Aspirin inhibits granulocyte and monocyte adherence to saphenous vein endothelia in a process not mediated by nitric oxide.

We examined the effects of aspirin on human immunocyte adherence to human saphenous vein preparations in vitro. Monocytes and granulocytes were analyzed by phase-contrast microscopy in conjunction with a time-lapse video recording system for cell counting in the medium. Saphenous vein samples taken from five volunteer subjects during their elective coronary artery bypass grafting procedures were used for an in vitro experiment in which each subject's immune cells were added to his/her respective endothelial tissues. In addition, aspirin or morphine was added to the preparations. After 30 min the endothelium and the medium were examined for cell numbers using feature color detection software. The endothelium exposed to a 10 min preincubation with 10 mmol/l aspirin was found to have significantly fewer monocytes and granulocytes attached. The saphenous vein preparations were examined for nitric oxide (NO) release using an NO-selective amperometric microprobe. Aspirin at its immunocyte inhibitory concentrations did not induce NO release from the endothelium, whereas morphine, which is known to stimulate NO production by endothelium, did so. These findings demonstrate that the administration of aspirin in high doses can diminish human granulocyte and monocyte adherence to saphenous vein endothelium in vitro through an NO-independent mechanism.