Chang R L, Ueki I F, Troy J L, Deen W M, Robertson C R, Brenner B M
Biophys J. 1975 Sep;15(9):887-906. doi: 10.1016/S0006-3495(75)85863-2.
To determine the permselectivity characteristics of the glomerular capillary wall, known molecular size fractions of [3H]dextran, prepared by gel chromatography, were infused into normally hydrated Wistar rats, thus permitting simultaneous measurement of Bowman's space/plasma water (BS/P) and urine/plasma water (U/P) concentration ratios, along with glomerular pressures and flows. Since (BS/P)inulin = 1.01 +/- 0.01 SE(n = 34, radius = approximately 14 A) and since (BS/P)dextran/(BS/P)inulin equaled (U/P)dextran/(U/P)inulin for dextrans ranging in molecular radius from 21 to 35 A, these findings validate that dextrans are neither secreted nor reabsorbed. For dextran radii of 20, 24, 28, 32, 36, 40, and 44 A, (U/P)dextran/(U/P)inulin averaged 0.99, 0.92, 0.69, 0.42, 0.19, 0.06, and 0.01, respectively. In accord with theoretical predictions that these fractional dextran clearances should vary appreciably with changes in glomerular transcapillary pressures and flows, an increase in glomerular plasma flow rate, induced in these same rats by plasma volume expansion, resulted in a highly significant lowering of fractional clearance of all but the smallest and largest dextrans studied. These findings emphasize that fractional solute clearances alone are inadequate to describe the permselective properties of the glomerular capillary wall unless glomerular pressures and flows are also known. This sensitivity of fractional dextran clearance to changes in plasma flow indicates that dextrans are transported across the capillary not only by bulk flow but also to an important extent by diffusion.
为了确定肾小球毛细血管壁的通透选择性特征，将通过凝胶色谱法制备的已知分子大小级分的[3H]葡聚糖注入正常水合的Wistar大鼠体内，从而能够同时测量鲍曼囊腔/血浆水（BS/P）和尿液/血浆水（U/P）浓度比，以及肾小球压力和血流量。由于（BS/P）菊粉 = 1.01 ± 0.01标准误（n = 34，半径约为14 Å），并且对于分子半径在21至35 Å范围内的葡聚糖，（BS/P）葡聚糖/（BS/P）菊粉等于（U/P）葡聚糖/（U/P）菊粉，这些发现证实葡聚糖既不被分泌也不被重吸收。对于半径为20、24、28、32、36、40和44 Å的葡聚糖，（U/P）葡聚糖/（U/P）菊粉的平均值分别为0.99、0.92、0.69、0.42、0.19、0.06和0.01。与理论预测一致，即这些葡聚糖分级清除率应随肾小球跨毛细血管压力和血流量的变化而显著变化，在这些相同的大鼠中通过血浆容量扩张诱导肾小球血浆流速增加，导致除研究的最小和最大葡聚糖外，所有葡聚糖的分级清除率都显著降低。这些发现强调，除非同时知道肾小球压力和血流量，仅分级溶质清除率不足以描述肾小球毛细血管壁的通透选择性特性。葡聚糖分级清除率对血浆流量变化的这种敏感性表明，葡聚糖不仅通过 bulk flow 穿过毛细血管，而且在很大程度上还通过扩散运输。
