Permeability of superficial lymphatic capillaries in human skin to FITC-labelled dextrans 40 000 and 150 000.

The paper describes a technique for measuring the permeability of superficial lymphatic capillaries of human skin. The microvessels were visualized under the fluorescence microscope after a subepidermal injection of 0.005 ml of a 25% solution of FITC-dextran 40 000 and 150 000. Pericapillary fluorescent light intensities (FLI) reflecting transcapillary passage of the dyes were determined at different sites and times by videodensitometers on single frames of the television recording. In 13 healthy volunteers (20 capillaries) permeability was assessed by injection of both dye molecules in the medial ankle region. As a rule the microlymphatics were permeable for dextran 40 000 and impermeable for dextran 150 000. For instance, 20 min after filling of the capillary selected for study, mean FLI 0.2 mm outside of the capillary centre (site C) was 94.2 +/- 44.7 arbitrary units for the smaller and 63.2 +/- 48.4 for the larger molecule (p less than 0.001). After 30 min the transcapillary passage of the tracer has to be differentiated from the interstitial diffusion of dye from the original deposit. Potentially, the method may be used to study the pathophysiology and pharmacology of lymphatic capillary permeability in human skin.