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Leukocyte infiltration of cerebral vessels in cocaine-associated vasculopathy suggests that cocaine may enhance leukocyte migration. We have investigated cocaine's effects on leukocyte adhesion in human brain microvascular endothelial cell (BMVEC) cultures and monocyte migration in an in vitro blood-brain barrier (BBB) model constructed with BMVEC and astrocytes. Cocaine (10(-5) to 10(-9) M) enhanced adhesion of monocytes and neutrophils to BMVEC. In the BBB model, cocaine (10(-4) to 10(-8) M) enhanced monocyte transmigration. Cocaine increased expression of endothelial adhesion molecules, intercellular adhesion molecule-1 (ICAM-1, CD54), vascular cell adhesion molecule-1 (VCAM-1), and endothelial leukocyte adhesion molecule-1 (ELAM-1) on BMVEC. The peak effect on ICAM-1 expression was between 6 and 18 h after treatment. ICAM-1 was increased by cocaine in BMVEC, but not in human umbilical vein endothelial cells, and the enhancement was greater in a coculture of BMVEC with monocytes. ICAM-1 expression was enhanced by a transcriptional mechanism. Polymyxin B inhibited up-regulation of adhesion molecules by LPS but not by cocaine. In LPS-activated BMVEC/monocyte coculture, cocaine increased secretion of tumor necrosis factor-alpha and interleukin-6. Taken together, these findings indicate that cocaine enhances leukocyte migration across the cerebral vessel wall, in particular under inflammatory conditions, but the effects are variable in different individuals. Cocaine's effects are exerted through a cascade of augmented expression of inflammatory cytokines and endothelial adhesion molecules. These could underlie the cerebrovascular complications of cocaine abuse.

Techniques of intravital microscopy were used to assess the effect of the nonsteroidal anti-inflammatory drugs (NSAIDs), indomethacin and ibuprofen, on the microcirculation. Hemodynamics in venules of the rat mesentery were studied in terms of vessel diameter, red blood cell velocity, and leukocyte-endothelium interactions: leukocyte-endothelium adhesion (LEA), white blood cell (WBC) marginating flux, and WBC velocity. Measurements were made during (1) control conditions (topical suffusion with ringer-gelatin drip), (2) topically suffused indomethacin or ibuprofen, (3) an induced inflammatory response (suffusion with the chemoattractant N-Formyl-Methionyl-Leucyl-Phenylalanine (FMLP)), and (4) concomitant suffusion with FMLP and NSAID. Short term topical suffusion (90 sec) with indomethacin and ibuprofen had little or no effect on control hemodynamics. Five-minute suffusions with indomethacin (5 x 10(-5) to 5 x 10(-4) M) significantly increased LEA while ibuprofen (5 x 10(-3) M) significantly decreased LEA. Topical suffusion with the chemotactic agent FMLP induced inflammation and significantly increased LEA in venules. Treatment with indomethacin during induced inflammation had no effect on the inflammatory reaction in terms of the microvascular hemodynamics measured in this study. Treatment with ibuprofen during induced inflammation significantly reduced LEA and increased red blood cell velocity. In conclusion, although both of the NSAIDs studied here are known to block the cyclooxygenase pathway of arachidonic acid metabolism, the actions of indomethacin and ibuprofen on the inflammatory process are very different with an important effect of ibuprofen being to decrease LEA.

In vivo microscopy was used to assess the relative contribution of hydrodynamic forces (network topography and shear rate) and the specificity for leukocytes to interact with venular endothelium as determinants of leukocyte-endothelium interactions. To ascertain this, microvascular networks in the rat and rabbit mesentery were examined under normograde and mechanically induced retrograde flows to determine the effect of reversed flow on leukocyte-endothelium interactions in arterioles and venules. The data indicate that retrograde perfusion under hemodynamic (red blood cell velocity and shear rate) states equivalent to normograde flow significantly increased leukocyte marginating flux in arterioles (from 0 to 0.5 cells/5 sec) and decreased flux significantly in venules (from 1.0 to 0.2 cells/5 sec). The increased flux in arterioles under retrograde conditions, however, was significantly lower than the flux in venules under normograde conditions and the decreased flux in venules during retrograde flow was significantly greater than the flux in arterioles during normograde flow. This apparent discrepancy appears to be the result of a heterogeneous distribution of adhesive receptors on vascular endothelium. Furthermore, marginating leukocytes in arterioles made only brief contact with the endothelium before being swept away while marginating leukocytes in venules during normal and retrograde perfusion rolled along the vascular wall, with similar velocities in both directions. In conclusion, although hydrodynamic forces are important in facilitating leukocyte margination through mechanisms of radial migration, it is leukocyte-endothelium specificity in venules that ultimately determines leukocyte-endothelium interactions.

In vivo dynamics of the interaction between leukocytes and the endothelium following direct activation of the white blood cells (WBCs), apart from possible endothelial cell activation, were studied in arterioles, capillaries, and venules of splanchnic tissue (rabbit omentum). WBCs were isolated using either density gradient or centrifugation techniques, labeled with fluorescent dyes, and exposed to physiological solutions with or without the chemoactivator N-formyl-methionyl-leucyl-phenlyalanine (FMLP). WBCs isolated using standard density gradient separation techniques rapidly disappeared from the circulating pool following a bolus injection and were sequestered in lung microvessels. The centrifugation technique produced cells that circulated for at least 60 min. WBCs directly activated with FMLP adhered to venular endothelium but not to arteriolar endothelium, suggesting that differences in hydrodynamics in the arteriolar and venular network or fundamental differences between arteriolar and venular endothelia may explain the lack of leukocyte-endothelium adhesion (LEA) in arterioles. WBCs pretreated with FMLP had significantly longer attachment times than nontreated cells, 13.4 and 2.5 sec respectively, which may be indicative of specific receptor chemistry. Similarities in the LEA attachment-detachment process for splanchnic tissue with that previously reported for lymphoid tissue suggest that a fundamental process of cell to cell interaction may exist in all tissues.

The effects of leukocyte-endothelium adhesion on microhemodynamics were studied in cat mesentery under control conditions and following tissue suffusion with the chemotactic agent N-formyl-methionyl-leucyl-phenylalanine (FMLP). The results indicate that under normophysiological conditions there is little or no leukocyte-endothelium adhesion in arterioles and venules. Tissue suffusion with FMLP significantly increases the number of adhering leukocytes in venules, but not in arterioles. Analysis of the number of adhering leukocytes (in venules) as a function of wall shear rate suggested that increased adhesion of leukocytes was primarily due to elevated adhesive forces and not the result of decreases in dispersal forces, i.e., wall shear stress. From measurements of upstream to downstream pressure drop, red cell velocity, and microvessel hematocrit in 16 unbranched venules, no significant changes in diameter (mean of 39.9 +/- 7.8 (SD) micron), intravascular pressure gradient (0.59 +/- 0.40 X 10(-2) cm H2O/micron), nor microvessel hematocrit (31.0 +/- 9.8%) occurred in response to FMLP. There were significant decreases in upstream pressure (8%) and estimated bulk flow (28%) as well as significant increases in the number of adhering leukocytes, from 1.5 +/- 2.8 to 11.4 +/- 8.3 cells/100 micron, and vessel resistance (81%). Changes in hemodynamics were found to be more pronounced in venules with small diameters. The observed response to FMLP suggests that changes in hemodynamics during leukocyte-endothelium adhesion can be accounted for by a decrease in the effective diameter due to obstruction of the lumen by WBCs, and that adhesive interactions between WBCs and endothelium are a major determinant of blood flow resistance in the microcirculation.