CAPILLARY FILTRATION DURING ACUTE-INFLAMMATION - ROLE OF ADHERENT NEUTROPHILS

Fluid filtration rate with respect to surface area (J(v)/S) was measur ed in capillaries of rat mesentery by a micro-occlusion technique. Sup erfusion of the mesentery with 100 nM platelet-activating factor (PAF) caused a fivefold increase in J(v)/S (control, mean +/- SE = 0.016 +/ - 0.002 mum/s, n = 44 rats; PAF, 0.078 +/- 0.010, n = 10), whereas 20 nM leukotriene B4 (LTB4) had no effect (0.010 +/- 0.003, n = 8). These doses of PAF and LTB4 induced a similar level of leukocyte adherence to venular endothelium. Neutrophils play a role in PAF-mediated increa ses in J(v)/S, since a significantly lower J(v)/S was elicited by PAF superfusion in neutropenic rats (0.024 +/- 0.006, n = 7). Monoclonal a ntibodies (MAb) directed against either the leukocyte adhesion glycopr otein CD11/CD18 (0.037 +/- 0.006, n = 8) or the endothelial cell adhes ion molecule P-selectin (0.025 +/- 0.004, n = 8) also attenuated PAF-i nduced capillary filtration, whereas a nonbinding form of the P-select in MAb had no inhibitory effect (0.066 +/- 0.024, n = 3). These result s indicate that PAF, but not LTB4, enhances capillary fluid filtration rate. While neutrophils do not adhere to endothelium in capillaries e xposed to PAF, they do appear to contribute significantly to the PAF-i nduced capillary fluid filtration.