Influence of arteriovenular pairing on PAF-induced capillary filtration.

The purpose of this study was to determine the basic mechanism by which leukocyte-endothelial cell adhesion mediates platelet-activating factor (PAF)-induced increases in capillary fluid filtration rate. A modified Landis technique was used to observe fluid filtration from capillaries in the rat mesentery. Hypothetical mechanisms of increased filtration that were tested included 1) a direct action of leukocytes on endothelial cells during transit through the capillaries; 2) an upstream propagated response (via gap junction communication by adjacent endothelial cells) originating at sites of venular leukocyte adhesion; and 3) venule-to-arteriole communication, where mediators produced at the site of venular leukocyte adhesion reach a nearby paired arteriole that delivers the mediators to branching capillaries. Evidence was obtained in opposition to the first two hypotheses. However, in support of the third hypothesis, a significant correlation was found between the extent of arteriolar pairing to venules and the PAF-induced increase in capillary fluid filtration rate. These findings suggest that venule-to-arteriole communication might modify capillary filtration rate during acute inflammation.