Leukocyte margination and deformation in mesenteric venules of rat.

White blood cell (WBC) margination and rolling were studied in venules (20-60 microns in diameter) in rat mesentery to examine the relationship between WBC rolling velocity (Vwbc), flux (Fwbc, cells/min), and deformation; and red blood cell (RBC) velocity (Vrbc), wall shear rate (gamma), and microvessel hematocrit (Hmicro). For a range of 1.0 less than or equal to Vrbc less than or equal to 5.0 mm/s, Vwbc remained constant (congruent to 50 microns/s). The volume flux of WBCs rolling along the venular wall (normalized to systemic WBC concentration) decreased nonlinearly from 30 to 5% of total luminal flux as gamma ranged from 50 to 800 s-1 and was more strongly correlated with gamma compared with Fwbc vs. gamma. As indicated by the rolling volumetric flux, margination was weakly affected by Hmicro, except for Hmicro greater than 50% where margination increased. Deformation of WBCs was quantitated during their rolling contact with the endothelium (EC) in terms of their length and height. As gamma increased from 50 to 800 s-1, WBCs elongated to 140% of their estimated undeformed diameter, and the contact area between WBC and EC increased 3.6-fold. These data suggest that with increased gamma rolling of WBCs along the EC decreases, since only the most deformable WBCs of the circulating population persist in maintaining contact with the endothelium. It is concluded that Vwbc is invariant with elevations in gamma, since the greater deformations of rolling WBCs at high shear result in greater adhesive forces attendant to increased WBC-EC contact area, which attenuate increases in Vwbc.