Influence of platelet-vessel wall interactions on leukocyte rolling in vivo

The influence of platelet-vessel wall interactions on leukocyte rolling was investigated in rabbit mesenteric venules (diameter, 21-40 microns) using intravital videomicroscopy. Puncture of the wall with glass micropipettes (tip, 6-8 microns) evoked the formation of a thrombus in all venules. In most vessels, emboli were produced as well. The rolling of leukocytes (i.e., their movement along the vessel wall at a velocity clearly lower than that of the other blood cells) was quantitated simultaneously in vessel segments upstream and downstream from a thrombus up to 10 minutes after puncture. During embolization the number of rolling leukocytes decreased significantly from the upstream to the downstream vessel segment (median decrease, 45%; p less than or equal to 0.001). It was still decreased by approximately 50% after embolization had stopped, indicating that the decrease in leukocyte rolling was not caused by inclusion of leukocytes in the emboli. In venules without embolization, leukocyte rolling did not change systematically, indicating that fluid dynamic changes induced by the thrombus do not influence leukocyte rolling. Inhibition of prostaglandin formation with aspirin (100 mg/kg) almost completely abolished the influence of the thromboembolic reaction on leukocyte rolling, but blockade of thromboxane A2 receptors with sulotroban (30 mg/kg) had no effect. In conclusion, this is the first report on a functional interaction in vivo, at a site of vessel wall injury, between platelets, vascular cells, and leukocytes. The findings suggest that substances produced by activated platelets and/or damaged vascular cells diminish leukocyte rolling. The identity of these substances is not yet clear, but the present study indicates that prostaglandins other than thromboxane A2 are involved.