TRANSPORT IN LYMPHATIC CAPILLARIES .1. MACROSCOPIC MEASUREMENTS USINGRESIDENCE TIME DISTRIBUTION-THEORY

We present a novel integrative method for characterizing transport in the lymphatic capillaries in the tail of the anesthetized mouse, which is both sensitive and reproducible for quantifying uptake and flow. I nterstitially injected, fluorescently labeled macromolecules were used to visualize and quantify these processes. Residence time distributio n (RTD) theory was employed to measure net flow velocity in the lympha tic network as well as to provide a relative measure of lymphatic upta ke of macromolecules from the interstitium. The effects of particle si ze and injection pressure were determined. The uptake rate was found t o be independent of particle size in the range of a 6- to 18-nm radius ; beyond this size, the interstitial matrix seemed to pose a greater b arrier. A comparison of 10 vs. 40 cmH(2)O injection pressure showed a significant influence on the relative uptake rate but not on the net v elocity within the network (3.3 +/- 0.8 vs. 3.8 +/- 1.0 mu m/s). This suggested the presence of a systemic driving force for baseline lymph propulsion that is independent of the local pressure gradients driving the uptake. This model can be used to examine various aspects of tran sport physiology of the initial lymphatics.