Figure 4.

Video images showing rat venules under control conditions (left panels) and after TNF-α and PAF application (right panels) with (A) and without (B) PAF-induced initial increases in microvessel permeability. (A) The addition of PAF that induces endothelial gap formation and a transient increase in permeability results in platelet/leucocyte aggregate adhesion to the vessel walls (the right image is one example), which was accompanied by a prolonged increase in L_p. (B) Applying isoproterenol, an agent that inhibits PAF-induced permeability increases, prior to TNF-α and PAF application changed the adhesion pattern from aggregated blood cells (right image in A) to single attached leucocytes (right image in B). L_p measured in the presence of single attached leucocytes showed no significant increase. These results support the hypothesis that an increase in permeability with formed endothelial gaps plays a key role in platelet adhesion and platelet/leucocyte aggregation, as well as the subsequent prolonged permeability increases (modified from He et al.⁴⁶ and used with permission).