A decrease in effective diameter of rat mesenteric venules due to leukocyte margination after a bolus injection of pentoxifylline--digital image analysis of an intravital microscopic observation.

The ability of leukocytes to adhere to endothelial cells (EC) and then to migrate out of the blood stream into tissues enable them to perform their surveillance functions. Adhesion of leukocytes to EC is, however, only possible if the cells have marginated as a result of rheological interaction with other blood cells in flow. Using Pentoxifylline (PTX), a rheologically active drug, to manipulate this interaction, we have imaged and quantified this margination phenomenon in vivo. A system has been developing to perform this imaging via an intravital microscope connected to an image processing system. Albino rats were anesthetized and cannulated for intravenous bolus injection (0.5 ml) of PTX (1.25 mg/ml) through the femoral vein. A longitudinal incision exposed the mesentery, part of which was observed under microscope to visualize microcirculation. The image of interest was then stored on computer hard drive. Individual leukocyte velocities were determined before and after PTX infusion. The leukocytes, marginating and sticking after PTX infusion either remained attached, constituting the peripheral marginating leukocyte pool in the postcapillary venules, or detached with different step velocities. The reduction in effective venular diameters as a result of leukocyte margination was estimated to be 32-44%. These results demonstrate the biological importance of hemodynamic displacement leading to docking, adhesion, rolling and migration processes of leukocytes in blood.