Summary
No platelet-clumping activity was detected in the serum collected from 10 rabbits.
After incubation of the alkalinized serum for 2 to 4 min at 37° C with 1.6 or 3.2
mg/ml of trypsin, platelet-clumping activity was observed in all samples. The strongest
response was observed in the serum incubated for 4 min with 3.2 mg/ml of trypsin.
After incubation for over 8 min, the clumping activity decreased gradually. At any
incubation time, the serum without trypsin or with 0.4 or 6.4 mg/ml of trypsin showed
no clumping activity. After the above measurements of the activity, 100 u/ml of heparin
was added to the serum and its pH value was adjusted to 5.6. In the serum without
trypsin the clumping activity appeared. However, in the active serum with trypsin,
the activity remained the same or decreased. The serum acidified to pH 5.6 with heparin,
which showed platelet-clumping activity, was incubated at 37° C with 1.6, 3.2 or 6.4
mg/ml of trypsin. After incubation of the serum with 3.2 mg/ml of trypsin for 16 min,
the activity was markedly reduced. After incubation with 6.4 mg/ml of trypsin for
2 min, the activity disappeared. After incubation with trypsin, the clumping activity
was observed in BaSO4-adsorbed serum but was not observed in serum heated at 56° C for 1 min nor in serum
to which EDTA was added in a final concentration of 0.1%. These results suggest that
the precursor of the platelet-clumping substance was activated by trypsin, and the
platelet-clumping substance and/or its precursor was destroyed by trypsin.
