 +2H2 O→尿素 +2…     

Molecular Mechanisms of Urea Transport

Physiologic data provided evidence for specific urea transporter proteins in red blood cells and kidney inner medulla. During the past decade, molecular approaches resulted in the cloning of several urea transporter cDNA isoforms derived from two gene families: UT-A and UT-B. Polyclonal antibodies were generated to the cloned urea transporter proteins, and their use in integrative animal studies resulted in several novel findings, including: (1) UT-B is the Kidd blood group antigen; (2) UT-B is also expressed in many non-renal tissues and endothelial cells; (3) vasopressin increases UT-A1 phosphorylation in rat inner medullary collecting duct; (4) the surprising finding that UT-A1 protein abundance and urea transport are increased in the inner medulla during conditions in which urine concentrating ability is reduced; and (5) UT-A protein abundance is increased in uremia in both liver and heart. This review will summarize the knowledge gained from studying molecular mechanisms of urea transport and from integrative studies into urea transporter protein regulation.