Salmon Andrew H J, Neal Christopher R, Bates David O, Harper Steven J
Microvascular Research Laboratories, Department of Physiology, School of Veterinary Sciences, University of Bristol, Southwell Street, Bristol BS2 8EJ, UK.
J Physiol. 2006 Jan 1;570(Pt 1):141-56. doi: 10.1113/jphysiol.2005.099184. Epub 2005 Oct 20.
Vascular endothelial growth factor (VEGF) is expressed by the podocytes of renal glomeruli, and has profound influences on systemic microvascular permeability and haemodynamics. We describe an extensive refinement of a model that permits evaluation of the ultrafiltration coefficient (LpA) of isolated mammalian glomeruli, in the absence of circulating and haemodynamic influences, and tested the hypothesis that VEGF influences glomerular LpA via an effect on endothelial cells. Glomeruli were isolated by sieving Wistar rat renal cortical tissue, and individually loaded onto a suction micropipette. Flowing perifusate containing 1% bovine serum albumin (BSA) was rapidly switched to an oncopressive perifusate containing 8% BSA, eliciting transglomerular fluid efflux. The rate of the resultant reduction in glomerular volume was used to calculate glomerular LpA (1.07 +/- 0.53 nl min(-1) mmHg(-1) (mean +/-s.d.), n= 51), which compares favourably with those reported in the same rat strain using different techniques. A significant relationship between LpA and initial glomerular volume (Vi) (r= 0.72, n= 41, P < 0.0001) necessitated correction of LpA for Vi. The initial rate of change of glomerular volume, normalized for Vi, showed a strong positive correlation with applied oncotic gradient (Pearson r= 0.59, n= 28, P < 0.001), as predicted by Starling's law of filtration. A 60 min exposure of glomeruli to 1 nm VEGF increased glomerular LpA/Vi (1.19 +/- 0.19 (n= 10) to 2.23 +/- 0.33 (n= 9) min(-1) mmHg(-1) (mean +/-s.e.m.); P < 0.02). Time- and concentration-dependent relations between VEGF and LpA/Vi were observed. The VEGF-induced elevation of LpA/Vi was blocked by the selective VEGF-R2 inhibitor ZM323881. We suggest that glomerular VEGF contributes to the high physiological permeability of mammalian glomeruli to water through an action on endothelial cells.
血管内皮生长因子（VEGF）由肾小球的足细胞表达，对全身微血管通透性和血流动力学有深远影响。我们描述了一种模型的广泛改进，该模型允许在无循环和血流动力学影响的情况下评估分离的哺乳动物肾小球的超滤系数（LpA），并检验了VEGF通过对内皮细胞的作用影响肾小球LpA的假设。通过筛分Wistar大鼠肾皮质组织分离肾小球，并将其分别加载到吸液微量移液器上。将含有1%牛血清白蛋白（BSA）的流动灌流液迅速切换为含有8% BSA的等渗灌流液，引发跨肾小球液体流出。用由此产生的肾小球体积减少率来计算肾小球LpA（1.07±0.53 nl min⁻¹ mmHg⁻¹（平均值±标准差），n = 51），这与使用不同技术在同一大鼠品系中报道的结果相当。LpA与初始肾小球体积（Vi）之间存在显著关系（r = 0.72，n = 41，P < 0.0001），因此需要对LpA进行Vi校正。经Vi归一化后的肾小球体积初始变化率与施加的胶体渗透压梯度呈强正相关（皮尔逊r = 0.59，n = 28，P < 0.001），这与斯塔林滤过定律的预测一致。将肾小球暴露于1 nM VEGF 60分钟可使肾小球LpA/Vi升高（从1.19±0.19（n = 10）升高至2.23±0.33（n = 9）min⁻¹ mmHg⁻¹（平均值±标准误）；P < 0.02）。观察到VEGF与LpA/Vi之间存在时间和浓度依赖性关系。VEGF诱导的LpA/Vi升高被选择性VEGF-R2抑制剂ZM323881阻断。我们认为肾小球VEGF通过对内皮细胞的作用，有助于哺乳动物肾小球对水具有较高的生理通透性。
