Summary
The presence of hirudin at the time adsorbed plasma and serum were combined in TGT
inhibited the formation of the prothrombin converting activity. Hirudin, a potent
antithrombin, probably exerted its inhibitory effect by neutralizing any thrombin
which might form. If adsorbed plasma and serum were incubated together for a period
as short as 1 to 3 min before the addition of hirudin, calcium and lipid, hirudin
no longer exerted the same inhibitory effect, but, in order to exert the same inhibitory
effect, had to be present in higher concentration. Preincubation of factor VIII deficient
plasma with serum and calcium was not effective in overcoming hirudin inhibition,
but preincubation with factor IX deficient serum with adsorbed plasma and calcium
was able to overcome inhibition due to hirudin equally as well as normal serum.
Once again the importance of traces of thrombin in the formation of activity capable
of rapidly clotting substrate plasma in TGT has been shown by using a specific thrombin
inhibitor. A thrombin dependent interaction appears to take place between adsorbed
plasma and serum and also between product I and phospholipid.