PROTHROMBIN FRAGMENT 1-ANTITHROMBIN III-COMPLEXES AND FIBRINOPE PTIDE-A IN SPONTANEOUSLY CLOTTING WHOLE-BLOOD IN-VITRO - EFFECTS OF HEPARINADDITION AND ANTITHROMBIN-III DEFICIENCY(2, THROMBIN)

Previous in vitro studies using spontaneously clotting whole blood rev ealed thrombin formation and high fibrinopeptide A (FPA) concentration s measured during incubation time. This occurred in spite of normal co ncentrations of thrombin antagonists present in the blood of the healt hy subjects examined. However, there are several reports showing that in vivo increased thrombin-antithrombin III-complex (TAT) concentratio ns and relatively low FPA concentrations may occur e. g. in patients w ith (pre)thrombotic disorders. These in vivo findings indicate more ef fective thrombin inhibition by antithrombin III, with almost no fibrin formation. To find an explanation for the differences observed in vit ro and in vivo, we extended the in vitro studies by measuring concentr ations of prothrombin fragment 1 + 2 (F1 + 2), TAT and FPA at several time points until 30 min. Our goal was to test whether thrombin at lea st initially is neutralized by antithrombin III, resulting in a lack o f fibrin formation, either in the absence or in the presence of hepari n (0.2 and 0.5 U/ml whole blood, respectively). In the absence of hepa rin a simultaneous increase in the concentrations of F1 + 2, TAT and F PA was observed. Thrombin was only partially neutralized by antithromb in III and large amounts of fibrin were formed. The addition of hepari n virtually suppressed thrombin formation since the F1 + 2 concentrati on remained low. Moreover, the small amounts of thrombin formed were n eutralized by antithrombin III to a greater extent than in the absence of heparin. Thus, in the presence of heparin less fibrin was produced as evidenced by significantly lower FPA concentrations. Experiments u sing blood of two patients with antithrombin III deficiency showed tha t fibrin formation was not different from the healthy controls in spit e of the significantly higher initial F1 + 2 concentration measured. D uring incubation, the patients tended to form more thrombin, of which proportionally less was neutralized by antithrombin III, and more fibr in as compared to the healthy controls. Heparin addition suppressed th rombin formation less efficiently.