Protein concentration in interstitial and lymphatic fluids from the subcutaneous tissue

Area of Science:

• Physiology
• Biochemistry
• Microcirculation Research

Background:

• Understanding protein transport between plasma, interstitial fluid, and lymph is crucial for fluid balance and immune function.
• Previous methods for analyzing protein content in small fluid volumes were limited.
• The permeability of lymphatic endothelium to macromolecules remains an area of investigation.

Purpose of the Study:

• To develop and validate a sensitive method for quantifying protein concentrations in nanolitre volumes of interstitial fluid and lymph.
• To compare the protein composition of interstitial fluid and lymph in the same tissue.
• To assess the role of lymphatic endothelial permeability in macromolecule uptake.

Main Methods:

• Micropuncture technique to collect nanolitre-scale interstitial fluid and lymph samples from rabbit subcutaneous tissue.
• Capillary polyacrylamide gel electrophoresis for protein separation and analysis.
• Microscope-based densitometry to quantify protein band areas, establishing a linear relationship with concentration.

Main Results:

• A linear correlation was established between protein amount and densitogram band area, enabling accurate quantification.
• Interstitial fluid/plasma concentration ratios were determined: albumin (0.42), transferrin (0.42), globulins (0.32), and total proteins (0.37).
• Albumin/globulin ratio in interstitial fluid was 1.60 times the plasma value; lymph values closely mirrored interstitial fluid values.

Conclusions:

• The developed electrophoretic method allows precise protein quantification in minimal fluid volumes.
• Protein concentrations in interstitial fluid and lymph are remarkably similar.
• Terminal lymphatic endothelium appears to permit unrestricted passage of macromolecules, supporting efficient lymph formation.