Interacfions between platelets,leukocytes and the vessel wall in vivo

Abstract

Intravital videomicroscopy was used to investigate interactions between blood platelets, vascular cells and leukocytes at a site of vessel wall injury in rabbit mesenteric venules (diameter 21–40 μm). A thromboembolic reaction was evoked by puncture of the wall with a glass micropipet (tip 6–8 μm); in all vessels a thrombus was formed, while in most vessels emboli were produced as well. Leukocyte rolling, i.e. their movement along the wall at a clearly lower velocity than the other blood cells flow, was quantitated simultaneously in vessel segments upstream and downstream of a thrombus. In venules without embolization the degree of leukoycte rolling was not different upstream and downstream of the thrombus, indicating that fluid dynamic changes induced by the thrombus do not influence leukocyte rolling. In venules, in which emboli were produced, leukocyte rolling decreased significantly from upstream to downstream of the thrombus during embolization (median decrease: 45%; p≤0.001). This decrease in leukocyte rolling still existed after embolization had stopped (50%; p≤0.01), indicating that it cannot be explained by inclusion of leukocytes in emboli. Inhibition of prostaglandin formation with aspirin (100 mg/kg) significantly diminished the influence of the thromboembolic reaction on leukocyte rolling (p≤0.05), but blockade of TXA₂-receptors with sulotroban (30 mg/kg) had no effect. The findings suggest that substances, produced by activated blood platelets and/or damaged vascular cells, diminish leukocyte rolling. The identity of the substances is not yet clear, but prostaglandins, other than TXA₂, are probably involved.