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Bioengineering Program, The Pennsylvania State University, University Park, Pennsylvania 16802
The role of erythrocyte
(red blood cell; RBC) aggregation in affecting leukocyte (white blood
cell; WBC) margination in postcapillary venules of the mesentery (rat)
was explored by direct intravital microscopy. Optical techniques were
refined and applied to relate the light-scattering properties of RBCs
to obtain a quantitative index of aggregate size (G), which,
under idealized conditions, represents the number of RBCs per
aggregate. WBC margination, defined as the radial migration of WBCs to
the venular wall and their subsequent rolling along the endothelium,
was measured as the percentage of the potentially maximal WBC
volumetric flux within the microvessel lumen
(FWBC*). In normal blood,
FWBC* increased exponentially
fourfold, and G increased from 1 to 1.15 as wall shear rates
(
) were reduced from a steady-state value of ~600 to <100
s
1 by proximal occlusion with a blunt microprobe.
Enhancement of aggregation by infusion (iv) of dextran 500 (428 kDa),
to attain a systemic concentration of 3 g/100 ml, resulted in a four-
and sevenfold increase in G and
FWBC*, respectively, as
was reduced below 100 s
1. Inhibition of RBC aggregation
by infusion of dextran 40 (37.5 kDa) caused
FWBC* to fall to one-half of its
steady-state level for
< 100 s
1. Thus it
appears that the well-known increase of WBC margination with reductions
in
is strongly dependent on the occurrence of RBC
aggregation. Increasing the extent of RBC aggregation during reductions
in
also increased the firm adhesion of WBCs to the endothelium because of an enhanced probability of contact between leukocytes and the postcapillary venular wall.
erythrocyte sequestration; dextran; Wistar-Furth rats; leukocyte-endothelium adhesion
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