Influence of arteriovenular pairing on PAF-induced capillary filtration

The purpose of this study was to determine the basic mechanism by which leu kocyte-endothelial cell adhesion mediates platelet-activating factor (PAF)- induced increases in capillary fluid filtration rate. A modified Landis tec hnique was used to observe fluid filtration from capillaries in the rat mes entery. Hypothetical mechanisms of increased filtration that were tested in cluded I) a direct action of leukocytes on endothelial cells during transit through the capillaries; 2) an upstream propagated response (via gap junct ion communication by adjacent endothelial cells) originating at sites of ve nular leukocyte adhesion; and 3) venule-to-arteriole communication, where m ediators produced at the site of venular leukocyte adhesion reach a nearby paired arteriole that delivers the mediators to branching capillaries. Evid ence was obtained in opposition to the first two hypotheses. However, in su pport 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-art eriole communication might modify capillary filtration rate during acute in flammation.