Summary
The total platelet cofactor activity in plasma and the platelet cofactor II activity
in serum was measured. The normal variations are high. Some individuals have less
serum platelet cofactor II than found in certain cases of PTC “deficiency”; and when
the serum platelet cofactor II concentration was reduced to zero with the use of anticoagulants,
there was no bleeding tendency observed. With the use of Sintrom and phenylindanedione,
the total platelet cofactor activity of plasma was reduced and the platelet cofactor
II activity of serum was reduced to near zero. With the latter drug platelet cofactor
II of serum was still low 10 days after the drug was withdrawn. With Sintrom given
intermittently the fluctuations in prothrombin concentration are noticeably more rapid
than the changes in platelet cofactor II. In a preliminary study of other drugs, there
were indications that platelet cofactor II concentration is not altered with some
anticoagulants even though the prothrombin concentration is reduced. Apparently, the
platelet cofactor II changes which occur are characteristic for each anticoagulant.
The platelet cofactor I levels of the plasma are not appreciably, and most likely
not at all altered by the drugs studied.