In vivo evaluation of platelet-endothelial interactions after transient retinal ischemia

PURPOSE. Accumulating evidence suggests that platelets play an important ro le in ischemia-reperfusion injury. To fulfill that role, platelets flowing in the bloodstream would have to interact with retinal endothelial cells an d to accumulate in the postischemic retina. This study was designed to inve stigate quantitatively platelet-endothelial interactions in postischemic re tina after transient retinal ischemia. METHODS. Transient retinal ischemia was induced in Long-Evans rats for 60 m inutes by temporal ligation of the optic nerve. Isolated platelet samples l abeled with carboxyfluorescein diacetate succinimidyl. ester were administe red intravenously to recipient rats after various reperfusion periods. Plat elet-endothelial interactions in postischemic retina were evaluated in vivo with a scanning laser ophthalmoscope. Anti-P-selectin monoclonal antibody (mAb) was administered 5 minutes before the injection of labeled platelets. P-selectin gene expression in the postischemic retina was studied by semiq uantitative polymerase chain reaction. RESULTS. Under basal conditions, infused platelets showed minimal interacti ons with retinal endothelial cells. In contrast, postischemic retinas showe d active platelet-endothelial interactions. Many platelets were observed ro lling along and adhering to the major retinal veins. The number of rolling and adhering platelets reached a peak (555 +/- 65/mm per min and 25.8 +/- 3 .2/mm(2)) 12 hours after reperfusion. However, the interactions between pla telets and postischemic retinal endothelial cells were substantially inhibi ted by neutralizing P-selectin expressed on endothelial cells. In addition, P-selectin gene expression in postischemic retina corresponded with the ti me course of platelet-endothelial interactions during the reperfusion perio d. CONCLUSIONS. This study demonstrated that platelets actively interacted wit h retinal endothelial cells in the postischemic retina through P-selectin e xpressed on the retinal endothelial cells.