Summary
As evaluated in a recording “coagulometer” the Stypven time of 16 to 19 days pregnant
Holtzman rats was shorter than that of the controls solely in platelet-rich plasma
but not in platelet-poor plasma collected in siliconized material when most of the
platelets were removed by slow speed centrifugation (1000 G × 20 minutes). If the
same blood was centrifuged at a higher speed (2000 G) the Stypven time was considerably
shorter in the pregnant rats even if no platelets were left indicating that platelet
factor 3 had been released in plasma during centrifugation.
Identical results were obtained in 10 women taking oral contraceptives as compared
to 10 controls. Depending on whether blood was collected in siliconized glassware
or not, and final determination performed in plastic or glass, the cephalin clotting
time of oral contraceptives treated women was found to be longer, equal or shorter
than this of the controls. When it was shorter, a comparable reduction in the Stypven
time indicated that the shortening was probably due to “release” of platelet factor
3 in the platelet-poor plasma, in the course of its preparation.
