Pressure-related capillary leukostasis following ischemia-reperfusion and hemorrhagic shock.

Although the receptor-dependent venular adhesion of leukocyte adherence has been relatively well characterized, less is known about capillary leukostasis. With the use of fluorescence intravital microscopy, leukocyte behavior in the capillaries of rabbit tenuissimus muscle was evaluated after ischemia-reperfusion or hemorrhage. After fixed volume hemorrhage or 4 h of total ischemia, inflammatory injury was manifest by broken fibrils, edema, leukocyte infiltration, and margination along the postcapillary venular walls. Nevertheless, as long as arterial perfusion pressure was between 27 and 72 mmHg, the frequency of capillary leukostasis was low (4-8 cells/mm2) and similar in all groups, including animals treated with the antiadhesion antibody IB4. In contrast, when perfusion pressure decreased to 20 mmHg, capillary leukostasis increased similarly (to 16-21 cells/mm2) in controls (with or without IB4) and in those subjected to ischemia. Furthermore, when perfusion pressure was increased to more than 27 mmHg, (27-72 mmHg) stationary leukocytes returned to the original low level (4-5 cells/mm2). These results are consistent with the conclusion that during some inflammatory injuries, capillary leukostasis is a pressure-related phenomena that is not receptor dependent and is freely reversible with the early restoration of perfusion pressure.