ISCHEMIA-REPERFUSION INJURY IN SKELETAL-MUSCLE - CD18-DEPENDENT NEUTROPHIL-ENDOTHELIAL ADHESION AND ARTERIOLAR VASOCONSTRICTION

The purpose of this study was to evaluate if the venular neutrophil-en dothelial adhesion associated with ischemia-reperfusion of skeletal mu scle is dependent on leukocyte adhesion glycoprotein CD18 function and to determine if this interaction influences the vasoactive response i n nearby arterioles. An in vivo microscopy preparation of transillumin ated gracilis muscle in 13 male Wistar rats was used for this experime nt. Observations of nonischemic muscle (sham) demonstrated this prepar ation to be stable for 8 hours with negligible change in neutrophil ad herence or arteriole diameter. Three groups were evaluated in this stu dy: (1) sham, no ischemia, no treatment (n = 5, 20 arterioles, 20 venu les), (2) 4 hours of global ischemia only (n = 4, 19 venules, 22 arter ioles), and (3) 4 hours of ischemia plus monoclonal antibody against C D18 (n = 4, 12 venules, 9 arterioles). The murine monoclonal antibody (WT.3, Seikagaku America, Inc.), which binds the rat leukocyte functio n antigen 1 CD18 chain, was infused into the contralateral femoral vei n 30 minutes prior to reperfusion. The number of leukocytes rolling an d adherent to endothelium (15 seconds of observation) was counted in 1 00-mu m venular segments, and arteriole diameters were measured at var ious times during reperfusion. All counts and measurements were normal ized to baseline preischemic readings for each animal. Mean changes fr om baseline were compared between groups. The increase in ischemia-rep erfusion-induced neutrophil-endothelial adherence in venules was block ed by monoclonal antibody, but rolling behavior was not changed. The i schemia-reperfusion-induced progressive vasoconstriction in arterioles was blocked by monoclonal antibody. These results suggest that (1) ne utrophil-endothelial adherence function associated with ischemia-reper fusion in this model is CD18-dependent, (2) neutrophil rolling functio n does not appear to he dependent on CD18, and (3) neutrophil CD18 fun ction is a prerequisite for ischemia-reperfusion-induced arteriolar va soconstriction. These findings provide important mechanistic informati on that may help explain the deleterious microcirculatory events assoc iated with ischemia-reperfusion injury of skeletal muscle.