The aim of this study was to determine whether immunoneutralization of P-selectin or intercellular adhesion molecule-1 (ICAM-1) (endothelial cell adhesion molecules involved in leukocyte rolling and firm adhesion, respectively) would attenuate the development of postischemic capillary no-reflow. Microvascular patency was assessed in vascularly isolated canine gracilis muscles by perfusion with contrast media (India ink) at the end of the experimental protocol. Computerized video imaging was used to quantitate the number of ink-containing microvessels (< 10 microns diam) per muscle fiber in histological samples obtained from isolated canine gracilis muscles subjected to 4.5 h of continuous perfusion (nonischemic control), 4 h of ischemia and 30 min of reperfusion (I-R), I-R + P-selectin monoclonal antibodies (MAbs) (MD6 or PB1.3), and I-R + ICAM-1 MAbs (CL18/6C7 or R6.5). The efficacy of a P-selectin MAb (MD3) that binds to a nonfunctional epitope was also evaluated. I-R was associated with a marked reduction in the number of patent capillaries per fiber (3.1 +/- 0.2 vs. 1.1 +/- 0.2 patent capillaries/fiber for control and I-R, respectively). Immunoneutralization with MAbs directed against functional epitopes on P-selectin (MD6 or PB1.3) significantly improved capillary perfusion (2.3 +/- 0.3 and 3.6 +/- 0.6 patent capillaries/fiber, respectively). On the other hand, MAb MD3, which binds to nonfunctional epitopes on P-selectin, failed to limit the development of postischemic no-reflow (1.0 +/- 0.2 patent capillaries/fiber). Immunoneutralization of ICAM-1 with CL18/6C7 and R6.5 increased the number of patent capillaries per fiber to 1.8 +/- 0.1 and 2.5 +/- 0.3, respectively. These data indicate that P-selectin and ICAM-1-dependent adherence reactions play an important role in the development of the no-reflow phenomenon in postischemic skeletal muscle.