MONOCYTE PROCOAGULANT ACTIVITY-INDUCED BY ADHERENCE TO AN ARTIFICIAL SURFACE IS REDUCED BY END-POINT IMMOBILIZED HEPARIN-COATING OF THE SURFACE

Heparin-coating improves the biocompatibility of blood contacting arti ficial surfaces. This led us to investigate the impact of heparin-coat ing (Carmeda AB, Stockholm) of polymetylmetacrylate on the expression of monocyte tissue factor procoagulant activity (TF-PCA) by surface ad hesion. Also, the anticoagulant effect of heparin-coating in the prese nce or absence of adherent procoagulant monocytes was assessed. This i s of particular interest, since activation of extrinsic coagulation by adherent monocyte TF-PCA may play a significant role in thrombin gene ration during extracorporeal circulation. Monocytes exposed to heparin -coated or non-coated polymetylmetacrylate expressed TF-PCA. The hepar in coat did not affect the rate of monocyte adhesion. However, heparin -coating reduced the induction of TF-PCA of non-adherent and adherent monocytes by 17 and 33% (p <0.001 and p <0.0003), respectively. Hepari n-coating in the absence of monocytes, totally inhibited the clotting of recalcified plasma (p <0.003). In contrast, in the presence of adhe rent monocytes expressing TF-PCA. surface-bound heparin did not inhibi t clotting. However, inclusion of heparin in a plasma concentration of 8.9 IU/ml totally inhibited the activation of coagulation. It is appa rent that heparin-coating of an artificial surface is an efficient mea ns to inhibit coagulation of recalcified plasma, but much less so when procoagulant monocytes are adherent to the coated surface. The presen t findings are of clinical relevance, since monocytes will adhere to b lood contacting surfaces of extracorporeal circuits or to implanted va scular prostheses and subsequently express TF-PCA, and this may promot e thromboembolism.