Effect of hyperbaric oxygen on neutrophil CD18 expression

Previous work has shown that treatment with hyperbaric oxygen significantly reduces neutrophil adhesion to postcapillary venules in a rat microcircula tion model of ischemia-reperfusion injury. The mechanism of this process is unknown. The purpose of this study tvas to evaluate the effect of hyperbar ic oxygen on neutrophil CD18 adhesion sites by flow cytometry in an animal model of ischemia-reperfusion injury. The gracilis muscle flap was raised in three groups of male Wistar rats: (1 ) a sham group (n = 25), (2) a group that underwent 4 hours of ischemia (n = 25), and (3) a group that underwent 4 hours of ischemia and received hype rbaric oxygen (100% O-2, 2.5 atmospheres absolute, during the last 90 minut es of ischemia) (n = 25). Samples from one subgroup of each group (n = 5) w ere divided into two portions, and one portion was stimulated with phorbol- 12 myristate 13-acetate (PMA). Samples from another subgroup of each group (n = 5) were treated in the same manner, and a flap hush was added at the e nd of reperfusion to determine the number of CD18 adhesion sites on adheren t neutrophils remaining in the flap. Ve nous blood was drawn 10 minutes aft er the operation, at 5 minutes of reperfusion, and at 90 minutes of reperfu sion. Hematocrit and white brood cell count were measured. Samples were ana lyzed by flow cytometry, and the antibody binding capacity was assessed usi ng microbead standards and linear regression (antibody binding capacity was expressed as the mean number of sites per cell +/- SEM). Microbeads were u sed to align the flow cytometer and to provide external and internal standa rds. Ischemia-reperfusion injury increased the expression of CD18 by neutro phils (p < 0.05). Expression of CD18 was not decreased by hyperbaric oxygen treatment. Stimulation with PMA increased the expression of CD18 in all gr oups (p < 0.01). These results suggest that ischemia-reperfusion injury doe s increase the expression of CD18 by neutrophils. Hyperbaric oxygen, as adm inistered in this experiment, did not prevent the increase in CD18 expressi on.