Protein concentration of lymph and interstitial fluid in the rat tail

Lymph was collected from tail lymphatics of anesthetized rats, subcutaneous interstitial fluid was obtained by implanting nylon wicks, and tendon interstitial fluid was obtained by centrifugation of pieces of tendon. Spontaneous lymph flow rates averaged 70 nl.min^-1.g skin^-1. Protein concentrations and colloid osmotic pressure of sampled fluids differed significantly. Tail lymph had the highest protein concentration relative to plasma [lymph-to-plasma ratio 0.71 ± 0.03 (SE) n = 10], followed by wick fluid (0.62 ± 0.02, n = 9), with tendon fluid lowest (0.50 ± 0.03, n = 10). Albumin and immunolgobulin G (IgG) concentrations in samples of tail skin and tendon were assayed by rocket immunoelectrophoresis. Comparison of their distribution volumes at lymph or tendon fluid concentrations, respectively, with interstitial fluid volumes measured as 2-h ⁵¹Cr-ethylenediaminetetraacetic acid space minus 5-min ¹²⁵I-albumin space indicated that 50-60% of the interstitial volume in these tissues is not available for distribution of albumin or IgG. Low lymph flow and high interstitial protein content or rat tail indicate a slow turnover of interstitial protein. This suggests that interstitial washout of protein plays a role in limiting edema only after a sustained or chronic increase in fluid filtration.