INITIATION AND PROPAGATION OF BLOOD-COAGULATION AT ARTIFICIAL SURFACES STUDIED IN A CAPILLARY-FLOW REACTOR

We have made use of a novel flow reactor to study the initiation and p ropagation of the ex vivo blood coagulation processes at artificial su rfaces. The flow reactor consisted of a primary glass or polymer capil lary that is connected to a secondary glass capillary, which inner wal l was coated with a phospholipid bilayer of 25 mol% dioleoylphosphatid ylserine/75 mol% dioleoylphosphatidylcholine (DOPS/DOPC). Citrated pla telet free plasma and a CaCl2 solution were delivered by syringe pumps and mixed just before the entrance of the flow reactor. The outflowin g plasma was assayed for factor XIa, factor IXa, factor Xa and thrombi n activity. Perfusion of recalcified plasma through a bare glass capil lary resulted in a transient generation of fluid phase factor XIa. In contrast, factor IXa production increased slowly to attain a stable st eady-state level. We established that surface-bound factor XIa was res ponsible for a continuous production of factor IXa. Factor IXa-induced generation of factor Xa and thrombin was only observed when contact a ctivated plasma was subsequently perfused through a DOPS/DOPC-coated c apillary, showing that propagation of the factor IXa trigger requires a procoagulant, phosphatidylserine-containing, phospholipid membrane. The negatively charged inner surface of a heparin-coated polyurethane capillary, generated like the glass capillary significant amounts of f actor XIa and factor IXa when perfused with recalcified plasma. No dif ferences were found between unfractionated heparin and heparin devoid of anticoagulant activity. Thus, it is concluded that contact activati on and factor IXa generation in flowing plasma is not inhibited by imm obilised anticoagulant active heparin. Consequently, factor IXa-depend ent thrombin generation at a downstream located phospholipid membrane was similar, regardless the specific anticoagulant activity of immobil ised heparin.