The relationship between interstitial fluid, initial lymphatics and collecting lymphatics was investigated in the subcutaneous tissue of rabbits. 24 hours after intravascular injection of FITC-dextran (FITC-dx) of
plasma, interstitial fluid and lymph from initial and collecting lymphatics were collected using a micropuncture technique and analysed for the content of FITC-dx and endogenous proteins. The fluid concentration of interstitium, initial and collecting lymphatics was found not to be statistically different from each other. These findings support previous studies demonstrating high permeability of the lymphatic endothelium to macromolecules. The hypothesis of a concentrating mechanism at the initial lymphatics was not supported by the present results. Integrated with previous data on the distribution volume of macromolecules in the same tissue, the present results suggest that the fluid flow in the interstitium takes place through the fluid phase only.
