Canaan-Kühl S, Venkatraman E S, Ernst S I, Olshen R A, Myers B D
Department of Medicine, Stanford University School of Medicine, California 94305.
Am J Physiol. 1993 Jun;264(6 Pt 2):F1052-9. doi: 10.1152/ajprenal.1993.264.6.F1052.
We determined oncotic pressure (pi) by membrane osmometry and assayed total protein (TP) and albumin (Alb) concentrations in plasma of 102 nephrotic subjects and 27 healthy controls. All three quantities were markedly depressed in the nephrotic group. When plasma was serially diluted and concentrated, nephrotic but not control plasma also exhibited a highly variable change point in the nonlinear relationship between TP or Alb and pi. Absent a unique change point, we developed quadratic models which incorporated TP, Alb, and (TP x Alb) to prospectively predict pi in unperturbed plasma. The ability of the most successful quadratic model to predict pi in afferent or efferent arteriolar plasma was limited; the prediction errors reached 10 mmHg in nephrotic and 6 mmHg in control subjects. The nephrotic model coefficients also differed significantly from control and pointed to an important influence of nonalbumin proteins on pi in nephrotic plasma. Investigation of the intrinsic membrane properties of diseased glomerular capillary walls requires precise knowledge of pi. For this purpose we recommend that pi be directly determined by membrane osmometry rather than calculated from protein concentration(s).
我们通过膜渗透压测定法测定了102名肾病患者和27名健康对照者血浆中的胶体渗透压（π），并检测了总蛋白（TP）和白蛋白（Alb）浓度。肾病组的这三个指标均显著降低。当血浆进行系列稀释和浓缩时，肾病患者而非对照者的血浆在TP或Alb与π的非线性关系中也表现出高度可变的变化点。由于不存在唯一的变化点，我们建立了包含TP、Alb和（TP×Alb）的二次模型，以前瞻性地预测未受干扰血浆中的π。最成功的二次模型预测入球或出球小动脉血浆中π的能力有限；肾病患者的预测误差达到10 mmHg，对照者为6 mmHg。肾病模型系数也与对照者有显著差异，表明非白蛋白蛋白对肾病血浆中π有重要影响。研究病变肾小球毛细血管壁的内在膜特性需要精确了解π。为此，我们建议通过膜渗透压测定法直接测定π，而不是根据蛋白质浓度计算。
