Effect of platelet activating factor on endothelial permeability to plasma macromolecules

We have examined the effect of intrajugular administration of platelet activating factor (PAF-C16) on vascular permeability in the guinea pig. To examine the loss of selective endothelial permeability, the extravasative effect of PAF was assessed by monitoring hemoconcentration and the plasma loss of 125I-albumin (6.7 nm), 125I-low density lipoproteins (22.0 nm) or 125I-very low density lipoproteins (62.1 nm). Extravasation was dose-dependent and began 1 min after PAF administration, continuing for 5-7 min. During extravasation, there was no evidence for selective plasma retention of any of the labeled plasma tracers, as measured by plasma radioactivity. These results suggest that PAF-induced extravasation is dose-dependent, with increases in vascular permeability sufficient to permit similar plasma efflux rates of albumin, low density lipoproteins and very low density lipoproteins.