ENDOTHELIAL PERMEABILITY‐THE PASSAGE OF PARTICLES INTO AND OUT OF DIAPHRAGMATIC LYMPHATICS

Abstract

The passage of particles from the peritoneal cavities of mice into their diaphragmatic lymphatics, and from these vessels into the peri‐lymphatic connective tissues has been studied. The particles used were chylomicra, carbon, lipoproteins, thorium dioxide and ferritin. Particles passed through the endothelial layers via open intercellular junctions, small (50 m, µ) and large (0‐1‐1 µ) vesicles, and directly through the cytoplasm. Quantitative interpretation of the electron micrographs was difficult, but it was possible to observe gross differences between the amounts of the various particles which traversed the endothelium by each of these routes. The routes also varied markedly in their importance. Open junctions were of overwhelming importance for the passage of all the particles from the peritoneal cavity; some of the particles used them relatively very little when they passed out of the lymphatics. The open junctions probably alter in size with the respiratory inovements of the diaphragm. This would permit the lymphatics to act as pumps, with the flaps of endothelium as "inlet valves". The large vesicles were of two kinds. Some contained chylomicra which they seemed to transport rapidly across the cells. Others were probably formed by the coalescence of many small vesicles and the agglutination of their contents. These large vesicles lost little material and remained in the cells for at least 12 weeks (the longest period studied). They grew larger and denser as time went by. The endothelial cells which contained these vesicles appeared eventually to leave the lymphatics and lodge in the connective tissue.