Onses as well as on remodeling events within the vessel wall have now been elucidated, the mechanisms underlying plasmin-dependent neutrophil recruitment in vivo remain poorly understood. Plasmin is primarily generated in the liver and subsequently released into the systemic circulation where it is known to play a major role in the fibrinolytic Eleutheroside A;β-Sitosterol β-D-glucoside system. Our in vivo data demonstrate that intravascularly circulating plasmin is not able to induce significant leukocyte responses. In this context, physiological plasmin antagonists such as a2- antiplasmin are thought to minimize excessive proteolytic activity of plasmin within the vascular compartment and might thereby prevent inflammatory effects of this protease under physiological conditions. In the initial reperfusion phase, however, permeability of the postischemic microvasculature rapidly increases enabling plasmin to extravasate to the perivascular tissue. Interestingly, extravascular administration of plasmin caused a dosedependent elevation in numbers of firmly adherent and transmigrated neutrophils. Our results confirm previous observations as intrastriatal injection of plasmin has been reported to induce neutrophil infiltration of the brain. Consequently, these data indicate that intravascularly circulating plasmin does not exert inflammatory effects until it extravasates to the perivascular tissue. Moreover, we found that incubation with plasmin did not alter surface expression of CD11b/Mac-1 and CD62L/L-selectin on murine neutrophils suggesting that plasmin is not able to directly activate neutrophils. Notably, it cannot be excluded that I/R creates a favorable environment for direct actions of plasmin on neutrophils and it might also be possible that plasmin is able to induce affinity changes of integrins ultimately facilitating extravasation of neutrophils. In addition, it might be possible that receptor-bound plasminogen KJ Pyr 9 cost presented on the surface of circulating leukocytes might already be activated within the vascular compartment during I/R and might thereby contribute to leukocyte extravasation as hypothetized by previous in vitro studies. Because of their close vicinity to the vascular endothelium and their ability to generate an abundance of inflammatory mediators, tissue mast cells are considered as key players in the postischemic inflammatory response. In this context, it is worth to be noted that the involvement of mast cells might be variable in different organs since tissue specific diversity in the phenotype, density, and distribution of mast cells has previously been reported. In our experiments, we found that treatment with aprotinin as well as with the plasmin inhibitors almost completely prevents postischemic activation of mast cells. Furthermore, we demonstrate that plasmin is a
