The Reversible Antithrombin Activity of Incubated Plasma

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Abstract
The thrombin time of normal citrated plasma is progressively prolonged on incubation in open glass tubes at 37° C. The phenomenon is dependent on the temperature and duration of incubation, on the pH, and on the concentration of calcium ions present. Platelet-rich citrated plasma fails to exhibit augmented antithrombin activity when similarly incubated, and the addition of washed platelets to platelet-poor plasma inhibits this activity. The clot retarding action of incubated plasma against thrombin is also manifested against Arvin (Ancrod), but not against Reptilase-R. This thrombin time lenghening may be inhibited by incubation with anti-antithrombin III antiserum thus indicating that the phenomenon of thrombin time lengthening is consistent with enhanced activity of antithrombin III. It is unlikely that alterations in the activity of α2-macroglobulin, is important in the reduced thrombin-coagulability of incubated plasma. Interference with the polymerisation of fibrin monomers by the physicochemical changes may contribute to the observed phenomenon.