Ischemic preconditioning attenuates postischemic leukocyte adhesion and emigration.

Intravital microscopy was used to determine whether ischemic preconditioning (IPC; 5 min ischemia and 10 min reperfusion) would attenuate leukocyte adhesion and emigration induced by subsequent prolonged ischemia (60 min) and reperfusion (60 min) (I/R) in murine cremaster muscle and whether adenosine produced during IPC and/or reperfusion contributed to these beneficial effects. I/R elicited a marked increase in the number of adherent and emigrated leukocytes compared with the nonischemic control muscles, an effect that was largely prevented by IPC. Superfusion of the cremaster with adenosine deaminase only during IPC or only during 60-min reperfusion attenuated the inhibitory effect of IPC on postischemic leukocyte adhesion and emigration. However, the beneficial effects of IPC were mimicked in cremaster muscles preconditioned with adenosine (topical application for 10 min beginning 20 min before the onset of prolonged ischemia). Similar results were obtained in experiments in which adenosine was topically applied to the cremaster only during the 60-min reperfusion period. Our findings suggest that the ability of IPC to attenuate postischemic leukocyte adhesion and emigration may be mediated by adenosine released during IPC and during reperfusion after prolonged ischemia.