Lipid hydroperoxide stimulates leukocyte-endothelium interaction in the retinal microcirculation

Leukocyte dynamics were evaluatyed in vivo in rat retinal microcirculation following exposure to lipid hydroperoxide (LHP) in the vitreous.Various amounts (1, 5, 10 or 100 microg) of LHP (18:2) dissolved in 5 microl of sodium borate buffer (SBB, 0.02M) were injected into the vitreous of Brown-Norway rats. As a comparative study, 10 microg of linoleic acid (LA) dissolved in 5 microl of SBB was injected in the same way. Rats that did not undergo injection were evaluated as un-treated. At 2 to 48 hr after LHP exposure, the following were examined: (1) the flux of rolling leukocytes along the major retinal veins, (2) the number of leukocytes that accumulated in the retinal microvasculature using acridine orange digital fluorography and (3) the diameter of major retinal vessels. In the LHP-treated eyes, leukocyte rolling along the major retinal veins was observed and the number increased in a dose-dependent manner ( 1 to 10 microg). The flux of rolling leukocytes peaked at 6 hr after LHP (10-100 microg) injection. No rolling leukocytes were observed in LA-treated or un-treated eyes. The number of accumulated leukocytes started to increase at 4 hr and peaked at 24 hr after LHP (10 microg) injection. This number was significantly higher than that in LA-treated and un-treated eyes. Venous dilation was seen from 4 hr after LHP (10 microg) injection and became significant at 6 and 24 hr as compared with LA-treated and un-treated eyes. The results indicate that increased LHP levels in the vitreous due to oxidative stress enhance leukocyte-enothelium interaction in the retinal microcirculation.