Effect of heparin and thrombin on platelet adherence to the surface of rabbit aorta

Platelet adherence to both the damaged and undamaged surfaces of rabbit aorta in perfusion experiments in vitro was inhibited by heparin. The preparation of the vessel segments for these perfusion studies required 30 to 60 minutes because of the need to tie off all of the small vessels. In other experiments in which damaged or undamaged vessel segments were everted on a probe, the preparation of the vessels could be done more quickly and heparin did not inhibit platelet adherence. However, exposure of either the damaged or undamaged surfaces used in the latter type of experiment to thrombin markedly promoted platelet adherence to the surfaces. Heparin inhibited this effect. It seems likely that during the preparation of the aortas for the perfusion studies, thrombin generation occurred in the vessels. Thus, in preparing aortic segments for studies of platelet adherence, thrombin generation must be avoided. Since thrombin enhanced platelet adherence to undamaged endothelial surfaces, it may be that thrombin formation in vivo could cause platelet adherence to vessel walls from which endothelial cells have not been lost.