Delayed "spontaneous" adhesion of leukocytes to rat mesenteric venules is dependent upon reactive oxidants.

We investigated the role of reactive oxygen metabolites (ROMs) as potential mediators of delayed "spontaneous" leukocyte adhesion to rat mesenteric venules after the manipulation for in vivo microscopy. Rats were anesthetized via tail vein and prepared for intravital microscopic viewing of a segment of mesenteric venule. Leukocyte rolling, adhesion, and emigration were quantitated every 30 min for 3 h. Intravital observation immediately after routine gentle manipulation revealed a substantial leukocyte rolling and a small number of adherent and emigrated leukocytes. This rolling leukocyte flux then declined to a minimal level for 60 min. The number of adherent and emigrated leukocytes did not change during the initial 90 min. After 120 min, the flux of rolling leukocytes, and adherent and emigrated leukocyte number began to increase and reached significant levels at 180 min. To determine the possible role of ROMs in this "spontaneous" adhesion, rats were treated continuously with superoxide dismutase (SOD) plus catalase given intravenously over 3 h. Rolling leukocyte flux after 120 min was significantly attenuated by SOD plus catalase. SOD + catalase also significantly inhibited delayed leukocyte adhesion and emigration. Allopurinol substantially inhibited xanthine oxidase activity but had no significant effects on the above parameters of neutrophil dynamics. These findings suggest that ROMs, probably derived from a source other than xanthine oxidase, constitute important mediators of "spontaneous" leukocyte adhesion in rat mesenteric venules.