Effects of increased venous pressure on albumin- and IgG-excluded volumes in muscle

The effect of elevated venous pressure on the extravascular distribution space of albumin and γ-immunoglobulin G (IgG) in muscle was studied in anesthetized rabbits. In nine rabbits, venous pressure in one leg was increased from 8 to 28 mmHg while the other leg served as a control. Samples of plasma and prenodal muscle lymph were collected for 4 h before taking samples of the gastrocnemius muscle. Lymph was collected from a femoral lymphatic after ligating the popliteal efferent lymphatic. The extracellular and plasma spaces in the tissue samples were measured using ⁵¹Cr-labeled ethylenediaminetetraacetic acid (EDTA) and ¹²⁵I-human serum albumin, respectively. The protein spaces were calculated from measurements of endogenous albumin and IgG concentrations using rocket electroimmunoassay. Albumin and IgG were both excluded from 50% of the interstitial space at lymph concentration. After venous congestion, the interstitial volume was twice that of control. Lymph flow increased from 0.82 ± 0.18 to 4.44 ± 0.64 μl/min. The extravascular mass of albumin and IgG increased. There was no change in the excluded volume fraction for albumin but a decrease in that for IgG. Changes in interstitial protein exclusion in skeletal muscle after pressure elevation may not be important in oncotic buffering of the edema.