Plasma protein concentration and colloid osmotic pressure in nephrotic rats

Colloid osmotic pressure (COP) was related to plasma total protein concentration in rats with adriamycin nephrosis. Nephrotic rats were divided into three groups on the basis of plasma albumin concentration. Measured values for COP were 6 to 8 mm Hg below those predicted by the Landis-Pappenheimer equation in group 3 plasma samples with albumin concentrations 0.5 to 1.0 g/dl. In contrast, measured values for COP were only slightly below those predicted by the Landis-Pappenheimer equation in group 2 plasma samples with albumin concentrations 1.0 to 1.5 g/dl and in group 1 plasma samples with albumin concentrations 1.5 to 2.0 g/dl. The reduction in concentration of albumin was accompanied by an increase in the concentration of non-albumin proteins in each group of nephrotic rats. COP exerted by these non-albumin proteins partially offset the reduction in COP attributable to reduced albumin concentration. Results show that the Landis-Pappenheimer equation significantly overestimates COP only in nephrotic rats whose plasma albumin concentration is very markedly reduced.